| 1 | The LTTng Documentation |
| 2 | ======================= |
| 3 | Philippe Proulx <pproulx@efficios.com> |
| 4 | v2.13, 28 November 2023 |
| 5 | |
| 6 | |
| 7 | include::../common/copyright.txt[] |
| 8 | |
| 9 | |
| 10 | include::../common/welcome.txt[] |
| 11 | |
| 12 | |
| 13 | include::../common/audience.txt[] |
| 14 | |
| 15 | |
| 16 | [[chapters]] |
| 17 | === What's in this documentation? |
| 18 | |
| 19 | The LTTng Documentation is divided into the following sections: |
| 20 | |
| 21 | * ``**<<nuts-and-bolts,Nuts and bolts>>**'' explains the |
| 22 | rudiments of software tracing and the rationale behind the |
| 23 | LTTng project. |
| 24 | + |
| 25 | Skip this section if you’re familiar with software tracing and with the |
| 26 | LTTng project. |
| 27 | |
| 28 | * ``**<<installing-lttng,Installation>>**'' describes the steps to |
| 29 | install the LTTng packages on common Linux distributions and from |
| 30 | their sources. |
| 31 | + |
| 32 | Skip this section if you already properly installed LTTng on your target |
| 33 | system. |
| 34 | |
| 35 | * ``**<<getting-started,Quick start>>**'' is a concise guide to |
| 36 | get started quickly with LTTng kernel and user space tracing. |
| 37 | + |
| 38 | We recommend this section if you're new to LTTng or to software tracing |
| 39 | in general. |
| 40 | + |
| 41 | Skip this section if you're not new to LTTng. |
| 42 | |
| 43 | * ``**<<core-concepts,Core concepts>>**'' explains the concepts at |
| 44 | the heart of LTTng. |
| 45 | + |
| 46 | It's a good idea to become familiar with the core concepts |
| 47 | before attempting to use the toolkit. |
| 48 | |
| 49 | * ``**<<plumbing,Components of LTTng>>**'' describes the various |
| 50 | components of the LTTng machinery, like the daemons, the libraries, |
| 51 | and the command-line interface. |
| 52 | |
| 53 | * ``**<<instrumenting,Instrumentation>>**'' shows different ways to |
| 54 | instrument user applications and the Linux kernel for LTTng tracing. |
| 55 | + |
| 56 | Instrumenting source code is essential to provide a meaningful |
| 57 | source of events. |
| 58 | + |
| 59 | Skip this section if you don't have a programming background. |
| 60 | |
| 61 | * ``**<<controlling-tracing,Tracing control>>**'' is divided into topics |
| 62 | which demonstrate how to use the vast array of features that |
| 63 | LTTng{nbsp}{revision} offers. |
| 64 | |
| 65 | * ``**<<reference,Reference>>**'' contains API reference tables. |
| 66 | |
| 67 | * ``**<<glossary,Glossary>>**'' is a specialized dictionary of terms |
| 68 | related to LTTng or to the field of software tracing. |
| 69 | |
| 70 | |
| 71 | include::../common/convention.txt[] |
| 72 | |
| 73 | |
| 74 | include::../common/acknowledgements.txt[] |
| 75 | |
| 76 | |
| 77 | [[whats-new]] |
| 78 | == What's new in LTTng{nbsp}{revision}? |
| 79 | |
| 80 | LTTng{nbsp}{revision} bears the name _Nordicité_, the product of a |
| 81 | collaboration between https://champlibre.co/[Champ Libre] and |
| 82 | https://www.boreale.com/[Boréale]. This farmhouse IPA is brewed with |
| 83 | https://en.wikipedia.org/wiki/Kveik[Kveik] yeast and Québec-grown |
| 84 | barley, oats, and juniper branches. The result is a remarkable, fruity, |
| 85 | hazy golden IPA that offers a balanced touch of resinous and woodsy |
| 86 | bitterness. |
| 87 | |
| 88 | New features and changes in LTTng{nbsp}{revision}: |
| 89 | |
| 90 | General:: |
| 91 | + |
| 92 | * The LTTng trigger API of <<liblttng-ctl-lttng,`liblttng-ctl`>> now |
| 93 | offers the ``__event rule matches__'' condition (an <<event-rule,event |
| 94 | rule>> matches an event) as well as the following new actions: |
| 95 | + |
| 96 | -- |
| 97 | * <<basic-tracing-session-control,Start or stop>> a recording session. |
| 98 | * <<session-rotation,Archive the current trace chunk>> of a |
| 99 | recording session (rotate). |
| 100 | * <<taking-a-snapshot,Take a snapshot>> of a recording session. |
| 101 | -- |
| 102 | + |
| 103 | As a reminder, a <<trigger,trigger>> is a condition-actions pair. When |
| 104 | the condition of a trigger is satisfied, LTTng attempts to execute its |
| 105 | actions. |
| 106 | + |
| 107 | This feature is also available with the new man:lttng-add-trigger(1), |
| 108 | man:lttng-remove-trigger(1), and man:lttng-list-triggers(1) |
| 109 | <<lttng-cli,cmd:lttng>> commands. |
| 110 | + |
| 111 | Starting from LTTng{nbsp}{revision}, a trigger may have more than one |
| 112 | action. |
| 113 | + |
| 114 | See “<<add-event-rule-matches-trigger,Add an ``event rule matches'' |
| 115 | trigger to a session daemon>>” to learn more. |
| 116 | |
| 117 | * The LTTng <<lttng-ust,user space>> and <<lttng-modules,kernel>> |
| 118 | tracers offer the new namespace context field `time_ns`, which is the |
| 119 | inode number, in the proc file system, of the current clock namespace. |
| 120 | + |
| 121 | See man:lttng-add-context(1), man:lttng-ust(3), and |
| 122 | man:time_namespaces(7). |
| 123 | |
| 124 | * The link:/man[manual pages] of LTTng-tools now have a terminology and |
| 125 | style which match the LTTng Documentation, many fixes, more internal |
| 126 | and manual page links, clearer lists and procedures, superior |
| 127 | consistency, and usage examples. |
| 128 | + |
| 129 | The new man:lttng-event-rule(7) manual page explains the new, common |
| 130 | way to specify an event rule on the command line. |
| 131 | + |
| 132 | The new man:lttng-concepts(7) manual page explains the core concepts of |
| 133 | LTTng. Its contents is essentially the ``<<core-concepts,Core |
| 134 | concepts>>'' section of this documentation, but more adapted to the |
| 135 | manual page style. |
| 136 | |
| 137 | User space tracing:: |
| 138 | + |
| 139 | [IMPORTANT] |
| 140 | ==== |
| 141 | The major version part of the `liblttng-ust` |
| 142 | https://en.wikipedia.org/wiki/Soname[soname] is bumped, which means you |
| 143 | **must recompile** your instrumented applications/libraries and |
| 144 | <<tracepoint-provider,tracepoint provider packages>> to use |
| 145 | LTTng-UST{nbsp}{revision}. |
| 146 | |
| 147 | This change became a necessity to clean up the library and for |
| 148 | `liblttng-ust` to stop exporting private symbols. |
| 149 | |
| 150 | Also, LTTng{nbsp}{revision} prepends the `lttng_ust_` and `LTTNG_UST_` |
| 151 | prefix to all public macro/definition/function names to offer a |
| 152 | consistent API namespace. The LTTng{nbsp}2.12 API is still available; |
| 153 | see the ``Compatibility with previous APIs'' section of |
| 154 | man:lttng-ust(3). |
| 155 | ==== |
| 156 | + |
| 157 | Other notable changes: |
| 158 | + |
| 159 | * The `liblttng-ust` C{nbsp}API offers the new man:lttng_ust_vtracef(3) |
| 160 | and man:lttng_ust_vtracelog(3) macros which are to |
| 161 | man:lttng_ust_tracef(3) and man:lttng_ust_tracelog(3) what |
| 162 | man:vprintf(3) is to man:printf(3). |
| 163 | |
| 164 | * LTTng-UST now only depends on https://liburcu.org/[`liburcu`] at build |
| 165 | time, not at run time. |
| 166 | |
| 167 | Kernel tracing:: |
| 168 | + |
| 169 | * The preferred display base of event record integer fields which |
| 170 | contain memory addresses is now hexadecimal instead of decimal. |
| 171 | |
| 172 | * The `pid` field is removed from `lttng_statedump_file_descriptor` |
| 173 | event records and the `file_table_address` field is added. |
| 174 | + |
| 175 | This new field is the address of the `files_struct` structure which |
| 176 | contains the file descriptor. |
| 177 | + |
| 178 | See the |
| 179 | ``https://github.com/lttng/lttng-modules/commit/e7a0ca7205fd4be7c829d171baa8823fe4784c90[statedump: introduce `file_table_address`]'' |
| 180 | patch to learn more. |
| 181 | |
| 182 | * The `flags` field of `syscall_entry_clone` event records is now a |
| 183 | structure containing two enumerations (exit signal and options). |
| 184 | + |
| 185 | This change makes the flag values more readable and meaningful. |
| 186 | + |
| 187 | See the |
| 188 | ``https://github.com/lttng/lttng-modules/commit/d775625e2ba4825b73b5897e7701ad6e2bdba115[syscalls: Make `clone()`'s `flags` field a 2 enum struct]'' |
| 189 | patch to learn more. |
| 190 | |
| 191 | * The memory footprint of the kernel tracer is improved: the latter only |
| 192 | generates metadata for the specific system call recording event rules |
| 193 | that you <<enabling-disabling-events,create>>. |
| 194 | |
| 195 | |
| 196 | [[nuts-and-bolts]] |
| 197 | == Nuts and bolts |
| 198 | |
| 199 | What is LTTng? As its name suggests, the _Linux Trace Toolkit: next |
| 200 | generation_ is a modern toolkit for tracing Linux systems and |
| 201 | applications. So your first question might be: |
| 202 | **what is tracing?** |
| 203 | |
| 204 | |
| 205 | [[what-is-tracing]] |
| 206 | === What is tracing? |
| 207 | |
| 208 | As the history of software engineering progressed and led to what |
| 209 | we now take for granted--complex, numerous and |
| 210 | interdependent software applications running in parallel on |
| 211 | sophisticated operating systems like Linux--the authors of such |
| 212 | components, software developers, began feeling a natural |
| 213 | urge to have tools that would ensure the robustness and good performance |
| 214 | of their masterpieces. |
| 215 | |
| 216 | One major achievement in this field is, inarguably, the |
| 217 | https://www.gnu.org/software/gdb/[GNU debugger (GDB)], |
| 218 | an essential tool for developers to find and fix bugs. But even the best |
| 219 | debugger won't help make your software run faster, and nowadays, faster |
| 220 | software means either more work done by the same hardware, or cheaper |
| 221 | hardware for the same work. |
| 222 | |
| 223 | A _profiler_ is often the tool of choice to identify performance |
| 224 | bottlenecks. Profiling is suitable to identify _where_ performance is |
| 225 | lost in a given piece of software. The profiler outputs a profile, a |
| 226 | statistical summary of observed events, which you may use to discover |
| 227 | which functions took the most time to execute. However, a profiler won't |
| 228 | report _why_ some identified functions are the bottleneck. Bottlenecks |
| 229 | might only occur when specific conditions are met, conditions that are |
| 230 | sometimes impossible to capture by a statistical profiler, or impossible |
| 231 | to reproduce with an application altered by the overhead of an |
| 232 | event-based profiler. For a thorough investigation of software |
| 233 | performance issues, a history of execution is essential, with the |
| 234 | recorded values of variables and context fields you choose, and with as |
| 235 | little influence as possible on the instrumented application. This is |
| 236 | where tracing comes in handy. |
| 237 | |
| 238 | _Tracing_ is a technique used to understand what goes on in a running |
| 239 | software system. The piece of software used for tracing is called a |
| 240 | _tracer_, which is conceptually similar to a tape recorder. When |
| 241 | recording, specific instrumentation points placed in the software source |
| 242 | code generate events that are saved on a giant tape: a _trace_ file. You |
| 243 | can record user application and operating system events at the same |
| 244 | time, opening the possibility of resolving a wide range of problems that |
| 245 | would otherwise be extremely challenging. |
| 246 | |
| 247 | Tracing is often compared to _logging_. However, tracers and loggers are |
| 248 | two different tools, serving two different purposes. Tracers are |
| 249 | designed to record much lower-level events that occur much more |
| 250 | frequently than log messages, often in the range of thousands per |
| 251 | second, with very little execution overhead. Logging is more appropriate |
| 252 | for a very high-level analysis of less frequent events: user accesses, |
| 253 | exceptional conditions (errors and warnings, for example), database |
| 254 | transactions, instant messaging communications, and such. Simply put, |
| 255 | logging is one of the many use cases that can be satisfied with tracing. |
| 256 | |
| 257 | The list of recorded events inside a trace file can be read manually |
| 258 | like a log file for the maximum level of detail, but it's generally |
| 259 | much more interesting to perform application-specific analyses to |
| 260 | produce reduced statistics and graphs that are useful to resolve a |
| 261 | given problem. Trace viewers and analyzers are specialized tools |
| 262 | designed to do this. |
| 263 | |
| 264 | In the end, this is what LTTng is: a powerful, open source set of |
| 265 | tools to trace the Linux kernel and user applications at the same time. |
| 266 | LTTng is composed of several components actively maintained and |
| 267 | developed by its link:/community/#where[community]. |
| 268 | |
| 269 | |
| 270 | [[lttng-alternatives]] |
| 271 | === Alternatives to noch:{LTTng} |
| 272 | |
| 273 | Excluding proprietary solutions, a few competing software tracers |
| 274 | exist for Linux: |
| 275 | |
| 276 | https://github.com/dtrace4linux/linux[dtrace4linux]:: |
| 277 | A port of Sun Microsystems' DTrace to Linux. |
| 278 | + |
| 279 | The cmd:dtrace tool interprets user scripts and is responsible for |
| 280 | loading code into the Linux kernel for further execution and collecting |
| 281 | the outputted data. |
| 282 | |
| 283 | https://en.wikipedia.org/wiki/Berkeley_Packet_Filter[eBPF]:: |
| 284 | A subsystem in the Linux kernel in which a virtual machine can |
| 285 | execute programs passed from the user space to the kernel. |
| 286 | + |
| 287 | You can attach such programs to tracepoints and kprobes thanks to a |
| 288 | system call, and they can output data to the user space when executed |
| 289 | thanks to different mechanisms (pipe, VM register values, and eBPF maps, |
| 290 | to name a few). |
| 291 | |
| 292 | https://www.kernel.org/doc/Documentation/trace/ftrace.txt[ftrace]:: |
| 293 | The de facto function tracer of the Linux kernel. |
| 294 | + |
| 295 | Its user interface is a set of special files in sysfs. |
| 296 | |
| 297 | https://perf.wiki.kernel.org/[perf]:: |
| 298 | A performance analysis tool for Linux which supports hardware |
| 299 | performance counters, tracepoints, as well as other counters and |
| 300 | types of probes. |
| 301 | + |
| 302 | The controlling utility of perf is the cmd:perf command line/text UI |
| 303 | tool. |
| 304 | |
| 305 | https://linux.die.net/man/1/strace[strace]:: |
| 306 | A command-line utility which records system calls made by a |
| 307 | user process, as well as signal deliveries and changes of process |
| 308 | state. |
| 309 | + |
| 310 | strace makes use of https://en.wikipedia.org/wiki/Ptrace[ptrace] to |
| 311 | fulfill its function. |
| 312 | |
| 313 | https://www.sysdig.org/[sysdig]:: |
| 314 | Like SystemTap, uses scripts to analyze Linux kernel events. |
| 315 | + |
| 316 | You write scripts, or _chisels_ in the jargon of sysdig, in Lua and |
| 317 | sysdig executes them while it traces the system or afterwards. The |
| 318 | interface of sysdig is the cmd:sysdig command-line tool as well as the |
| 319 | text UI-based cmd:csysdig tool. |
| 320 | |
| 321 | https://sourceware.org/systemtap/[SystemTap]:: |
| 322 | A Linux kernel and user space tracer which uses custom user scripts |
| 323 | to produce plain text traces. |
| 324 | + |
| 325 | SystemTap converts the scripts to the C language, and then compiles them |
| 326 | as Linux kernel modules which are loaded to produce trace data. The |
| 327 | primary user interface of SystemTap is the cmd:stap command-line tool. |
| 328 | |
| 329 | The main distinctive features of LTTng is that it produces correlated |
| 330 | kernel and user space traces, as well as doing so with the lowest |
| 331 | overhead amongst other solutions. It produces trace files in the |
| 332 | https://diamon.org/ctf[CTF] format, a file format optimized |
| 333 | for the production and analyses of multi-gigabyte data. |
| 334 | |
| 335 | LTTng is the result of more than 10{nbsp}years of active open source |
| 336 | development by a community of passionate developers. LTTng is currently |
| 337 | available on major desktop and server Linux distributions. |
| 338 | |
| 339 | The main interface for tracing control is a single command-line tool |
| 340 | named cmd:lttng. The latter can create several recording sessions, enable |
| 341 | and disable recording event rules on the fly, filter events efficiently |
| 342 | with custom user expressions, start and stop tracing, and much more. |
| 343 | LTTng can write the traces on the file system or send them over the |
| 344 | network, and keep them totally or partially. You can make LTTng execute |
| 345 | user-defined actions when LTTng emits an event. You can view the traces |
| 346 | once tracing becomes inactive or as LTTng records events. |
| 347 | |
| 348 | <<installing-lttng,Install LTTng now>> and |
| 349 | <<getting-started,start tracing>>! |
| 350 | |
| 351 | |
| 352 | [[installing-lttng]] |
| 353 | == Installation |
| 354 | |
| 355 | **LTTng** is a set of software <<plumbing,components>> which interact to |
| 356 | <<instrumenting,instrument>> the Linux kernel and user applications, and |
| 357 | to <<controlling-tracing,control tracing>> (start and stop |
| 358 | recording, create recording event rules, and the rest). Those |
| 359 | components are bundled into the following packages: |
| 360 | |
| 361 | LTTng-tools:: |
| 362 | Libraries and command-line interface to control tracing. |
| 363 | |
| 364 | LTTng-modules:: |
| 365 | Linux kernel modules to instrument and trace the kernel. |
| 366 | |
| 367 | LTTng-UST:: |
| 368 | Libraries and Java/Python packages to instrument and trace user |
| 369 | applications. |
| 370 | |
| 371 | Most distributions mark the LTTng-modules and LTTng-UST packages as |
| 372 | optional when installing LTTng-tools (which is always required). In the |
| 373 | following sections, we always provide the steps to install all three, |
| 374 | but note that: |
| 375 | |
| 376 | * You only need to install LTTng-modules if you intend to use |
| 377 | the Linux kernel LTTng tracer. |
| 378 | |
| 379 | * You only need to install LTTng-UST if you intend to use the user |
| 380 | space LTTng tracer. |
| 381 | |
| 382 | [role="growable"] |
| 383 | .Availability of LTTng{nbsp}{revision} for major Linux distributions as of 17{nbsp}October{nbsp}2023. |
| 384 | |
| 385 | |=== |
| 386 | |Distribution |Available in releases |
| 387 | |
| 388 | |https://www.ubuntu.com/[Ubuntu] |
| 389 | |xref:ubuntu[Ubuntu 22.04 LTS _Jammy Jellyfish_, Ubuntu 23.04 _Lunar Lobster_, and Ubuntu 23.10 _Mantic Minotaur_]. |
| 390 | |
| 391 | Ubuntu{nbsp}18.04 LTS _Bionic Beaver_ and Ubuntu{nbsp}20.04 LTS _Focal Fossa_: |
| 392 | <<ubuntu-ppa,use the LTTng Stable{nbsp}{revision} PPA>>. |
| 393 | |
| 394 | |https://www.debian.org/[Debian] |
| 395 | |<<debian,Debian{nbsp}12 _bookworm_>>. |
| 396 | |
| 397 | |https://getfedora.org/[Fedora] |
| 398 | |xref:fedora[Fedora{nbsp}37, Fedora{nbsp}38, and Fedora{nbsp}39]. |
| 399 | |
| 400 | |https://www.archlinux.org/[Arch Linux] |
| 401 | |<<arch-linux,_extra_ repository and AUR>>. |
| 402 | |
| 403 | |https://alpinelinux.org/[Alpine Linux] |
| 404 | |xref:alpine-linux[Alpine Linux{nbsp}3.16, Alpine Linux{nbsp}3.17, and Alpine Linux{nbsp}3.18]. |
| 405 | |
| 406 | |https://buildroot.org/[Buildroot] |
| 407 | |xref:buildroot[Buildroot{nbsp}2022.02, Buildroot{nbsp}2022.05, |
| 408 | Buildroot{nbsp}2022.08, Buildroot{nbsp}2022.11, Buildroot{nbsp}2023.02, |
| 409 | Buildroot{nbsp}2023.05, and Buildroot{nbsp}2023.08]. |
| 410 | |
| 411 | |https://www.openembedded.org/wiki/Main_Page[OpenEmbedded] and |
| 412 | https://www.yoctoproject.org/[Yocto] |
| 413 | |xref:oe-yocto[Yocto Project{nbsp}3.3 _Honister_, Yocto Project{nbsp}4.0 _Kirkstone_, |
| 414 | Yocto Project{nbsp}4.1 _Langdale_, Yocto Project{nbsp}4.2 _Mickledore_, and |
| 415 | Yocto Project{nbsp}4.3 _Nanbield_]. |
| 416 | |
| 417 | |==== |
| 418 | |
| 419 | [NOTE] |
| 420 | ==== |
| 421 | For https://www.redhat.com/[RHEL] and https://www.suse.com/[SLES] |
| 422 | packages, see https://packages.efficios.com/[EfficiOS Enterprise |
| 423 | Packages]. |
| 424 | |
| 425 | For other distributions, <<building-from-source,build LTTng from |
| 426 | source>>. |
| 427 | ==== |
| 428 | |
| 429 | [[ubuntu]] |
| 430 | === [[ubuntu-official-repository]]Ubuntu |
| 431 | |
| 432 | LTTng{nbsp}{revision} is available on Ubuntu 22.04 LTS _Jammy Jellyfish_, Ubuntu 23.04 _Lunar Lobster_, and Ubuntu 23.10 _Mantic Minotaur_. For previous supported releases of Ubuntu, <<ubuntu-ppa,use the LTTng Stable{nbsp}{revision} PPA>>. |
| 433 | |
| 434 | To install LTTng{nbsp}{revision} on Ubuntu{nbsp}22.04 LTS _Jammy Jellyfish_: |
| 435 | |
| 436 | . Install the main LTTng{nbsp}{revision} packages: |
| 437 | + |
| 438 | -- |
| 439 | [role="term"] |
| 440 | ---- |
| 441 | # apt-get install lttng-tools |
| 442 | # apt-get install lttng-modules-dkms |
| 443 | # apt-get install liblttng-ust-dev |
| 444 | ---- |
| 445 | -- |
| 446 | |
| 447 | . **If you need to instrument and trace <<java-application,Java applications>>**, |
| 448 | install the LTTng-UST Java agent: |
| 449 | + |
| 450 | -- |
| 451 | [role="term"] |
| 452 | ---- |
| 453 | # apt-get install liblttng-ust-agent-java |
| 454 | ---- |
| 455 | -- |
| 456 | |
| 457 | . **If you need to instrument and trace <<python-application,Python{nbsp}3 |
| 458 | applications>>**, install the LTTng-UST Python agent: |
| 459 | + |
| 460 | -- |
| 461 | [role="term"] |
| 462 | ---- |
| 463 | # apt-get install python3-lttngust |
| 464 | ---- |
| 465 | -- |
| 466 | |
| 467 | [[ubuntu-ppa]] |
| 468 | === Ubuntu: noch:{LTTng} Stable {revision} PPA |
| 469 | |
| 470 | The https://launchpad.net/~lttng/+archive/ubuntu/stable-{revision}[LTTng |
| 471 | Stable{nbsp}{revision} PPA] offers the latest stable LTTng{nbsp}{revision} |
| 472 | packages for Ubuntu{nbsp}18.04 LTS _Bionic Beaver_, Ubuntu{nbsp}20.04 LTS _Focal Fossa_, |
| 473 | and Ubuntu{nbsp}22.04 LTS _Jammy Jellyfish_. |
| 474 | |
| 475 | To install LTTng{nbsp}{revision} from the LTTng Stable{nbsp}{revision} |
| 476 | PPA: |
| 477 | |
| 478 | . Add the LTTng Stable{nbsp}{revision} PPA repository and update the |
| 479 | list of packages: |
| 480 | + |
| 481 | -- |
| 482 | [role="term",subs="attributes"] |
| 483 | ---- |
| 484 | # apt-add-repository ppa:lttng/stable-{revision} |
| 485 | # apt-get update |
| 486 | ---- |
| 487 | -- |
| 488 | |
| 489 | . Install the main LTTng{nbsp}{revision} packages: |
| 490 | + |
| 491 | -- |
| 492 | [role="term"] |
| 493 | ---- |
| 494 | # apt-get install lttng-tools |
| 495 | # apt-get install lttng-modules-dkms |
| 496 | # apt-get install liblttng-ust-dev |
| 497 | ---- |
| 498 | -- |
| 499 | |
| 500 | . **If you need to instrument and trace |
| 501 | <<java-application,Java applications>>**, install the LTTng-UST |
| 502 | Java agent: |
| 503 | + |
| 504 | -- |
| 505 | [role="term"] |
| 506 | ---- |
| 507 | # apt-get install liblttng-ust-agent-java |
| 508 | ---- |
| 509 | -- |
| 510 | |
| 511 | . **If you need to instrument and trace |
| 512 | <<python-application,Python{nbsp}3 applications>>**, install the |
| 513 | LTTng-UST Python agent: |
| 514 | + |
| 515 | -- |
| 516 | [role="term"] |
| 517 | ---- |
| 518 | # apt-get install python3-lttngust |
| 519 | ---- |
| 520 | -- |
| 521 | |
| 522 | [[debian]] |
| 523 | === Debian |
| 524 | |
| 525 | To install LTTng{nbsp}{revision} on Debian{nbsp}12 _bookworm_: |
| 526 | |
| 527 | . Install the main LTTng{nbsp}{revision} packages: |
| 528 | + |
| 529 | -- |
| 530 | [role="term"] |
| 531 | ---- |
| 532 | # apt install lttng-modules-dkms |
| 533 | # apt install liblttng-ust-dev |
| 534 | # apt install lttng-tools |
| 535 | ---- |
| 536 | -- |
| 537 | |
| 538 | . **If you need to instrument and trace <<java-application,Java |
| 539 | applications>>**, install the LTTng-UST Java agent: |
| 540 | + |
| 541 | -- |
| 542 | [role="term"] |
| 543 | ---- |
| 544 | # apt install liblttng-ust-agent-java |
| 545 | ---- |
| 546 | -- |
| 547 | |
| 548 | . **If you need to instrument and trace <<python-application,Python |
| 549 | applications>>**, install the LTTng-UST Python agent: |
| 550 | + |
| 551 | -- |
| 552 | [role="term"] |
| 553 | ---- |
| 554 | # apt install python3-lttngust |
| 555 | ---- |
| 556 | -- |
| 557 | |
| 558 | [[fedora]] |
| 559 | === Fedora |
| 560 | |
| 561 | To install LTTng{nbsp}{revision} on Fedora{nbsp}37, Fedora{nbsp}38, or |
| 562 | Fedora{nbsp}39: |
| 563 | |
| 564 | . Install the LTTng-tools{nbsp}{revision} and LTTng-UST{nbsp}{revision} |
| 565 | packages: |
| 566 | + |
| 567 | -- |
| 568 | [role="term"] |
| 569 | ---- |
| 570 | # yum install lttng-tools |
| 571 | # yum install lttng-ust |
| 572 | ---- |
| 573 | -- |
| 574 | |
| 575 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: |
| 576 | + |
| 577 | -- |
| 578 | [role="term",subs="attributes,specialcharacters"] |
| 579 | ---- |
| 580 | $ cd $(mktemp -d) && |
| 581 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-{revision}.tar.bz2 && |
| 582 | tar -xf lttng-modules-latest-{revision}.tar.bz2 && |
| 583 | cd lttng-modules-{revision}.* && |
| 584 | make && |
| 585 | sudo make modules_install && |
| 586 | sudo depmod -a |
| 587 | ---- |
| 588 | -- |
| 589 | |
| 590 | [IMPORTANT] |
| 591 | .Java and Python application instrumentation and tracing |
| 592 | ==== |
| 593 | If you need to instrument and trace <<java-application,Java |
| 594 | applications>> on Fedora, you need to build and install |
| 595 | LTTng-UST{nbsp}{revision} <<building-from-source,from source>> and pass |
| 596 | the `--enable-java-agent-jul`, `--enable-java-agent-log4j`, or |
| 597 | `--enable-java-agent-all` options to the `configure` script, depending |
| 598 | on which Java logging framework you use. |
| 599 | |
| 600 | If you need to instrument and trace <<python-application,Python |
| 601 | applications>> on Fedora, you need to build and install |
| 602 | LTTng-UST{nbsp}{revision} from source and pass the |
| 603 | `--enable-python-agent` option to the `configure` script. |
| 604 | ==== |
| 605 | |
| 606 | |
| 607 | [[arch-linux]] |
| 608 | === Arch Linux |
| 609 | |
| 610 | LTTng-UST{nbsp}{revision} is available in the _extra_ |
| 611 | repository of Arch Linux, while LTTng-tools{nbsp}{revision} and |
| 612 | LTTng-modules{nbsp}{revision} are available in the |
| 613 | https://aur.archlinux.org/[AUR]. |
| 614 | |
| 615 | To install LTTng{nbsp}{revision} on Arch Linux, using |
| 616 | https://github.com/Jguer/yay[yay] for the AUR packages: |
| 617 | |
| 618 | . Install the main LTTng{nbsp}{revision} packages: |
| 619 | + |
| 620 | -- |
| 621 | [role="term"] |
| 622 | ---- |
| 623 | # pacman -Sy lttng-ust |
| 624 | $ yay -Sy lttng-tools |
| 625 | $ yay -Sy lttng-modules |
| 626 | ---- |
| 627 | -- |
| 628 | |
| 629 | . **If you need to instrument and trace <<python-application,Python |
| 630 | applications>>**, install the LTTng-UST Python agent: |
| 631 | + |
| 632 | -- |
| 633 | [role="term"] |
| 634 | ---- |
| 635 | # pacman -Sy python-lttngust |
| 636 | ---- |
| 637 | -- |
| 638 | |
| 639 | |
| 640 | [[alpine-linux]] |
| 641 | === Alpine Linux |
| 642 | |
| 643 | To install LTTng-tools{nbsp}{revision} and LTTng-UST{nbsp}{revision} on |
| 644 | Alpine Linux{nbsp}3.16, Alpine Linux{nbsp}3.17, or Alpine Linux{nbsp}3.18: |
| 645 | |
| 646 | . Add the LTTng packages: |
| 647 | + |
| 648 | -- |
| 649 | [role="term"] |
| 650 | ---- |
| 651 | # apk add lttng-tools |
| 652 | # apk add lttng-ust-dev |
| 653 | ---- |
| 654 | -- |
| 655 | |
| 656 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: |
| 657 | + |
| 658 | -- |
| 659 | [role="term",subs="attributes,specialcharacters"] |
| 660 | ---- |
| 661 | $ cd $(mktemp -d) && |
| 662 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-{revision}.tar.bz2 && |
| 663 | tar -xf lttng-modules-latest-{revision}.tar.bz2 && |
| 664 | cd lttng-modules-{revision}.* && |
| 665 | make && |
| 666 | sudo make modules_install && |
| 667 | sudo depmod -a |
| 668 | ---- |
| 669 | -- |
| 670 | |
| 671 | |
| 672 | [[buildroot]] |
| 673 | === Buildroot |
| 674 | |
| 675 | To install LTTng{nbsp}{revision} on Buildroot{nbsp}2022.02, Buildroot{nbsp}2022.05, |
| 676 | Buildroot{nbsp}2022.08, Buildroot{nbsp}2022.11, Buildroot{nbsp}2023.02, |
| 677 | Buildroot{nbsp}2023.05, or Buildroot{nbsp}2023.08: |
| 678 | |
| 679 | . Launch the Buildroot configuration tool: |
| 680 | + |
| 681 | -- |
| 682 | [role="term"] |
| 683 | ---- |
| 684 | $ make menuconfig |
| 685 | ---- |
| 686 | -- |
| 687 | |
| 688 | . In **Kernel**, check **Linux kernel**. |
| 689 | . In **Toolchain**, check **Enable WCHAR support**. |
| 690 | . In **Target packages**{nbsp}→ **Debugging, profiling and benchmark**, |
| 691 | check **lttng-modules** and **lttng-tools**. |
| 692 | . In **Target packages**{nbsp}→ **Libraries**{nbsp}→ |
| 693 | **Other**, check **lttng-libust**. |
| 694 | |
| 695 | |
| 696 | [[oe-yocto]] |
| 697 | === OpenEmbedded and Yocto |
| 698 | |
| 699 | LTTng{nbsp}{revision} recipes are available in the |
| 700 | https://layers.openembedded.org/layerindex/branch/master/layer/openembedded-core/[`openembedded-core`] |
| 701 | layer for Yocto Project{nbsp}3.3 _Honister_, Yocto Project{nbsp}4.0 _Kirkstone_, |
| 702 | Yocto Project{nbsp}4.1 _Langdale_, Yocto Project{nbsp}4.2 _Mickledore_, and |
| 703 | Yocto Project{nbsp}4.3 _Nanbield_ under the following names: |
| 704 | |
| 705 | * `lttng-tools` |
| 706 | * `lttng-modules` |
| 707 | * `lttng-ust` |
| 708 | |
| 709 | With BitBake, the simplest way to include LTTng recipes in your target |
| 710 | image is to add them to `IMAGE_INSTALL_append` in path:{conf/local.conf}: |
| 711 | |
| 712 | ---- |
| 713 | IMAGE_INSTALL_append = " lttng-tools lttng-modules lttng-ust" |
| 714 | ---- |
| 715 | |
| 716 | If you use Hob: |
| 717 | |
| 718 | . Select a machine and an image recipe. |
| 719 | . Click **Edit image recipe**. |
| 720 | . Under the **All recipes** tab, search for **lttng**. |
| 721 | . Check the desired LTTng recipes. |
| 722 | |
| 723 | |
| 724 | [[building-from-source]] |
| 725 | === Build from source |
| 726 | |
| 727 | To build and install LTTng{nbsp}{revision} from source: |
| 728 | |
| 729 | . Using the package manager of your distribution, or from source, |
| 730 | install the following dependencies of LTTng-tools and LTTng-UST: |
| 731 | + |
| 732 | -- |
| 733 | * https://sourceforge.net/projects/libuuid/[libuuid] |
| 734 | * https://directory.fsf.org/wiki/Popt[popt] |
| 735 | * https://liburcu.org/[Userspace RCU] |
| 736 | * http://www.xmlsoft.org/[libxml2] |
| 737 | * **Optional**: https://github.com/numactl/numactl[numactl] |
| 738 | -- |
| 739 | |
| 740 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: |
| 741 | + |
| 742 | -- |
| 743 | [role="term"] |
| 744 | ---- |
| 745 | $ cd $(mktemp -d) && |
| 746 | wget https://lttng.org/files/lttng-modules/lttng-modules-latest-2.13.tar.bz2 && |
| 747 | tar -xf lttng-modules-latest-2.13.tar.bz2 && |
| 748 | cd lttng-modules-2.13.* && |
| 749 | make && |
| 750 | sudo make modules_install && |
| 751 | sudo depmod -a |
| 752 | ---- |
| 753 | -- |
| 754 | |
| 755 | . Download, build, and install the latest LTTng-UST{nbsp}{revision}: |
| 756 | + |
| 757 | -- |
| 758 | [role="term"] |
| 759 | ---- |
| 760 | $ cd $(mktemp -d) && |
| 761 | wget https://lttng.org/files/lttng-ust/lttng-ust-latest-2.13.tar.bz2 && |
| 762 | tar -xf lttng-ust-latest-2.13.tar.bz2 && |
| 763 | cd lttng-ust-2.13.* && |
| 764 | ./configure && |
| 765 | make && |
| 766 | sudo make install && |
| 767 | sudo ldconfig |
| 768 | ---- |
| 769 | -- |
| 770 | + |
| 771 | Add `--disable-numa` to `./configure` if you don't have |
| 772 | https://github.com/numactl/numactl[numactl]. |
| 773 | + |
| 774 | -- |
| 775 | [IMPORTANT] |
| 776 | .Java and Python application tracing |
| 777 | ==== |
| 778 | If you need to instrument and have LTTng trace <<java-application,Java |
| 779 | applications>>, pass the `--enable-java-agent-jul`, |
| 780 | `--enable-java-agent-log4j`, or `--enable-java-agent-all` options to the |
| 781 | `configure` script, depending on which Java logging framework you use. |
| 782 | |
| 783 | If you need to instrument and have LTTng trace |
| 784 | <<python-application,Python applications>>, pass the |
| 785 | `--enable-python-agent` option to the `configure` script. You can set |
| 786 | the env:PYTHON environment variable to the path to the Python interpreter |
| 787 | for which to install the LTTng-UST Python agent package. |
| 788 | ==== |
| 789 | -- |
| 790 | + |
| 791 | -- |
| 792 | [NOTE] |
| 793 | ==== |
| 794 | By default, LTTng-UST libraries are installed to |
| 795 | dir:{/usr/local/lib}, which is the de facto directory in which to |
| 796 | keep self-compiled and third-party libraries. |
| 797 | |
| 798 | When <<building-tracepoint-providers-and-user-application,linking an |
| 799 | instrumented user application with `liblttng-ust`>>: |
| 800 | |
| 801 | * Append `/usr/local/lib` to the env:LD_LIBRARY_PATH environment |
| 802 | variable. |
| 803 | |
| 804 | * Pass the `-L/usr/local/lib` and `-Wl,-rpath,/usr/local/lib` options to |
| 805 | man:gcc(1), man:g++(1), or man:clang(1). |
| 806 | ==== |
| 807 | -- |
| 808 | |
| 809 | . Download, build, and install the latest LTTng-tools{nbsp}{revision}: |
| 810 | + |
| 811 | -- |
| 812 | [role="term"] |
| 813 | ---- |
| 814 | $ cd $(mktemp -d) && |
| 815 | wget https://lttng.org/files/lttng-tools/lttng-tools-latest-2.13.tar.bz2 && |
| 816 | tar -xf lttng-tools-latest-2.13.tar.bz2 && |
| 817 | cd lttng-tools-2.13.* && |
| 818 | ./configure && |
| 819 | make && |
| 820 | sudo make install && |
| 821 | sudo ldconfig |
| 822 | ---- |
| 823 | -- |
| 824 | |
| 825 | TIP: The https://github.com/eepp/vlttng[vlttng tool] can do all the |
| 826 | previous steps automatically for a given version of LTTng and confine |
| 827 | the installed files to a specific directory. This can be useful to try |
| 828 | LTTng without installing it on your system. |
| 829 | |
| 830 | [[linux-kernel-sig]] |
| 831 | === Linux kernel module signature |
| 832 | |
| 833 | Linux kernel modules require trusted signatures in order to be loaded |
| 834 | when any of the following is true: |
| 835 | |
| 836 | * The system boots with |
| 837 | https://uefi.org/specs/UEFI/2.10/32_Secure_Boot_and_Driver_Signing.html#secure-boot-and-driver-signing[Secure Boot] |
| 838 | enabled. |
| 839 | |
| 840 | * The Linux kernel which boots is configured with |
| 841 | `CONFIG_MODULE_SIG_FORCE`. |
| 842 | |
| 843 | * The Linux kernel boots with a command line containing |
| 844 | `module.sig_enforce=1`. |
| 845 | |
| 846 | .`root` user running <<lttng-sessiond,`lttng-sessiond`>> which fails to load a required <<lttng-modules,kernel module>> due to the signature enforcement policies. |
| 847 | ==== |
| 848 | [role="term"] |
| 849 | ---- |
| 850 | # lttng-sessiond |
| 851 | Warning: No tracing group detected |
| 852 | modprobe: ERROR: could not insert 'lttng_ring_buffer_client_discard': Key was rejected by service |
| 853 | Error: Unable to load required module lttng-ring-buffer-client-discard |
| 854 | Warning: No kernel tracer available |
| 855 | ---- |
| 856 | ==== |
| 857 | |
| 858 | There are several methods to enroll trusted keys for signing modules |
| 859 | that are built from source. The precise details vary from one Linux |
| 860 | version to another, and distributions may have their own mechanisms. For |
| 861 | example, https://github.com/dell/dkms[DKMS] may autogenerate a key and |
| 862 | sign modules, but the key isn't automatically enrolled. |
| 863 | |
| 864 | See |
| 865 | https://www.kernel.org/doc/html/latest/admin-guide/module-signing.html[Kernel |
| 866 | module signing facility] and the documentation of your distribution |
| 867 | to learn more about signing Linux kernel modules. |
| 868 | |
| 869 | [[getting-started]] |
| 870 | == Quick start |
| 871 | |
| 872 | This is a short guide to get started quickly with LTTng kernel and user |
| 873 | space tracing. |
| 874 | |
| 875 | Before you follow this guide, make sure to <<installing-lttng,install>> |
| 876 | LTTng. |
| 877 | |
| 878 | This tutorial walks you through the steps to: |
| 879 | |
| 880 | . <<tracing-the-linux-kernel,Record Linux kernel events>>. |
| 881 | |
| 882 | . <<tracing-your-own-user-application,Record the events of a user |
| 883 | application>> written in C. |
| 884 | |
| 885 | . <<viewing-and-analyzing-your-traces,View and analyze the |
| 886 | recorded events>>. |
| 887 | |
| 888 | |
| 889 | [[tracing-the-linux-kernel]] |
| 890 | === Record Linux kernel events |
| 891 | |
| 892 | NOTE: The following command lines start with the `#` prompt because you |
| 893 | need root privileges to control the Linux kernel LTTng tracer. You can |
| 894 | also control the kernel tracer as a regular user if your Unix user is a |
| 895 | member of the <<tracing-group,tracing group>>. |
| 896 | |
| 897 | . Create a <<tracing-session,recording session>> to write LTTng traces |
| 898 | to dir:{/tmp/my-kernel-trace}: |
| 899 | + |
| 900 | -- |
| 901 | [role="term"] |
| 902 | ---- |
| 903 | # lttng create my-kernel-session --output=/tmp/my-kernel-trace |
| 904 | ---- |
| 905 | -- |
| 906 | |
| 907 | . List the available kernel tracepoints and system calls: |
| 908 | + |
| 909 | -- |
| 910 | [role="term"] |
| 911 | ---- |
| 912 | # lttng list --kernel |
| 913 | # lttng list --kernel --syscall |
| 914 | ---- |
| 915 | -- |
| 916 | |
| 917 | . Create <<event,recording event rules>> which match events having |
| 918 | the desired names, for example the `sched_switch` and |
| 919 | `sched_process_fork` tracepoints, and the man:open(2) and man:close(2) |
| 920 | system calls: |
| 921 | + |
| 922 | -- |
| 923 | [role="term"] |
| 924 | ---- |
| 925 | # lttng enable-event --kernel sched_switch,sched_process_fork |
| 926 | # lttng enable-event --kernel --syscall open,close |
| 927 | ---- |
| 928 | -- |
| 929 | + |
| 930 | Create a recording event rule which matches _all_ the Linux kernel |
| 931 | tracepoint events with the opt:lttng-enable-event(1):--all option |
| 932 | (recording with such a recording event rule generates a lot of data): |
| 933 | + |
| 934 | -- |
| 935 | [role="term"] |
| 936 | ---- |
| 937 | # lttng enable-event --kernel --all |
| 938 | ---- |
| 939 | -- |
| 940 | |
| 941 | . <<basic-tracing-session-control,Start recording>>: |
| 942 | + |
| 943 | -- |
| 944 | [role="term"] |
| 945 | ---- |
| 946 | # lttng start |
| 947 | ---- |
| 948 | -- |
| 949 | |
| 950 | . Do some operation on your system for a few seconds. For example, |
| 951 | load a website, or list the files of a directory. |
| 952 | |
| 953 | . <<creating-destroying-tracing-sessions,Destroy>> the current |
| 954 | recording session: |
| 955 | + |
| 956 | -- |
| 957 | [role="term"] |
| 958 | ---- |
| 959 | # lttng destroy |
| 960 | ---- |
| 961 | -- |
| 962 | + |
| 963 | The man:lttng-destroy(1) command doesn't destroy the trace data; it |
| 964 | only destroys the state of the recording session. |
| 965 | + |
| 966 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) command |
| 967 | implicitly (see ``<<basic-tracing-session-control,Start and stop a |
| 968 | recording session>>''). You need to stop recording to make LTTng flush |
| 969 | the remaining trace data and make the trace readable. |
| 970 | |
| 971 | . For the sake of this example, make the recorded trace accessible to |
| 972 | the non-root users: |
| 973 | + |
| 974 | -- |
| 975 | [role="term"] |
| 976 | ---- |
| 977 | # chown -R $(whoami) /tmp/my-kernel-trace |
| 978 | ---- |
| 979 | -- |
| 980 | |
| 981 | See ``<<viewing-and-analyzing-your-traces,View and analyze the |
| 982 | recorded events>>'' to view the recorded events. |
| 983 | |
| 984 | |
| 985 | [[tracing-your-own-user-application]] |
| 986 | === Record user application events |
| 987 | |
| 988 | This section walks you through a simple example to record the events of |
| 989 | a _Hello world_ program written in{nbsp}C. |
| 990 | |
| 991 | To create the traceable user application: |
| 992 | |
| 993 | . Create the tracepoint provider header file, which defines the |
| 994 | tracepoints and the events they can generate: |
| 995 | + |
| 996 | -- |
| 997 | [source,c] |
| 998 | .path:{hello-tp.h} |
| 999 | ---- |
| 1000 | #undef LTTNG_UST_TRACEPOINT_PROVIDER |
| 1001 | #define LTTNG_UST_TRACEPOINT_PROVIDER hello_world |
| 1002 | |
| 1003 | #undef LTTNG_UST_TRACEPOINT_INCLUDE |
| 1004 | #define LTTNG_UST_TRACEPOINT_INCLUDE "./hello-tp.h" |
| 1005 | |
| 1006 | #if !defined(_HELLO_TP_H) || defined(LTTNG_UST_TRACEPOINT_HEADER_MULTI_READ) |
| 1007 | #define _HELLO_TP_H |
| 1008 | |
| 1009 | #include <lttng/tracepoint.h> |
| 1010 | |
| 1011 | LTTNG_UST_TRACEPOINT_EVENT( |
| 1012 | hello_world, |
| 1013 | my_first_tracepoint, |
| 1014 | LTTNG_UST_TP_ARGS( |
| 1015 | int, my_integer_arg, |
| 1016 | char *, my_string_arg |
| 1017 | ), |
| 1018 | LTTNG_UST_TP_FIELDS( |
| 1019 | lttng_ust_field_string(my_string_field, my_string_arg) |
| 1020 | lttng_ust_field_integer(int, my_integer_field, my_integer_arg) |
| 1021 | ) |
| 1022 | ) |
| 1023 | |
| 1024 | #endif /* _HELLO_TP_H */ |
| 1025 | |
| 1026 | #include <lttng/tracepoint-event.h> |
| 1027 | ---- |
| 1028 | -- |
| 1029 | |
| 1030 | . Create the tracepoint provider package source file: |
| 1031 | + |
| 1032 | -- |
| 1033 | [source,c] |
| 1034 | .path:{hello-tp.c} |
| 1035 | ---- |
| 1036 | #define LTTNG_UST_TRACEPOINT_CREATE_PROBES |
| 1037 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 1038 | |
| 1039 | #include "hello-tp.h" |
| 1040 | ---- |
| 1041 | -- |
| 1042 | |
| 1043 | . Build the tracepoint provider package: |
| 1044 | + |
| 1045 | -- |
| 1046 | [role="term"] |
| 1047 | ---- |
| 1048 | $ gcc -c -I. hello-tp.c |
| 1049 | ---- |
| 1050 | -- |
| 1051 | |
| 1052 | . Create the _Hello World_ application source file: |
| 1053 | + |
| 1054 | -- |
| 1055 | [source,c] |
| 1056 | .path:{hello.c} |
| 1057 | ---- |
| 1058 | #include <stdio.h> |
| 1059 | #include "hello-tp.h" |
| 1060 | |
| 1061 | int main(int argc, char *argv[]) |
| 1062 | { |
| 1063 | unsigned int i; |
| 1064 | |
| 1065 | puts("Hello, World!\nPress Enter to continue..."); |
| 1066 | |
| 1067 | /* |
| 1068 | * The following getchar() call only exists for the purpose of this |
| 1069 | * demonstration, to pause the application in order for you to have |
| 1070 | * time to list its tracepoints. You don't need it otherwise. |
| 1071 | */ |
| 1072 | getchar(); |
| 1073 | |
| 1074 | /* |
| 1075 | * An lttng_ust_tracepoint() call. |
| 1076 | * |
| 1077 | * Arguments, as defined in `hello-tp.h`: |
| 1078 | * |
| 1079 | * 1. Tracepoint provider name (required) |
| 1080 | * 2. Tracepoint name (required) |
| 1081 | * 3. `my_integer_arg` (first user-defined argument) |
| 1082 | * 4. `my_string_arg` (second user-defined argument) |
| 1083 | * |
| 1084 | * Notice the tracepoint provider and tracepoint names are |
| 1085 | * C identifiers, NOT strings: they're in fact parts of variables |
| 1086 | * that the macros in `hello-tp.h` create. |
| 1087 | */ |
| 1088 | lttng_ust_tracepoint(hello_world, my_first_tracepoint, 23, |
| 1089 | "hi there!"); |
| 1090 | |
| 1091 | for (i = 0; i < argc; i++) { |
| 1092 | lttng_ust_tracepoint(hello_world, my_first_tracepoint, |
| 1093 | i, argv[i]); |
| 1094 | } |
| 1095 | |
| 1096 | puts("Quitting now!"); |
| 1097 | lttng_ust_tracepoint(hello_world, my_first_tracepoint, |
| 1098 | i * i, "i^2"); |
| 1099 | return 0; |
| 1100 | } |
| 1101 | ---- |
| 1102 | -- |
| 1103 | |
| 1104 | . Build the application: |
| 1105 | + |
| 1106 | -- |
| 1107 | [role="term"] |
| 1108 | ---- |
| 1109 | $ gcc -c hello.c |
| 1110 | ---- |
| 1111 | -- |
| 1112 | |
| 1113 | . Link the application with the tracepoint provider package, |
| 1114 | `liblttng-ust` and `libdl`: |
| 1115 | + |
| 1116 | -- |
| 1117 | [role="term"] |
| 1118 | ---- |
| 1119 | $ gcc -o hello hello.o hello-tp.o -llttng-ust -ldl |
| 1120 | ---- |
| 1121 | -- |
| 1122 | |
| 1123 | Here's the whole build process: |
| 1124 | |
| 1125 | [role="img-100"] |
| 1126 | .Build steps of the user space tracing tutorial. |
| 1127 | image::ust-flow.png[] |
| 1128 | |
| 1129 | To record the events of the user application: |
| 1130 | |
| 1131 | . Run the application with a few arguments: |
| 1132 | + |
| 1133 | -- |
| 1134 | [role="term"] |
| 1135 | ---- |
| 1136 | $ ./hello world and beyond |
| 1137 | ---- |
| 1138 | -- |
| 1139 | + |
| 1140 | You see: |
| 1141 | + |
| 1142 | -- |
| 1143 | ---- |
| 1144 | Hello, World! |
| 1145 | Press Enter to continue... |
| 1146 | ---- |
| 1147 | -- |
| 1148 | |
| 1149 | . Start an LTTng <<lttng-sessiond,session daemon>>: |
| 1150 | + |
| 1151 | -- |
| 1152 | [role="term"] |
| 1153 | ---- |
| 1154 | $ lttng-sessiond --daemonize |
| 1155 | ---- |
| 1156 | -- |
| 1157 | + |
| 1158 | NOTE: A session daemon might already be running, for example as a |
| 1159 | service that the service manager of your distribution started. |
| 1160 | |
| 1161 | . List the available user space tracepoints: |
| 1162 | + |
| 1163 | -- |
| 1164 | [role="term"] |
| 1165 | ---- |
| 1166 | $ lttng list --userspace |
| 1167 | ---- |
| 1168 | -- |
| 1169 | + |
| 1170 | You see the `hello_world:my_first_tracepoint` tracepoint listed |
| 1171 | under the `./hello` process. |
| 1172 | |
| 1173 | . Create a <<tracing-session,recording session>>: |
| 1174 | + |
| 1175 | -- |
| 1176 | [role="term"] |
| 1177 | ---- |
| 1178 | $ lttng create my-user-space-session |
| 1179 | ---- |
| 1180 | -- |
| 1181 | |
| 1182 | . Create a <<event,recording event rule>> which matches user space |
| 1183 | tracepoint events named `hello_world:my_first_tracepoint`: |
| 1184 | + |
| 1185 | -- |
| 1186 | [role="term"] |
| 1187 | ---- |
| 1188 | $ lttng enable-event --userspace hello_world:my_first_tracepoint |
| 1189 | ---- |
| 1190 | -- |
| 1191 | |
| 1192 | . <<basic-tracing-session-control,Start recording>>: |
| 1193 | + |
| 1194 | -- |
| 1195 | [role="term"] |
| 1196 | ---- |
| 1197 | $ lttng start |
| 1198 | ---- |
| 1199 | -- |
| 1200 | |
| 1201 | . Go back to the running `hello` application and press **Enter**. |
| 1202 | + |
| 1203 | The program executes all `lttng_ust_tracepoint()` instrumentation |
| 1204 | points, emitting events as the event rule you created in step{nbsp}5 |
| 1205 | matches them, and |
| 1206 | exits. |
| 1207 | |
| 1208 | . <<creating-destroying-tracing-sessions,Destroy>> the current |
| 1209 | recording session: |
| 1210 | + |
| 1211 | -- |
| 1212 | [role="term"] |
| 1213 | ---- |
| 1214 | $ lttng destroy |
| 1215 | ---- |
| 1216 | -- |
| 1217 | + |
| 1218 | The man:lttng-destroy(1) command doesn't destroy the trace data; it |
| 1219 | only destroys the state of the recording session. |
| 1220 | + |
| 1221 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) command |
| 1222 | implicitly (see ``<<basic-tracing-session-control,Start and stop a |
| 1223 | recording session>>''). You need to stop recording to make LTTng flush |
| 1224 | the remaining trace data and make the trace readable. |
| 1225 | |
| 1226 | By default, LTTng saves the traces to the |
| 1227 | +$LTTNG_HOME/lttng-traces/__NAME__-__DATE__-__TIME__+ directory, where |
| 1228 | +__NAME__+ is the recording session name. The env:LTTNG_HOME environment |
| 1229 | variable defaults to `$HOME` if not set. |
| 1230 | |
| 1231 | |
| 1232 | [[viewing-and-analyzing-your-traces]] |
| 1233 | === View and analyze the recorded events |
| 1234 | |
| 1235 | Once you have completed the <<tracing-the-linux-kernel,Record Linux |
| 1236 | kernel events>> and <<tracing-your-own-user-application,Record user |
| 1237 | application events>> tutorials, you can inspect the recorded events. |
| 1238 | |
| 1239 | There are tools you can use to read LTTng traces: |
| 1240 | |
| 1241 | https://babeltrace.org/[Babeltrace{nbsp}2]:: |
| 1242 | A rich, flexible trace manipulation toolkit which includes |
| 1243 | a versatile command-line interface |
| 1244 | (man:babeltrace2(1)), |
| 1245 | a https://babeltrace.org/docs/v2.0/libbabeltrace2/[C{nbsp}library], |
| 1246 | and https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings] |
| 1247 | so that you can easily process or convert an LTTng trace with |
| 1248 | your own script. |
| 1249 | + |
| 1250 | The Babeltrace{nbsp}2 project ships with a plugin |
| 1251 | (man:babeltrace2-plugin-ctf(7)) which supports the format of the traces |
| 1252 | which LTTng produces, https://diamon.org/ctf/[CTF]. |
| 1253 | |
| 1254 | http://tracecompass.org/[Trace Compass]:: |
| 1255 | A graphical user interface for viewing and analyzing any type of |
| 1256 | logs or traces, including those of LTTng. |
| 1257 | |
| 1258 | NOTE: This section assumes that LTTng wrote the traces it recorded |
| 1259 | during the previous tutorials to their default location, in the |
| 1260 | dir:{$LTTNG_HOME/lttng-traces} directory. The env:LTTNG_HOME |
| 1261 | environment variable defaults to `$HOME` if not set. |
| 1262 | |
| 1263 | |
| 1264 | [[viewing-and-analyzing-your-traces-bt]] |
| 1265 | ==== Use the cmd:babeltrace2 command-line tool |
| 1266 | |
| 1267 | The simplest way to list all the recorded events of an LTTng trace is to |
| 1268 | pass its path to man:babeltrace2(1), without options: |
| 1269 | |
| 1270 | [role="term"] |
| 1271 | ---- |
| 1272 | $ babeltrace2 ~/lttng-traces/my-user-space-session* |
| 1273 | ---- |
| 1274 | |
| 1275 | The cmd:babeltrace2 command finds all traces recursively within the |
| 1276 | given path and prints all their events, sorting them chronologically. |
| 1277 | |
| 1278 | Pipe the output of cmd:babeltrace2 into a tool like man:grep(1) for |
| 1279 | further filtering: |
| 1280 | |
| 1281 | [role="term"] |
| 1282 | ---- |
| 1283 | $ babeltrace2 /tmp/my-kernel-trace | grep _switch |
| 1284 | ---- |
| 1285 | |
| 1286 | Pipe the output of cmd:babeltrace2 into a tool like man:wc(1) to count |
| 1287 | the recorded events: |
| 1288 | |
| 1289 | [role="term"] |
| 1290 | ---- |
| 1291 | $ babeltrace2 /tmp/my-kernel-trace | grep _open | wc --lines |
| 1292 | ---- |
| 1293 | |
| 1294 | |
| 1295 | [[viewing-and-analyzing-your-traces-bt-python]] |
| 1296 | ==== Use the Babeltrace{nbsp}2 Python bindings |
| 1297 | |
| 1298 | The <<viewing-and-analyzing-your-traces-bt,text output of |
| 1299 | cmd:babeltrace2>> is useful to isolate event records by simple matching |
| 1300 | using man:grep(1) and similar utilities. However, more elaborate |
| 1301 | filters, such as keeping only event records with a field value falling |
| 1302 | within a specific range, are not trivial to write using a shell. |
| 1303 | Moreover, reductions and even the most basic computations involving |
| 1304 | multiple event records are virtually impossible to implement. |
| 1305 | |
| 1306 | Fortunately, Babeltrace{nbsp}2 ships with |
| 1307 | https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings] |
| 1308 | which make it easy to read the event records of an LTTng trace |
| 1309 | sequentially and compute the desired information. |
| 1310 | |
| 1311 | The following script accepts an LTTng Linux kernel trace path as its |
| 1312 | first argument and prints the short names of the top five running |
| 1313 | processes on CPU{nbsp}0 during the whole trace: |
| 1314 | |
| 1315 | [source,python] |
| 1316 | .path:{top5proc.py} |
| 1317 | ---- |
| 1318 | import bt2 |
| 1319 | import sys |
| 1320 | import collections |
| 1321 | |
| 1322 | |
| 1323 | def top5proc(): |
| 1324 | # Get the trace path from the first command-line argument |
| 1325 | it = bt2.TraceCollectionMessageIterator(sys.argv[1]) |
| 1326 | |
| 1327 | # This counter dictionary will hold execution times: |
| 1328 | # |
| 1329 | # Task command name -> Total execution time (ns) |
| 1330 | exec_times = collections.Counter() |
| 1331 | |
| 1332 | # This holds the last `sched_switch` timestamp |
| 1333 | last_ts = None |
| 1334 | |
| 1335 | for msg in it: |
| 1336 | # We only care about event messages |
| 1337 | if type(msg) is not bt2._EventMessageConst: |
| 1338 | continue |
| 1339 | |
| 1340 | # Event of the event message |
| 1341 | event = msg.event |
| 1342 | |
| 1343 | # Keep only `sched_switch` events |
| 1344 | if event.cls.name != 'sched_switch': |
| 1345 | continue |
| 1346 | |
| 1347 | # Keep only records of events which LTTng emitted from CPU 0 |
| 1348 | if event.packet.context_field['cpu_id'] != 0: |
| 1349 | continue |
| 1350 | |
| 1351 | # Event timestamp (ns) |
| 1352 | cur_ts = msg.default_clock_snapshot.ns_from_origin |
| 1353 | |
| 1354 | if last_ts is None: |
| 1355 | # Start here |
| 1356 | last_ts = cur_ts |
| 1357 | |
| 1358 | # (Short) name of the previous task command |
| 1359 | prev_comm = str(event.payload_field['prev_comm']) |
| 1360 | |
| 1361 | # Initialize an entry in our dictionary if not done yet |
| 1362 | if prev_comm not in exec_times: |
| 1363 | exec_times[prev_comm] = 0 |
| 1364 | |
| 1365 | # Compute previous command execution time |
| 1366 | diff = cur_ts - last_ts |
| 1367 | |
| 1368 | # Update execution time of this command |
| 1369 | exec_times[prev_comm] += diff |
| 1370 | |
| 1371 | # Update last timestamp |
| 1372 | last_ts = cur_ts |
| 1373 | |
| 1374 | # Print top 5 |
| 1375 | for name, ns in exec_times.most_common(5): |
| 1376 | print('{:20}{} s'.format(name, ns / 1e9)) |
| 1377 | |
| 1378 | |
| 1379 | if __name__ == '__main__': |
| 1380 | top5proc() |
| 1381 | ---- |
| 1382 | |
| 1383 | Run this script: |
| 1384 | |
| 1385 | [role="term"] |
| 1386 | ---- |
| 1387 | $ python3 top5proc.py /tmp/my-kernel-trace/kernel |
| 1388 | ---- |
| 1389 | |
| 1390 | Output example: |
| 1391 | |
| 1392 | ---- |
| 1393 | swapper/0 48.607245889 s |
| 1394 | chromium 7.192738188 s |
| 1395 | pavucontrol 0.709894415 s |
| 1396 | Compositor 0.660867933 s |
| 1397 | Xorg.bin 0.616753786 s |
| 1398 | ---- |
| 1399 | |
| 1400 | Note that `swapper/0` is the ``idle'' process of CPU{nbsp}0 on Linux; |
| 1401 | since we weren't using the CPU that much when recording, its first |
| 1402 | position in the list makes sense. |
| 1403 | |
| 1404 | |
| 1405 | [[core-concepts]] |
| 1406 | == [[understanding-lttng]]Core concepts |
| 1407 | |
| 1408 | From a user's perspective, the LTTng system is built on a few concepts, |
| 1409 | or objects, on which the <<lttng-cli,cmd:lttng command-line tool>> |
| 1410 | operates by sending commands to the <<lttng-sessiond,session daemon>> |
| 1411 | (through <<liblttng-ctl-lttng,`liblttng-ctl`>>). |
| 1412 | |
| 1413 | Understanding how those objects relate to each other is key to master |
| 1414 | the toolkit. |
| 1415 | |
| 1416 | The core concepts of LTTng are: |
| 1417 | |
| 1418 | * <<"event-rule","Instrumentation point, event rule, and event">> |
| 1419 | * <<trigger,Trigger>> |
| 1420 | * <<tracing-session,Recording session>> |
| 1421 | * <<domain,Tracing domain>> |
| 1422 | * <<channel,Channel and ring buffer>> |
| 1423 | * <<event,Recording event rule and event record>> |
| 1424 | |
| 1425 | NOTE: The man:lttng-concepts(7) manual page also documents the core |
| 1426 | concepts of LTTng, with more links to other LTTng-tools manual pages. |
| 1427 | |
| 1428 | |
| 1429 | [[event-rule]] |
| 1430 | === Instrumentation point, event rule, and event |
| 1431 | |
| 1432 | An _instrumentation point_ is a point, within a piece of software, |
| 1433 | which, when executed, creates an LTTng _event_. |
| 1434 | |
| 1435 | LTTng offers various <<instrumentation-point-types,types of |
| 1436 | instrumentation>>. |
| 1437 | |
| 1438 | An _event rule_ is a set of conditions to match a set of events. |
| 1439 | |
| 1440 | When LTTng creates an event{nbsp}__E__, an event rule{nbsp}__ER__ is |
| 1441 | said to __match__{nbsp}__E__ when{nbsp}__E__ satisfies _all_ the |
| 1442 | conditions of{nbsp}__ER__. This concept is similar to a |
| 1443 | https://en.wikipedia.org/wiki/Regular_expression[regular expression] |
| 1444 | which matches a set of strings. |
| 1445 | |
| 1446 | When an event rule matches an event, LTTng _emits_ the event, therefore |
| 1447 | attempting to execute one or more actions. |
| 1448 | |
| 1449 | [IMPORTANT] |
| 1450 | ==== |
| 1451 | [[event-creation-emission-opti]]The event creation and emission |
| 1452 | processes are documentation concepts to help understand the journey from |
| 1453 | an instrumentation point to the execution of actions. |
| 1454 | |
| 1455 | The actual creation of an event can be costly because LTTng needs to |
| 1456 | evaluate the arguments of the instrumentation point. |
| 1457 | |
| 1458 | In practice, LTTng implements various optimizations for the Linux kernel |
| 1459 | and user space <<domain,tracing domains>> to avoid actually creating an |
| 1460 | event when the tracer knows, thanks to properties which are independent |
| 1461 | from the event payload and current context, that it would never emit |
| 1462 | such an event. Those properties are: |
| 1463 | |
| 1464 | * The <<instrumentation-point-types,instrumentation point type>>. |
| 1465 | |
| 1466 | * The instrumentation point name. |
| 1467 | |
| 1468 | * The instrumentation point log level. |
| 1469 | |
| 1470 | * For a <<event,recording event rule>>: |
| 1471 | ** The status of the rule itself. |
| 1472 | ** The status of the <<channel,channel>>. |
| 1473 | ** The activity of the <<tracing-session,recording session>>. |
| 1474 | ** Whether or not the process for which LTTng would create the event is |
| 1475 | <<pid-tracking,allowed to record events>>. |
| 1476 | |
| 1477 | In other words: if, for a given instrumentation point{nbsp}__IP__, the |
| 1478 | LTTng tracer knows that it would never emit an event, |
| 1479 | executing{nbsp}__IP__ represents a simple boolean variable check and, |
| 1480 | for a Linux kernel recording event rule, a few process attribute checks. |
| 1481 | ==== |
| 1482 | |
| 1483 | As of LTTng{nbsp}{revision}, there are two places where you can find an |
| 1484 | event rule: |
| 1485 | |
| 1486 | <<event,Recording event rule>>:: |
| 1487 | A specific type of event rule of which the action is to record the |
| 1488 | matched event as an event record. |
| 1489 | + |
| 1490 | See ``<<enabling-disabling-events,Create and enable a recording event |
| 1491 | rule>>'' to learn more. |
| 1492 | |
| 1493 | ``Event rule matches'' <<trigger,trigger>> condition (since LTTng{nbsp}2.13):: |
| 1494 | When the event rule of the trigger condition matches an event, LTTng |
| 1495 | can execute user-defined actions such as sending an LTTng |
| 1496 | notification, |
| 1497 | <<basic-tracing-session-control,starting a recording session>>, |
| 1498 | and more. |
| 1499 | + |
| 1500 | See “<<add-event-rule-matches-trigger,Add an ``event rule matches'' |
| 1501 | trigger to a session daemon>>” to learn more. |
| 1502 | |
| 1503 | For LTTng to emit an event{nbsp}__E__,{nbsp}__E__ must satisfy _all_ the |
| 1504 | basic conditions of an event rule{nbsp}__ER__, that is: |
| 1505 | |
| 1506 | * The instrumentation point from which LTTng |
| 1507 | creates{nbsp}__E__ has a specific |
| 1508 | <<instrumentation-point-types,type>>. |
| 1509 | |
| 1510 | * A pattern matches the name of{nbsp}__E__ while another pattern |
| 1511 | doesn't. |
| 1512 | |
| 1513 | * The log level of the instrumentation point from which LTTng |
| 1514 | creates{nbsp}__E__ is at least as severe as some value, or is exactly |
| 1515 | some value. |
| 1516 | |
| 1517 | * The fields of the payload of{nbsp}__E__ and the current context fields |
| 1518 | satisfy a filter expression. |
| 1519 | |
| 1520 | A <<event,recording event rule>> has additional, implicit conditions to |
| 1521 | satisfy. |
| 1522 | |
| 1523 | |
| 1524 | [[instrumentation-point-types]] |
| 1525 | ==== Instrumentation point types |
| 1526 | |
| 1527 | As of LTTng{nbsp}{revision}, the available instrumentation point |
| 1528 | types are, depending on the <<domain,tracing domain>>: |
| 1529 | |
| 1530 | Linux kernel:: |
| 1531 | LTTng tracepoint::: |
| 1532 | A statically defined point in the source code of the kernel |
| 1533 | image or of a kernel module using the |
| 1534 | <<lttng-modules,LTTng-modules>> macros. |
| 1535 | |
| 1536 | Linux kernel system call::: |
| 1537 | Entry, exit, or both of a Linux kernel system call. |
| 1538 | |
| 1539 | Linux https://www.kernel.org/doc/html/latest/trace/kprobes.html[kprobe]::: |
| 1540 | A single probe dynamically placed in the compiled kernel code. |
| 1541 | + |
| 1542 | When you create such an instrumentation point, you set its memory |
| 1543 | address or symbol name. |
| 1544 | |
| 1545 | Linux user space probe::: |
| 1546 | A single probe dynamically placed at the entry of a compiled |
| 1547 | user space application/library function through the kernel. |
| 1548 | + |
| 1549 | When you create such an instrumentation point, you set: |
| 1550 | + |
| 1551 | -- |
| 1552 | With the ELF method:: |
| 1553 | Its application/library path and its symbol name. |
| 1554 | |
| 1555 | With the USDT method:: |
| 1556 | Its application/library path, its provider name, and its probe name. |
| 1557 | + |
| 1558 | ``USDT'' stands for _SystemTap User-level Statically Defined Tracing_, |
| 1559 | a http://dtrace.org/blogs/about/[DTrace]-style marker. |
| 1560 | -- |
| 1561 | + |
| 1562 | As of LTTng{nbsp}{revision}, LTTng only supports USDT probes which |
| 1563 | are _not_ reference-counted. |
| 1564 | |
| 1565 | Linux https://www.kernel.org/doc/html/latest/trace/kprobes.html[kretprobe]::: |
| 1566 | Entry, exit, or both of a Linux kernel function. |
| 1567 | + |
| 1568 | When you create such an instrumentation point, you set the memory |
| 1569 | address or symbol name of its function. |
| 1570 | |
| 1571 | User space:: |
| 1572 | LTTng tracepoint::: |
| 1573 | A statically defined point in the source code of a C/$$C++$$ |
| 1574 | application/library using the |
| 1575 | <<lttng-ust,LTTng-UST>> macros. |
| 1576 | |
| 1577 | `java.util.logging`, Apache log4j, and Python:: |
| 1578 | Java or Python logging statement::: |
| 1579 | A method call on a Java or Python logger attached to an |
| 1580 | LTTng-UST handler. |
| 1581 | |
| 1582 | See ``<<list-instrumentation-points,List the available instrumentation |
| 1583 | points>>'' to learn how to list available Linux kernel, user space, and |
| 1584 | logging instrumentation points. |
| 1585 | |
| 1586 | |
| 1587 | [[trigger]] |
| 1588 | === Trigger |
| 1589 | |
| 1590 | A _trigger_ associates a condition to one or more actions. |
| 1591 | |
| 1592 | When the condition of a trigger is satisfied, LTTng attempts to execute |
| 1593 | its actions. |
| 1594 | |
| 1595 | As of LTTng{nbsp}{revision}, the available trigger conditions and |
| 1596 | actions are: |
| 1597 | |
| 1598 | Conditions:: |
| 1599 | + |
| 1600 | * The consumed buffer size of a given <<tracing-session,recording |
| 1601 | session>> becomes greater than some value. |
| 1602 | |
| 1603 | * The buffer usage of a given <<channel,channel>> becomes greater than |
| 1604 | some value. |
| 1605 | |
| 1606 | * The buffer usage of a given channel becomes less than some value. |
| 1607 | |
| 1608 | * There's an ongoing <<session-rotation,recording session rotation>>. |
| 1609 | |
| 1610 | * A recording session rotation becomes completed. |
| 1611 | |
| 1612 | * An <<add-event-rule-matches-trigger,event rule matches>> an event. |
| 1613 | |
| 1614 | Actions:: |
| 1615 | + |
| 1616 | * <<trigger-event-notif,Send a notification>> to a user application. |
| 1617 | * <<basic-tracing-session-control,Start>> a given recording session. |
| 1618 | * <<basic-tracing-session-control,Stop>> a given recording session. |
| 1619 | * <<session-rotation,Archive the current trace chunk>> of a given |
| 1620 | recording session (rotate). |
| 1621 | * <<taking-a-snapshot,Take a snapshot>> of a given recording session. |
| 1622 | |
| 1623 | A trigger belongs to a <<lttng-sessiond,session daemon>>, not to a |
| 1624 | specific recording session. For a given session daemon, each Unix user has |
| 1625 | its own, private triggers. Note, however, that the `root` Unix user may, |
| 1626 | for the root session daemon: |
| 1627 | |
| 1628 | * Add a trigger as another Unix user. |
| 1629 | |
| 1630 | * List all the triggers, regardless of their owner. |
| 1631 | |
| 1632 | * Remove a trigger which belongs to another Unix user. |
| 1633 | |
| 1634 | For a given session daemon and Unix user, a trigger has a unique name. |
| 1635 | |
| 1636 | |
| 1637 | [[tracing-session]] |
| 1638 | === Recording session |
| 1639 | |
| 1640 | A _recording session_ (named ``tracing session'' prior to |
| 1641 | LTTng{nbsp}2.13) is a stateful dialogue between you and a |
| 1642 | <<lttng-sessiond,session daemon>> for everything related to |
| 1643 | <<event,event recording>>. |
| 1644 | |
| 1645 | Everything that you do when you control LTTng tracers to record events |
| 1646 | happens within a recording session. In particular, a recording session: |
| 1647 | |
| 1648 | * Has its own name, unique for a given session daemon. |
| 1649 | |
| 1650 | * Has its own set of trace files, if any. |
| 1651 | |
| 1652 | * Has its own state of activity (started or stopped). |
| 1653 | + |
| 1654 | An active recording session is an implicit <<event,recording event rule>> |
| 1655 | condition. |
| 1656 | |
| 1657 | * Has its own <<tracing-session-mode,mode>> (local, network streaming, |
| 1658 | snapshot, or live). |
| 1659 | |
| 1660 | * Has its own <<channel,channels>> to which are attached their own |
| 1661 | recording event rules. |
| 1662 | |
| 1663 | * Has its own <<pid-tracking,process attribute inclusion sets>>. |
| 1664 | |
| 1665 | [role="img-100"] |
| 1666 | .A _recording session_ contains <<channel,channels>> that are members of <<domain,tracing domains>> and contain <<event,recording event rules>>. |
| 1667 | image::concepts.png[] |
| 1668 | |
| 1669 | Those attributes and objects are completely isolated between different |
| 1670 | recording sessions. |
| 1671 | |
| 1672 | A recording session is like an |
| 1673 | https://en.wikipedia.org/wiki/Automated_teller_machine[ATM] session: the |
| 1674 | operations you do on the banking system through the ATM don't alter the |
| 1675 | data of other users of the same system. In the case of the ATM, a |
| 1676 | session lasts as long as your bank card is inside. In the case of LTTng, |
| 1677 | a recording session lasts from the man:lttng-create(1) command to the |
| 1678 | man:lttng-destroy(1) command. |
| 1679 | |
| 1680 | [role="img-100"] |
| 1681 | .Each Unix user has its own set of recording sessions. |
| 1682 | image::many-sessions.png[] |
| 1683 | |
| 1684 | A recording session belongs to a <<lttng-sessiond,session daemon>>. For a |
| 1685 | given session daemon, each Unix user has its own, private recording |
| 1686 | sessions. Note, however, that the `root` Unix user may operate on or |
| 1687 | destroy another user's recording session. |
| 1688 | |
| 1689 | |
| 1690 | [[tracing-session-mode]] |
| 1691 | ==== Recording session mode |
| 1692 | |
| 1693 | LTTng offers four recording session modes: |
| 1694 | |
| 1695 | [[local-mode]]Local mode:: |
| 1696 | Write the trace data to the local file system. |
| 1697 | |
| 1698 | [[net-streaming-mode]]Network streaming mode:: |
| 1699 | Send the trace data over the network to a listening |
| 1700 | <<lttng-relayd,relay daemon>>. |
| 1701 | |
| 1702 | [[snapshot-mode]]Snapshot mode:: |
| 1703 | Only write the trace data to the local file system or send it to a |
| 1704 | listening relay daemon when LTTng <<taking-a-snapshot,takes a |
| 1705 | snapshot>>. |
| 1706 | + |
| 1707 | LTTng forces all the <<channel,channels>> |
| 1708 | to be created to be configured to be snapshot-ready. |
| 1709 | + |
| 1710 | LTTng takes a snapshot of such a recording session when: |
| 1711 | + |
| 1712 | -- |
| 1713 | * You run the man:lttng-snapshot(1) command. |
| 1714 | |
| 1715 | * LTTng executes a `snapshot-session` <<trigger,trigger>> action. |
| 1716 | -- |
| 1717 | |
| 1718 | [[live-mode]]Live mode:: |
| 1719 | Send the trace data over the network to a listening relay daemon |
| 1720 | for <<lttng-live,live reading>>. |
| 1721 | + |
| 1722 | An LTTng live reader (for example, man:babeltrace2(1)) can connect to |
| 1723 | the same relay daemon to receive trace data while the recording session is |
| 1724 | active. |
| 1725 | |
| 1726 | |
| 1727 | [[domain]] |
| 1728 | === Tracing domain |
| 1729 | |
| 1730 | A _tracing domain_ identifies a type of LTTng tracer. |
| 1731 | |
| 1732 | A tracing domain has its own properties and features. |
| 1733 | |
| 1734 | There are currently five available tracing domains: |
| 1735 | |
| 1736 | * Linux kernel |
| 1737 | * User space |
| 1738 | * `java.util.logging` (JUL) |
| 1739 | * log4j |
| 1740 | * Python |
| 1741 | |
| 1742 | You must specify a tracing domain to target a type of LTTng tracer when |
| 1743 | using some <<lttng-cli,cmd:lttng>> commands to avoid ambiguity. For |
| 1744 | example, because the Linux kernel and user space tracing domains support |
| 1745 | named tracepoints as <<event-rule,instrumentation points>>, you need to |
| 1746 | specify a tracing domain when you <<enabling-disabling-events,create |
| 1747 | an event rule>> because both tracing domains could have tracepoints |
| 1748 | sharing the same name. |
| 1749 | |
| 1750 | You can create <<channel,channels>> in the Linux kernel and user space |
| 1751 | tracing domains. The other tracing domains have a single, default |
| 1752 | channel. |
| 1753 | |
| 1754 | |
| 1755 | [[channel]] |
| 1756 | === Channel and ring buffer |
| 1757 | |
| 1758 | A _channel_ is an object which is responsible for a set of |
| 1759 | _ring buffers_. |
| 1760 | |
| 1761 | Each ring buffer is divided into multiple _sub-buffers_. When a |
| 1762 | <<event,recording event rule>> |
| 1763 | matches an event, LTTng can record it to one or more sub-buffers of one |
| 1764 | or more channels. |
| 1765 | |
| 1766 | When you <<enabling-disabling-channels,create a channel>>, you set its |
| 1767 | final attributes, that is: |
| 1768 | |
| 1769 | * Its <<channel-buffering-schemes,buffering scheme>>. |
| 1770 | |
| 1771 | * What to do <<channel-overwrite-mode-vs-discard-mode,when there's no |
| 1772 | space left>> for a new event record because all sub-buffers are full. |
| 1773 | |
| 1774 | * The <<channel-subbuf-size-vs-subbuf-count,size of each ring buffer and |
| 1775 | how many sub-buffers>> a ring buffer has. |
| 1776 | |
| 1777 | * The <<tracefile-rotation,size of each trace file LTTng writes for this |
| 1778 | channel and the maximum count>> of trace files. |
| 1779 | |
| 1780 | * The periods of its <<channel-read-timer,read>>, |
| 1781 | <<channel-switch-timer,switch>>, and <<channel-monitor-timer,monitor>> |
| 1782 | timers. |
| 1783 | |
| 1784 | * For a Linux kernel channel: its output type. |
| 1785 | + |
| 1786 | See the opt:lttng-enable-channel(1):--output option of the |
| 1787 | man:lttng-enable-channel(1) command. |
| 1788 | |
| 1789 | * For a user space channel: the value of its |
| 1790 | <<blocking-timeout-example,blocking timeout>>. |
| 1791 | |
| 1792 | A channel is always associated to a <<domain,tracing domain>>. The |
| 1793 | `java.util.logging` (JUL), log4j, and Python tracing domains each have a |
| 1794 | default channel which you can't configure. |
| 1795 | |
| 1796 | A channel owns <<event,recording event rules>>. |
| 1797 | |
| 1798 | |
| 1799 | [[channel-buffering-schemes]] |
| 1800 | ==== Buffering scheme |
| 1801 | |
| 1802 | A channel has at least one ring buffer _per CPU_. LTTng always records |
| 1803 | an event to the ring buffer dedicated to the CPU which emits it. |
| 1804 | |
| 1805 | The buffering scheme of a user space channel determines what has its own |
| 1806 | set of per-CPU ring buffers: |
| 1807 | |
| 1808 | Per-user buffering:: |
| 1809 | Allocate one set of ring buffers--one per CPU--shared by all the |
| 1810 | instrumented processes of: |
| 1811 | If your Unix user is `root`::: |
| 1812 | Each Unix user. |
| 1813 | + |
| 1814 | -- |
| 1815 | [role="img-100"] |
| 1816 | .Per-user buffering scheme (recording session belongs to the `root` Unix user). |
| 1817 | image::per-user-buffering-root.png[] |
| 1818 | -- |
| 1819 | |
| 1820 | Otherwise::: |
| 1821 | Your Unix user. |
| 1822 | + |
| 1823 | -- |
| 1824 | [role="img-100"] |
| 1825 | .Per-user buffering scheme (recording session belongs to the `Bob` Unix user). |
| 1826 | image::per-user-buffering.png[] |
| 1827 | -- |
| 1828 | |
| 1829 | Per-process buffering:: |
| 1830 | Allocate one set of ring buffers--one per CPU--for each |
| 1831 | instrumented process of: |
| 1832 | If your Unix user is `root`::: |
| 1833 | All Unix users. |
| 1834 | + |
| 1835 | -- |
| 1836 | [role="img-100"] |
| 1837 | .Per-process buffering scheme (recording session belongs to the `root` Unix user). |
| 1838 | image::per-process-buffering-root.png[] |
| 1839 | -- |
| 1840 | |
| 1841 | Otherwise::: |
| 1842 | Your Unix user. |
| 1843 | + |
| 1844 | -- |
| 1845 | [role="img-100"] |
| 1846 | .Per-process buffering scheme (recording session belongs to the `Bob` Unix user). |
| 1847 | image::per-process-buffering.png[] |
| 1848 | -- |
| 1849 | |
| 1850 | The per-process buffering scheme tends to consume more memory than the |
| 1851 | per-user option because systems generally have more instrumented |
| 1852 | processes than Unix users running instrumented processes. However, the |
| 1853 | per-process buffering scheme ensures that one process having a high |
| 1854 | event throughput won't fill all the shared sub-buffers of the same Unix |
| 1855 | user, only its own. |
| 1856 | |
| 1857 | The buffering scheme of a Linux kernel channel is always to allocate a |
| 1858 | single set of ring buffers for the whole system. This scheme is similar |
| 1859 | to the per-user option, but with a single, global user ``running'' the |
| 1860 | kernel. |
| 1861 | |
| 1862 | |
| 1863 | [[channel-overwrite-mode-vs-discard-mode]] |
| 1864 | ==== Event record loss mode |
| 1865 | |
| 1866 | When LTTng emits an event, LTTng can record it to a specific, available |
| 1867 | sub-buffer within the ring buffers of specific channels. When there's no |
| 1868 | space left in a sub-buffer, the tracer marks it as consumable and |
| 1869 | another, available sub-buffer starts receiving the following event |
| 1870 | records. An LTTng <<lttng-consumerd,consumer daemon>> eventually |
| 1871 | consumes the marked sub-buffer, which returns to the available state. |
| 1872 | |
| 1873 | [NOTE] |
| 1874 | [role="docsvg-channel-subbuf-anim"] |
| 1875 | ==== |
| 1876 | {note-no-anim} |
| 1877 | ==== |
| 1878 | |
| 1879 | In an ideal world, sub-buffers are consumed faster than they're filled, |
| 1880 | as it's the case in the previous animation. In the real world, |
| 1881 | however, all sub-buffers can be full at some point, leaving no space to |
| 1882 | record the following events. |
| 1883 | |
| 1884 | By default, <<lttng-modules,LTTng-modules>> and <<lttng-ust,LTTng-UST>> |
| 1885 | are _non-blocking_ tracers: when there's no available sub-buffer to |
| 1886 | record an event, it's acceptable to lose event records when the |
| 1887 | alternative would be to cause substantial delays in the execution of the |
| 1888 | instrumented application. LTTng privileges performance over integrity; |
| 1889 | it aims at perturbing the instrumented application as little as possible |
| 1890 | in order to make the detection of subtle race conditions and rare |
| 1891 | interrupt cascades possible. |
| 1892 | |
| 1893 | Since LTTng{nbsp}2.10, the LTTng user space tracer, LTTng-UST, supports |
| 1894 | a _blocking mode_. See the <<blocking-timeout-example,blocking timeout |
| 1895 | example>> to learn how to use the blocking mode. |
| 1896 | |
| 1897 | When it comes to losing event records because there's no available |
| 1898 | sub-buffer, or because the blocking timeout of |
| 1899 | the channel is reached, the _event record loss mode_ of the channel |
| 1900 | determines what to do. The available event record loss modes are: |
| 1901 | |
| 1902 | [[discard-mode]]Discard mode:: |
| 1903 | Drop the newest event records until a sub-buffer becomes available. |
| 1904 | + |
| 1905 | This is the only available mode when you specify a blocking timeout. |
| 1906 | + |
| 1907 | With this mode, LTTng increments a count of lost event records when an |
| 1908 | event record is lost and saves this count to the trace. A trace reader |
| 1909 | can use the saved discarded event record count of the trace to decide |
| 1910 | whether or not to perform some analysis even if trace data is known to |
| 1911 | be missing. |
| 1912 | |
| 1913 | [[overwrite-mode]]Overwrite mode:: |
| 1914 | Clear the sub-buffer containing the oldest event records and start |
| 1915 | writing the newest event records there. |
| 1916 | + |
| 1917 | This mode is sometimes called _flight recorder mode_ because it's |
| 1918 | similar to a https://en.wikipedia.org/wiki/Flight_recorder[flight |
| 1919 | recorder]: always keep a fixed amount of the latest data. It's also |
| 1920 | similar to the roll mode of an oscilloscope. |
| 1921 | + |
| 1922 | Since LTTng{nbsp}2.8, with this mode, LTTng writes to a given sub-buffer |
| 1923 | its sequence number within its data stream. With a <<local-mode,local>>, |
| 1924 | <<net-streaming-mode,network streaming>>, or <<live-mode,live>> recording |
| 1925 | session, a trace reader can use such sequence numbers to report lost |
| 1926 | packets. A trace reader can use the saved discarded sub-buffer (packet) |
| 1927 | count of the trace to decide whether or not to perform some analysis |
| 1928 | even if trace data is known to be missing. |
| 1929 | + |
| 1930 | With this mode, LTTng doesn't write to the trace the exact number of |
| 1931 | lost event records in the lost sub-buffers. |
| 1932 | |
| 1933 | Which mechanism you should choose depends on your context: prioritize |
| 1934 | the newest or the oldest event records in the ring buffer? |
| 1935 | |
| 1936 | Beware that, in overwrite mode, the tracer abandons a _whole sub-buffer_ |
| 1937 | as soon as a there's no space left for a new event record, whereas in |
| 1938 | discard mode, the tracer only discards the event record that doesn't |
| 1939 | fit. |
| 1940 | |
| 1941 | There are a few ways to decrease your probability of losing event |
| 1942 | records. The ``<<channel-subbuf-size-vs-subbuf-count,Sub-buffer size and |
| 1943 | count>>'' section shows how to fine-tune the sub-buffer size and count |
| 1944 | of a channel to virtually stop losing event records, though at the cost |
| 1945 | of greater memory usage. |
| 1946 | |
| 1947 | |
| 1948 | [[channel-subbuf-size-vs-subbuf-count]] |
| 1949 | ==== Sub-buffer size and count |
| 1950 | |
| 1951 | A channel has one or more ring buffer for each CPU of the target system. |
| 1952 | |
| 1953 | See the ``<<channel-buffering-schemes,Buffering scheme>>'' section to |
| 1954 | learn how many ring buffers of a given channel are dedicated to each CPU |
| 1955 | depending on its buffering scheme. |
| 1956 | |
| 1957 | Set the size of each sub-buffer the ring buffers of a channel contain |
| 1958 | and how many there are |
| 1959 | when you <<enabling-disabling-channels,create it>>. |
| 1960 | |
| 1961 | Note that LTTng switching the current sub-buffer of a ring buffer |
| 1962 | (marking a full one as consumable and switching to an available one for |
| 1963 | LTTng to record the next events) introduces noticeable CPU overhead. |
| 1964 | Knowing this, the following list presents a few practical situations |
| 1965 | along with how to configure the sub-buffer size and count for them: |
| 1966 | |
| 1967 | High event throughput:: |
| 1968 | In general, prefer large sub-buffers to lower the risk of losing |
| 1969 | event records. |
| 1970 | + |
| 1971 | Having larger sub-buffers also ensures a lower sub-buffer switching |
| 1972 | frequency. |
| 1973 | + |
| 1974 | The sub-buffer count is only meaningful if you create the channel in |
| 1975 | <<overwrite-mode,overwrite mode>>: in this case, if LTTng overwrites a |
| 1976 | sub-buffer, then the other sub-buffers are left unaltered. |
| 1977 | |
| 1978 | Low event throughput:: |
| 1979 | In general, prefer smaller sub-buffers since the risk of losing |
| 1980 | event records is low. |
| 1981 | + |
| 1982 | Because LTTng emits events less frequently, the sub-buffer switching |
| 1983 | frequency should remain low and therefore the overhead of the tracer |
| 1984 | shouldn't be a problem. |
| 1985 | |
| 1986 | Low memory system:: |
| 1987 | If your target system has a low memory limit, prefer fewer first, |
| 1988 | then smaller sub-buffers. |
| 1989 | + |
| 1990 | Even if the system is limited in memory, you want to keep the |
| 1991 | sub-buffers as large as possible to avoid a high sub-buffer switching |
| 1992 | frequency. |
| 1993 | |
| 1994 | Note that LTTng uses https://diamon.org/ctf/[CTF] as its trace format, |
| 1995 | which means event record data is very compact. For example, the average |
| 1996 | LTTng kernel event record weights about 32{nbsp}bytes. Therefore, a |
| 1997 | sub-buffer size of 1{nbsp}MiB is considered large. |
| 1998 | |
| 1999 | The previous scenarios highlight the major trade-off between a few large |
| 2000 | sub-buffers and more, smaller sub-buffers: sub-buffer switching |
| 2001 | frequency vs. how many event records are lost in overwrite mode. |
| 2002 | Assuming a constant event throughput and using the overwrite mode, the |
| 2003 | two following configurations have the same ring buffer total size: |
| 2004 | |
| 2005 | [NOTE] |
| 2006 | [role="docsvg-channel-subbuf-size-vs-count-anim"] |
| 2007 | ==== |
| 2008 | {note-no-anim} |
| 2009 | ==== |
| 2010 | |
| 2011 | Two sub-buffers of 4{nbsp}MiB each:: |
| 2012 | Expect a very low sub-buffer switching frequency, but if LTTng |
| 2013 | ever needs to overwrite a sub-buffer, half of the event records so |
| 2014 | far (4{nbsp}MiB) are definitely lost. |
| 2015 | |
| 2016 | Eight sub-buffers of 1{nbsp}MiB each:: |
| 2017 | Expect four times the tracer overhead of the configuration above, |
| 2018 | but if LTTng needs to overwrite a sub-buffer, only the eighth of |
| 2019 | event records so far (1{nbsp}MiB) are definitely lost. |
| 2020 | |
| 2021 | In <<discard-mode,discard mode>>, the sub-buffer count parameter is |
| 2022 | pointless: use two sub-buffers and set their size according to your |
| 2023 | requirements. |
| 2024 | |
| 2025 | |
| 2026 | [[tracefile-rotation]] |
| 2027 | ==== Maximum trace file size and count (trace file rotation) |
| 2028 | |
| 2029 | By default, trace files can grow as large as needed. |
| 2030 | |
| 2031 | Set the maximum size of each trace file that LTTng writes of a given |
| 2032 | channel when you <<enabling-disabling-channels,create it>>. |
| 2033 | |
| 2034 | When the size of a trace file reaches the fixed maximum size of the |
| 2035 | channel, LTTng creates another file to contain the next event records. |
| 2036 | LTTng appends a file count to each trace file name in this case. |
| 2037 | |
| 2038 | If you set the trace file size attribute when you create a channel, the |
| 2039 | maximum number of trace files that LTTng creates is _unlimited_ by |
| 2040 | default. To limit them, set a maximum number of trace files. When the |
| 2041 | number of trace files reaches the fixed maximum count of the channel, |
| 2042 | LTTng overwrites the oldest trace file. This mechanism is called _trace |
| 2043 | file rotation_. |
| 2044 | |
| 2045 | [IMPORTANT] |
| 2046 | ==== |
| 2047 | Even if you don't limit the trace file count, always assume that LTTng |
| 2048 | manages all the trace files of the recording session. |
| 2049 | |
| 2050 | In other words, there's no safe way to know if LTTng still holds a given |
| 2051 | trace file open with the trace file rotation feature. |
| 2052 | |
| 2053 | The only way to obtain an unmanaged, self-contained LTTng trace before |
| 2054 | you <<creating-destroying-tracing-sessions,destroy the recording session>> |
| 2055 | is with the <<session-rotation,recording session rotation>> feature, which |
| 2056 | is available since LTTng{nbsp}2.11. |
| 2057 | ==== |
| 2058 | |
| 2059 | |
| 2060 | [[channel-timers]] |
| 2061 | ==== Timers |
| 2062 | |
| 2063 | Each channel can have up to three optional timers: |
| 2064 | |
| 2065 | [[channel-switch-timer]]Switch timer:: |
| 2066 | When this timer expires, a sub-buffer switch happens: for each ring |
| 2067 | buffer of the channel, LTTng marks the current sub-buffer as |
| 2068 | consumable and _switches_ to an available one to record the next |
| 2069 | events. |
| 2070 | + |
| 2071 | [NOTE] |
| 2072 | [role="docsvg-channel-switch-timer"] |
| 2073 | ==== |
| 2074 | {note-no-anim} |
| 2075 | ==== |
| 2076 | + |
| 2077 | A switch timer is useful to ensure that LTTng consumes and commits trace |
| 2078 | data to trace files or to a distant <<lttng-relayd,relay daemon>> |
| 2079 | periodically in case of a low event throughput. |
| 2080 | + |
| 2081 | Such a timer is also convenient when you use large |
| 2082 | <<channel-subbuf-size-vs-subbuf-count,sub-buffers>> to cope with a |
| 2083 | sporadic high event throughput, even if the throughput is otherwise low. |
| 2084 | + |
| 2085 | Set the period of the switch timer of a channel when you |
| 2086 | <<enabling-disabling-channels,create it>> with |
| 2087 | the opt:lttng-enable-channel(1):--switch-timer option. |
| 2088 | |
| 2089 | [[channel-read-timer]]Read timer:: |
| 2090 | When this timer expires, LTTng checks for full, consumable |
| 2091 | sub-buffers. |
| 2092 | + |
| 2093 | By default, the LTTng tracers use an asynchronous message mechanism to |
| 2094 | signal a full sub-buffer so that a <<lttng-consumerd,consumer daemon>> |
| 2095 | can consume it. |
| 2096 | + |
| 2097 | When such messages must be avoided, for example in real-time |
| 2098 | applications, use this timer instead. |
| 2099 | + |
| 2100 | Set the period of the read timer of a channel when you |
| 2101 | <<enabling-disabling-channels,create it>> with the |
| 2102 | opt:lttng-enable-channel(1):--read-timer option. |
| 2103 | |
| 2104 | [[channel-monitor-timer]]Monitor timer:: |
| 2105 | When this timer expires, the consumer daemon samples some channel |
| 2106 | statistics to evaluate the following <<trigger,trigger>> |
| 2107 | conditions: |
| 2108 | + |
| 2109 | -- |
| 2110 | . The consumed buffer size of a given <<tracing-session,recording |
| 2111 | session>> becomes greater than some value. |
| 2112 | . The buffer usage of a given channel becomes greater than some value. |
| 2113 | . The buffer usage of a given channel becomes less than some value. |
| 2114 | -- |
| 2115 | + |
| 2116 | If you disable the monitor timer of a channel{nbsp}__C__: |
| 2117 | + |
| 2118 | -- |
| 2119 | * The consumed buffer size value of the recording session of{nbsp}__C__ |
| 2120 | could be wrong for trigger condition type{nbsp}1: the consumed buffer |
| 2121 | size of{nbsp}__C__ won't be part of the grand total. |
| 2122 | |
| 2123 | * The buffer usage trigger conditions (types{nbsp}2 and{nbsp}3) |
| 2124 | for{nbsp}__C__ will never be satisfied. |
| 2125 | -- |
| 2126 | + |
| 2127 | Set the period of the monitor timer of a channel when you |
| 2128 | <<enabling-disabling-channels,create it>> with the |
| 2129 | opt:lttng-enable-channel(1):--monitor-timer option. |
| 2130 | |
| 2131 | |
| 2132 | [[event]] |
| 2133 | === Recording event rule and event record |
| 2134 | |
| 2135 | A _recording event rule_ is a specific type of <<event-rule,event rule>> |
| 2136 | of which the action is to serialize and record the matched event as an |
| 2137 | _event record_. |
| 2138 | |
| 2139 | Set the explicit conditions of a recording event rule when you |
| 2140 | <<enabling-disabling-events,create it>>. A recording event rule also has |
| 2141 | the following implicit conditions: |
| 2142 | |
| 2143 | * The recording event rule itself is enabled. |
| 2144 | + |
| 2145 | A recording event rule is enabled on creation. |
| 2146 | |
| 2147 | * The <<channel,channel>> to which the recording event rule is attached |
| 2148 | is enabled. |
| 2149 | + |
| 2150 | A channel is enabled on creation. |
| 2151 | |
| 2152 | * The <<tracing-session,recording session>> of the recording event rule is |
| 2153 | <<basic-tracing-session-control,active>> (started). |
| 2154 | + |
| 2155 | A recording session is inactive (stopped) on creation. |
| 2156 | |
| 2157 | * The process for which LTTng creates an event to match is |
| 2158 | <<pid-tracking,allowed to record events>>. |
| 2159 | + |
| 2160 | All processes are allowed to record events on recording session |
| 2161 | creation. |
| 2162 | |
| 2163 | You always attach a recording event rule to a channel, which belongs to |
| 2164 | a recording session, when you create it. |
| 2165 | |
| 2166 | When a recording event rule{nbsp}__ER__ matches an event{nbsp}__E__, |
| 2167 | LTTng attempts to serialize and record{nbsp}__E__ to one of the |
| 2168 | available sub-buffers of the channel to which{nbsp}__E__ is attached. |
| 2169 | |
| 2170 | When multiple matching recording event rules are attached to the same |
| 2171 | channel, LTTng attempts to serialize and record the matched event |
| 2172 | _once_. In the following example, the second recording event rule is |
| 2173 | redundant when both are enabled: |
| 2174 | |
| 2175 | [role="term"] |
| 2176 | ---- |
| 2177 | $ lttng enable-event --userspace hello:world |
| 2178 | $ lttng enable-event --userspace hello:world --loglevel=INFO |
| 2179 | ---- |
| 2180 | |
| 2181 | [role="img-100"] |
| 2182 | .Logical path from an instrumentation point to an event record. |
| 2183 | image::event-rule.png[] |
| 2184 | |
| 2185 | As of LTTng{nbsp}{revision}, you cannot remove a recording event |
| 2186 | rule: it exists as long as its recording session exists. |
| 2187 | |
| 2188 | |
| 2189 | [[plumbing]] |
| 2190 | == Components of noch:{LTTng} |
| 2191 | |
| 2192 | The second _T_ in _LTTng_ stands for _toolkit_: it would be wrong |
| 2193 | to call LTTng a simple _tool_ since it's composed of multiple |
| 2194 | interacting components. |
| 2195 | |
| 2196 | This section describes those components, explains their respective |
| 2197 | roles, and shows how they connect together to form the LTTng ecosystem. |
| 2198 | |
| 2199 | The following diagram shows how the most important components of LTTng |
| 2200 | interact with user applications, the Linux kernel, and you: |
| 2201 | |
| 2202 | [role="img-100"] |
| 2203 | .Control and trace data paths between LTTng components. |
| 2204 | image::plumbing.png[] |
| 2205 | |
| 2206 | The LTTng project integrates: |
| 2207 | |
| 2208 | LTTng-tools:: |
| 2209 | Libraries and command-line interface to control recording sessions: |
| 2210 | + |
| 2211 | * <<lttng-sessiond,Session daemon>> (man:lttng-sessiond(8)). |
| 2212 | * <<lttng-consumerd,Consumer daemon>> (cmd:lttng-consumerd). |
| 2213 | * <<lttng-relayd,Relay daemon>> (man:lttng-relayd(8)). |
| 2214 | * <<liblttng-ctl-lttng,Tracing control library>> (`liblttng-ctl`). |
| 2215 | * <<lttng-cli,Tracing control command-line tool>> (man:lttng(1)). |
| 2216 | * <<persistent-memory-file-systems,`lttng-crash` command-line tool>> |
| 2217 | (man:lttng-crash(1)). |
| 2218 | |
| 2219 | LTTng-UST:: |
| 2220 | Libraries and Java/Python packages to instrument and trace user |
| 2221 | applications: |
| 2222 | + |
| 2223 | * <<lttng-ust,User space tracing library>> (`liblttng-ust`) and its |
| 2224 | headers to instrument and trace any native user application. |
| 2225 | * <<prebuilt-ust-helpers,Preloadable user space tracing helpers>>: |
| 2226 | ** `liblttng-ust-libc-wrapper` |
| 2227 | ** `liblttng-ust-pthread-wrapper` |
| 2228 | ** `liblttng-ust-cyg-profile` |
| 2229 | ** `liblttng-ust-cyg-profile-fast` |
| 2230 | ** `liblttng-ust-dl` |
| 2231 | * <<lttng-ust-agents,LTTng-UST Java agent>> to instrument and trace |
| 2232 | Java applications using `java.util.logging` or |
| 2233 | Apache log4j{nbsp}1.2 logging. |
| 2234 | * <<lttng-ust-agents,LTTng-UST Python agent>> to instrument |
| 2235 | Python applications using the standard `logging` package. |
| 2236 | |
| 2237 | LTTng-modules:: |
| 2238 | <<lttng-modules,Linux kernel modules>> to instrument and trace the |
| 2239 | kernel: |
| 2240 | + |
| 2241 | * LTTng kernel tracer module. |
| 2242 | * Recording ring buffer kernel modules. |
| 2243 | * Probe kernel modules. |
| 2244 | * LTTng logger kernel module. |
| 2245 | |
| 2246 | |
| 2247 | [[lttng-cli]] |
| 2248 | === Tracing control command-line interface |
| 2249 | |
| 2250 | The _man:lttng(1) command-line tool_ is the standard user interface to |
| 2251 | control LTTng <<tracing-session,recording sessions>>. |
| 2252 | |
| 2253 | The cmd:lttng tool is part of LTTng-tools. |
| 2254 | |
| 2255 | The cmd:lttng tool is linked with |
| 2256 | <<liblttng-ctl-lttng,`liblttng-ctl`>> to communicate with |
| 2257 | one or more <<lttng-sessiond,session daemons>> behind the scenes. |
| 2258 | |
| 2259 | The cmd:lttng tool has a Git-like interface: |
| 2260 | |
| 2261 | [role="term"] |
| 2262 | ---- |
| 2263 | $ lttng [GENERAL OPTIONS] <COMMAND> [COMMAND OPTIONS] |
| 2264 | ---- |
| 2265 | |
| 2266 | The ``<<controlling-tracing,Tracing control>>'' section explores the |
| 2267 | available features of LTTng through its cmd:lttng tool. |
| 2268 | |
| 2269 | |
| 2270 | [[liblttng-ctl-lttng]] |
| 2271 | === Tracing control library |
| 2272 | |
| 2273 | [role="img-100"] |
| 2274 | .The tracing control library. |
| 2275 | image::plumbing-liblttng-ctl.png[] |
| 2276 | |
| 2277 | The _LTTng control library_, `liblttng-ctl`, is used to communicate with |
| 2278 | a <<lttng-sessiond,session daemon>> using a C{nbsp}API that hides the |
| 2279 | underlying details of the protocol. |
| 2280 | |
| 2281 | `liblttng-ctl` is part of LTTng-tools. |
| 2282 | |
| 2283 | The <<lttng-cli,cmd:lttng command-line tool>> is linked with |
| 2284 | `liblttng-ctl`. |
| 2285 | |
| 2286 | Use `liblttng-ctl` in C or $$C++$$ source code by including its |
| 2287 | ``master'' header: |
| 2288 | |
| 2289 | [source,c] |
| 2290 | ---- |
| 2291 | #include <lttng/lttng.h> |
| 2292 | ---- |
| 2293 | |
| 2294 | As of LTTng{nbsp}{revision}, the best available developer documentation |
| 2295 | for `liblttng-ctl` is its installed header files. Functions and |
| 2296 | structures are documented with header comments. |
| 2297 | |
| 2298 | |
| 2299 | [[lttng-ust]] |
| 2300 | === User space tracing library |
| 2301 | |
| 2302 | [role="img-100"] |
| 2303 | .The user space tracing library. |
| 2304 | image::plumbing-liblttng-ust.png[] |
| 2305 | |
| 2306 | The _user space tracing library_, `liblttng-ust` (see man:lttng-ust(3)), |
| 2307 | is the LTTng user space tracer. |
| 2308 | |
| 2309 | `liblttng-ust` receives commands from a <<lttng-sessiond,session |
| 2310 | daemon>>, for example to allow specific instrumentation points to emit |
| 2311 | LTTng <<event-rule,events>>, and writes event records to <<channel,ring |
| 2312 | buffers>> shared with a <<lttng-consumerd,consumer daemon>>. |
| 2313 | |
| 2314 | `liblttng-ust` is part of LTTng-UST. |
| 2315 | |
| 2316 | `liblttng-ust` can also send asynchronous messages to the session daemon |
| 2317 | when it emits an event. This supports the ``event rule matches'' |
| 2318 | <<trigger,trigger>> condition feature (see |
| 2319 | “<<add-event-rule-matches-trigger,Add an ``event rule matches'' trigger |
| 2320 | to a session daemon>>”). |
| 2321 | |
| 2322 | Public C{nbsp}header files are installed beside `liblttng-ust` to |
| 2323 | instrument any <<c-application,C or $$C++$$ application>>. |
| 2324 | |
| 2325 | <<lttng-ust-agents,LTTng-UST agents>>, which are regular Java and Python |
| 2326 | packages, use their own <<tracepoint-provider,tracepoint provider |
| 2327 | package>> which is linked with `liblttng-ust`. |
| 2328 | |
| 2329 | An application or library doesn't have to initialize `liblttng-ust` |
| 2330 | manually: its constructor does the necessary tasks to register the |
| 2331 | application to a session daemon. The initialization phase also |
| 2332 | configures instrumentation points depending on the <<event-rule,event |
| 2333 | rules>> that you already created. |
| 2334 | |
| 2335 | |
| 2336 | [[lttng-ust-agents]] |
| 2337 | === User space tracing agents |
| 2338 | |
| 2339 | [role="img-100"] |
| 2340 | .The user space tracing agents. |
| 2341 | image::plumbing-lttng-ust-agents.png[] |
| 2342 | |
| 2343 | The _LTTng-UST Java and Python agents_ are regular Java and Python |
| 2344 | packages which add LTTng tracing capabilities to the |
| 2345 | native logging frameworks. |
| 2346 | |
| 2347 | The LTTng-UST agents are part of LTTng-UST. |
| 2348 | |
| 2349 | In the case of Java, the |
| 2350 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[`java.util.logging` |
| 2351 | core logging facilities] and |
| 2352 | https://logging.apache.org/log4j/1.2/[Apache log4j{nbsp}1.2] are supported. |
| 2353 | Note that Apache Log4j{nbsp}2 isn't supported. |
| 2354 | |
| 2355 | In the case of Python, the standard |
| 2356 | https://docs.python.org/3/library/logging.html[`logging`] package |
| 2357 | is supported. Both Python{nbsp}2 and Python{nbsp}3 modules can import the |
| 2358 | LTTng-UST Python agent package. |
| 2359 | |
| 2360 | The applications using the LTTng-UST agents are in the |
| 2361 | `java.util.logging` (JUL), log4j, and Python <<domain,tracing domains>>. |
| 2362 | |
| 2363 | Both agents use the same mechanism to convert log statements to LTTng |
| 2364 | events. When an agent initializes, it creates a log handler that |
| 2365 | attaches to the root logger. The agent also registers to a |
| 2366 | <<lttng-sessiond,session daemon>>. When the user application executes a |
| 2367 | log statement, the root logger passes it to the log handler of the |
| 2368 | agent. The custom log handler of the agent calls a native function in a |
| 2369 | tracepoint provider package shared library linked with |
| 2370 | <<lttng-ust,`liblttng-ust`>>, passing the formatted log message and |
| 2371 | other fields, like its logger name and its log level. This native |
| 2372 | function contains a user space instrumentation point, therefore tracing |
| 2373 | the log statement. |
| 2374 | |
| 2375 | The log level condition of a <<event,recording event rule>> is |
| 2376 | considered when tracing a Java or a Python application, and it's |
| 2377 | compatible with the standard `java.util.logging`, log4j, and Python log |
| 2378 | levels. |
| 2379 | |
| 2380 | |
| 2381 | [[lttng-modules]] |
| 2382 | === LTTng kernel modules |
| 2383 | |
| 2384 | [role="img-100"] |
| 2385 | .The LTTng kernel modules. |
| 2386 | image::plumbing-lttng-modules.png[] |
| 2387 | |
| 2388 | The _LTTng kernel modules_ are a set of Linux kernel modules |
| 2389 | which implement the kernel tracer of the LTTng project. |
| 2390 | |
| 2391 | The LTTng kernel modules are part of LTTng-modules. |
| 2392 | |
| 2393 | The LTTng kernel modules include: |
| 2394 | |
| 2395 | * A set of _probe_ modules. |
| 2396 | + |
| 2397 | Each module attaches to a specific subsystem |
| 2398 | of the Linux kernel using its tracepoint instrument points. |
| 2399 | + |
| 2400 | There are also modules to attach to the entry and return points of the |
| 2401 | Linux system call functions. |
| 2402 | |
| 2403 | * _Ring buffer_ modules. |
| 2404 | + |
| 2405 | A ring buffer implementation is provided as kernel modules. The LTTng |
| 2406 | kernel tracer writes to ring buffers; a |
| 2407 | <<lttng-consumerd,consumer daemon>> reads from ring buffers. |
| 2408 | |
| 2409 | * The _LTTng kernel tracer_ module. |
| 2410 | * The <<proc-lttng-logger-abi,_LTTng logger_>> module. |
| 2411 | + |
| 2412 | The LTTng logger module implements the special path:{/proc/lttng-logger} |
| 2413 | (and path:{/dev/lttng-logger}, since LTTng{nbsp}2.11) files so that any |
| 2414 | executable can generate LTTng events by opening those files and |
| 2415 | writing to them. |
| 2416 | |
| 2417 | The LTTng kernel tracer can also send asynchronous messages to the |
| 2418 | <<lttng-sessiond,session daemon>> when it emits an event. |
| 2419 | This supports the ``event rule matches'' |
| 2420 | <<trigger,trigger>> condition feature (see |
| 2421 | “<<add-event-rule-matches-trigger,Add an ``event rule matches'' trigger |
| 2422 | to a session daemon>>”). |
| 2423 | |
| 2424 | Generally, you don't have to load the LTTng kernel modules manually |
| 2425 | (using man:modprobe(8), for example): a root session daemon loads the |
| 2426 | necessary modules when starting. If you have extra probe modules, you |
| 2427 | can specify to load them to the session daemon on the command line |
| 2428 | (see the opt:lttng-sessiond(8):--extra-kmod-probes option). See also |
| 2429 | <<linux-kernel-sig,Linux kernel module signature>>. |
| 2430 | |
| 2431 | The LTTng kernel modules are installed in |
| 2432 | +/usr/lib/modules/__release__/extra+ by default, where +__release__+ is |
| 2433 | the kernel release (output of `uname --kernel-release`). |
| 2434 | |
| 2435 | |
| 2436 | [[lttng-sessiond]] |
| 2437 | === Session daemon |
| 2438 | |
| 2439 | [role="img-100"] |
| 2440 | .The session daemon. |
| 2441 | image::plumbing-sessiond.png[] |
| 2442 | |
| 2443 | The _session daemon_, man:lttng-sessiond(8), is a |
| 2444 | https://en.wikipedia.org/wiki/Daemon_(computing)[daemon] which: |
| 2445 | |
| 2446 | * Manages <<tracing-session,recording sessions>>. |
| 2447 | |
| 2448 | * Controls the various components (like tracers and |
| 2449 | <<lttng-consumerd,consumer daemons>>) of LTTng. |
| 2450 | |
| 2451 | * Sends <<notif-trigger-api,asynchronous notifications>> to user |
| 2452 | applications. |
| 2453 | |
| 2454 | The session daemon is part of LTTng-tools. |
| 2455 | |
| 2456 | The session daemon sends control requests to and receives control |
| 2457 | responses from: |
| 2458 | |
| 2459 | * The <<lttng-ust,user space tracing library>>. |
| 2460 | + |
| 2461 | Any instance of the user space tracing library first registers to |
| 2462 | a session daemon. Then, the session daemon can send requests to |
| 2463 | this instance, such as: |
| 2464 | + |
| 2465 | -- |
| 2466 | ** Get the list of tracepoints. |
| 2467 | ** Share a <<event,recording event rule>> so that the user space tracing |
| 2468 | library can decide whether or not a given tracepoint can emit events. |
| 2469 | Amongst the possible conditions of a recording event rule is a filter |
| 2470 | expression which `liblttng-ust` evaluates before it emits an event. |
| 2471 | ** Share <<channel,channel>> attributes and ring buffer locations. |
| 2472 | -- |
| 2473 | + |
| 2474 | The session daemon and the user space tracing library use a Unix |
| 2475 | domain socket to communicate. |
| 2476 | |
| 2477 | * The <<lttng-ust-agents,user space tracing agents>>. |
| 2478 | + |
| 2479 | Any instance of a user space tracing agent first registers to |
| 2480 | a session daemon. Then, the session daemon can send requests to |
| 2481 | this instance, such as: |
| 2482 | + |
| 2483 | -- |
| 2484 | ** Get the list of loggers. |
| 2485 | ** Enable or disable a specific logger. |
| 2486 | -- |
| 2487 | + |
| 2488 | The session daemon and the user space tracing agent use a TCP connection |
| 2489 | to communicate. |
| 2490 | |
| 2491 | * The <<lttng-modules,LTTng kernel tracer>>. |
| 2492 | * The <<lttng-consumerd,consumer daemon>>. |
| 2493 | + |
| 2494 | The session daemon sends requests to the consumer daemon to instruct |
| 2495 | it where to send the trace data streams, amongst other information. |
| 2496 | |
| 2497 | * The <<lttng-relayd,relay daemon>>. |
| 2498 | |
| 2499 | The session daemon receives commands from the |
| 2500 | <<liblttng-ctl-lttng,tracing control library>>. |
| 2501 | |
| 2502 | The session daemon can receive asynchronous messages from the |
| 2503 | <<lttng-ust,user space>> and <<lttng-modules,kernel>> tracers |
| 2504 | when they emit events. This supports the ``event rule matches'' |
| 2505 | <<trigger,trigger>> condition feature (see |
| 2506 | “<<add-event-rule-matches-trigger,Add an ``event rule matches'' trigger |
| 2507 | to a session daemon>>”). |
| 2508 | |
| 2509 | The root session daemon loads the appropriate |
| 2510 | <<lttng-modules,LTTng kernel modules>> on startup. It also spawns |
| 2511 | one or more <<lttng-consumerd,consumer daemons>> as soon as you create |
| 2512 | a <<event,recording event rule>>. |
| 2513 | |
| 2514 | The session daemon doesn't send and receive trace data: this is the |
| 2515 | role of the <<lttng-consumerd,consumer daemon>> and |
| 2516 | <<lttng-relayd,relay daemon>>. It does, however, generate the |
| 2517 | https://diamon.org/ctf/[CTF] metadata stream. |
| 2518 | |
| 2519 | Each Unix user can have its own session daemon instance. The |
| 2520 | recording sessions which different session daemons manage are completely |
| 2521 | independent. |
| 2522 | |
| 2523 | The root user's session daemon is the only one which is |
| 2524 | allowed to control the LTTng kernel tracer, and its spawned consumer |
| 2525 | daemon is the only one which is allowed to consume trace data from the |
| 2526 | LTTng kernel tracer. Note, however, that any Unix user which is a member |
| 2527 | of the <<tracing-group,tracing group>> is allowed |
| 2528 | to create <<channel,channels>> in the |
| 2529 | Linux kernel <<domain,tracing domain>>, and therefore to use the Linux |
| 2530 | kernel LTTng tracer. |
| 2531 | |
| 2532 | The <<lttng-cli,cmd:lttng command-line tool>> automatically starts a |
| 2533 | session daemon when using its `create` command if none is currently |
| 2534 | running. You can also start the session daemon manually. |
| 2535 | |
| 2536 | |
| 2537 | [[lttng-consumerd]] |
| 2538 | === Consumer daemon |
| 2539 | |
| 2540 | [role="img-100"] |
| 2541 | .The consumer daemon. |
| 2542 | image::plumbing-consumerd.png[] |
| 2543 | |
| 2544 | The _consumer daemon_, cmd:lttng-consumerd, is a |
| 2545 | https://en.wikipedia.org/wiki/Daemon_(computing)[daemon] which shares |
| 2546 | ring buffers with user applications or with the LTTng kernel modules to |
| 2547 | collect trace data and send it to some location (file system or to a |
| 2548 | <<lttng-relayd,relay daemon>> over the network). |
| 2549 | |
| 2550 | The consumer daemon is part of LTTng-tools. |
| 2551 | |
| 2552 | You don't start a consumer daemon manually: a consumer daemon is always |
| 2553 | spawned by a <<lttng-sessiond,session daemon>> as soon as you create a |
| 2554 | <<event,recording event rule>>, that is, before you start recording. When |
| 2555 | you kill its owner session daemon, the consumer daemon also exits |
| 2556 | because it's the child process of the session daemon. Command-line |
| 2557 | options of man:lttng-sessiond(8) target the consumer daemon process. |
| 2558 | |
| 2559 | There are up to two running consumer daemons per Unix user, whereas only |
| 2560 | one session daemon can run per user. This is because each process can be |
| 2561 | either 32-bit or 64-bit: if the target system runs a mixture of 32-bit |
| 2562 | and 64-bit processes, it's more efficient to have separate |
| 2563 | corresponding 32-bit and 64-bit consumer daemons. The root user is an |
| 2564 | exception: it can have up to _three_ running consumer daemons: 32-bit |
| 2565 | and 64-bit instances for its user applications, and one more |
| 2566 | reserved for collecting kernel trace data. |
| 2567 | |
| 2568 | |
| 2569 | [[lttng-relayd]] |
| 2570 | === Relay daemon |
| 2571 | |
| 2572 | [role="img-100"] |
| 2573 | .The relay daemon. |
| 2574 | image::plumbing-relayd.png[] |
| 2575 | |
| 2576 | The _relay daemon_, man:lttng-relayd(8), is a |
| 2577 | https://en.wikipedia.org/wiki/Daemon_(computing)[daemon] acting as a bridge |
| 2578 | between remote session and consumer daemons, local trace files, and a |
| 2579 | remote live trace reader. |
| 2580 | |
| 2581 | The relay daemon is part of LTTng-tools. |
| 2582 | |
| 2583 | The main purpose of the relay daemon is to implement a receiver of |
| 2584 | <<sending-trace-data-over-the-network,trace data over the network>>. |
| 2585 | This is useful when the target system doesn't have much file system |
| 2586 | space to write trace files locally. |
| 2587 | |
| 2588 | The relay daemon is also a server to which a |
| 2589 | <<lttng-live,live trace reader>> can |
| 2590 | connect. The live trace reader sends requests to the relay daemon to |
| 2591 | receive trace data as the target system records events. The |
| 2592 | communication protocol is named _LTTng live_; it's used over TCP |
| 2593 | connections. |
| 2594 | |
| 2595 | Note that you can start the relay daemon on the target system directly. |
| 2596 | This is the setup of choice when the use case is to view/analyze events |
| 2597 | as the target system records them without the need of a remote system. |
| 2598 | |
| 2599 | |
| 2600 | [[instrumenting]] |
| 2601 | == [[using-lttng]]Instrumentation |
| 2602 | |
| 2603 | There are many examples of tracing and monitoring in our everyday life: |
| 2604 | |
| 2605 | * You have access to real-time and historical weather reports and |
| 2606 | forecasts thanks to weather stations installed around the country. |
| 2607 | * You know your heart is safe thanks to an electrocardiogram. |
| 2608 | * You make sure not to drive your car too fast and to have enough fuel |
| 2609 | to reach your destination thanks to gauges visible on your dashboard. |
| 2610 | |
| 2611 | All the previous examples have something in common: they rely on |
| 2612 | **instruments**. Without the electrodes attached to the surface of your |
| 2613 | body skin, cardiac monitoring is futile. |
| 2614 | |
| 2615 | LTTng, as a tracer, is no different from those real life examples. If |
| 2616 | you're about to trace a software system or, in other words, record its |
| 2617 | history of execution, you better have **instrumentation points** in the |
| 2618 | subject you're tracing, that is, the actual software system. |
| 2619 | |
| 2620 | <<instrumentation-point-types,Various ways>> were developed to |
| 2621 | instrument a piece of software for LTTng tracing. The most |
| 2622 | straightforward one is to manually place static instrumentation points, |
| 2623 | called _tracepoints_, in the source code of the application. The Linux |
| 2624 | kernel <<domain,tracing domain>> also makes it possible to dynamically |
| 2625 | add instrumentation points. |
| 2626 | |
| 2627 | If you're only interested in tracing the Linux kernel, your |
| 2628 | instrumentation needs are probably already covered by the built-in |
| 2629 | <<lttng-modules,Linux kernel instrumentation points>> of LTTng. You may |
| 2630 | also wish to have LTTng trace a user application which is already |
| 2631 | instrumented for LTTng tracing. In such cases, skip this whole section |
| 2632 | and read the topics of the ``<<controlling-tracing,Tracing control>>'' |
| 2633 | section. |
| 2634 | |
| 2635 | Many methods are available to instrument a piece of software for LTTng |
| 2636 | tracing: |
| 2637 | |
| 2638 | * <<c-application,Instrument a C/$$C++$$ user application>>. |
| 2639 | * <<prebuilt-ust-helpers,Load a prebuilt user space tracing helper>>. |
| 2640 | * <<java-application,Instrument a Java application>>. |
| 2641 | * <<python-application,Instrument a Python application>>. |
| 2642 | * <<proc-lttng-logger-abi,Use the LTTng logger>>. |
| 2643 | * <<instrumenting-linux-kernel,Instrument a Linux kernel image or module>>. |
| 2644 | |
| 2645 | |
| 2646 | [[c-application]] |
| 2647 | === [[cxx-application]]Instrument a C/$$C++$$ user application |
| 2648 | |
| 2649 | The high level procedure to instrument a C or $$C++$$ user application |
| 2650 | with the <<lttng-ust,LTTng user space tracing library>>, `liblttng-ust`, |
| 2651 | is: |
| 2652 | |
| 2653 | . <<tracepoint-provider,Create the source files of a tracepoint provider |
| 2654 | package>>. |
| 2655 | |
| 2656 | . <<probing-the-application-source-code,Add tracepoints to |
| 2657 | the source code of the application>>. |
| 2658 | |
| 2659 | . <<building-tracepoint-providers-and-user-application,Build and link |
| 2660 | a tracepoint provider package and the user application>>. |
| 2661 | |
| 2662 | If you need quick, man:printf(3)-like instrumentation, skip those steps |
| 2663 | and use <<tracef,`lttng_ust_tracef()`>> or |
| 2664 | <<tracelog,`lttng_ust_tracelog()`>> instead. |
| 2665 | |
| 2666 | IMPORTANT: You need to <<installing-lttng,install>> LTTng-UST to |
| 2667 | instrument a user application with `liblttng-ust`. |
| 2668 | |
| 2669 | |
| 2670 | [[tracepoint-provider]] |
| 2671 | ==== Create the source files of a tracepoint provider package |
| 2672 | |
| 2673 | A _tracepoint provider_ is a set of compiled functions which provide |
| 2674 | **tracepoints** to an application, the type of instrumentation point |
| 2675 | which LTTng-UST provides. |
| 2676 | |
| 2677 | Those functions can make LTTng emit events with user-defined fields and |
| 2678 | serialize those events as event records to one or more LTTng-UST |
| 2679 | <<channel,channel>> sub-buffers. The `lttng_ust_tracepoint()` macro, |
| 2680 | which you <<probing-the-application-source-code,insert in the source |
| 2681 | code of a user application>>, calls those functions. |
| 2682 | |
| 2683 | A _tracepoint provider package_ is an object file (`.o`) or a shared |
| 2684 | library (`.so`) which contains one or more tracepoint providers. Its |
| 2685 | source files are: |
| 2686 | |
| 2687 | * One or more <<tpp-header,tracepoint provider header>> (`.h`). |
| 2688 | * A <<tpp-source,tracepoint provider package source>> (`.c`). |
| 2689 | |
| 2690 | A tracepoint provider package is dynamically linked with `liblttng-ust`, |
| 2691 | the LTTng user space tracer, at run time. |
| 2692 | |
| 2693 | [role="img-100"] |
| 2694 | .User application linked with `liblttng-ust` and containing a tracepoint provider. |
| 2695 | image::ust-app.png[] |
| 2696 | |
| 2697 | NOTE: If you need quick, man:printf(3)-like instrumentation, skip |
| 2698 | creating and using a tracepoint provider and use |
| 2699 | <<tracef,`lttng_ust_tracef()`>> or <<tracelog,`lttng_ust_tracelog()`>> |
| 2700 | instead. |
| 2701 | |
| 2702 | |
| 2703 | [[tpp-header]] |
| 2704 | ===== Create a tracepoint provider header file template |
| 2705 | |
| 2706 | A _tracepoint provider header file_ contains the tracepoint definitions |
| 2707 | of a tracepoint provider. |
| 2708 | |
| 2709 | To create a tracepoint provider header file: |
| 2710 | |
| 2711 | . Start from this template: |
| 2712 | + |
| 2713 | -- |
| 2714 | [source,c] |
| 2715 | .Tracepoint provider header file template (`.h` file extension). |
| 2716 | ---- |
| 2717 | #undef LTTNG_UST_TRACEPOINT_PROVIDER |
| 2718 | #define LTTNG_UST_TRACEPOINT_PROVIDER provider_name |
| 2719 | |
| 2720 | #undef LTTNG_UST_TRACEPOINT_INCLUDE |
| 2721 | #define LTTNG_UST_TRACEPOINT_INCLUDE "./tp.h" |
| 2722 | |
| 2723 | #if !defined(_TP_H) || defined(LTTNG_UST_TRACEPOINT_HEADER_MULTI_READ) |
| 2724 | #define _TP_H |
| 2725 | |
| 2726 | #include <lttng/tracepoint.h> |
| 2727 | |
| 2728 | /* |
| 2729 | * Use LTTNG_UST_TRACEPOINT_EVENT(), LTTNG_UST_TRACEPOINT_EVENT_CLASS(), |
| 2730 | * LTTNG_UST_TRACEPOINT_EVENT_INSTANCE(), and |
| 2731 | * LTTNG_UST_TRACEPOINT_LOGLEVEL() here. |
| 2732 | */ |
| 2733 | |
| 2734 | #endif /* _TP_H */ |
| 2735 | |
| 2736 | #include <lttng/tracepoint-event.h> |
| 2737 | ---- |
| 2738 | -- |
| 2739 | + |
| 2740 | Replace: |
| 2741 | + |
| 2742 | * +__provider_name__+ with the name of your tracepoint provider. |
| 2743 | * `"tp.h"` with the name of your tracepoint provider header file. |
| 2744 | |
| 2745 | . Below the `#include <lttng/tracepoint.h>` line, put your |
| 2746 | <<defining-tracepoints,tracepoint definitions>>. |
| 2747 | |
| 2748 | Your tracepoint provider name must be unique amongst all the possible |
| 2749 | tracepoint provider names used on the same target system. We suggest to |
| 2750 | include the name of your project or company in the name, for example, |
| 2751 | `org_lttng_my_project_tpp`. |
| 2752 | |
| 2753 | |
| 2754 | [[defining-tracepoints]] |
| 2755 | ===== Create a tracepoint definition |
| 2756 | |
| 2757 | A _tracepoint definition_ defines, for a given tracepoint: |
| 2758 | |
| 2759 | * Its **input arguments**. |
| 2760 | + |
| 2761 | They're the macro parameters that the `lttng_ust_tracepoint()` macro |
| 2762 | accepts for this particular tracepoint in the source code of the user |
| 2763 | application. |
| 2764 | |
| 2765 | * Its **output event fields**. |
| 2766 | + |
| 2767 | They're the sources of event fields that form the payload of any event |
| 2768 | that the execution of the `lttng_ust_tracepoint()` macro emits for this |
| 2769 | particular tracepoint. |
| 2770 | |
| 2771 | Create a tracepoint definition with the |
| 2772 | `LTTNG_UST_TRACEPOINT_EVENT()` macro below the `#include <lttng/tracepoint.h>` |
| 2773 | line in the |
| 2774 | <<tpp-header,tracepoint provider header file template>>. |
| 2775 | |
| 2776 | The syntax of the `LTTNG_UST_TRACEPOINT_EVENT()` macro is: |
| 2777 | |
| 2778 | [source,c] |
| 2779 | .`LTTNG_UST_TRACEPOINT_EVENT()` macro syntax. |
| 2780 | ---- |
| 2781 | LTTNG_UST_TRACEPOINT_EVENT( |
| 2782 | /* Tracepoint provider name */ |
| 2783 | provider_name, |
| 2784 | |
| 2785 | /* Tracepoint name */ |
| 2786 | tracepoint_name, |
| 2787 | |
| 2788 | /* Input arguments */ |
| 2789 | LTTNG_UST_TP_ARGS( |
| 2790 | arguments |
| 2791 | ), |
| 2792 | |
| 2793 | /* Output event fields */ |
| 2794 | LTTNG_UST_TP_FIELDS( |
| 2795 | fields |
| 2796 | ) |
| 2797 | ) |
| 2798 | ---- |
| 2799 | |
| 2800 | Replace: |
| 2801 | |
| 2802 | * +__provider_name__+ with your tracepoint provider name. |
| 2803 | * +__tracepoint_name__+ with your tracepoint name. |
| 2804 | * +__arguments__+ with the <<tpp-def-input-args,input arguments>>. |
| 2805 | * +__fields__+ with the <<tpp-def-output-fields,output event field>> |
| 2806 | definitions. |
| 2807 | |
| 2808 | The full name of this tracepoint is `provider_name:tracepoint_name`. |
| 2809 | |
| 2810 | [IMPORTANT] |
| 2811 | .Event name length limitation |
| 2812 | ==== |
| 2813 | The concatenation of the tracepoint provider name and the tracepoint |
| 2814 | name must not exceed **254{nbsp}characters**. If it does, the |
| 2815 | instrumented application compiles and runs, but LTTng throws multiple |
| 2816 | warnings and you could experience serious issues. |
| 2817 | ==== |
| 2818 | |
| 2819 | [[tpp-def-input-args]]The syntax of the `LTTNG_UST_TP_ARGS()` macro is: |
| 2820 | |
| 2821 | [source,c] |
| 2822 | .`LTTNG_UST_TP_ARGS()` macro syntax. |
| 2823 | ---- |
| 2824 | LTTNG_UST_TP_ARGS( |
| 2825 | type, arg_name |
| 2826 | ) |
| 2827 | ---- |
| 2828 | |
| 2829 | Replace: |
| 2830 | |
| 2831 | * +__type__+ with the C{nbsp}type of the argument. |
| 2832 | * +__arg_name__+ with the argument name. |
| 2833 | |
| 2834 | You can repeat +__type__+ and +__arg_name__+ up to 10{nbsp}times to have |
| 2835 | more than one argument. |
| 2836 | |
| 2837 | .`LTTNG_UST_TP_ARGS()` usage with three arguments. |
| 2838 | ==== |
| 2839 | [source,c] |
| 2840 | ---- |
| 2841 | LTTNG_UST_TP_ARGS( |
| 2842 | int, count, |
| 2843 | float, ratio, |
| 2844 | const char*, query |
| 2845 | ) |
| 2846 | ---- |
| 2847 | ==== |
| 2848 | |
| 2849 | The `LTTNG_UST_TP_ARGS()` and `LTTNG_UST_TP_ARGS(void)` forms are valid |
| 2850 | to create a tracepoint definition with no input arguments. |
| 2851 | |
| 2852 | [[tpp-def-output-fields]]The `LTTNG_UST_TP_FIELDS()` macro contains a |
| 2853 | list of `lttng_ust_field_*()` macros. Each `lttng_ust_field_*()` macro |
| 2854 | defines one event field. See man:lttng-ust(3) for a complete description |
| 2855 | of the available `lttng_ust_field_*()` macros. A `lttng_ust_field_*()` |
| 2856 | macro specifies the type, size, and byte order of one event field. |
| 2857 | |
| 2858 | Each `lttng_ust_field_*()` macro takes an _argument expression_ |
| 2859 | parameter. This is a C{nbsp}expression that the tracer evaluates at the |
| 2860 | `lttng_ust_tracepoint()` macro site in the source code of the |
| 2861 | application. This expression provides the source of data of a field. The |
| 2862 | argument expression can include input argument names listed in the |
| 2863 | `LTTNG_UST_TP_ARGS()` macro. |
| 2864 | |
| 2865 | Each `lttng_ust_field_*()` macro also takes a _field name_ parameter. |
| 2866 | Field names must be unique within a given tracepoint definition. |
| 2867 | |
| 2868 | Here's a complete tracepoint definition example: |
| 2869 | |
| 2870 | .Tracepoint definition. |
| 2871 | ==== |
| 2872 | The following tracepoint definition defines a tracepoint which takes |
| 2873 | three input arguments and has four output event fields. |
| 2874 | |
| 2875 | [source,c] |
| 2876 | ---- |
| 2877 | #include "my-custom-structure.h" |
| 2878 | |
| 2879 | LTTNG_UST_TRACEPOINT_EVENT( |
| 2880 | my_provider, |
| 2881 | my_tracepoint, |
| 2882 | LTTNG_UST_TP_ARGS( |
| 2883 | const struct my_custom_structure *, my_custom_structure, |
| 2884 | float, ratio, |
| 2885 | const char *, query |
| 2886 | ), |
| 2887 | LTTNG_UST_TP_FIELDS( |
| 2888 | lttng_ust_field_string(query_field, query) |
| 2889 | lttng_ust_field_float(double, ratio_field, ratio) |
| 2890 | lttng_ust_field_integer(int, recv_size, |
| 2891 | my_custom_structure->recv_size) |
| 2892 | lttng_ust_field_integer(int, send_size, |
| 2893 | my_custom_structure->send_size) |
| 2894 | ) |
| 2895 | ) |
| 2896 | ---- |
| 2897 | |
| 2898 | Refer to this tracepoint definition with the `lttng_ust_tracepoint()` |
| 2899 | macro in the source code of your application like this: |
| 2900 | |
| 2901 | [source,c] |
| 2902 | ---- |
| 2903 | lttng_ust_tracepoint(my_provider, my_tracepoint, |
| 2904 | my_structure, some_ratio, the_query); |
| 2905 | ---- |
| 2906 | ==== |
| 2907 | |
| 2908 | NOTE: The LTTng-UST tracer only evaluates the arguments of a tracepoint |
| 2909 | at run time when such a tracepoint _could_ emit an event. See |
| 2910 | <<event-creation-emission-opti,this note>> to learn more. |
| 2911 | |
| 2912 | |
| 2913 | [[using-tracepoint-classes]] |
| 2914 | ===== Use a tracepoint class |
| 2915 | |
| 2916 | A _tracepoint class_ is a class of tracepoints which share the same |
| 2917 | output event field definitions. A _tracepoint instance_ is one |
| 2918 | instance of such a defined tracepoint class, with its own tracepoint |
| 2919 | name. |
| 2920 | |
| 2921 | The <<defining-tracepoints,`LTTNG_UST_TRACEPOINT_EVENT()` macro>> is |
| 2922 | actually a shorthand which defines both a tracepoint class and a |
| 2923 | tracepoint instance at the same time. |
| 2924 | |
| 2925 | When you build a tracepoint provider package, the C or $$C++$$ compiler |
| 2926 | creates one serialization function for each **tracepoint class**. A |
| 2927 | serialization function is responsible for serializing the event fields |
| 2928 | of a tracepoint to a sub-buffer when recording. |
| 2929 | |
| 2930 | For various performance reasons, when your situation requires multiple |
| 2931 | tracepoint definitions with different names, but with the same event |
| 2932 | fields, we recommend that you manually create a tracepoint class and |
| 2933 | instantiate as many tracepoint instances as needed. One positive effect |
| 2934 | of such a design, amongst other advantages, is that all tracepoint |
| 2935 | instances of the same tracepoint class reuse the same serialization |
| 2936 | function, thus reducing |
| 2937 | https://en.wikipedia.org/wiki/Cache_pollution[cache pollution]. |
| 2938 | |
| 2939 | .Use a tracepoint class and tracepoint instances. |
| 2940 | ==== |
| 2941 | Consider the following three tracepoint definitions: |
| 2942 | |
| 2943 | [source,c] |
| 2944 | ---- |
| 2945 | LTTNG_UST_TRACEPOINT_EVENT( |
| 2946 | my_app, |
| 2947 | get_account, |
| 2948 | LTTNG_UST_TP_ARGS( |
| 2949 | int, userid, |
| 2950 | size_t, len |
| 2951 | ), |
| 2952 | LTTNG_UST_TP_FIELDS( |
| 2953 | lttng_ust_field_integer(int, userid, userid) |
| 2954 | lttng_ust_field_integer(size_t, len, len) |
| 2955 | ) |
| 2956 | ) |
| 2957 | |
| 2958 | LTTNG_UST_TRACEPOINT_EVENT( |
| 2959 | my_app, |
| 2960 | get_settings, |
| 2961 | LTTNG_UST_TP_ARGS( |
| 2962 | int, userid, |
| 2963 | size_t, len |
| 2964 | ), |
| 2965 | LTTNG_UST_TP_FIELDS( |
| 2966 | lttng_ust_field_integer(int, userid, userid) |
| 2967 | lttng_ust_field_integer(size_t, len, len) |
| 2968 | ) |
| 2969 | ) |
| 2970 | |
| 2971 | LTTNG_UST_TRACEPOINT_EVENT( |
| 2972 | my_app, |
| 2973 | get_transaction, |
| 2974 | LTTNG_UST_TP_ARGS( |
| 2975 | int, userid, |
| 2976 | size_t, len |
| 2977 | ), |
| 2978 | LTTNG_UST_TP_FIELDS( |
| 2979 | lttng_ust_field_integer(int, userid, userid) |
| 2980 | lttng_ust_field_integer(size_t, len, len) |
| 2981 | ) |
| 2982 | ) |
| 2983 | ---- |
| 2984 | |
| 2985 | In this case, we create three tracepoint classes, with one implicit |
| 2986 | tracepoint instance for each of them: `get_account`, `get_settings`, and |
| 2987 | `get_transaction`. However, they all share the same event field names |
| 2988 | and types. Hence three identical, yet independent serialization |
| 2989 | functions are created when you build the tracepoint provider package. |
| 2990 | |
| 2991 | A better design choice is to define a single tracepoint class and three |
| 2992 | tracepoint instances: |
| 2993 | |
| 2994 | [source,c] |
| 2995 | ---- |
| 2996 | /* The tracepoint class */ |
| 2997 | LTTNG_UST_TRACEPOINT_EVENT_CLASS( |
| 2998 | /* Tracepoint class provider name */ |
| 2999 | my_app, |
| 3000 | |
| 3001 | /* Tracepoint class name */ |
| 3002 | my_class, |
| 3003 | |
| 3004 | /* Input arguments */ |
| 3005 | LTTNG_UST_TP_ARGS( |
| 3006 | int, userid, |
| 3007 | size_t, len |
| 3008 | ), |
| 3009 | |
| 3010 | /* Output event fields */ |
| 3011 | LTTNG_UST_TP_FIELDS( |
| 3012 | lttng_ust_field_integer(int, userid, userid) |
| 3013 | lttng_ust_field_integer(size_t, len, len) |
| 3014 | ) |
| 3015 | ) |
| 3016 | |
| 3017 | /* The tracepoint instances */ |
| 3018 | LTTNG_UST_TRACEPOINT_EVENT_INSTANCE( |
| 3019 | /* Tracepoint class provider name */ |
| 3020 | my_app, |
| 3021 | |
| 3022 | /* Tracepoint class name */ |
| 3023 | my_class, |
| 3024 | |
| 3025 | /* Instance provider name */ |
| 3026 | my_app, |
| 3027 | |
| 3028 | /* Tracepoint name */ |
| 3029 | get_account, |
| 3030 | |
| 3031 | /* Input arguments */ |
| 3032 | LTTNG_UST_TP_ARGS( |
| 3033 | int, userid, |
| 3034 | size_t, len |
| 3035 | ) |
| 3036 | ) |
| 3037 | LTTNG_UST_TRACEPOINT_EVENT_INSTANCE( |
| 3038 | my_app, |
| 3039 | my_class, |
| 3040 | get_settings, |
| 3041 | LTTNG_UST_TP_ARGS( |
| 3042 | int, userid, |
| 3043 | size_t, len |
| 3044 | ) |
| 3045 | ) |
| 3046 | LTTNG_UST_TRACEPOINT_EVENT_INSTANCE( |
| 3047 | my_app, |
| 3048 | my_class, |
| 3049 | get_transaction, |
| 3050 | LTTNG_UST_TP_ARGS( |
| 3051 | int, userid, |
| 3052 | size_t, len |
| 3053 | ) |
| 3054 | ) |
| 3055 | ---- |
| 3056 | ==== |
| 3057 | |
| 3058 | The tracepoint class and instance provider names must be the same if the |
| 3059 | `LTTNG_UST_TRACEPOINT_EVENT_CLASS()` and |
| 3060 | `LTTNG_UST_TRACEPOINT_EVENT_INSTANCE()` expansions are part of the same |
| 3061 | translation unit. See man:lttng-ust(3) to learn more. |
| 3062 | |
| 3063 | |
| 3064 | [[assigning-log-levels]] |
| 3065 | ===== Assign a log level to a tracepoint definition |
| 3066 | |
| 3067 | Assign a _log level_ to a <<defining-tracepoints,tracepoint definition>> |
| 3068 | with the `LTTNG_UST_TRACEPOINT_LOGLEVEL()` macro. |
| 3069 | |
| 3070 | Assigning different levels of severity to tracepoint definitions can be |
| 3071 | useful: when you <<enabling-disabling-events,create a recording event |
| 3072 | rule>>, you can target tracepoints having a log level at least as severe |
| 3073 | as a specific value. |
| 3074 | |
| 3075 | The concept of LTTng-UST log levels is similar to the levels found |
| 3076 | in typical logging frameworks: |
| 3077 | |
| 3078 | * In a logging framework, the log level is given by the function |
| 3079 | or method name you use at the log statement site: `debug()`, |
| 3080 | `info()`, `warn()`, `error()`, and so on. |
| 3081 | |
| 3082 | * In LTTng-UST, you statically assign the log level to a tracepoint |
| 3083 | definition; any `lttng_ust_tracepoint()` macro invocation which refers |
| 3084 | to this definition has this log level. |
| 3085 | |
| 3086 | You must use `LTTNG_UST_TRACEPOINT_LOGLEVEL()` _after_ the |
| 3087 | <<defining-tracepoints,`LTTNG_UST_TRACEPOINT_EVENT()`>> or |
| 3088 | <<using-tracepoint-classes,`LTTNG_UST_TRACEPOINT_INSTANCE()`>> macro for |
| 3089 | a given tracepoint. |
| 3090 | |
| 3091 | The syntax of the `LTTNG_UST_TRACEPOINT_LOGLEVEL()` macro is: |
| 3092 | |
| 3093 | [source,c] |
| 3094 | .`LTTNG_UST_TRACEPOINT_LOGLEVEL()` macro syntax. |
| 3095 | ---- |
| 3096 | LTTNG_UST_TRACEPOINT_LOGLEVEL(provider_name, tracepoint_name, log_level) |
| 3097 | ---- |
| 3098 | |
| 3099 | Replace: |
| 3100 | |
| 3101 | * +__provider_name__+ with the tracepoint provider name. |
| 3102 | * +__tracepoint_name__+ with the tracepoint name. |
| 3103 | * +__log_level__+ with the log level to assign to the tracepoint |
| 3104 | definition named +__tracepoint_name__+ in the +__provider_name__+ |
| 3105 | tracepoint provider. |
| 3106 | + |
| 3107 | See man:lttng-ust(3) for a list of available log level names. |
| 3108 | |
| 3109 | .Assign the `LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_UNIT` log level to a tracepoint definition. |
| 3110 | ==== |
| 3111 | [source,c] |
| 3112 | ---- |
| 3113 | /* Tracepoint definition */ |
| 3114 | LTTNG_UST_TRACEPOINT_EVENT( |
| 3115 | my_app, |
| 3116 | get_transaction, |
| 3117 | LTTNG_UST_TP_ARGS( |
| 3118 | int, userid, |
| 3119 | size_t, len |
| 3120 | ), |
| 3121 | LTTNG_UST_TP_FIELDS( |
| 3122 | lttng_ust_field_integer(int, userid, userid) |
| 3123 | lttng_ust_field_integer(size_t, len, len) |
| 3124 | ) |
| 3125 | ) |
| 3126 | |
| 3127 | /* Log level assignment */ |
| 3128 | LTTNG_UST_TRACEPOINT_LOGLEVEL(my_app, get_transaction, |
| 3129 | LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_UNIT) |
| 3130 | ---- |
| 3131 | ==== |
| 3132 | |
| 3133 | |
| 3134 | [[tpp-source]] |
| 3135 | ===== Create a tracepoint provider package source file |
| 3136 | |
| 3137 | A _tracepoint provider package source file_ is a C source file which |
| 3138 | includes a <<tpp-header,tracepoint provider header file>> to expand its |
| 3139 | macros into event serialization and other functions. |
| 3140 | |
| 3141 | Use the following tracepoint provider package source file template: |
| 3142 | |
| 3143 | [source,c] |
| 3144 | .Tracepoint provider package source file template. |
| 3145 | ---- |
| 3146 | #define LTTNG_UST_TRACEPOINT_CREATE_PROBES |
| 3147 | |
| 3148 | #include "tp.h" |
| 3149 | ---- |
| 3150 | |
| 3151 | Replace `tp.h` with the name of your <<tpp-header,tracepoint provider |
| 3152 | header file>> name. You may also include more than one tracepoint |
| 3153 | provider header file here to create a tracepoint provider package |
| 3154 | holding more than one tracepoint providers. |
| 3155 | |
| 3156 | |
| 3157 | [[probing-the-application-source-code]] |
| 3158 | ==== Add tracepoints to the source code of an application |
| 3159 | |
| 3160 | Once you <<tpp-header,create a tracepoint provider header file>>, use |
| 3161 | the `lttng_ust_tracepoint()` macro in the source code of your |
| 3162 | application to insert the tracepoints that this header |
| 3163 | <<defining-tracepoints,defines>>. |
| 3164 | |
| 3165 | The `lttng_ust_tracepoint()` macro takes at least two parameters: the |
| 3166 | tracepoint provider name and the tracepoint name. The corresponding |
| 3167 | tracepoint definition defines the other parameters. |
| 3168 | |
| 3169 | .`lttng_ust_tracepoint()` usage. |
| 3170 | ==== |
| 3171 | The following <<defining-tracepoints,tracepoint definition>> defines a |
| 3172 | tracepoint which takes two input arguments and has two output event |
| 3173 | fields. |
| 3174 | |
| 3175 | [source,c] |
| 3176 | .Tracepoint provider header file. |
| 3177 | ---- |
| 3178 | #include "my-custom-structure.h" |
| 3179 | |
| 3180 | LTTNG_UST_TRACEPOINT_EVENT( |
| 3181 | my_provider, |
| 3182 | my_tracepoint, |
| 3183 | LTTNG_UST_TP_ARGS( |
| 3184 | int, argc, |
| 3185 | const char *, cmd_name |
| 3186 | ), |
| 3187 | LTTNG_UST_TP_FIELDS( |
| 3188 | lttng_ust_field_string(cmd_name, cmd_name) |
| 3189 | lttng_ust_field_integer(int, number_of_args, argc) |
| 3190 | ) |
| 3191 | ) |
| 3192 | ---- |
| 3193 | |
| 3194 | Refer to this tracepoint definition with the `lttng_ust_tracepoint()` |
| 3195 | macro in the source code of your application like this: |
| 3196 | |
| 3197 | [source,c] |
| 3198 | .Application source file. |
| 3199 | ---- |
| 3200 | #include "tp.h" |
| 3201 | |
| 3202 | int main(int argc, char* argv[]) |
| 3203 | { |
| 3204 | lttng_ust_tracepoint(my_provider, my_tracepoint, argc, argv[0]); |
| 3205 | return 0; |
| 3206 | } |
| 3207 | ---- |
| 3208 | |
| 3209 | Note how the source code of the application includes |
| 3210 | the tracepoint provider header file containing the tracepoint |
| 3211 | definitions to use, path:{tp.h}. |
| 3212 | ==== |
| 3213 | |
| 3214 | .`lttng_ust_tracepoint()` usage with a complex tracepoint definition. |
| 3215 | ==== |
| 3216 | Consider this complex tracepoint definition, where multiple event |
| 3217 | fields refer to the same input arguments in their argument expression |
| 3218 | parameter: |
| 3219 | |
| 3220 | [source,c] |
| 3221 | .Tracepoint provider header file. |
| 3222 | ---- |
| 3223 | /* For `struct stat` */ |
| 3224 | #include <sys/types.h> |
| 3225 | #include <sys/stat.h> |
| 3226 | #include <unistd.h> |
| 3227 | |
| 3228 | LTTNG_UST_TRACEPOINT_EVENT( |
| 3229 | my_provider, |
| 3230 | my_tracepoint, |
| 3231 | LTTNG_UST_TP_ARGS( |
| 3232 | int, my_int_arg, |
| 3233 | char *, my_str_arg, |
| 3234 | struct stat *, st |
| 3235 | ), |
| 3236 | LTTNG_UST_TP_FIELDS( |
| 3237 | lttng_ust_field_integer(int, my_constant_field, 23 + 17) |
| 3238 | lttng_ust_field_integer(int, my_int_arg_field, my_int_arg) |
| 3239 | lttng_ust_field_integer(int, my_int_arg_field2, |
| 3240 | my_int_arg * my_int_arg) |
| 3241 | lttng_ust_field_integer(int, sum4_field, |
| 3242 | my_str_arg[0] + my_str_arg[1] + |
| 3243 | my_str_arg[2] + my_str_arg[3]) |
| 3244 | lttng_ust_field_string(my_str_arg_field, my_str_arg) |
| 3245 | lttng_ust_field_integer_hex(off_t, size_field, st->st_size) |
| 3246 | lttng_ust_field_float(double, size_dbl_field, (double) st->st_size) |
| 3247 | lttng_ust_field_sequence_text(char, half_my_str_arg_field, |
| 3248 | my_str_arg, size_t, |
| 3249 | strlen(my_str_arg) / 2) |
| 3250 | ) |
| 3251 | ) |
| 3252 | ---- |
| 3253 | |
| 3254 | Refer to this tracepoint definition with the `lttng_ust_tracepoint()` |
| 3255 | macro in the source code of your application like this: |
| 3256 | |
| 3257 | [source,c] |
| 3258 | .Application source file. |
| 3259 | ---- |
| 3260 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3261 | #include "tp.h" |
| 3262 | |
| 3263 | int main(void) |
| 3264 | { |
| 3265 | struct stat s; |
| 3266 | |
| 3267 | stat("/etc/fstab", &s); |
| 3268 | lttng_ust_tracepoint(my_provider, my_tracepoint, 23, |
| 3269 | "Hello, World!", &s); |
| 3270 | |
| 3271 | return 0; |
| 3272 | } |
| 3273 | ---- |
| 3274 | |
| 3275 | If you look at the event record that LTTng writes when recording this |
| 3276 | program, assuming the file size of path:{/etc/fstab} is 301{nbsp}bytes, |
| 3277 | it should look like this: |
| 3278 | |
| 3279 | .Event record fields |
| 3280 | |==== |
| 3281 | |Field name |Field value |
| 3282 | |`my_constant_field` |40 |
| 3283 | |`my_int_arg_field` |23 |
| 3284 | |`my_int_arg_field2` |529 |
| 3285 | |`sum4_field` |389 |
| 3286 | |`my_str_arg_field` |`Hello, World!` |
| 3287 | |`size_field` |0x12d |
| 3288 | |`size_dbl_field` |301.0 |
| 3289 | |`half_my_str_arg_field` |`Hello,` |
| 3290 | |==== |
| 3291 | ==== |
| 3292 | |
| 3293 | Sometimes, the arguments you pass to `lttng_ust_tracepoint()` are |
| 3294 | expensive to evaluate--they use the call stack, for example. To avoid |
| 3295 | this computation when LTTng wouldn't emit any event anyway, use the |
| 3296 | `lttng_ust_tracepoint_enabled()` and `lttng_ust_do_tracepoint()` macros. |
| 3297 | |
| 3298 | The syntax of the `lttng_ust_tracepoint_enabled()` and |
| 3299 | `lttng_ust_do_tracepoint()` macros is: |
| 3300 | |
| 3301 | [source,c] |
| 3302 | .`lttng_ust_tracepoint_enabled()` and `lttng_ust_do_tracepoint()` macros syntax. |
| 3303 | ---- |
| 3304 | lttng_ust_tracepoint_enabled(provider_name, tracepoint_name) |
| 3305 | |
| 3306 | lttng_ust_do_tracepoint(provider_name, tracepoint_name, ...) |
| 3307 | ---- |
| 3308 | |
| 3309 | Replace: |
| 3310 | |
| 3311 | * +__provider_name__+ with the tracepoint provider name. |
| 3312 | * +__tracepoint_name__+ with the tracepoint name. |
| 3313 | |
| 3314 | `lttng_ust_tracepoint_enabled()` returns a non-zero value if executing |
| 3315 | the tracepoint named `tracepoint_name` from the provider named |
| 3316 | `provider_name` _could_ make LTTng emit an event, depending on the |
| 3317 | payload of said event. |
| 3318 | |
| 3319 | `lttng_ust_do_tracepoint()` is like `lttng_ust_tracepoint()`, except |
| 3320 | that it doesn't check what `lttng_ust_tracepoint_enabled()` checks. |
| 3321 | Using `lttng_ust_tracepoint()` with `lttng_ust_tracepoint_enabled()` is |
| 3322 | dangerous because `lttng_ust_tracepoint()` also contains the |
| 3323 | `lttng_ust_tracepoint_enabled()` check; therefore, a race condition is |
| 3324 | possible in this situation: |
| 3325 | |
| 3326 | [source,c] |
| 3327 | .Possible race condition when using `lttng_ust_tracepoint_enabled()` with `lttng_ust_tracepoint()`. |
| 3328 | ---- |
| 3329 | if (lttng_ust_tracepoint_enabled(my_provider, my_tracepoint)) { |
| 3330 | stuff = prepare_stuff(); |
| 3331 | } |
| 3332 | |
| 3333 | lttng_ust_tracepoint(my_provider, my_tracepoint, stuff); |
| 3334 | ---- |
| 3335 | |
| 3336 | If `lttng_ust_tracepoint_enabled()` is false, but would be true after |
| 3337 | the conditional block, then `stuff` isn't prepared: the emitted event |
| 3338 | will either contain wrong data, or the whole application could crash |
| 3339 | (with a segmentation fault, for example). |
| 3340 | |
| 3341 | NOTE: Neither `lttng_ust_tracepoint_enabled()` nor |
| 3342 | `lttng_ust_do_tracepoint()` have an `STAP_PROBEV()` call. If you need |
| 3343 | it, you must emit this call yourself. |
| 3344 | |
| 3345 | |
| 3346 | [[building-tracepoint-providers-and-user-application]] |
| 3347 | ==== Build and link a tracepoint provider package and an application |
| 3348 | |
| 3349 | Once you have one or more <<tpp-header,tracepoint provider header |
| 3350 | files>> and a <<tpp-source,tracepoint provider package source file>>, |
| 3351 | create the tracepoint provider package by compiling its source |
| 3352 | file. From here, multiple build and run scenarios are possible. The |
| 3353 | following table shows common application and library configurations |
| 3354 | along with the required command lines to achieve them. |
| 3355 | |
| 3356 | In the following diagrams, we use the following file names: |
| 3357 | |
| 3358 | `app`:: |
| 3359 | Executable application. |
| 3360 | |
| 3361 | `app.o`:: |
| 3362 | Application object file. |
| 3363 | |
| 3364 | `tpp.o`:: |
| 3365 | Tracepoint provider package object file. |
| 3366 | |
| 3367 | `tpp.a`:: |
| 3368 | Tracepoint provider package archive file. |
| 3369 | |
| 3370 | `libtpp.so`:: |
| 3371 | Tracepoint provider package shared object file. |
| 3372 | |
| 3373 | `emon.o`:: |
| 3374 | User library object file. |
| 3375 | |
| 3376 | `libemon.so`:: |
| 3377 | User library shared object file. |
| 3378 | |
| 3379 | We use the following symbols in the diagrams of table below: |
| 3380 | |
| 3381 | [role="img-100"] |
| 3382 | .Symbols used in the build scenario diagrams. |
| 3383 | image::ust-sit-symbols.png[] |
| 3384 | |
| 3385 | We assume that path:{.} is part of the env:LD_LIBRARY_PATH environment |
| 3386 | variable in the following instructions. |
| 3387 | |
| 3388 | [role="growable ust-scenarios",cols="asciidoc,asciidoc"] |
| 3389 | .Common tracepoint provider package scenarios. |
| 3390 | |==== |
| 3391 | |Scenario |Instructions |
| 3392 | |
| 3393 | | |
| 3394 | The instrumented application is statically linked with |
| 3395 | the tracepoint provider package object. |
| 3396 | |
| 3397 | image::ust-sit+app-linked-with-tp-o+app-instrumented.png[] |
| 3398 | |
| 3399 | | |
| 3400 | include::../common/ust-sit-step-tp-o.txt[] |
| 3401 | |
| 3402 | To build the instrumented application: |
| 3403 | |
| 3404 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 3405 | + |
| 3406 | -- |
| 3407 | [source,c] |
| 3408 | ---- |
| 3409 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3410 | ---- |
| 3411 | -- |
| 3412 | |
| 3413 | . Compile the application source file: |
| 3414 | + |
| 3415 | -- |
| 3416 | [role="term"] |
| 3417 | ---- |
| 3418 | $ gcc -c app.c |
| 3419 | ---- |
| 3420 | -- |
| 3421 | |
| 3422 | . Build the application: |
| 3423 | + |
| 3424 | -- |
| 3425 | [role="term"] |
| 3426 | ---- |
| 3427 | $ gcc -o app app.o tpp.o -llttng-ust -ldl |
| 3428 | ---- |
| 3429 | -- |
| 3430 | |
| 3431 | To run the instrumented application: |
| 3432 | |
| 3433 | * Start the application: |
| 3434 | + |
| 3435 | -- |
| 3436 | [role="term"] |
| 3437 | ---- |
| 3438 | $ ./app |
| 3439 | ---- |
| 3440 | -- |
| 3441 | |
| 3442 | | |
| 3443 | The instrumented application is statically linked with the |
| 3444 | tracepoint provider package archive file. |
| 3445 | |
| 3446 | image::ust-sit+app-linked-with-tp-a+app-instrumented.png[] |
| 3447 | |
| 3448 | | |
| 3449 | To create the tracepoint provider package archive file: |
| 3450 | |
| 3451 | . Compile the <<tpp-source,tracepoint provider package source file>>: |
| 3452 | + |
| 3453 | -- |
| 3454 | [role="term"] |
| 3455 | ---- |
| 3456 | $ gcc -I. -c tpp.c |
| 3457 | ---- |
| 3458 | -- |
| 3459 | |
| 3460 | . Create the tracepoint provider package archive file: |
| 3461 | + |
| 3462 | -- |
| 3463 | [role="term"] |
| 3464 | ---- |
| 3465 | $ ar rcs tpp.a tpp.o |
| 3466 | ---- |
| 3467 | -- |
| 3468 | |
| 3469 | To build the instrumented application: |
| 3470 | |
| 3471 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 3472 | + |
| 3473 | -- |
| 3474 | [source,c] |
| 3475 | ---- |
| 3476 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3477 | ---- |
| 3478 | -- |
| 3479 | |
| 3480 | . Compile the application source file: |
| 3481 | + |
| 3482 | -- |
| 3483 | [role="term"] |
| 3484 | ---- |
| 3485 | $ gcc -c app.c |
| 3486 | ---- |
| 3487 | -- |
| 3488 | |
| 3489 | . Build the application: |
| 3490 | + |
| 3491 | -- |
| 3492 | [role="term"] |
| 3493 | ---- |
| 3494 | $ gcc -o app app.o tpp.a -llttng-ust -ldl |
| 3495 | ---- |
| 3496 | -- |
| 3497 | |
| 3498 | To run the instrumented application: |
| 3499 | |
| 3500 | * Start the application: |
| 3501 | + |
| 3502 | -- |
| 3503 | [role="term"] |
| 3504 | ---- |
| 3505 | $ ./app |
| 3506 | ---- |
| 3507 | -- |
| 3508 | |
| 3509 | | |
| 3510 | The instrumented application is linked with the tracepoint provider |
| 3511 | package shared object. |
| 3512 | |
| 3513 | image::ust-sit+app-linked-with-tp-so+app-instrumented.png[] |
| 3514 | |
| 3515 | | |
| 3516 | include::../common/ust-sit-step-tp-so.txt[] |
| 3517 | |
| 3518 | To build the instrumented application: |
| 3519 | |
| 3520 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 3521 | + |
| 3522 | -- |
| 3523 | [source,c] |
| 3524 | ---- |
| 3525 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3526 | ---- |
| 3527 | -- |
| 3528 | |
| 3529 | . Compile the application source file: |
| 3530 | + |
| 3531 | -- |
| 3532 | [role="term"] |
| 3533 | ---- |
| 3534 | $ gcc -c app.c |
| 3535 | ---- |
| 3536 | -- |
| 3537 | |
| 3538 | . Build the application: |
| 3539 | + |
| 3540 | -- |
| 3541 | [role="term"] |
| 3542 | ---- |
| 3543 | $ gcc -o app app.o -ldl -L. -ltpp |
| 3544 | ---- |
| 3545 | -- |
| 3546 | |
| 3547 | To run the instrumented application: |
| 3548 | |
| 3549 | * Start the application: |
| 3550 | + |
| 3551 | -- |
| 3552 | [role="term"] |
| 3553 | ---- |
| 3554 | $ ./app |
| 3555 | ---- |
| 3556 | -- |
| 3557 | |
| 3558 | | |
| 3559 | The tracepoint provider package shared object is preloaded before the |
| 3560 | instrumented application starts. |
| 3561 | |
| 3562 | image::ust-sit+tp-so-preloaded+app-instrumented.png[] |
| 3563 | |
| 3564 | | |
| 3565 | include::../common/ust-sit-step-tp-so.txt[] |
| 3566 | |
| 3567 | To build the instrumented application: |
| 3568 | |
| 3569 | . In path:{app.c}, before including path:{tpp.h}, add the |
| 3570 | following lines: |
| 3571 | + |
| 3572 | -- |
| 3573 | [source,c] |
| 3574 | ---- |
| 3575 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3576 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3577 | ---- |
| 3578 | -- |
| 3579 | |
| 3580 | . Compile the application source file: |
| 3581 | + |
| 3582 | -- |
| 3583 | [role="term"] |
| 3584 | ---- |
| 3585 | $ gcc -c app.c |
| 3586 | ---- |
| 3587 | -- |
| 3588 | |
| 3589 | . Build the application: |
| 3590 | + |
| 3591 | -- |
| 3592 | [role="term"] |
| 3593 | ---- |
| 3594 | $ gcc -o app app.o -ldl |
| 3595 | ---- |
| 3596 | -- |
| 3597 | |
| 3598 | To run the instrumented application with tracing support: |
| 3599 | |
| 3600 | * Preload the tracepoint provider package shared object and |
| 3601 | start the application: |
| 3602 | + |
| 3603 | -- |
| 3604 | [role="term"] |
| 3605 | ---- |
| 3606 | $ LD_PRELOAD=./libtpp.so ./app |
| 3607 | ---- |
| 3608 | -- |
| 3609 | |
| 3610 | To run the instrumented application without tracing support: |
| 3611 | |
| 3612 | * Start the application: |
| 3613 | + |
| 3614 | -- |
| 3615 | [role="term"] |
| 3616 | ---- |
| 3617 | $ ./app |
| 3618 | ---- |
| 3619 | -- |
| 3620 | |
| 3621 | | |
| 3622 | The instrumented application dynamically loads the tracepoint provider |
| 3623 | package shared object. |
| 3624 | |
| 3625 | image::ust-sit+app-dlopens-tp-so+app-instrumented.png[] |
| 3626 | |
| 3627 | | |
| 3628 | include::../common/ust-sit-step-tp-so.txt[] |
| 3629 | |
| 3630 | To build the instrumented application: |
| 3631 | |
| 3632 | . In path:{app.c}, before including path:{tpp.h}, add the |
| 3633 | following lines: |
| 3634 | + |
| 3635 | -- |
| 3636 | [source,c] |
| 3637 | ---- |
| 3638 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3639 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3640 | ---- |
| 3641 | -- |
| 3642 | |
| 3643 | . Compile the application source file: |
| 3644 | + |
| 3645 | -- |
| 3646 | [role="term"] |
| 3647 | ---- |
| 3648 | $ gcc -c app.c |
| 3649 | ---- |
| 3650 | -- |
| 3651 | |
| 3652 | . Build the application: |
| 3653 | + |
| 3654 | -- |
| 3655 | [role="term"] |
| 3656 | ---- |
| 3657 | $ gcc -o app app.o -ldl |
| 3658 | ---- |
| 3659 | -- |
| 3660 | |
| 3661 | To run the instrumented application: |
| 3662 | |
| 3663 | * Start the application: |
| 3664 | + |
| 3665 | -- |
| 3666 | [role="term"] |
| 3667 | ---- |
| 3668 | $ ./app |
| 3669 | ---- |
| 3670 | -- |
| 3671 | |
| 3672 | | |
| 3673 | The application is linked with the instrumented user library. |
| 3674 | |
| 3675 | The instrumented user library is statically linked with the tracepoint |
| 3676 | provider package object file. |
| 3677 | |
| 3678 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-o+lib-instrumented.png[] |
| 3679 | |
| 3680 | | |
| 3681 | include::../common/ust-sit-step-tp-o-fpic.txt[] |
| 3682 | |
| 3683 | To build the instrumented user library: |
| 3684 | |
| 3685 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3686 | following line: |
| 3687 | + |
| 3688 | -- |
| 3689 | [source,c] |
| 3690 | ---- |
| 3691 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3692 | ---- |
| 3693 | -- |
| 3694 | |
| 3695 | . Compile the user library source file: |
| 3696 | + |
| 3697 | -- |
| 3698 | [role="term"] |
| 3699 | ---- |
| 3700 | $ gcc -I. -fpic -c emon.c |
| 3701 | ---- |
| 3702 | -- |
| 3703 | |
| 3704 | . Build the user library shared object: |
| 3705 | + |
| 3706 | -- |
| 3707 | [role="term"] |
| 3708 | ---- |
| 3709 | $ gcc -shared -o libemon.so emon.o tpp.o -llttng-ust -ldl |
| 3710 | ---- |
| 3711 | -- |
| 3712 | |
| 3713 | To build the application: |
| 3714 | |
| 3715 | . Compile the application source file: |
| 3716 | + |
| 3717 | -- |
| 3718 | [role="term"] |
| 3719 | ---- |
| 3720 | $ gcc -c app.c |
| 3721 | ---- |
| 3722 | -- |
| 3723 | |
| 3724 | . Build the application: |
| 3725 | + |
| 3726 | -- |
| 3727 | [role="term"] |
| 3728 | ---- |
| 3729 | $ gcc -o app app.o -L. -lemon |
| 3730 | ---- |
| 3731 | -- |
| 3732 | |
| 3733 | To run the application: |
| 3734 | |
| 3735 | * Start the application: |
| 3736 | + |
| 3737 | -- |
| 3738 | [role="term"] |
| 3739 | ---- |
| 3740 | $ ./app |
| 3741 | ---- |
| 3742 | -- |
| 3743 | |
| 3744 | | |
| 3745 | The application is linked with the instrumented user library. |
| 3746 | |
| 3747 | The instrumented user library is linked with the tracepoint provider |
| 3748 | package shared object. |
| 3749 | |
| 3750 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-so+lib-instrumented.png[] |
| 3751 | |
| 3752 | | |
| 3753 | include::../common/ust-sit-step-tp-so.txt[] |
| 3754 | |
| 3755 | To build the instrumented user library: |
| 3756 | |
| 3757 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3758 | following line: |
| 3759 | + |
| 3760 | -- |
| 3761 | [source,c] |
| 3762 | ---- |
| 3763 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3764 | ---- |
| 3765 | -- |
| 3766 | |
| 3767 | . Compile the user library source file: |
| 3768 | + |
| 3769 | -- |
| 3770 | [role="term"] |
| 3771 | ---- |
| 3772 | $ gcc -I. -fpic -c emon.c |
| 3773 | ---- |
| 3774 | -- |
| 3775 | |
| 3776 | . Build the user library shared object: |
| 3777 | + |
| 3778 | -- |
| 3779 | [role="term"] |
| 3780 | ---- |
| 3781 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
| 3782 | ---- |
| 3783 | -- |
| 3784 | |
| 3785 | To build the application: |
| 3786 | |
| 3787 | . Compile the application source file: |
| 3788 | + |
| 3789 | -- |
| 3790 | [role="term"] |
| 3791 | ---- |
| 3792 | $ gcc -c app.c |
| 3793 | ---- |
| 3794 | -- |
| 3795 | |
| 3796 | . Build the application: |
| 3797 | + |
| 3798 | -- |
| 3799 | [role="term"] |
| 3800 | ---- |
| 3801 | $ gcc -o app app.o -L. -lemon |
| 3802 | ---- |
| 3803 | -- |
| 3804 | |
| 3805 | To run the application: |
| 3806 | |
| 3807 | * Start the application: |
| 3808 | + |
| 3809 | -- |
| 3810 | [role="term"] |
| 3811 | ---- |
| 3812 | $ ./app |
| 3813 | ---- |
| 3814 | -- |
| 3815 | |
| 3816 | | |
| 3817 | The tracepoint provider package shared object is preloaded before the |
| 3818 | application starts. |
| 3819 | |
| 3820 | The application is linked with the instrumented user library. |
| 3821 | |
| 3822 | image::ust-sit+tp-so-preloaded+app-linked-with-lib+lib-instrumented.png[] |
| 3823 | |
| 3824 | | |
| 3825 | include::../common/ust-sit-step-tp-so.txt[] |
| 3826 | |
| 3827 | To build the instrumented user library: |
| 3828 | |
| 3829 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3830 | following lines: |
| 3831 | + |
| 3832 | -- |
| 3833 | [source,c] |
| 3834 | ---- |
| 3835 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3836 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3837 | ---- |
| 3838 | -- |
| 3839 | |
| 3840 | . Compile the user library source file: |
| 3841 | + |
| 3842 | -- |
| 3843 | [role="term"] |
| 3844 | ---- |
| 3845 | $ gcc -I. -fpic -c emon.c |
| 3846 | ---- |
| 3847 | -- |
| 3848 | |
| 3849 | . Build the user library shared object: |
| 3850 | + |
| 3851 | -- |
| 3852 | [role="term"] |
| 3853 | ---- |
| 3854 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3855 | ---- |
| 3856 | -- |
| 3857 | |
| 3858 | To build the application: |
| 3859 | |
| 3860 | . Compile the application source file: |
| 3861 | + |
| 3862 | -- |
| 3863 | [role="term"] |
| 3864 | ---- |
| 3865 | $ gcc -c app.c |
| 3866 | ---- |
| 3867 | -- |
| 3868 | |
| 3869 | . Build the application: |
| 3870 | + |
| 3871 | -- |
| 3872 | [role="term"] |
| 3873 | ---- |
| 3874 | $ gcc -o app app.o -L. -lemon |
| 3875 | ---- |
| 3876 | -- |
| 3877 | |
| 3878 | To run the application with tracing support: |
| 3879 | |
| 3880 | * Preload the tracepoint provider package shared object and |
| 3881 | start the application: |
| 3882 | + |
| 3883 | -- |
| 3884 | [role="term"] |
| 3885 | ---- |
| 3886 | $ LD_PRELOAD=./libtpp.so ./app |
| 3887 | ---- |
| 3888 | -- |
| 3889 | |
| 3890 | To run the application without tracing support: |
| 3891 | |
| 3892 | * Start the application: |
| 3893 | + |
| 3894 | -- |
| 3895 | [role="term"] |
| 3896 | ---- |
| 3897 | $ ./app |
| 3898 | ---- |
| 3899 | -- |
| 3900 | |
| 3901 | | |
| 3902 | The application is linked with the instrumented user library. |
| 3903 | |
| 3904 | The instrumented user library dynamically loads the tracepoint provider |
| 3905 | package shared object. |
| 3906 | |
| 3907 | image::ust-sit+app-linked-with-lib+lib-dlopens-tp-so+lib-instrumented.png[] |
| 3908 | |
| 3909 | | |
| 3910 | include::../common/ust-sit-step-tp-so.txt[] |
| 3911 | |
| 3912 | To build the instrumented user library: |
| 3913 | |
| 3914 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3915 | following lines: |
| 3916 | + |
| 3917 | -- |
| 3918 | [source,c] |
| 3919 | ---- |
| 3920 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3921 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3922 | ---- |
| 3923 | -- |
| 3924 | |
| 3925 | . Compile the user library source file: |
| 3926 | + |
| 3927 | -- |
| 3928 | [role="term"] |
| 3929 | ---- |
| 3930 | $ gcc -I. -fpic -c emon.c |
| 3931 | ---- |
| 3932 | -- |
| 3933 | |
| 3934 | . Build the user library shared object: |
| 3935 | + |
| 3936 | -- |
| 3937 | [role="term"] |
| 3938 | ---- |
| 3939 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3940 | ---- |
| 3941 | -- |
| 3942 | |
| 3943 | To build the application: |
| 3944 | |
| 3945 | . Compile the application source file: |
| 3946 | + |
| 3947 | -- |
| 3948 | [role="term"] |
| 3949 | ---- |
| 3950 | $ gcc -c app.c |
| 3951 | ---- |
| 3952 | -- |
| 3953 | |
| 3954 | . Build the application: |
| 3955 | + |
| 3956 | -- |
| 3957 | [role="term"] |
| 3958 | ---- |
| 3959 | $ gcc -o app app.o -L. -lemon |
| 3960 | ---- |
| 3961 | -- |
| 3962 | |
| 3963 | To run the application: |
| 3964 | |
| 3965 | * Start the application: |
| 3966 | + |
| 3967 | -- |
| 3968 | [role="term"] |
| 3969 | ---- |
| 3970 | $ ./app |
| 3971 | ---- |
| 3972 | -- |
| 3973 | |
| 3974 | | |
| 3975 | The application dynamically loads the instrumented user library. |
| 3976 | |
| 3977 | The instrumented user library is linked with the tracepoint provider |
| 3978 | package shared object. |
| 3979 | |
| 3980 | image::ust-sit+app-dlopens-lib+lib-linked-with-tp-so+lib-instrumented.png[] |
| 3981 | |
| 3982 | | |
| 3983 | include::../common/ust-sit-step-tp-so.txt[] |
| 3984 | |
| 3985 | To build the instrumented user library: |
| 3986 | |
| 3987 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3988 | following line: |
| 3989 | + |
| 3990 | -- |
| 3991 | [source,c] |
| 3992 | ---- |
| 3993 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 3994 | ---- |
| 3995 | -- |
| 3996 | |
| 3997 | . Compile the user library source file: |
| 3998 | + |
| 3999 | -- |
| 4000 | [role="term"] |
| 4001 | ---- |
| 4002 | $ gcc -I. -fpic -c emon.c |
| 4003 | ---- |
| 4004 | -- |
| 4005 | |
| 4006 | . Build the user library shared object: |
| 4007 | + |
| 4008 | -- |
| 4009 | [role="term"] |
| 4010 | ---- |
| 4011 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
| 4012 | ---- |
| 4013 | -- |
| 4014 | |
| 4015 | To build the application: |
| 4016 | |
| 4017 | . Compile the application source file: |
| 4018 | + |
| 4019 | -- |
| 4020 | [role="term"] |
| 4021 | ---- |
| 4022 | $ gcc -c app.c |
| 4023 | ---- |
| 4024 | -- |
| 4025 | |
| 4026 | . Build the application: |
| 4027 | + |
| 4028 | -- |
| 4029 | [role="term"] |
| 4030 | ---- |
| 4031 | $ gcc -o app app.o -ldl -L. -lemon |
| 4032 | ---- |
| 4033 | -- |
| 4034 | |
| 4035 | To run the application: |
| 4036 | |
| 4037 | * Start the application: |
| 4038 | + |
| 4039 | -- |
| 4040 | [role="term"] |
| 4041 | ---- |
| 4042 | $ ./app |
| 4043 | ---- |
| 4044 | -- |
| 4045 | |
| 4046 | | |
| 4047 | The application dynamically loads the instrumented user library. |
| 4048 | |
| 4049 | The instrumented user library dynamically loads the tracepoint provider |
| 4050 | package shared object. |
| 4051 | |
| 4052 | image::ust-sit+app-dlopens-lib+lib-dlopens-tp-so+lib-instrumented.png[] |
| 4053 | |
| 4054 | | |
| 4055 | include::../common/ust-sit-step-tp-so.txt[] |
| 4056 | |
| 4057 | To build the instrumented user library: |
| 4058 | |
| 4059 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 4060 | following lines: |
| 4061 | + |
| 4062 | -- |
| 4063 | [source,c] |
| 4064 | ---- |
| 4065 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 4066 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 4067 | ---- |
| 4068 | -- |
| 4069 | |
| 4070 | . Compile the user library source file: |
| 4071 | + |
| 4072 | -- |
| 4073 | [role="term"] |
| 4074 | ---- |
| 4075 | $ gcc -I. -fpic -c emon.c |
| 4076 | ---- |
| 4077 | -- |
| 4078 | |
| 4079 | . Build the user library shared object: |
| 4080 | + |
| 4081 | -- |
| 4082 | [role="term"] |
| 4083 | ---- |
| 4084 | $ gcc -shared -o libemon.so emon.o -ldl |
| 4085 | ---- |
| 4086 | -- |
| 4087 | |
| 4088 | To build the application: |
| 4089 | |
| 4090 | . Compile the application source file: |
| 4091 | + |
| 4092 | -- |
| 4093 | [role="term"] |
| 4094 | ---- |
| 4095 | $ gcc -c app.c |
| 4096 | ---- |
| 4097 | -- |
| 4098 | |
| 4099 | . Build the application: |
| 4100 | + |
| 4101 | -- |
| 4102 | [role="term"] |
| 4103 | ---- |
| 4104 | $ gcc -o app app.o -ldl -L. -lemon |
| 4105 | ---- |
| 4106 | -- |
| 4107 | |
| 4108 | To run the application: |
| 4109 | |
| 4110 | * Start the application: |
| 4111 | + |
| 4112 | -- |
| 4113 | [role="term"] |
| 4114 | ---- |
| 4115 | $ ./app |
| 4116 | ---- |
| 4117 | -- |
| 4118 | |
| 4119 | | |
| 4120 | The tracepoint provider package shared object is preloaded before the |
| 4121 | application starts. |
| 4122 | |
| 4123 | The application dynamically loads the instrumented user library. |
| 4124 | |
| 4125 | image::ust-sit+tp-so-preloaded+app-dlopens-lib+lib-instrumented.png[] |
| 4126 | |
| 4127 | | |
| 4128 | include::../common/ust-sit-step-tp-so.txt[] |
| 4129 | |
| 4130 | To build the instrumented user library: |
| 4131 | |
| 4132 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 4133 | following lines: |
| 4134 | + |
| 4135 | -- |
| 4136 | [source,c] |
| 4137 | ---- |
| 4138 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 4139 | #define LTTNG_UST_TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 4140 | ---- |
| 4141 | -- |
| 4142 | |
| 4143 | . Compile the user library source file: |
| 4144 | + |
| 4145 | -- |
| 4146 | [role="term"] |
| 4147 | ---- |
| 4148 | $ gcc -I. -fpic -c emon.c |
| 4149 | ---- |
| 4150 | -- |
| 4151 | |
| 4152 | . Build the user library shared object: |
| 4153 | + |
| 4154 | -- |
| 4155 | [role="term"] |
| 4156 | ---- |
| 4157 | $ gcc -shared -o libemon.so emon.o -ldl |
| 4158 | ---- |
| 4159 | -- |
| 4160 | |
| 4161 | To build the application: |
| 4162 | |
| 4163 | . Compile the application source file: |
| 4164 | + |
| 4165 | -- |
| 4166 | [role="term"] |
| 4167 | ---- |
| 4168 | $ gcc -c app.c |
| 4169 | ---- |
| 4170 | -- |
| 4171 | |
| 4172 | . Build the application: |
| 4173 | + |
| 4174 | -- |
| 4175 | [role="term"] |
| 4176 | ---- |
| 4177 | $ gcc -o app app.o -L. -lemon |
| 4178 | ---- |
| 4179 | -- |
| 4180 | |
| 4181 | To run the application with tracing support: |
| 4182 | |
| 4183 | * Preload the tracepoint provider package shared object and |
| 4184 | start the application: |
| 4185 | + |
| 4186 | -- |
| 4187 | [role="term"] |
| 4188 | ---- |
| 4189 | $ LD_PRELOAD=./libtpp.so ./app |
| 4190 | ---- |
| 4191 | -- |
| 4192 | |
| 4193 | To run the application without tracing support: |
| 4194 | |
| 4195 | * Start the application: |
| 4196 | + |
| 4197 | -- |
| 4198 | [role="term"] |
| 4199 | ---- |
| 4200 | $ ./app |
| 4201 | ---- |
| 4202 | -- |
| 4203 | |
| 4204 | | |
| 4205 | The application is statically linked with the tracepoint provider |
| 4206 | package object file. |
| 4207 | |
| 4208 | The application is linked with the instrumented user library. |
| 4209 | |
| 4210 | image::ust-sit+app-linked-with-tp-o+app-linked-with-lib+lib-instrumented.png[] |
| 4211 | |
| 4212 | | |
| 4213 | include::../common/ust-sit-step-tp-o.txt[] |
| 4214 | |
| 4215 | To build the instrumented user library: |
| 4216 | |
| 4217 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 4218 | following line: |
| 4219 | + |
| 4220 | -- |
| 4221 | [source,c] |
| 4222 | ---- |
| 4223 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 4224 | ---- |
| 4225 | -- |
| 4226 | |
| 4227 | . Compile the user library source file: |
| 4228 | + |
| 4229 | -- |
| 4230 | [role="term"] |
| 4231 | ---- |
| 4232 | $ gcc -I. -fpic -c emon.c |
| 4233 | ---- |
| 4234 | -- |
| 4235 | |
| 4236 | . Build the user library shared object: |
| 4237 | + |
| 4238 | -- |
| 4239 | [role="term"] |
| 4240 | ---- |
| 4241 | $ gcc -shared -o libemon.so emon.o |
| 4242 | ---- |
| 4243 | -- |
| 4244 | |
| 4245 | To build the application: |
| 4246 | |
| 4247 | . Compile the application source file: |
| 4248 | + |
| 4249 | -- |
| 4250 | [role="term"] |
| 4251 | ---- |
| 4252 | $ gcc -c app.c |
| 4253 | ---- |
| 4254 | -- |
| 4255 | |
| 4256 | . Build the application: |
| 4257 | + |
| 4258 | -- |
| 4259 | [role="term"] |
| 4260 | ---- |
| 4261 | $ gcc -o app app.o tpp.o -llttng-ust -ldl -L. -lemon |
| 4262 | ---- |
| 4263 | -- |
| 4264 | |
| 4265 | To run the instrumented application: |
| 4266 | |
| 4267 | * Start the application: |
| 4268 | + |
| 4269 | -- |
| 4270 | [role="term"] |
| 4271 | ---- |
| 4272 | $ ./app |
| 4273 | ---- |
| 4274 | -- |
| 4275 | |
| 4276 | | |
| 4277 | The application is statically linked with the tracepoint provider |
| 4278 | package object file. |
| 4279 | |
| 4280 | The application dynamically loads the instrumented user library. |
| 4281 | |
| 4282 | image::ust-sit+app-linked-with-tp-o+app-dlopens-lib+lib-instrumented.png[] |
| 4283 | |
| 4284 | | |
| 4285 | include::../common/ust-sit-step-tp-o.txt[] |
| 4286 | |
| 4287 | To build the application: |
| 4288 | |
| 4289 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 4290 | + |
| 4291 | -- |
| 4292 | [source,c] |
| 4293 | ---- |
| 4294 | #define LTTNG_UST_TRACEPOINT_DEFINE |
| 4295 | ---- |
| 4296 | -- |
| 4297 | |
| 4298 | . Compile the application source file: |
| 4299 | + |
| 4300 | -- |
| 4301 | [role="term"] |
| 4302 | ---- |
| 4303 | $ gcc -c app.c |
| 4304 | ---- |
| 4305 | -- |
| 4306 | |
| 4307 | . Build the application: |
| 4308 | + |
| 4309 | -- |
| 4310 | [role="term"] |
| 4311 | ---- |
| 4312 | $ gcc -Wl,--export-dynamic -o app app.o tpp.o \ |
| 4313 | -llttng-ust -ldl |
| 4314 | ---- |
| 4315 | -- |
| 4316 | + |
| 4317 | The `--export-dynamic` option passed to the linker is necessary for the |
| 4318 | dynamically loaded library to ``see'' the tracepoint symbols defined in |
| 4319 | the application. |
| 4320 | |
| 4321 | To build the instrumented user library: |
| 4322 | |
| 4323 | . Compile the user library source file: |
| 4324 | + |
| 4325 | -- |
| 4326 | [role="term"] |
| 4327 | ---- |
| 4328 | $ gcc -I. -fpic -c emon.c |
| 4329 | ---- |
| 4330 | -- |
| 4331 | |
| 4332 | . Build the user library shared object: |
| 4333 | + |
| 4334 | -- |
| 4335 | [role="term"] |
| 4336 | ---- |
| 4337 | $ gcc -shared -o libemon.so emon.o |
| 4338 | ---- |
| 4339 | -- |
| 4340 | |
| 4341 | To run the application: |
| 4342 | |
| 4343 | * Start the application: |
| 4344 | + |
| 4345 | -- |
| 4346 | [role="term"] |
| 4347 | ---- |
| 4348 | $ ./app |
| 4349 | ---- |
| 4350 | -- |
| 4351 | |==== |
| 4352 | |
| 4353 | |
| 4354 | [[using-lttng-ust-with-daemons]] |
| 4355 | ===== Use noch:{LTTng-UST} with daemons |
| 4356 | |
| 4357 | If your instrumented application calls man:fork(2), man:clone(2), |
| 4358 | or BSD's man:rfork(2), without a following man:exec(3)-family |
| 4359 | system call, you must preload the path:{liblttng-ust-fork.so} shared |
| 4360 | object when you start the application. |
| 4361 | |
| 4362 | [role="term"] |
| 4363 | ---- |
| 4364 | $ LD_PRELOAD=liblttng-ust-fork.so ./my-app |
| 4365 | ---- |
| 4366 | |
| 4367 | If your tracepoint provider package is |
| 4368 | a shared library which you also preload, you must put both |
| 4369 | shared objects in env:LD_PRELOAD: |
| 4370 | |
| 4371 | [role="term"] |
| 4372 | ---- |
| 4373 | $ LD_PRELOAD=liblttng-ust-fork.so:/path/to/tp.so ./my-app |
| 4374 | ---- |
| 4375 | |
| 4376 | |
| 4377 | [role="since-2.9"] |
| 4378 | [[liblttng-ust-fd]] |
| 4379 | ===== Use noch:{LTTng-UST} with applications which close file descriptors that don't belong to them |
| 4380 | |
| 4381 | If your instrumented application closes one or more file descriptors |
| 4382 | which it did not open itself, you must preload the |
| 4383 | path:{liblttng-ust-fd.so} shared object when you start the application: |
| 4384 | |
| 4385 | [role="term"] |
| 4386 | ---- |
| 4387 | $ LD_PRELOAD=liblttng-ust-fd.so ./my-app |
| 4388 | ---- |
| 4389 | |
| 4390 | Typical use cases include closing all the file descriptors after |
| 4391 | man:fork(2) or man:rfork(2) and buggy applications doing |
| 4392 | ``double closes''. |
| 4393 | |
| 4394 | |
| 4395 | [[lttng-ust-pkg-config]] |
| 4396 | ===== Use noch:{pkg-config} |
| 4397 | |
| 4398 | On some distributions, LTTng-UST ships with a |
| 4399 | https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config] |
| 4400 | metadata file. If this is your case, then use cmd:pkg-config to |
| 4401 | build an application on the command line: |
| 4402 | |
| 4403 | [role="term"] |
| 4404 | ---- |
| 4405 | $ gcc -o my-app my-app.o tp.o $(pkg-config --cflags --libs lttng-ust) |
| 4406 | ---- |
| 4407 | |
| 4408 | |
| 4409 | [[instrumenting-32-bit-app-on-64-bit-system]] |
| 4410 | ===== [[advanced-instrumenting-techniques]]Build a 32-bit instrumented application for a 64-bit target system |
| 4411 | |
| 4412 | In order to trace a 32-bit application running on a 64-bit system, |
| 4413 | LTTng must use a dedicated 32-bit |
| 4414 | <<lttng-consumerd,consumer daemon>>. |
| 4415 | |
| 4416 | The following steps show how to build and install a 32-bit consumer |
| 4417 | daemon, which is _not_ part of the default 64-bit LTTng build, how to |
| 4418 | build and install the 32-bit LTTng-UST libraries, and how to build and |
| 4419 | link an instrumented 32-bit application in that context. |
| 4420 | |
| 4421 | To build a 32-bit instrumented application for a 64-bit target system, |
| 4422 | assuming you have a fresh target system with no installed Userspace RCU |
| 4423 | or LTTng packages: |
| 4424 | |
| 4425 | . Download, build, and install a 32-bit version of Userspace RCU: |
| 4426 | + |
| 4427 | -- |
| 4428 | [role="term"] |
| 4429 | ---- |
| 4430 | $ cd $(mktemp -d) && |
| 4431 | wget https://lttng.org/files/urcu/userspace-rcu-latest-0.13.tar.bz2 && |
| 4432 | tar -xf userspace-rcu-latest-0.13.tar.bz2 && |
| 4433 | cd userspace-rcu-0.13.* && |
| 4434 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 && |
| 4435 | make && |
| 4436 | sudo make install && |
| 4437 | sudo ldconfig |
| 4438 | ---- |
| 4439 | -- |
| 4440 | |
| 4441 | . Using the package manager of your distribution, or from source, |
| 4442 | install the 32-bit versions of the following dependencies of |
| 4443 | LTTng-tools and LTTng-UST: |
| 4444 | + |
| 4445 | -- |
| 4446 | * https://sourceforge.net/projects/libuuid/[libuuid] |
| 4447 | * https://directory.fsf.org/wiki/Popt[popt] |
| 4448 | * https://www.xmlsoft.org/[libxml2] |
| 4449 | * **Optional**: https://github.com/numactl/numactl[numactl] |
| 4450 | -- |
| 4451 | |
| 4452 | . Download, build, and install a 32-bit version of the latest |
| 4453 | LTTng-UST{nbsp}{revision}: |
| 4454 | + |
| 4455 | -- |
| 4456 | [role="term"] |
| 4457 | ---- |
| 4458 | $ cd $(mktemp -d) && |
| 4459 | wget https://lttng.org/files/lttng-ust/lttng-ust-latest-2.13.tar.bz2 && |
| 4460 | tar -xf lttng-ust-latest-2.13.tar.bz2 && |
| 4461 | cd lttng-ust-2.13.* && |
| 4462 | ./configure --libdir=/usr/local/lib32 \ |
| 4463 | CFLAGS=-m32 CXXFLAGS=-m32 \ |
| 4464 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' && |
| 4465 | make && |
| 4466 | sudo make install && |
| 4467 | sudo ldconfig |
| 4468 | ---- |
| 4469 | -- |
| 4470 | + |
| 4471 | Add `--disable-numa` to `./configure` if you don't have |
| 4472 | https://github.com/numactl/numactl[numactl]. |
| 4473 | + |
| 4474 | [NOTE] |
| 4475 | ==== |
| 4476 | Depending on your distribution, 32-bit libraries could be installed at a |
| 4477 | different location than `/usr/lib32`. For example, Debian is known to |
| 4478 | install some 32-bit libraries in `/usr/lib/i386-linux-gnu`. |
| 4479 | |
| 4480 | In this case, make sure to set `LDFLAGS` to all the |
| 4481 | relevant 32-bit library paths, for example: |
| 4482 | |
| 4483 | [role="term"] |
| 4484 | ---- |
| 4485 | $ LDFLAGS='-L/usr/lib/i386-linux-gnu -L/usr/lib32' |
| 4486 | ---- |
| 4487 | ==== |
| 4488 | |
| 4489 | . Download the latest LTTng-tools{nbsp}{revision}, build, and install |
| 4490 | the 32-bit consumer daemon: |
| 4491 | + |
| 4492 | -- |
| 4493 | [role="term"] |
| 4494 | ---- |
| 4495 | $ cd $(mktemp -d) && |
| 4496 | wget https://lttng.org/files/lttng-tools/lttng-tools-latest-2.13.tar.bz2 && |
| 4497 | tar -xf lttng-tools-latest-2.13.tar.bz2 && |
| 4498 | cd lttng-tools-2.13.* && |
| 4499 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 CXXFLAGS=-m32 \ |
| 4500 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' \ |
| 4501 | --disable-bin-lttng --disable-bin-lttng-crash \ |
| 4502 | --disable-bin-lttng-relayd --disable-bin-lttng-sessiond && |
| 4503 | make && |
| 4504 | cd src/bin/lttng-consumerd && |
| 4505 | sudo make install && |
| 4506 | sudo ldconfig |
| 4507 | ---- |
| 4508 | -- |
| 4509 | |
| 4510 | . From your distribution or from source, <<installing-lttng,install>> |
| 4511 | the 64-bit versions of LTTng-UST and Userspace RCU. |
| 4512 | |
| 4513 | . Download, build, and install the 64-bit version of the |
| 4514 | latest LTTng-tools{nbsp}{revision}: |
| 4515 | + |
| 4516 | -- |
| 4517 | [role="term"] |
| 4518 | ---- |
| 4519 | $ cd $(mktemp -d) && |
| 4520 | wget https://lttng.org/files/lttng-tools/lttng-tools-latest-2.13.tar.bz2 && |
| 4521 | tar -xf lttng-tools-latest-2.13.tar.bz2 && |
| 4522 | cd lttng-tools-2.13.* && |
| 4523 | ./configure --with-consumerd32-libdir=/usr/local/lib32 \ |
| 4524 | --with-consumerd32-bin=/usr/local/lib32/lttng/libexec/lttng-consumerd && |
| 4525 | make && |
| 4526 | sudo make install && |
| 4527 | sudo ldconfig |
| 4528 | ---- |
| 4529 | -- |
| 4530 | |
| 4531 | . Pass the following options to man:gcc(1), man:g++(1), or man:clang(1) |
| 4532 | when linking your 32-bit application: |
| 4533 | + |
| 4534 | ---- |
| 4535 | -m32 -L/usr/lib32 -L/usr/local/lib32 \ |
| 4536 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 |
| 4537 | ---- |
| 4538 | + |
| 4539 | For example, let's rebuild the quick start example in |
| 4540 | ``<<tracing-your-own-user-application,Record user application events>>'' |
| 4541 | as an instrumented 32-bit application: |
| 4542 | + |
| 4543 | -- |
| 4544 | [role="term"] |
| 4545 | ---- |
| 4546 | $ gcc -m32 -c -I. hello-tp.c |
| 4547 | $ gcc -m32 -c hello.c |
| 4548 | $ gcc -m32 -o hello hello.o hello-tp.o \ |
| 4549 | -L/usr/lib32 -L/usr/local/lib32 \ |
| 4550 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 \ |
| 4551 | -llttng-ust -ldl |
| 4552 | ---- |
| 4553 | -- |
| 4554 | |
| 4555 | No special action is required to execute the 32-bit application and |
| 4556 | for LTTng to trace it: use the command-line man:lttng(1) tool as usual. |
| 4557 | |
| 4558 | |
| 4559 | [role="since-2.5"] |
| 4560 | [[tracef]] |
| 4561 | ==== Use `lttng_ust_tracef()` |
| 4562 | |
| 4563 | man:lttng_ust_tracef(3) is a small LTTng-UST API designed for quick, |
| 4564 | man:printf(3)-like instrumentation without the burden of |
| 4565 | <<tracepoint-provider,creating>> and |
| 4566 | <<building-tracepoint-providers-and-user-application,building>> |
| 4567 | a tracepoint provider package. |
| 4568 | |
| 4569 | To use `lttng_ust_tracef()` in your application: |
| 4570 | |
| 4571 | . In the C or $$C++$$ source files where you need to use |
| 4572 | `lttng_ust_tracef()`, include `<lttng/tracef.h>`: |
| 4573 | + |
| 4574 | -- |
| 4575 | [source,c] |
| 4576 | ---- |
| 4577 | #include <lttng/tracef.h> |
| 4578 | ---- |
| 4579 | -- |
| 4580 | |
| 4581 | . In the source code of the application, use `lttng_ust_tracef()` like |
| 4582 | you would use man:printf(3): |
| 4583 | + |
| 4584 | -- |
| 4585 | [source,c] |
| 4586 | ---- |
| 4587 | /* ... */ |
| 4588 | |
| 4589 | lttng_ust_tracef("my message: %d (%s)", my_integer, my_string); |
| 4590 | |
| 4591 | /* ... */ |
| 4592 | ---- |
| 4593 | -- |
| 4594 | |
| 4595 | . Link your application with `liblttng-ust`: |
| 4596 | + |
| 4597 | -- |
| 4598 | [role="term"] |
| 4599 | ---- |
| 4600 | $ gcc -o app app.c -llttng-ust |
| 4601 | ---- |
| 4602 | -- |
| 4603 | |
| 4604 | To record the events that `lttng_ust_tracef()` calls emit: |
| 4605 | |
| 4606 | * <<enabling-disabling-events,Create a recording event rule>> which |
| 4607 | matches user space events named `lttng_ust_tracef:*`: |
| 4608 | + |
| 4609 | -- |
| 4610 | [role="term"] |
| 4611 | ---- |
| 4612 | $ lttng enable-event --userspace 'lttng_ust_tracef:*' |
| 4613 | ---- |
| 4614 | -- |
| 4615 | |
| 4616 | [IMPORTANT] |
| 4617 | .Limitations of `lttng_ust_tracef()` |
| 4618 | ==== |
| 4619 | The `lttng_ust_tracef()` utility function was developed to make user |
| 4620 | space tracing super simple, albeit with notable disadvantages compared |
| 4621 | to <<defining-tracepoints,user-defined tracepoints>>: |
| 4622 | |
| 4623 | * All the created events have the same tracepoint provider and |
| 4624 | tracepoint names, respectively `lttng_ust_tracef` and `event`. |
| 4625 | * There's no static type checking. |
| 4626 | * The only event record field you actually get, named `msg`, is a string |
| 4627 | potentially containing the values you passed to `lttng_ust_tracef()` |
| 4628 | using your own format string. This also means that you can't filter |
| 4629 | events with a custom expression at run time because there are no |
| 4630 | isolated fields. |
| 4631 | * Since `lttng_ust_tracef()` uses the man:vasprintf(3) function of the |
| 4632 | C{nbsp}standard library behind the scenes to format the strings at run |
| 4633 | time, its expected performance is lower than with user-defined |
| 4634 | tracepoints, which don't require a conversion to a string. |
| 4635 | |
| 4636 | Taking this into consideration, `lttng_ust_tracef()` is useful for some |
| 4637 | quick prototyping and debugging, but you shouldn't consider it for any |
| 4638 | permanent and serious applicative instrumentation. |
| 4639 | ==== |
| 4640 | |
| 4641 | |
| 4642 | [role="since-2.7"] |
| 4643 | [[tracelog]] |
| 4644 | ==== Use `lttng_ust_tracelog()` |
| 4645 | |
| 4646 | The man:tracelog(3) API is very similar to |
| 4647 | <<tracef,`lttng_ust_tracef()`>>, with the difference that it accepts an |
| 4648 | additional log level parameter. |
| 4649 | |
| 4650 | The goal of `lttng_ust_tracelog()` is to ease the migration from logging |
| 4651 | to tracing. |
| 4652 | |
| 4653 | To use `lttng_ust_tracelog()` in your application: |
| 4654 | |
| 4655 | . In the C or $$C++$$ source files where you need to use `tracelog()`, |
| 4656 | include `<lttng/tracelog.h>`: |
| 4657 | + |
| 4658 | -- |
| 4659 | [source,c] |
| 4660 | ---- |
| 4661 | #include <lttng/tracelog.h> |
| 4662 | ---- |
| 4663 | -- |
| 4664 | |
| 4665 | . In the source code of the application, use `lttng_ust_tracelog()` like |
| 4666 | you would use man:printf(3), except for the first parameter which is |
| 4667 | the log level: |
| 4668 | + |
| 4669 | -- |
| 4670 | [source,c] |
| 4671 | ---- |
| 4672 | /* ... */ |
| 4673 | |
| 4674 | tracelog(LTTNG_UST_TRACEPOINT_LOGLEVEL_WARNING, |
| 4675 | "my message: %d (%s)", my_integer, my_string); |
| 4676 | |
| 4677 | /* ... */ |
| 4678 | ---- |
| 4679 | -- |
| 4680 | + |
| 4681 | See man:lttng-ust(3) for a list of available log level names. |
| 4682 | |
| 4683 | . Link your application with `liblttng-ust`: |
| 4684 | + |
| 4685 | -- |
| 4686 | [role="term"] |
| 4687 | ---- |
| 4688 | $ gcc -o app app.c -llttng-ust |
| 4689 | ---- |
| 4690 | -- |
| 4691 | |
| 4692 | To record the events that `lttng_ust_tracelog()` calls emit with a log |
| 4693 | level _at least as severe as_ a specific log level: |
| 4694 | |
| 4695 | * <<enabling-disabling-events,Create a recording event rule>> which |
| 4696 | matches user space tracepoint events named `lttng_ust_tracelog:*` and |
| 4697 | with some minimum level of severity: |
| 4698 | + |
| 4699 | -- |
| 4700 | [role="term"] |
| 4701 | ---- |
| 4702 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' \ |
| 4703 | --loglevel=WARNING |
| 4704 | ---- |
| 4705 | -- |
| 4706 | |
| 4707 | To record the events that `lttng_ust_tracelog()` calls emit with a |
| 4708 | _specific log level_: |
| 4709 | |
| 4710 | * Create a recording event rule which matches tracepoint events named |
| 4711 | `lttng_ust_tracelog:*` and with a specific log level: |
| 4712 | + |
| 4713 | -- |
| 4714 | [role="term"] |
| 4715 | ---- |
| 4716 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' \ |
| 4717 | --loglevel-only=INFO |
| 4718 | ---- |
| 4719 | -- |
| 4720 | |
| 4721 | |
| 4722 | [[prebuilt-ust-helpers]] |
| 4723 | === Load a prebuilt user space tracing helper |
| 4724 | |
| 4725 | The LTTng-UST package provides a few helpers in the form of preloadable |
| 4726 | shared objects which automatically instrument system functions and |
| 4727 | calls. |
| 4728 | |
| 4729 | The helper shared objects are normally found in dir:{/usr/lib}. If you |
| 4730 | built LTTng-UST <<building-from-source,from source>>, they're probably |
| 4731 | located in dir:{/usr/local/lib}. |
| 4732 | |
| 4733 | The installed user space tracing helpers in LTTng-UST{nbsp}{revision} |
| 4734 | are: |
| 4735 | |
| 4736 | path:{liblttng-ust-libc-wrapper.so}:: |
| 4737 | path:{liblttng-ust-pthread-wrapper.so}:: |
| 4738 | <<liblttng-ust-libc-pthread-wrapper,C{nbsp}standard library |
| 4739 | memory and POSIX threads function tracing>>. |
| 4740 | |
| 4741 | path:{liblttng-ust-cyg-profile.so}:: |
| 4742 | path:{liblttng-ust-cyg-profile-fast.so}:: |
| 4743 | <<liblttng-ust-cyg-profile,Function entry and exit tracing>>. |
| 4744 | |
| 4745 | path:{liblttng-ust-dl.so}:: |
| 4746 | <<liblttng-ust-dl,Dynamic linker tracing>>. |
| 4747 | |
| 4748 | To use a user space tracing helper with any user application: |
| 4749 | |
| 4750 | * Preload the helper shared object when you start the application: |
| 4751 | + |
| 4752 | -- |
| 4753 | [role="term"] |
| 4754 | ---- |
| 4755 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so my-app |
| 4756 | ---- |
| 4757 | -- |
| 4758 | + |
| 4759 | You can preload more than one helper: |
| 4760 | + |
| 4761 | -- |
| 4762 | [role="term"] |
| 4763 | ---- |
| 4764 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so:liblttng-ust-dl.so my-app |
| 4765 | ---- |
| 4766 | -- |
| 4767 | |
| 4768 | |
| 4769 | [role="since-2.3"] |
| 4770 | [[liblttng-ust-libc-pthread-wrapper]] |
| 4771 | ==== Instrument C standard library memory and POSIX threads functions |
| 4772 | |
| 4773 | The path:{liblttng-ust-libc-wrapper.so} and |
| 4774 | path:{liblttng-ust-pthread-wrapper.so} helpers |
| 4775 | add instrumentation to some C standard library and POSIX |
| 4776 | threads functions. |
| 4777 | |
| 4778 | [role="growable"] |
| 4779 | .Functions instrumented by preloading path:{liblttng-ust-libc-wrapper.so}. |
| 4780 | |==== |
| 4781 | |TP provider name |TP name |Instrumented function |
| 4782 | |
| 4783 | .6+|`lttng_ust_libc` |`malloc` |man:malloc(3) |
| 4784 | |`calloc` |man:calloc(3) |
| 4785 | |`realloc` |man:realloc(3) |
| 4786 | |`free` |man:free(3) |
| 4787 | |`memalign` |man:memalign(3) |
| 4788 | |`posix_memalign` |man:posix_memalign(3) |
| 4789 | |==== |
| 4790 | |
| 4791 | [role="growable"] |
| 4792 | .Functions instrumented by preloading path:{liblttng-ust-pthread-wrapper.so}. |
| 4793 | |==== |
| 4794 | |TP provider name |TP name |Instrumented function |
| 4795 | |
| 4796 | .4+|`lttng_ust_pthread` |`pthread_mutex_lock_req` |man:pthread_mutex_lock(3p) (request time) |
| 4797 | |`pthread_mutex_lock_acq` |man:pthread_mutex_lock(3p) (acquire time) |
| 4798 | |`pthread_mutex_trylock` |man:pthread_mutex_trylock(3p) |
| 4799 | |`pthread_mutex_unlock` |man:pthread_mutex_unlock(3p) |
| 4800 | |==== |
| 4801 | |
| 4802 | When you preload the shared object, it replaces the functions listed |
| 4803 | in the previous tables by wrappers which contain tracepoints and call |
| 4804 | the replaced functions. |
| 4805 | |
| 4806 | |
| 4807 | [[liblttng-ust-cyg-profile]] |
| 4808 | ==== Instrument function entry and exit |
| 4809 | |
| 4810 | The path:{liblttng-ust-cyg-profile*.so} helpers can add instrumentation |
| 4811 | to the entry and exit points of functions. |
| 4812 | |
| 4813 | man:gcc(1) and man:clang(1) have an option named |
| 4814 | https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html[`-finstrument-functions`] |
| 4815 | which generates instrumentation calls for entry and exit to functions. |
| 4816 | The LTTng-UST function tracing helpers, |
| 4817 | path:{liblttng-ust-cyg-profile.so} and |
| 4818 | path:{liblttng-ust-cyg-profile-fast.so}, take advantage of this feature |
| 4819 | to add tracepoints to the two generated functions (which contain |
| 4820 | `cyg_profile` in their names, hence the name of the helper). |
| 4821 | |
| 4822 | To use the LTTng-UST function tracing helper, the source files to |
| 4823 | instrument must be built using the `-finstrument-functions` compiler |
| 4824 | flag. |
| 4825 | |
| 4826 | There are two versions of the LTTng-UST function tracing helper: |
| 4827 | |
| 4828 | * **path:{liblttng-ust-cyg-profile-fast.so}** is a lightweight variant |
| 4829 | that you should only use when it can be _guaranteed_ that the |
| 4830 | complete event stream is recorded without any lost event record. |
| 4831 | Any kind of duplicate information is left out. |
| 4832 | + |
| 4833 | Assuming no event record is lost, having only the function addresses on |
| 4834 | entry is enough to create a call graph, since an event record always |
| 4835 | contains the ID of the CPU that generated it. |
| 4836 | + |
| 4837 | Use a tool like man:addr2line(1) to convert function addresses back to |
| 4838 | source file names and line numbers. |
| 4839 | |
| 4840 | * **path:{liblttng-ust-cyg-profile.so}** is a more robust variant |
| 4841 | which also works in use cases where event records might get discarded or |
| 4842 | not recorded from application startup. |
| 4843 | In these cases, the trace analyzer needs more information to be |
| 4844 | able to reconstruct the program flow. |
| 4845 | |
| 4846 | See man:lttng-ust-cyg-profile(3) to learn more about the instrumentation |
| 4847 | points of this helper. |
| 4848 | |
| 4849 | All the tracepoints that this helper provides have the log level |
| 4850 | `LTTNG_UST_TRACEPOINT_LOGLEVEL_DEBUG_FUNCTION` (see man:lttng-ust(3)). |
| 4851 | |
| 4852 | TIP: It's sometimes a good idea to limit the number of source files that |
| 4853 | you compile with the `-finstrument-functions` option to prevent LTTng |
| 4854 | from writing an excessive amount of trace data at run time. When using |
| 4855 | man:gcc(1), use the |
| 4856 | `-finstrument-functions-exclude-function-list` option to avoid |
| 4857 | instrument entries and exits of specific function names. |
| 4858 | |
| 4859 | |
| 4860 | [role="since-2.4"] |
| 4861 | [[liblttng-ust-dl]] |
| 4862 | ==== Instrument the dynamic linker |
| 4863 | |
| 4864 | The path:{liblttng-ust-dl.so} helper adds instrumentation to the |
| 4865 | man:dlopen(3) and man:dlclose(3) function calls. |
| 4866 | |
| 4867 | See man:lttng-ust-dl(3) to learn more about the instrumentation points |
| 4868 | of this helper. |
| 4869 | |
| 4870 | |
| 4871 | [role="since-2.4"] |
| 4872 | [[java-application]] |
| 4873 | === Instrument a Java application |
| 4874 | |
| 4875 | You can instrument any Java application which uses one of the following |
| 4876 | logging frameworks: |
| 4877 | |
| 4878 | * The https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[**`java.util.logging`**] |
| 4879 | (JUL) core logging facilities. |
| 4880 | |
| 4881 | * https://logging.apache.org/log4j/1.2/[**Apache log4j{nbsp}1.2**], since |
| 4882 | LTTng{nbsp}2.6. Note that Apache Log4j{nbsp}2 isn't supported. |
| 4883 | |
| 4884 | [role="img-100"] |
| 4885 | .LTTng-UST Java agent imported by a Java application. |
| 4886 | image::java-app.png[] |
| 4887 | |
| 4888 | Note that the methods described below are new in LTTng{nbsp}2.8. |
| 4889 | Previous LTTng versions use another technique. |
| 4890 | |
| 4891 | NOTE: We use https://openjdk.java.net/[OpenJDK]{nbsp}8 for development |
| 4892 | and https://ci.lttng.org/[continuous integration], thus this version is |
| 4893 | directly supported. However, the LTTng-UST Java agent is also tested |
| 4894 | with OpenJDK{nbsp}7. |
| 4895 | |
| 4896 | |
| 4897 | [role="since-2.8"] |
| 4898 | [[jul]] |
| 4899 | ==== Use the LTTng-UST Java agent for `java.util.logging` |
| 4900 | |
| 4901 | To use the LTTng-UST Java agent in a Java application which uses |
| 4902 | `java.util.logging` (JUL): |
| 4903 | |
| 4904 | . In the source code of the Java application, import the LTTng-UST log |
| 4905 | handler package for `java.util.logging`: |
| 4906 | + |
| 4907 | -- |
| 4908 | [source,java] |
| 4909 | ---- |
| 4910 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 4911 | ---- |
| 4912 | -- |
| 4913 | |
| 4914 | . Create an LTTng-UST `java.util.logging` log handler: |
| 4915 | + |
| 4916 | -- |
| 4917 | [source,java] |
| 4918 | ---- |
| 4919 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 4920 | ---- |
| 4921 | -- |
| 4922 | |
| 4923 | . Add this handler to the `java.util.logging` loggers which should emit |
| 4924 | LTTng events: |
| 4925 | + |
| 4926 | -- |
| 4927 | [source,java] |
| 4928 | ---- |
| 4929 | Logger myLogger = Logger.getLogger("some-logger"); |
| 4930 | |
| 4931 | myLogger.addHandler(lttngUstLogHandler); |
| 4932 | ---- |
| 4933 | -- |
| 4934 | |
| 4935 | . Use `java.util.logging` log statements and configuration as usual. |
| 4936 | The loggers with an attached LTTng-UST log handler can emit |
| 4937 | LTTng events. |
| 4938 | |
| 4939 | . Before exiting the application, remove the LTTng-UST log handler from |
| 4940 | the loggers attached to it and call its `close()` method: |
| 4941 | + |
| 4942 | -- |
| 4943 | [source,java] |
| 4944 | ---- |
| 4945 | myLogger.removeHandler(lttngUstLogHandler); |
| 4946 | lttngUstLogHandler.close(); |
| 4947 | ---- |
| 4948 | -- |
| 4949 | + |
| 4950 | This isn't strictly necessary, but it's recommended for a clean |
| 4951 | disposal of the resources of the handler. |
| 4952 | |
| 4953 | . Include the common and JUL-specific JAR files of the LTTng-UST Java agent, |
| 4954 | path:{lttng-ust-agent-common.jar} and path:{lttng-ust-agent-jul.jar}, |
| 4955 | in the |
| 4956 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class |
| 4957 | path] when you build the Java application. |
| 4958 | + |
| 4959 | The JAR files are typically located in dir:{/usr/share/java}. |
| 4960 | + |
| 4961 | IMPORTANT: The LTTng-UST Java agent must be |
| 4962 | <<installing-lttng,installed>> for the logging framework your |
| 4963 | application uses. |
| 4964 | |
| 4965 | .Use the LTTng-UST Java agent for `java.util.logging`. |
| 4966 | ==== |
| 4967 | [source,java] |
| 4968 | .path:{Test.java} |
| 4969 | ---- |
| 4970 | import java.io.IOException; |
| 4971 | import java.util.logging.Handler; |
| 4972 | import java.util.logging.Logger; |
| 4973 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 4974 | |
| 4975 | public class Test |
| 4976 | { |
| 4977 | private static final int answer = 42; |
| 4978 | |
| 4979 | public static void main(String[] argv) throws Exception |
| 4980 | { |
| 4981 | // Create a logger |
| 4982 | Logger logger = Logger.getLogger("jello"); |
| 4983 | |
| 4984 | // Create an LTTng-UST log handler |
| 4985 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 4986 | |
| 4987 | // Add the LTTng-UST log handler to our logger |
| 4988 | logger.addHandler(lttngUstLogHandler); |
| 4989 | |
| 4990 | // Log at will! |
| 4991 | logger.info("some info"); |
| 4992 | logger.warning("some warning"); |
| 4993 | Thread.sleep(500); |
| 4994 | logger.finer("finer information; the answer is " + answer); |
| 4995 | Thread.sleep(123); |
| 4996 | logger.severe("error!"); |
| 4997 | |
| 4998 | // Not mandatory, but cleaner |
| 4999 | logger.removeHandler(lttngUstLogHandler); |
| 5000 | lttngUstLogHandler.close(); |
| 5001 | } |
| 5002 | } |
| 5003 | ---- |
| 5004 | |
| 5005 | Build this example: |
| 5006 | |
| 5007 | [role="term"] |
| 5008 | ---- |
| 5009 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
| 5010 | ---- |
| 5011 | |
| 5012 | <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 5013 | <<enabling-disabling-events,create a recording event rule>> matching JUL |
| 5014 | events named `jello`, and <<basic-tracing-session-control,start |
| 5015 | recording>>: |
| 5016 | |
| 5017 | [role="term"] |
| 5018 | ---- |
| 5019 | $ lttng create |
| 5020 | $ lttng enable-event --jul jello |
| 5021 | $ lttng start |
| 5022 | ---- |
| 5023 | |
| 5024 | Run the compiled class: |
| 5025 | |
| 5026 | [role="term"] |
| 5027 | ---- |
| 5028 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
| 5029 | ---- |
| 5030 | |
| 5031 | <<basic-tracing-session-control,Stop recording>> and inspect the |
| 5032 | recorded events: |
| 5033 | |
| 5034 | [role="term"] |
| 5035 | ---- |
| 5036 | $ lttng stop |
| 5037 | $ lttng view |
| 5038 | ---- |
| 5039 | ==== |
| 5040 | |
| 5041 | In the resulting trace, an <<event,event record>> which a Java |
| 5042 | application using `java.util.logging` generated is named |
| 5043 | `lttng_jul:event` and has the following fields: |
| 5044 | |
| 5045 | `msg`:: |
| 5046 | Log record message. |
| 5047 | |
| 5048 | `logger_name`:: |
| 5049 | Logger name. |
| 5050 | |
| 5051 | `class_name`:: |
| 5052 | Name of the class in which the log statement was executed. |
| 5053 | |
| 5054 | `method_name`:: |
| 5055 | Name of the method in which the log statement was executed. |
| 5056 | |
| 5057 | `long_millis`:: |
| 5058 | Logging time (timestamp in milliseconds). |
| 5059 | |
| 5060 | `int_loglevel`:: |
| 5061 | Log level integer value. |
| 5062 | |
| 5063 | `int_threadid`:: |
| 5064 | ID of the thread in which the log statement was executed. |
| 5065 | |
| 5066 | Use the opt:lttng-enable-event(1):--loglevel or |
| 5067 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 5068 | man:lttng-enable-event(1) command to target a range of |
| 5069 | `java.util.logging` log levels or a specific `java.util.logging` log |
| 5070 | level. |
| 5071 | |
| 5072 | |
| 5073 | [role="since-2.8"] |
| 5074 | [[log4j]] |
| 5075 | ==== Use the LTTng-UST Java agent for Apache log4j |
| 5076 | |
| 5077 | To use the LTTng-UST Java agent in a Java application which uses |
| 5078 | Apache log4j{nbsp}1.2: |
| 5079 | |
| 5080 | . In the source code of the Java application, import the LTTng-UST log |
| 5081 | appender package for Apache log4j: |
| 5082 | + |
| 5083 | -- |
| 5084 | [source,java] |
| 5085 | ---- |
| 5086 | import org.lttng.ust.agent.log4j.LttngLogAppender; |
| 5087 | ---- |
| 5088 | -- |
| 5089 | |
| 5090 | . Create an LTTng-UST log4j log appender: |
| 5091 | + |
| 5092 | -- |
| 5093 | [source,java] |
| 5094 | ---- |
| 5095 | Appender lttngUstLogAppender = new LttngLogAppender(); |
| 5096 | ---- |
| 5097 | -- |
| 5098 | |
| 5099 | . Add this appender to the log4j loggers which should emit LTTng events: |
| 5100 | + |
| 5101 | -- |
| 5102 | [source,java] |
| 5103 | ---- |
| 5104 | Logger myLogger = Logger.getLogger("some-logger"); |
| 5105 | |
| 5106 | myLogger.addAppender(lttngUstLogAppender); |
| 5107 | ---- |
| 5108 | -- |
| 5109 | |
| 5110 | . Use Apache log4j log statements and configuration as usual. The |
| 5111 | loggers with an attached LTTng-UST log appender can emit LTTng events. |
| 5112 | |
| 5113 | . Before exiting the application, remove the LTTng-UST log appender from |
| 5114 | the loggers attached to it and call its `close()` method: |
| 5115 | + |
| 5116 | -- |
| 5117 | [source,java] |
| 5118 | ---- |
| 5119 | myLogger.removeAppender(lttngUstLogAppender); |
| 5120 | lttngUstLogAppender.close(); |
| 5121 | ---- |
| 5122 | -- |
| 5123 | + |
| 5124 | This isn't strictly necessary, but it's recommended for a clean |
| 5125 | disposal of the resources of the appender. |
| 5126 | |
| 5127 | . Include the common and log4j-specific JAR |
| 5128 | files of the LTTng-UST Java agent, path:{lttng-ust-agent-common.jar} and |
| 5129 | path:{lttng-ust-agent-log4j.jar}, in the |
| 5130 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class |
| 5131 | path] when you build the Java application. |
| 5132 | + |
| 5133 | The JAR files are typically located in dir:{/usr/share/java}. |
| 5134 | + |
| 5135 | IMPORTANT: The LTTng-UST Java agent must be |
| 5136 | <<installing-lttng,installed>> for the logging framework your |
| 5137 | application uses. |
| 5138 | |
| 5139 | .Use the LTTng-UST Java agent for Apache log4j. |
| 5140 | ==== |
| 5141 | [source,java] |
| 5142 | .path:{Test.java} |
| 5143 | ---- |
| 5144 | import org.apache.log4j.Appender; |
| 5145 | import org.apache.log4j.Logger; |
| 5146 | import org.lttng.ust.agent.log4j.LttngLogAppender; |
| 5147 | |
| 5148 | public class Test |
| 5149 | { |
| 5150 | private static final int answer = 42; |
| 5151 | |
| 5152 | public static void main(String[] argv) throws Exception |
| 5153 | { |
| 5154 | // Create a logger |
| 5155 | Logger logger = Logger.getLogger("jello"); |
| 5156 | |
| 5157 | // Create an LTTng-UST log appender |
| 5158 | Appender lttngUstLogAppender = new LttngLogAppender(); |
| 5159 | |
| 5160 | // Add the LTTng-UST log appender to our logger |
| 5161 | logger.addAppender(lttngUstLogAppender); |
| 5162 | |
| 5163 | // Log at will! |
| 5164 | logger.info("some info"); |
| 5165 | logger.warn("some warning"); |
| 5166 | Thread.sleep(500); |
| 5167 | logger.debug("debug information; the answer is " + answer); |
| 5168 | Thread.sleep(123); |
| 5169 | logger.fatal("error!"); |
| 5170 | |
| 5171 | // Not mandatory, but cleaner |
| 5172 | logger.removeAppender(lttngUstLogAppender); |
| 5173 | lttngUstLogAppender.close(); |
| 5174 | } |
| 5175 | } |
| 5176 | |
| 5177 | ---- |
| 5178 | |
| 5179 | Build this example (`$LOG4JPATH` is the path to the Apache log4j JAR |
| 5180 | file): |
| 5181 | |
| 5182 | [role="term"] |
| 5183 | ---- |
| 5184 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH Test.java |
| 5185 | ---- |
| 5186 | |
| 5187 | <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 5188 | <<enabling-disabling-events,create a recording event rule>> matching |
| 5189 | log4j events named `jello`, and <<basic-tracing-session-control,start |
| 5190 | recording>>: |
| 5191 | |
| 5192 | [role="term"] |
| 5193 | ---- |
| 5194 | $ lttng create |
| 5195 | $ lttng enable-event --log4j jello |
| 5196 | $ lttng start |
| 5197 | ---- |
| 5198 | |
| 5199 | Run the compiled class: |
| 5200 | |
| 5201 | [role="term"] |
| 5202 | ---- |
| 5203 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH:. Test |
| 5204 | ---- |
| 5205 | |
| 5206 | <<basic-tracing-session-control,Stop recording>> and inspect the |
| 5207 | recorded events: |
| 5208 | |
| 5209 | [role="term"] |
| 5210 | ---- |
| 5211 | $ lttng stop |
| 5212 | $ lttng view |
| 5213 | ---- |
| 5214 | ==== |
| 5215 | |
| 5216 | In the resulting trace, an <<event,event record>> which a Java |
| 5217 | application using log4j generated is named `lttng_log4j:event` and |
| 5218 | has the following fields: |
| 5219 | |
| 5220 | `msg`:: |
| 5221 | Log record message. |
| 5222 | |
| 5223 | `logger_name`:: |
| 5224 | Logger name. |
| 5225 | |
| 5226 | `class_name`:: |
| 5227 | Name of the class in which the log statement was executed. |
| 5228 | |
| 5229 | `method_name`:: |
| 5230 | Name of the method in which the log statement was executed. |
| 5231 | |
| 5232 | `filename`:: |
| 5233 | Name of the file in which the executed log statement is located. |
| 5234 | |
| 5235 | `line_number`:: |
| 5236 | Line number at which the log statement was executed. |
| 5237 | |
| 5238 | `timestamp`:: |
| 5239 | Logging timestamp. |
| 5240 | |
| 5241 | `int_loglevel`:: |
| 5242 | Log level integer value. |
| 5243 | |
| 5244 | `thread_name`:: |
| 5245 | Name of the Java thread in which the log statement was executed. |
| 5246 | |
| 5247 | Use the opt:lttng-enable-event(1):--loglevel or |
| 5248 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 5249 | man:lttng-enable-event(1) command to target a range of Apache log4j |
| 5250 | log levels or a specific log4j log level. |
| 5251 | |
| 5252 | |
| 5253 | [role="since-2.8"] |
| 5254 | [[java-application-context]] |
| 5255 | ==== Provide application-specific context fields in a Java application |
| 5256 | |
| 5257 | A Java application-specific context field is a piece of state which |
| 5258 | the Java application provides. You can <<adding-context,add>> such |
| 5259 | a context field to be recorded, using the |
| 5260 | man:lttng-add-context(1) command, to each <<event,event record>> |
| 5261 | which the log statements of this application produce. |
| 5262 | |
| 5263 | For example, a given object might have a current request ID variable. |
| 5264 | You can create a context information retriever for this object and |
| 5265 | assign a name to this current request ID. You can then, using the |
| 5266 | man:lttng-add-context(1) command, add this context field by name so that |
| 5267 | LTTng writes it to the event records of a given `java.util.logging` or |
| 5268 | log4j <<channel,channel>>. |
| 5269 | |
| 5270 | To provide application-specific context fields in a Java application: |
| 5271 | |
| 5272 | . In the source code of the Java application, import the LTTng-UST |
| 5273 | Java agent context classes and interfaces: |
| 5274 | + |
| 5275 | -- |
| 5276 | [source,java] |
| 5277 | ---- |
| 5278 | import org.lttng.ust.agent.context.ContextInfoManager; |
| 5279 | import org.lttng.ust.agent.context.IContextInfoRetriever; |
| 5280 | ---- |
| 5281 | -- |
| 5282 | |
| 5283 | . Create a context information retriever class, that is, a class which |
| 5284 | implements the `IContextInfoRetriever` interface: |
| 5285 | + |
| 5286 | -- |
| 5287 | [source,java] |
| 5288 | ---- |
| 5289 | class MyContextInfoRetriever implements IContextInfoRetriever |
| 5290 | { |
| 5291 | @Override |
| 5292 | public Object retrieveContextInfo(String key) |
| 5293 | { |
| 5294 | if (key.equals("intCtx")) { |
| 5295 | return (short) 17; |
| 5296 | } else if (key.equals("strContext")) { |
| 5297 | return "context value!"; |
| 5298 | } else { |
| 5299 | return null; |
| 5300 | } |
| 5301 | } |
| 5302 | } |
| 5303 | ---- |
| 5304 | -- |
| 5305 | + |
| 5306 | This `retrieveContextInfo()` method is the only member of the |
| 5307 | `IContextInfoRetriever` interface. Its role is to return the current |
| 5308 | value of a state by name to create a context field. The names of the |
| 5309 | context fields and which state variables they return depends on your |
| 5310 | specific scenario. |
| 5311 | + |
| 5312 | All primitive types and objects are supported as context fields. |
| 5313 | When `retrieveContextInfo()` returns an object, the context field |
| 5314 | serializer calls its `toString()` method to add a string field to |
| 5315 | event records. The method can also return `null`, which means that |
| 5316 | no context field is available for the required name. |
| 5317 | |
| 5318 | . Register an instance of your context information retriever class to |
| 5319 | the context information manager singleton: |
| 5320 | + |
| 5321 | -- |
| 5322 | [source,java] |
| 5323 | ---- |
| 5324 | IContextInfoRetriever cir = new MyContextInfoRetriever(); |
| 5325 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 5326 | cim.registerContextInfoRetriever("retrieverName", cir); |
| 5327 | ---- |
| 5328 | -- |
| 5329 | |
| 5330 | . Before exiting the application, remove your context information |
| 5331 | retriever from the context information manager singleton: |
| 5332 | + |
| 5333 | -- |
| 5334 | [source,java] |
| 5335 | ---- |
| 5336 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 5337 | cim.unregisterContextInfoRetriever("retrieverName"); |
| 5338 | ---- |
| 5339 | -- |
| 5340 | + |
| 5341 | This isn't strictly necessary, but it's recommended for a clean |
| 5342 | disposal of some resources of the manager. |
| 5343 | |
| 5344 | . Build your Java application with LTTng-UST Java agent support as |
| 5345 | usual, following the procedure for either the |
| 5346 | <<jul,`java.util.logging`>> or <<log4j,Apache log4j>> framework. |
| 5347 | |
| 5348 | .Provide application-specific context fields in a Java application. |
| 5349 | ==== |
| 5350 | [source,java] |
| 5351 | .path:{Test.java} |
| 5352 | ---- |
| 5353 | import java.util.logging.Handler; |
| 5354 | import java.util.logging.Logger; |
| 5355 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 5356 | import org.lttng.ust.agent.context.ContextInfoManager; |
| 5357 | import org.lttng.ust.agent.context.IContextInfoRetriever; |
| 5358 | |
| 5359 | public class Test |
| 5360 | { |
| 5361 | // Our context information retriever class |
| 5362 | private static class MyContextInfoRetriever |
| 5363 | implements IContextInfoRetriever |
| 5364 | { |
| 5365 | @Override |
| 5366 | public Object retrieveContextInfo(String key) { |
| 5367 | if (key.equals("intCtx")) { |
| 5368 | return (short) 17; |
| 5369 | } else if (key.equals("strContext")) { |
| 5370 | return "context value!"; |
| 5371 | } else { |
| 5372 | return null; |
| 5373 | } |
| 5374 | } |
| 5375 | } |
| 5376 | |
| 5377 | private static final int answer = 42; |
| 5378 | |
| 5379 | public static void main(String args[]) throws Exception |
| 5380 | { |
| 5381 | // Get the context information manager instance |
| 5382 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 5383 | |
| 5384 | // Create and register our context information retriever |
| 5385 | IContextInfoRetriever cir = new MyContextInfoRetriever(); |
| 5386 | cim.registerContextInfoRetriever("myRetriever", cir); |
| 5387 | |
| 5388 | // Create a logger |
| 5389 | Logger logger = Logger.getLogger("jello"); |
| 5390 | |
| 5391 | // Create an LTTng-UST log handler |
| 5392 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 5393 | |
| 5394 | // Add the LTTng-UST log handler to our logger |
| 5395 | logger.addHandler(lttngUstLogHandler); |
| 5396 | |
| 5397 | // Log at will! |
| 5398 | logger.info("some info"); |
| 5399 | logger.warning("some warning"); |
| 5400 | Thread.sleep(500); |
| 5401 | logger.finer("finer information; the answer is " + answer); |
| 5402 | Thread.sleep(123); |
| 5403 | logger.severe("error!"); |
| 5404 | |
| 5405 | // Not mandatory, but cleaner |
| 5406 | logger.removeHandler(lttngUstLogHandler); |
| 5407 | lttngUstLogHandler.close(); |
| 5408 | cim.unregisterContextInfoRetriever("myRetriever"); |
| 5409 | } |
| 5410 | } |
| 5411 | ---- |
| 5412 | |
| 5413 | Build this example: |
| 5414 | |
| 5415 | [role="term"] |
| 5416 | ---- |
| 5417 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
| 5418 | ---- |
| 5419 | |
| 5420 | <<creating-destroying-tracing-sessions,Create a recording session>> and |
| 5421 | <<enabling-disabling-events,create a recording event rule>> matching |
| 5422 | `java.util.logging` events named `jello`: |
| 5423 | |
| 5424 | [role="term"] |
| 5425 | ---- |
| 5426 | $ lttng create |
| 5427 | $ lttng enable-event --jul jello |
| 5428 | ---- |
| 5429 | |
| 5430 | <<adding-context,Add the application-specific context fields>> to be |
| 5431 | recorded to the event records of the `java.util.logging` channel: |
| 5432 | |
| 5433 | [role="term"] |
| 5434 | ---- |
| 5435 | $ lttng add-context --jul --type='$app.myRetriever:intCtx' |
| 5436 | $ lttng add-context --jul --type='$app.myRetriever:strContext' |
| 5437 | ---- |
| 5438 | |
| 5439 | <<basic-tracing-session-control,Start recording>>: |
| 5440 | |
| 5441 | [role="term"] |
| 5442 | ---- |
| 5443 | $ lttng start |
| 5444 | ---- |
| 5445 | |
| 5446 | Run the compiled class: |
| 5447 | |
| 5448 | [role="term"] |
| 5449 | ---- |
| 5450 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
| 5451 | ---- |
| 5452 | |
| 5453 | <<basic-tracing-session-control,Stop recording>> and inspect the |
| 5454 | recorded events: |
| 5455 | |
| 5456 | [role="term"] |
| 5457 | ---- |
| 5458 | $ lttng stop |
| 5459 | $ lttng view |
| 5460 | ---- |
| 5461 | ==== |
| 5462 | |
| 5463 | |
| 5464 | [role="since-2.7"] |
| 5465 | [[python-application]] |
| 5466 | === Instrument a Python application |
| 5467 | |
| 5468 | You can instrument a Python{nbsp}2 or Python{nbsp}3 application which |
| 5469 | uses the standard |
| 5470 | https://docs.python.org/3/library/logging.html[`logging`] package. |
| 5471 | |
| 5472 | Each log statement creates an LTTng event once the application module |
| 5473 | imports the <<lttng-ust-agents,LTTng-UST Python agent>> package. |
| 5474 | |
| 5475 | [role="img-100"] |
| 5476 | .A Python application importing the LTTng-UST Python agent. |
| 5477 | image::python-app.png[] |
| 5478 | |
| 5479 | To use the LTTng-UST Python agent: |
| 5480 | |
| 5481 | . In the source code of the Python application, import the LTTng-UST |
| 5482 | Python agent: |
| 5483 | + |
| 5484 | -- |
| 5485 | [source,python] |
| 5486 | ---- |
| 5487 | import lttngust |
| 5488 | ---- |
| 5489 | -- |
| 5490 | + |
| 5491 | The LTTng-UST Python agent automatically adds its logging handler to the |
| 5492 | root logger at import time. |
| 5493 | + |
| 5494 | A log statement that the application executes before this import doesn't |
| 5495 | create an LTTng event. |
| 5496 | + |
| 5497 | IMPORTANT: The LTTng-UST Python agent must be |
| 5498 | <<installing-lttng,installed>>. |
| 5499 | |
| 5500 | . Use log statements and logging configuration as usual. |
| 5501 | Since the LTTng-UST Python agent adds a handler to the _root_ |
| 5502 | logger, any log statement from any logger can emit an LTTng event. |
| 5503 | |
| 5504 | .Use the LTTng-UST Python agent. |
| 5505 | ==== |
| 5506 | [source,python] |
| 5507 | .path:{test.py} |
| 5508 | ---- |
| 5509 | import lttngust |
| 5510 | import logging |
| 5511 | import time |
| 5512 | |
| 5513 | |
| 5514 | def example(): |
| 5515 | logging.basicConfig() |
| 5516 | logger = logging.getLogger('my-logger') |
| 5517 | |
| 5518 | while True: |
| 5519 | logger.debug('debug message') |
| 5520 | logger.info('info message') |
| 5521 | logger.warn('warn message') |
| 5522 | logger.error('error message') |
| 5523 | logger.critical('critical message') |
| 5524 | time.sleep(1) |
| 5525 | |
| 5526 | |
| 5527 | if __name__ == '__main__': |
| 5528 | example() |
| 5529 | ---- |
| 5530 | |
| 5531 | NOTE: `logging.basicConfig()`, which adds to the root logger a basic |
| 5532 | logging handler which prints to the standard error stream, isn't |
| 5533 | strictly required for LTTng-UST tracing to work, but in versions of |
| 5534 | Python preceding{nbsp}3.2, you could see a warning message which |
| 5535 | indicates that no handler exists for the logger `my-logger`. |
| 5536 | |
| 5537 | <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 5538 | <<enabling-disabling-events,create a recording event rule>> matching |
| 5539 | Python logging events named `my-logger`, and |
| 5540 | <<basic-tracing-session-control,start recording>>: |
| 5541 | |
| 5542 | [role="term"] |
| 5543 | ---- |
| 5544 | $ lttng create |
| 5545 | $ lttng enable-event --python my-logger |
| 5546 | $ lttng start |
| 5547 | ---- |
| 5548 | |
| 5549 | Run the Python script: |
| 5550 | |
| 5551 | [role="term"] |
| 5552 | ---- |
| 5553 | $ python test.py |
| 5554 | ---- |
| 5555 | |
| 5556 | <<basic-tracing-session-control,Stop recording>> and inspect the |
| 5557 | recorded events: |
| 5558 | |
| 5559 | [role="term"] |
| 5560 | ---- |
| 5561 | $ lttng stop |
| 5562 | $ lttng view |
| 5563 | ---- |
| 5564 | ==== |
| 5565 | |
| 5566 | In the resulting trace, an <<event,event record>> which a Python |
| 5567 | application generated is named `lttng_python:event` and has the |
| 5568 | following fields: |
| 5569 | |
| 5570 | `asctime`:: |
| 5571 | Logging time (string). |
| 5572 | |
| 5573 | `msg`:: |
| 5574 | Log record message. |
| 5575 | |
| 5576 | `logger_name`:: |
| 5577 | Logger name. |
| 5578 | |
| 5579 | `funcName`:: |
| 5580 | Name of the function in which the log statement was executed. |
| 5581 | |
| 5582 | `lineno`:: |
| 5583 | Line number at which the log statement was executed. |
| 5584 | |
| 5585 | `int_loglevel`:: |
| 5586 | Log level integer value. |
| 5587 | |
| 5588 | `thread`:: |
| 5589 | ID of the Python thread in which the log statement was executed. |
| 5590 | |
| 5591 | `threadName`:: |
| 5592 | Name of the Python thread in which the log statement was executed. |
| 5593 | |
| 5594 | Use the opt:lttng-enable-event(1):--loglevel or |
| 5595 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 5596 | man:lttng-enable-event(1) command to target a range of Python log levels |
| 5597 | or a specific Python log level. |
| 5598 | |
| 5599 | When an application imports the LTTng-UST Python agent, the agent tries |
| 5600 | to register to a <<lttng-sessiond,session daemon>>. Note that you must |
| 5601 | <<start-sessiond,start the session daemon>> _before_ you run the Python |
| 5602 | application. If a session daemon is found, the agent tries to register |
| 5603 | to it during five seconds, after which the application continues |
| 5604 | without LTTng tracing support. Override this timeout value with |
| 5605 | the env:LTTNG_UST_PYTHON_REGISTER_TIMEOUT environment variable |
| 5606 | (milliseconds). |
| 5607 | |
| 5608 | If the session daemon stops while a Python application with an imported |
| 5609 | LTTng-UST Python agent runs, the agent retries to connect and to |
| 5610 | register to a session daemon every three seconds. Override this |
| 5611 | delay with the env:LTTNG_UST_PYTHON_REGISTER_RETRY_DELAY environment |
| 5612 | variable. |
| 5613 | |
| 5614 | |
| 5615 | [role="since-2.5"] |
| 5616 | [[proc-lttng-logger-abi]] |
| 5617 | === Use the LTTng logger |
| 5618 | |
| 5619 | The `lttng-tracer` Linux kernel module, part of |
| 5620 | <<lttng-modules,LTTng-modules>>, creates the special LTTng logger files |
| 5621 | path:{/proc/lttng-logger} and path:{/dev/lttng-logger} (since |
| 5622 | LTTng{nbsp}2.11) when it's loaded. Any application can write text data |
| 5623 | to any of those files to create one or more LTTng events. |
| 5624 | |
| 5625 | [role="img-100"] |
| 5626 | .An application writes to the LTTng logger file to create one or more LTTng events. |
| 5627 | image::lttng-logger.png[] |
| 5628 | |
| 5629 | The LTTng logger is the quickest method--not the most efficient, |
| 5630 | however--to add instrumentation to an application. It's designed |
| 5631 | mostly to instrument shell scripts: |
| 5632 | |
| 5633 | [role="term"] |
| 5634 | ---- |
| 5635 | $ echo "Some message, some $variable" > /dev/lttng-logger |
| 5636 | ---- |
| 5637 | |
| 5638 | Any event that the LTTng logger creates is named `lttng_logger` and |
| 5639 | belongs to the Linux kernel <<domain,tracing domain>>. However, unlike |
| 5640 | other instrumentation points in the kernel tracing domain, **any Unix |
| 5641 | user** can <<enabling-disabling-events,create a recording event rule>> |
| 5642 | which matches events named `lttng_logger`, not only the root user or |
| 5643 | users in the <<tracing-group,tracing group>>. |
| 5644 | |
| 5645 | To use the LTTng logger: |
| 5646 | |
| 5647 | * From any application, write text data to the path:{/dev/lttng-logger} |
| 5648 | file. |
| 5649 | |
| 5650 | The `msg` field of `lttng_logger` event records contains the |
| 5651 | recorded message. |
| 5652 | |
| 5653 | NOTE: The maximum message length of an LTTng logger event is |
| 5654 | 1024{nbsp}bytes. Writing more than this makes the LTTng logger emit more |
| 5655 | than one event to contain the remaining data. |
| 5656 | |
| 5657 | You shouldn't use the LTTng logger to trace a user application which you |
| 5658 | can instrument in a more efficient way, namely: |
| 5659 | |
| 5660 | * <<c-application,C and $$C++$$ applications>>. |
| 5661 | * <<java-application,Java applications>>. |
| 5662 | * <<python-application,Python applications>>. |
| 5663 | |
| 5664 | .Use the LTTng logger. |
| 5665 | ==== |
| 5666 | [source,bash] |
| 5667 | .path:{test.bash} |
| 5668 | ---- |
| 5669 | echo 'Hello, World!' > /dev/lttng-logger |
| 5670 | sleep 2 |
| 5671 | df --human-readable --print-type / > /dev/lttng-logger |
| 5672 | ---- |
| 5673 | |
| 5674 | <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 5675 | <<enabling-disabling-events,create a recording event rule>> matching |
| 5676 | Linux kernel tracepoint events named `lttng_logger`, and |
| 5677 | <<basic-tracing-session-control,start recording>>: |
| 5678 | |
| 5679 | [role="term"] |
| 5680 | ---- |
| 5681 | $ lttng create |
| 5682 | $ lttng enable-event --kernel lttng_logger |
| 5683 | $ lttng start |
| 5684 | ---- |
| 5685 | |
| 5686 | Run the Bash script: |
| 5687 | |
| 5688 | [role="term"] |
| 5689 | ---- |
| 5690 | $ bash test.bash |
| 5691 | ---- |
| 5692 | |
| 5693 | <<basic-tracing-session-control,Stop recording>> and inspect the recorded |
| 5694 | events: |
| 5695 | |
| 5696 | [role="term"] |
| 5697 | ---- |
| 5698 | $ lttng stop |
| 5699 | $ lttng view |
| 5700 | ---- |
| 5701 | ==== |
| 5702 | |
| 5703 | |
| 5704 | [[instrumenting-linux-kernel]] |
| 5705 | === Instrument a Linux kernel image or module |
| 5706 | |
| 5707 | NOTE: This section shows how to _add_ instrumentation points to the |
| 5708 | Linux kernel. The subsystems of the kernel are already thoroughly |
| 5709 | instrumented at strategic points for LTTng when you |
| 5710 | <<installing-lttng,install>> the <<lttng-modules,LTTng-modules>> |
| 5711 | package. |
| 5712 | |
| 5713 | |
| 5714 | [[linux-add-lttng-layer]] |
| 5715 | ==== [[instrumenting-linux-kernel-itself]][[mainline-trace-event]][[lttng-adaptation-layer]]Add an LTTng layer to an existing ftrace tracepoint |
| 5716 | |
| 5717 | This section shows how to add an LTTng layer to existing ftrace |
| 5718 | instrumentation using the `TRACE_EVENT()` API. |
| 5719 | |
| 5720 | This section doesn't document the `TRACE_EVENT()` macro. Read the |
| 5721 | following articles to learn more about this API: |
| 5722 | |
| 5723 | * https://lwn.net/Articles/379903/[Using the TRACE_EVENT() macro (Part{nbsp}1)] |
| 5724 | * https://lwn.net/Articles/381064/[Using the TRACE_EVENT() macro (Part{nbsp}2)] |
| 5725 | * https://lwn.net/Articles/383362/[Using the TRACE_EVENT() macro (Part{nbsp}3)] |
| 5726 | |
| 5727 | The following procedure assumes that your ftrace tracepoints are |
| 5728 | correctly defined in their own header and that they're created in |
| 5729 | one source file using the `CREATE_TRACE_POINTS` definition. |
| 5730 | |
| 5731 | To add an LTTng layer over an existing ftrace tracepoint: |
| 5732 | |
| 5733 | . Make sure the following kernel configuration options are |
| 5734 | enabled: |
| 5735 | + |
| 5736 | -- |
| 5737 | * `CONFIG_MODULES` |
| 5738 | * `CONFIG_KALLSYMS` |
| 5739 | * `CONFIG_HIGH_RES_TIMERS` |
| 5740 | * `CONFIG_TRACEPOINTS` |
| 5741 | -- |
| 5742 | |
| 5743 | . Build the Linux source tree with your custom ftrace tracepoints. |
| 5744 | . Boot the resulting Linux image on your target system. |
| 5745 | + |
| 5746 | Confirm that the tracepoints exist by looking for their names in the |
| 5747 | dir:{/sys/kernel/debug/tracing/events/subsys} directory, where `subsys` |
| 5748 | is your subsystem name. |
| 5749 | |
| 5750 | . Get a copy of the latest LTTng-modules{nbsp}{revision}: |
| 5751 | + |
| 5752 | -- |
| 5753 | [role="term"] |
| 5754 | ---- |
| 5755 | $ cd $(mktemp -d) && |
| 5756 | wget https://lttng.org/files/lttng-modules/lttng-modules-latest-2.13.tar.bz2 && |
| 5757 | tar -xf lttng-modules-latest-2.13.tar.bz2 && |
| 5758 | cd lttng-modules-2.13.* |
| 5759 | ---- |
| 5760 | -- |
| 5761 | |
| 5762 | . In dir:{instrumentation/events/lttng-module}, relative to the root |
| 5763 | of the LTTng-modules source tree, create a header file named |
| 5764 | +__subsys__.h+ for your custom subsystem +__subsys__+ and write your |
| 5765 | LTTng-modules tracepoint definitions using the LTTng-modules |
| 5766 | macros in it. |
| 5767 | + |
| 5768 | Start with this template: |
| 5769 | + |
| 5770 | -- |
| 5771 | [source,c] |
| 5772 | .path:{instrumentation/events/lttng-module/my_subsys.h} |
| 5773 | ---- |
| 5774 | #undef TRACE_SYSTEM |
| 5775 | #define TRACE_SYSTEM my_subsys |
| 5776 | |
| 5777 | #if !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) |
| 5778 | #define _LTTNG_MY_SUBSYS_H |
| 5779 | |
| 5780 | #include "../../../probes/lttng-tracepoint-event.h" |
| 5781 | #include <linux/tracepoint.h> |
| 5782 | |
| 5783 | LTTNG_TRACEPOINT_EVENT( |
| 5784 | /* |
| 5785 | * Format is identical to the TRACE_EVENT() version for the three |
| 5786 | * following macro parameters: |
| 5787 | */ |
| 5788 | my_subsys_my_event, |
| 5789 | TP_PROTO(int my_int, const char *my_string), |
| 5790 | TP_ARGS(my_int, my_string), |
| 5791 | |
| 5792 | /* LTTng-modules specific macros */ |
| 5793 | TP_FIELDS( |
| 5794 | ctf_integer(int, my_int_field, my_int) |
| 5795 | ctf_string(my_bar_field, my_bar) |
| 5796 | ) |
| 5797 | ) |
| 5798 | |
| 5799 | #endif /* !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) */ |
| 5800 | |
| 5801 | #include "../../../probes/define_trace.h" |
| 5802 | ---- |
| 5803 | -- |
| 5804 | + |
| 5805 | The entries in the `TP_FIELDS()` section are the list of fields for the |
| 5806 | LTTng tracepoint. This is similar to the `TP_STRUCT__entry()` part of |
| 5807 | the `TRACE_EVENT()` ftrace macro. |
| 5808 | + |
| 5809 | See ``<<lttng-modules-tp-fields,Tracepoint fields macros>>'' for a |
| 5810 | complete description of the available `ctf_*()` macros. |
| 5811 | |
| 5812 | . Create the kernel module C{nbsp}source file of the LTTng-modules |
| 5813 | probe, +probes/lttng-probe-__subsys__.c+, where +__subsys__+ is your |
| 5814 | subsystem name: |
| 5815 | + |
| 5816 | -- |
| 5817 | [source,c] |
| 5818 | .path:{probes/lttng-probe-my-subsys.c} |
| 5819 | ---- |
| 5820 | #include <linux/module.h> |
| 5821 | #include "../lttng-tracer.h" |
| 5822 | |
| 5823 | /* |
| 5824 | * Build-time verification of mismatch between mainline |
| 5825 | * TRACE_EVENT() arguments and the LTTng-modules adaptation |
| 5826 | * layer LTTNG_TRACEPOINT_EVENT() arguments. |
| 5827 | */ |
| 5828 | #include <trace/events/my_subsys.h> |
| 5829 | |
| 5830 | /* Create LTTng tracepoint probes */ |
| 5831 | #define LTTNG_PACKAGE_BUILD |
| 5832 | #define CREATE_TRACE_POINTS |
| 5833 | #define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module |
| 5834 | |
| 5835 | #include "../instrumentation/events/lttng-module/my_subsys.h" |
| 5836 | |
| 5837 | MODULE_LICENSE("GPL and additional rights"); |
| 5838 | MODULE_AUTHOR("Your name <your-email>"); |
| 5839 | MODULE_DESCRIPTION("LTTng my_subsys probes"); |
| 5840 | MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "." |
| 5841 | __stringify(LTTNG_MODULES_MINOR_VERSION) "." |
| 5842 | __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION) |
| 5843 | LTTNG_MODULES_EXTRAVERSION); |
| 5844 | ---- |
| 5845 | -- |
| 5846 | |
| 5847 | . Edit path:{probes/KBuild} and add your new kernel module object |
| 5848 | next to the existing ones: |
| 5849 | + |
| 5850 | -- |
| 5851 | [source,make] |
| 5852 | .path:{probes/KBuild} |
| 5853 | ---- |
| 5854 | # ... |
| 5855 | |
| 5856 | obj-m += lttng-probe-module.o |
| 5857 | obj-m += lttng-probe-power.o |
| 5858 | |
| 5859 | obj-m += lttng-probe-my-subsys.o |
| 5860 | |
| 5861 | # ... |
| 5862 | ---- |
| 5863 | -- |
| 5864 | |
| 5865 | . Build and install the LTTng kernel modules: |
| 5866 | + |
| 5867 | -- |
| 5868 | [role="term"] |
| 5869 | ---- |
| 5870 | $ make KERNELDIR=/path/to/linux |
| 5871 | # make modules_install && depmod -a |
| 5872 | ---- |
| 5873 | -- |
| 5874 | + |
| 5875 | Replace `/path/to/linux` with the path to the Linux source tree where |
| 5876 | you defined and used tracepoints with the `TRACE_EVENT()` ftrace macro. |
| 5877 | |
| 5878 | Note that you can also use the |
| 5879 | <<lttng-tracepoint-event-code,`LTTNG_TRACEPOINT_EVENT_CODE()` macro>> |
| 5880 | instead of `LTTNG_TRACEPOINT_EVENT()` to use custom local variables and |
| 5881 | C{nbsp}code that need to be executed before LTTng records the event |
| 5882 | fields. |
| 5883 | |
| 5884 | The best way to learn how to use the previous LTTng-modules macros is to |
| 5885 | inspect the existing LTTng-modules tracepoint definitions in the |
| 5886 | dir:{instrumentation/events/lttng-module} header files. Compare them |
| 5887 | with the Linux kernel mainline versions in the |
| 5888 | dir:{include/trace/events} directory of the Linux source tree. |
| 5889 | |
| 5890 | |
| 5891 | [role="since-2.7"] |
| 5892 | [[lttng-tracepoint-event-code]] |
| 5893 | ===== Use custom C code to access the data for tracepoint fields |
| 5894 | |
| 5895 | Although we recommended to always use the |
| 5896 | <<lttng-adaptation-layer,`LTTNG_TRACEPOINT_EVENT()`>> macro to describe |
| 5897 | the arguments and fields of an LTTng-modules tracepoint when possible, |
| 5898 | sometimes you need a more complex process to access the data that the |
| 5899 | tracer records as event record fields. In other words, you need local |
| 5900 | variables and multiple C{nbsp}statements instead of simple |
| 5901 | argument-based expressions that you pass to the |
| 5902 | <<lttng-modules-tp-fields,`ctf_*()` macros of `TP_FIELDS()`>>. |
| 5903 | |
| 5904 | Use the `LTTNG_TRACEPOINT_EVENT_CODE()` macro instead of |
| 5905 | `LTTNG_TRACEPOINT_EVENT()` to declare custom local variables and define |
| 5906 | a block of C{nbsp}code to be executed before LTTng records the fields. |
| 5907 | The structure of this macro is: |
| 5908 | |
| 5909 | [source,c] |
| 5910 | .`LTTNG_TRACEPOINT_EVENT_CODE()` macro syntax. |
| 5911 | ---- |
| 5912 | LTTNG_TRACEPOINT_EVENT_CODE( |
| 5913 | /* |
| 5914 | * Format identical to the LTTNG_TRACEPOINT_EVENT() |
| 5915 | * version for the following three macro parameters: |
| 5916 | */ |
| 5917 | my_subsys_my_event, |
| 5918 | TP_PROTO(int my_int, const char *my_string), |
| 5919 | TP_ARGS(my_int, my_string), |
| 5920 | |
| 5921 | /* Declarations of custom local variables */ |
| 5922 | TP_locvar( |
| 5923 | int a = 0; |
| 5924 | unsigned long b = 0; |
| 5925 | const char *name = "(undefined)"; |
| 5926 | struct my_struct *my_struct; |
| 5927 | ), |
| 5928 | |
| 5929 | /* |
| 5930 | * Custom code which uses both tracepoint arguments |
| 5931 | * (in TP_ARGS()) and local variables (in TP_locvar()). |
| 5932 | * |
| 5933 | * Local variables are actually members of a structure pointed |
| 5934 | * to by the special variable tp_locvar. |
| 5935 | */ |
| 5936 | TP_code( |
| 5937 | if (my_int) { |
| 5938 | tp_locvar->a = my_int + 17; |
| 5939 | tp_locvar->my_struct = get_my_struct_at(tp_locvar->a); |
| 5940 | tp_locvar->b = my_struct_compute_b(tp_locvar->my_struct); |
| 5941 | tp_locvar->name = my_struct_get_name(tp_locvar->my_struct); |
| 5942 | put_my_struct(tp_locvar->my_struct); |
| 5943 | |
| 5944 | if (tp_locvar->b) { |
| 5945 | tp_locvar->a = 1; |
| 5946 | } |
| 5947 | } |
| 5948 | ), |
| 5949 | |
| 5950 | /* |
| 5951 | * Format identical to the LTTNG_TRACEPOINT_EVENT() |
| 5952 | * version for this, except that tp_locvar members can be |
| 5953 | * used in the argument expression parameters of |
| 5954 | * the ctf_*() macros. |
| 5955 | */ |
| 5956 | TP_FIELDS( |
| 5957 | ctf_integer(unsigned long, my_struct_b, tp_locvar->b) |
| 5958 | ctf_integer(int, my_struct_a, tp_locvar->a) |
| 5959 | ctf_string(my_string_field, my_string) |
| 5960 | ctf_string(my_struct_name, tp_locvar->name) |
| 5961 | ) |
| 5962 | ) |
| 5963 | ---- |
| 5964 | |
| 5965 | IMPORTANT: The C code defined in `TP_code()` must not have any side |
| 5966 | effects when executed. In particular, the code must not allocate |
| 5967 | memory or get resources without deallocating this memory or putting |
| 5968 | those resources afterwards. |
| 5969 | |
| 5970 | |
| 5971 | [[instrumenting-linux-kernel-tracing]] |
| 5972 | ==== Load and unload a custom probe kernel module |
| 5973 | |
| 5974 | You must load a <<lttng-adaptation-layer,created LTTng-modules probe |
| 5975 | kernel module>> in the kernel before it can emit LTTng events. |
| 5976 | |
| 5977 | To load the default probe kernel modules and a custom probe kernel |
| 5978 | module: |
| 5979 | |
| 5980 | * Use the opt:lttng-sessiond(8):--extra-kmod-probes option to give extra |
| 5981 | probe modules to load when starting a root <<lttng-sessiond,session |
| 5982 | daemon>>: |
| 5983 | + |
| 5984 | -- |
| 5985 | .Load the `my_subsys`, `usb`, and the default probe modules. |
| 5986 | ==== |
| 5987 | [role="term"] |
| 5988 | ---- |
| 5989 | # lttng-sessiond --extra-kmod-probes=my_subsys,usb |
| 5990 | ---- |
| 5991 | ==== |
| 5992 | -- |
| 5993 | + |
| 5994 | You only need to pass the subsystem name, not the whole kernel module |
| 5995 | name. |
| 5996 | |
| 5997 | To load _only_ a given custom probe kernel module: |
| 5998 | |
| 5999 | * Use the opt:lttng-sessiond(8):--kmod-probes option to give the probe |
| 6000 | modules to load when starting a root session daemon: |
| 6001 | + |
| 6002 | -- |
| 6003 | .Load only the `my_subsys` and `usb` probe modules. |
| 6004 | ==== |
| 6005 | [role="term"] |
| 6006 | ---- |
| 6007 | # lttng-sessiond --kmod-probes=my_subsys,usb |
| 6008 | ---- |
| 6009 | ==== |
| 6010 | -- |
| 6011 | |
| 6012 | To confirm that a probe module is loaded: |
| 6013 | |
| 6014 | * Use man:lsmod(8): |
| 6015 | + |
| 6016 | -- |
| 6017 | [role="term"] |
| 6018 | ---- |
| 6019 | $ lsmod | grep lttng_probe_usb |
| 6020 | ---- |
| 6021 | -- |
| 6022 | |
| 6023 | To unload the loaded probe modules: |
| 6024 | |
| 6025 | * Kill the session daemon with `SIGTERM`: |
| 6026 | + |
| 6027 | -- |
| 6028 | [role="term"] |
| 6029 | ---- |
| 6030 | # pkill lttng-sessiond |
| 6031 | ---- |
| 6032 | -- |
| 6033 | + |
| 6034 | You can also use the `--remove` option of man:modprobe(8) if the session |
| 6035 | daemon terminates abnormally. |
| 6036 | |
| 6037 | |
| 6038 | [[controlling-tracing]] |
| 6039 | == Tracing control |
| 6040 | |
| 6041 | Once an application or a Linux kernel is <<instrumenting,instrumented>> |
| 6042 | for LTTng tracing, you can _trace_ it. |
| 6043 | |
| 6044 | In the LTTng context, _tracing_ means making sure that LTTng attempts to |
| 6045 | execute some action(s) when a CPU executes an instrumentation point. |
| 6046 | |
| 6047 | This section is divided in topics on how to use the various |
| 6048 | <<plumbing,components of LTTng>>, in particular the |
| 6049 | <<lttng-cli,cmd:lttng command-line tool>>, to _control_ the LTTng |
| 6050 | daemons and tracers. |
| 6051 | |
| 6052 | NOTE: In the following subsections, we refer to an man:lttng(1) command |
| 6053 | using its man page name. For example, instead of ``Run the `create` |
| 6054 | command to'', we write ``Run the man:lttng-create(1) command to''. |
| 6055 | |
| 6056 | |
| 6057 | [[start-sessiond]] |
| 6058 | === Start a session daemon |
| 6059 | |
| 6060 | In some situations, you need to run a <<lttng-sessiond,session daemon>> |
| 6061 | (man:lttng-sessiond(8)) _before_ you can use the man:lttng(1) |
| 6062 | command-line tool. |
| 6063 | |
| 6064 | You will see the following error when you run a command while no session |
| 6065 | daemon is running: |
| 6066 | |
| 6067 | ---- |
| 6068 | Error: No session daemon is available |
| 6069 | ---- |
| 6070 | |
| 6071 | The only command that automatically runs a session daemon is |
| 6072 | man:lttng-create(1), which you use to |
| 6073 | <<creating-destroying-tracing-sessions,create a recording session>>. While |
| 6074 | this could be your most used first operation, sometimes it's not. Some |
| 6075 | examples are: |
| 6076 | |
| 6077 | * <<list-instrumentation-points,List the available instrumentation points>>. |
| 6078 | * <<saving-loading-tracing-session,Load a recording session configuration>>. |
| 6079 | * <<add-event-rule-matches-trigger,Add a trigger>>. |
| 6080 | |
| 6081 | All the examples above don't require a recording session to operate on. |
| 6082 | |
| 6083 | [[tracing-group]] Each Unix user can have its own running session daemon |
| 6084 | to use the user space LTTng tracer. The session daemon that the `root` |
| 6085 | user starts is the only one allowed to control the LTTng kernel tracer. |
| 6086 | Members of the Unix _tracing group_ may connect to and control the root |
| 6087 | session daemon, even for user space tracing. See the ``Session daemon |
| 6088 | connection'' section of man:lttng(1) to learn more about the Unix |
| 6089 | tracing group. |
| 6090 | |
| 6091 | To start a user session daemon: |
| 6092 | |
| 6093 | * Run man:lttng-sessiond(8): |
| 6094 | + |
| 6095 | -- |
| 6096 | [role="term"] |
| 6097 | ---- |
| 6098 | $ lttng-sessiond --daemonize |
| 6099 | ---- |
| 6100 | -- |
| 6101 | |
| 6102 | To start the root session daemon: |
| 6103 | |
| 6104 | * Run man:lttng-sessiond(8) as the `root` user: |
| 6105 | + |
| 6106 | -- |
| 6107 | [role="term"] |
| 6108 | ---- |
| 6109 | # lttng-sessiond --daemonize |
| 6110 | ---- |
| 6111 | -- |
| 6112 | |
| 6113 | In both cases, remove the opt:lttng-sessiond(8):--daemonize option to |
| 6114 | start the session daemon in foreground. |
| 6115 | |
| 6116 | To stop a session daemon, kill its process (see man:kill(1)) with the |
| 6117 | standard `TERM` signal. |
| 6118 | |
| 6119 | Note that some Linux distributions could manage the LTTng session daemon |
| 6120 | as a service. In this case, we suggest that you use the service manager |
| 6121 | to start, restart, and stop session daemons. |
| 6122 | |
| 6123 | |
| 6124 | [[creating-destroying-tracing-sessions]] |
| 6125 | === Create and destroy a recording session |
| 6126 | |
| 6127 | Many LTTng control operations happen in the scope of a |
| 6128 | <<tracing-session,recording session>>, which is the dialogue between the |
| 6129 | <<lttng-sessiond,session daemon>> and you for everything related to |
| 6130 | <<event,event recording>>. |
| 6131 | |
| 6132 | To create a recording session with a generated name: |
| 6133 | |
| 6134 | * Use the man:lttng-create(1) command: |
| 6135 | + |
| 6136 | -- |
| 6137 | [role="term"] |
| 6138 | ---- |
| 6139 | $ lttng create |
| 6140 | ---- |
| 6141 | -- |
| 6142 | |
| 6143 | The name of the created recording session is `auto` followed by the |
| 6144 | creation date. |
| 6145 | |
| 6146 | To create a recording session with a specific name: |
| 6147 | |
| 6148 | * Use the optional argument of the man:lttng-create(1) command: |
| 6149 | + |
| 6150 | -- |
| 6151 | [role="term"] |
| 6152 | ---- |
| 6153 | $ lttng create SESSION |
| 6154 | ---- |
| 6155 | -- |
| 6156 | + |
| 6157 | Replace +__SESSION__+ with your specific recording session name. |
| 6158 | |
| 6159 | In <<local-mode,local mode>>, LTTng writes the traces of a recording |
| 6160 | session to the +$LTTNG_HOME/lttng-traces/__NAME__-__DATE__-__TIME__+ |
| 6161 | directory by default, where +__NAME__+ is the name of the recording |
| 6162 | session. Note that the env:LTTNG_HOME environment variable defaults to |
| 6163 | `$HOME` if not set. |
| 6164 | |
| 6165 | To output LTTng traces to a non-default location: |
| 6166 | |
| 6167 | * Use the opt:lttng-create(1):--output option of the man:lttng-create(1) |
| 6168 | command: |
| 6169 | + |
| 6170 | -- |
| 6171 | [role="term"] |
| 6172 | ---- |
| 6173 | $ lttng create my-session --output=/tmp/some-directory |
| 6174 | ---- |
| 6175 | -- |
| 6176 | |
| 6177 | You may create as many recording sessions as you wish. |
| 6178 | |
| 6179 | To list all the existing recording sessions for your Unix user, or for |
| 6180 | all users if your Unix user is `root`: |
| 6181 | |
| 6182 | * Use the man:lttng-list(1) command: |
| 6183 | + |
| 6184 | -- |
| 6185 | [role="term"] |
| 6186 | ---- |
| 6187 | $ lttng list |
| 6188 | ---- |
| 6189 | -- |
| 6190 | |
| 6191 | [[cur-tracing-session]]When you create a recording session, the |
| 6192 | man:lttng-create(1) command sets it as the _current recording session_. |
| 6193 | The following man:lttng(1) commands operate on the current recording |
| 6194 | session when you don't specify one: |
| 6195 | |
| 6196 | [role="list-3-cols"] |
| 6197 | * man:lttng-add-context(1) |
| 6198 | * man:lttng-clear(1) |
| 6199 | * man:lttng-destroy(1) |
| 6200 | * man:lttng-disable-channel(1) |
| 6201 | * man:lttng-disable-event(1) |
| 6202 | * man:lttng-disable-rotation(1) |
| 6203 | * man:lttng-enable-channel(1) |
| 6204 | * man:lttng-enable-event(1) |
| 6205 | * man:lttng-enable-rotation(1) |
| 6206 | * man:lttng-load(1) |
| 6207 | * man:lttng-regenerate(1) |
| 6208 | * man:lttng-rotate(1) |
| 6209 | * man:lttng-save(1) |
| 6210 | * man:lttng-snapshot(1) |
| 6211 | * man:lttng-start(1) |
| 6212 | * man:lttng-status(1) |
| 6213 | * man:lttng-stop(1) |
| 6214 | * man:lttng-track(1) |
| 6215 | * man:lttng-untrack(1) |
| 6216 | * man:lttng-view(1) |
| 6217 | |
| 6218 | To change the current recording session: |
| 6219 | |
| 6220 | * Use the man:lttng-set-session(1) command: |
| 6221 | + |
| 6222 | -- |
| 6223 | [role="term"] |
| 6224 | ---- |
| 6225 | $ lttng set-session SESSION |
| 6226 | ---- |
| 6227 | -- |
| 6228 | + |
| 6229 | Replace +__SESSION__+ with the name of the new current recording session. |
| 6230 | |
| 6231 | When you're done recording in a given recording session, destroy it. |
| 6232 | This operation frees the resources taken by the recording session to |
| 6233 | destroy; it doesn't destroy the trace data that LTTng wrote for this |
| 6234 | recording session (see ``<<clear,Clear a recording session>>'' for one |
| 6235 | way to do this). |
| 6236 | |
| 6237 | To destroy the current recording session: |
| 6238 | |
| 6239 | * Use the man:lttng-destroy(1) command: |
| 6240 | + |
| 6241 | -- |
| 6242 | [role="term"] |
| 6243 | ---- |
| 6244 | $ lttng destroy |
| 6245 | ---- |
| 6246 | -- |
| 6247 | |
| 6248 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) command |
| 6249 | implicitly (see ``<<basic-tracing-session-control,Start and stop a |
| 6250 | recording session>>''). You need to stop recording to make LTTng flush the |
| 6251 | remaining trace data and make the trace readable. |
| 6252 | |
| 6253 | |
| 6254 | [[list-instrumentation-points]] |
| 6255 | === List the available instrumentation points |
| 6256 | |
| 6257 | The <<lttng-sessiond,session daemon>> can query the running instrumented |
| 6258 | user applications and the Linux kernel to get a list of available |
| 6259 | instrumentation points: |
| 6260 | |
| 6261 | * LTTng tracepoints and system calls for the Linux kernel |
| 6262 | <<domain,tracing domain>>. |
| 6263 | |
| 6264 | * LTTng tracepoints for the user space tracing domain. |
| 6265 | |
| 6266 | To list the available instrumentation points: |
| 6267 | |
| 6268 | . <<start-sessiond,Make sure>> there's a running |
| 6269 | <<lttng-sessiond,session daemon>> to which your Unix user can |
| 6270 | connect. |
| 6271 | |
| 6272 | . Use the man:lttng-list(1) command with the option of the requested |
| 6273 | tracing domain amongst: |
| 6274 | + |
| 6275 | -- |
| 6276 | opt:lttng-list(1):--kernel:: |
| 6277 | Linux kernel tracepoints. |
| 6278 | + |
| 6279 | Your Unix user must be `root`, or it must be a member of the Unix |
| 6280 | <<tracing-group,tracing group>>. |
| 6281 | |
| 6282 | opt:lttng-list(1):--kernel with opt:lttng-list(1):--syscall:: |
| 6283 | Linux kernel system calls. |
| 6284 | + |
| 6285 | Your Unix user must be `root`, or it must be a member of the Unix |
| 6286 | <<tracing-group,tracing group>>. |
| 6287 | |
| 6288 | opt:lttng-list(1):--userspace:: |
| 6289 | User space tracepoints. |
| 6290 | |
| 6291 | opt:lttng-list(1):--jul:: |
| 6292 | `java.util.logging` loggers. |
| 6293 | |
| 6294 | opt:lttng-list(1):--log4j:: |
| 6295 | Apache log4j loggers. |
| 6296 | |
| 6297 | opt:lttng-list(1):--python:: |
| 6298 | Python loggers. |
| 6299 | -- |
| 6300 | |
| 6301 | .List the available user space tracepoints. |
| 6302 | ==== |
| 6303 | [role="term"] |
| 6304 | ---- |
| 6305 | $ lttng list --userspace |
| 6306 | ---- |
| 6307 | ==== |
| 6308 | |
| 6309 | .List the available Linux kernel system calls. |
| 6310 | ==== |
| 6311 | [role="term"] |
| 6312 | ---- |
| 6313 | $ lttng list --kernel --syscall |
| 6314 | ---- |
| 6315 | ==== |
| 6316 | |
| 6317 | |
| 6318 | [[enabling-disabling-events]] |
| 6319 | === Create and enable a recording event rule |
| 6320 | |
| 6321 | Once you <<creating-destroying-tracing-sessions,create a recording |
| 6322 | session>>, you can create <<event,recording event rules>> with the |
| 6323 | man:lttng-enable-event(1) command. |
| 6324 | |
| 6325 | The man:lttng-enable-event(1) command always attaches an event rule to a |
| 6326 | <<channel,channel>> on creation. The command can create a _default |
| 6327 | channel_, named `channel0`, for you. The man:lttng-enable-event(1) |
| 6328 | command reuses the default channel each time you run it for the same |
| 6329 | tracing domain and session. |
| 6330 | |
| 6331 | A recording event rule is always enabled at creation time. |
| 6332 | |
| 6333 | The following examples show how to combine the command-line arguments of |
| 6334 | the man:lttng-enable-event(1) command to create simple to more complex |
| 6335 | recording event rules within the <<cur-tracing-session,current recording |
| 6336 | session>>. |
| 6337 | |
| 6338 | .Create a recording event rule matching specific Linux kernel tracepoint events (default channel). |
| 6339 | ==== |
| 6340 | [role="term"] |
| 6341 | ---- |
| 6342 | # lttng enable-event --kernel sched_switch |
| 6343 | ---- |
| 6344 | ==== |
| 6345 | |
| 6346 | .Create a recording event rule matching Linux kernel system call events with four specific names (default channel). |
| 6347 | ==== |
| 6348 | [role="term"] |
| 6349 | ---- |
| 6350 | # lttng enable-event --kernel --syscall open,write,read,close |
| 6351 | ---- |
| 6352 | ==== |
| 6353 | |
| 6354 | .Create recording event rules matching tracepoint events which satisfy a filter expressions (default channel). |
| 6355 | ==== |
| 6356 | [role="term"] |
| 6357 | ---- |
| 6358 | # lttng enable-event --kernel sched_switch --filter='prev_comm == "bash"' |
| 6359 | ---- |
| 6360 | |
| 6361 | [role="term"] |
| 6362 | ---- |
| 6363 | # lttng enable-event --kernel --all \ |
| 6364 | --filter='$ctx.tid == 1988 || $ctx.tid == 1534' |
| 6365 | ---- |
| 6366 | |
| 6367 | [role="term"] |
| 6368 | ---- |
| 6369 | $ lttng enable-event --jul my_logger \ |
| 6370 | --filter='$app.retriever:cur_msg_id > 3' |
| 6371 | ---- |
| 6372 | |
| 6373 | IMPORTANT: Make sure to always single-quote the filter string when you |
| 6374 | run man:lttng(1) from a shell. |
| 6375 | |
| 6376 | See also ``<<pid-tracking,Allow specific processes to record events>>'' |
| 6377 | which offers another, more efficient filtering mechanism for process ID, |
| 6378 | user ID, and group ID attributes. |
| 6379 | ==== |
| 6380 | |
| 6381 | .Create a recording event rule matching any user space event from the `my_app` tracepoint provider and with a log level range (default channel). |
| 6382 | ==== |
| 6383 | [role="term"] |
| 6384 | ---- |
| 6385 | $ lttng enable-event --userspace my_app:'*' --loglevel=INFO |
| 6386 | ---- |
| 6387 | |
| 6388 | IMPORTANT: Make sure to always single-quote the wildcard character when |
| 6389 | you run man:lttng(1) from a shell. |
| 6390 | ==== |
| 6391 | |
| 6392 | .Create a recording event rule matching user space events named specifically, but with name exclusions (default channel). |
| 6393 | ==== |
| 6394 | [role="term"] |
| 6395 | ---- |
| 6396 | $ lttng enable-event --userspace my_app:'*' \ |
| 6397 | --exclude=my_app:set_user,my_app:handle_sig |
| 6398 | ---- |
| 6399 | ==== |
| 6400 | |
| 6401 | .Create a recording event rule matching any Apache log4j event with a specific log level (default channel). |
| 6402 | ==== |
| 6403 | [role="term"] |
| 6404 | ---- |
| 6405 | $ lttng enable-event --log4j --all --loglevel-only=WARN |
| 6406 | ---- |
| 6407 | ==== |
| 6408 | |
| 6409 | .Create a recording event rule, attached to a specific channel, and matching user space tracepoint events named `my_app:my_tracepoint`. |
| 6410 | ==== |
| 6411 | [role="term"] |
| 6412 | ---- |
| 6413 | $ lttng enable-event --userspace my_app:my_tracepoint \ |
| 6414 | --channel=my-channel |
| 6415 | ---- |
| 6416 | ==== |
| 6417 | |
| 6418 | .Create a recording event rule matching user space probe events for the `malloc` function entry in path:{/usr/lib/libc.so.6}: |
| 6419 | ==== |
| 6420 | [role="term"] |
| 6421 | ---- |
| 6422 | # lttng enable-event --kernel \ |
| 6423 | --userspace-probe=/usr/lib/libc.so.6:malloc \ |
| 6424 | libc_malloc |
| 6425 | ---- |
| 6426 | ==== |
| 6427 | |
| 6428 | .Create a recording event rule matching user space probe events for the `server`/`accept_request` https://www.sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps[USDT probe] in path:{/usr/bin/serv}: |
| 6429 | ==== |
| 6430 | [role="term"] |
| 6431 | ---- |
| 6432 | # lttng enable-event --kernel \ |
| 6433 | --userspace-probe=sdt:serv:server:accept_request \ |
| 6434 | server_accept_request |
| 6435 | ---- |
| 6436 | ==== |
| 6437 | |
| 6438 | The recording event rules of a given channel form a whitelist: as soon |
| 6439 | as an event rule matches an event, LTTng emits it _once_ and therefore |
| 6440 | <<channel-overwrite-mode-vs-discard-mode,can>> record it. For example, |
| 6441 | the following rules both match user space tracepoint events named |
| 6442 | `my_app:my_tracepoint` with an `INFO` log level: |
| 6443 | |
| 6444 | [role="term"] |
| 6445 | ---- |
| 6446 | $ lttng enable-event --userspace my_app:my_tracepoint |
| 6447 | $ lttng enable-event --userspace my_app:my_tracepoint \ |
| 6448 | --loglevel=INFO |
| 6449 | ---- |
| 6450 | |
| 6451 | The second recording event rule is redundant: the first one includes the |
| 6452 | second one. |
| 6453 | |
| 6454 | |
| 6455 | [[disable-event-rule]] |
| 6456 | === Disable a recording event rule |
| 6457 | |
| 6458 | To disable a <<event,recording event rule>> that you |
| 6459 | <<enabling-disabling-events,created>> previously, use the |
| 6460 | man:lttng-disable-event(1) command. |
| 6461 | |
| 6462 | man:lttng-disable-event(1) can only find recording event rules to |
| 6463 | disable by their <<instrumentation-point-types,instrumentation point |
| 6464 | type>> and event name conditions. Therefore, you cannot disable |
| 6465 | recording event rules having a specific instrumentation point log level |
| 6466 | condition, for example. |
| 6467 | |
| 6468 | LTTng doesn't emit (and, therefore, won't record) an event which only |
| 6469 | _disabled_ recording event rules match. |
| 6470 | |
| 6471 | .Disable event rules matching Python logging events from the `my-logger` logger (default <<channel,channel>>, <<cur-tracing-session,current recording session>>). |
| 6472 | ==== |
| 6473 | [role="term"] |
| 6474 | ---- |
| 6475 | $ lttng disable-event --python my-logger |
| 6476 | ---- |
| 6477 | ==== |
| 6478 | |
| 6479 | .Disable event rules matching all `java.util.logging` events (default channel, recording session `my-session`). |
| 6480 | ==== |
| 6481 | [role="term"] |
| 6482 | ---- |
| 6483 | $ lttng disable-event --jul --session=my-session '*' |
| 6484 | ---- |
| 6485 | ==== |
| 6486 | |
| 6487 | .Disable _all_ the Linux kernel recording event rules (channel `my-chan`, current recording session). |
| 6488 | ==== |
| 6489 | The opt:lttng-disable-event(1):--all-events option isn't, like the |
| 6490 | opt:lttng-enable-event(1):--all option of the man:lttng-enable-event(1) |
| 6491 | command, an alias for the event name globbing pattern `*`: it disables |
| 6492 | _all_ the recording event rules of a given channel. |
| 6493 | |
| 6494 | [role="term"] |
| 6495 | ---- |
| 6496 | # lttng disable-event --kernel --channel=my-chan --all-events |
| 6497 | ---- |
| 6498 | ==== |
| 6499 | |
| 6500 | NOTE: You can't _remove_ a recording event rule once you create it. |
| 6501 | |
| 6502 | |
| 6503 | [[status]] |
| 6504 | === Get the status of a recording session |
| 6505 | |
| 6506 | To get the status of the <<cur-tracing-session,current recording |
| 6507 | session>>, that is, its parameters, its channels, recording event rules, |
| 6508 | and their attributes: |
| 6509 | |
| 6510 | * Use the man:lttng-status(1) command: |
| 6511 | + |
| 6512 | -- |
| 6513 | [role="term"] |
| 6514 | ---- |
| 6515 | $ lttng status |
| 6516 | ---- |
| 6517 | -- |
| 6518 | |
| 6519 | To get the status of any recording session: |
| 6520 | |
| 6521 | * Use the man:lttng-list(1) command with the name of the recording |
| 6522 | session: |
| 6523 | + |
| 6524 | -- |
| 6525 | [role="term"] |
| 6526 | ---- |
| 6527 | $ lttng list SESSION |
| 6528 | ---- |
| 6529 | -- |
| 6530 | + |
| 6531 | Replace +__SESSION__+ with the recording session name. |
| 6532 | |
| 6533 | |
| 6534 | [[basic-tracing-session-control]] |
| 6535 | === Start and stop a recording session |
| 6536 | |
| 6537 | Once you <<creating-destroying-tracing-sessions,create a recording |
| 6538 | session>> and <<enabling-disabling-events,create one or more recording |
| 6539 | event rules>>, you can start and stop the tracers for this recording |
| 6540 | session. |
| 6541 | |
| 6542 | To start the <<cur-tracing-session,current recording session>>: |
| 6543 | |
| 6544 | * Use the man:lttng-start(1) command: |
| 6545 | + |
| 6546 | -- |
| 6547 | [role="term"] |
| 6548 | ---- |
| 6549 | $ lttng start |
| 6550 | ---- |
| 6551 | -- |
| 6552 | |
| 6553 | LTTng is flexible: you can launch user applications before or after you |
| 6554 | start the tracers. An LTTng tracer only <<event,records an event>> if a |
| 6555 | recording event rule matches it, which means the tracer is active. |
| 6556 | |
| 6557 | The `start-session` <<trigger,trigger>> action can also start a recording |
| 6558 | session. |
| 6559 | |
| 6560 | To stop the current recording session: |
| 6561 | |
| 6562 | * Use the man:lttng-stop(1) command: |
| 6563 | + |
| 6564 | -- |
| 6565 | [role="term"] |
| 6566 | ---- |
| 6567 | $ lttng stop |
| 6568 | ---- |
| 6569 | -- |
| 6570 | + |
| 6571 | If there were <<channel-overwrite-mode-vs-discard-mode,lost event |
| 6572 | records>> or lost sub-buffers since the last time you ran |
| 6573 | man:lttng-start(1), the man:lttng-stop(1) command prints corresponding |
| 6574 | warnings. |
| 6575 | |
| 6576 | IMPORTANT: You need to stop recording to make LTTng flush the remaining |
| 6577 | trace data and make the trace readable. Note that the |
| 6578 | man:lttng-destroy(1) command (see |
| 6579 | ``<<creating-destroying-tracing-sessions,Create and destroy a recording |
| 6580 | session>>'') also runs the man:lttng-stop(1) command implicitly. |
| 6581 | |
| 6582 | The `stop-session` <<trigger,trigger>> action can also stop a recording |
| 6583 | session. |
| 6584 | |
| 6585 | [role="since-2.12"] |
| 6586 | [[clear]] |
| 6587 | === Clear a recording session |
| 6588 | |
| 6589 | You might need to remove all the current tracing data of one or more |
| 6590 | <<tracing-session,recording sessions>> between multiple attempts to |
| 6591 | reproduce a problem without interrupting the LTTng recording activity. |
| 6592 | |
| 6593 | To clear the tracing data of the |
| 6594 | <<cur-tracing-session,current recording session>>: |
| 6595 | |
| 6596 | * Use the man:lttng-clear(1) command: |
| 6597 | + |
| 6598 | -- |
| 6599 | [role="term"] |
| 6600 | ---- |
| 6601 | $ lttng clear |
| 6602 | ---- |
| 6603 | -- |
| 6604 | |
| 6605 | To clear the tracing data of all the recording sessions: |
| 6606 | |
| 6607 | * Use the `lttng clear` command with its opt:lttng-clear(1):--all |
| 6608 | option: |
| 6609 | + |
| 6610 | -- |
| 6611 | [role="term"] |
| 6612 | ---- |
| 6613 | $ lttng clear --all |
| 6614 | ---- |
| 6615 | -- |
| 6616 | |
| 6617 | |
| 6618 | [[enabling-disabling-channels]] |
| 6619 | === Create a channel |
| 6620 | |
| 6621 | Once you <<creating-destroying-tracing-sessions,create a recording |
| 6622 | session>>, you can create a <<channel,channel>> with the |
| 6623 | man:lttng-enable-channel(1) command. |
| 6624 | |
| 6625 | Note that LTTng can automatically create a default channel when you |
| 6626 | <<enabling-disabling-events,create a recording event rule>>. |
| 6627 | Therefore, you only need to create a channel when you need non-default |
| 6628 | attributes. |
| 6629 | |
| 6630 | Specify each non-default channel attribute with a command-line |
| 6631 | option when you run the man:lttng-enable-channel(1) command. |
| 6632 | |
| 6633 | You can only create a custom channel in the Linux kernel and user space |
| 6634 | <<domain,tracing domains>>: the Java/Python logging tracing domains have |
| 6635 | their own default channel which LTTng automatically creates when you |
| 6636 | <<enabling-disabling-events,create a recording event rule>>. |
| 6637 | |
| 6638 | [IMPORTANT] |
| 6639 | ==== |
| 6640 | As of LTTng{nbsp}{revision}, you may _not_ perform the |
| 6641 | following operations with the man:lttng-enable-channel(1) command: |
| 6642 | |
| 6643 | * Change an attribute of an existing channel. |
| 6644 | |
| 6645 | * Enable a disabled channel once its recording session has been |
| 6646 | <<basic-tracing-session-control,active>> at least once. |
| 6647 | |
| 6648 | * Create a channel once its recording session has been active at |
| 6649 | least once. |
| 6650 | |
| 6651 | * Create a user space channel with a given |
| 6652 | <<channel-buffering-schemes,buffering scheme>> and create a second |
| 6653 | user space channel with a different buffering scheme in the same |
| 6654 | recording session. |
| 6655 | ==== |
| 6656 | |
| 6657 | The following examples show how to combine the command-line options of |
| 6658 | the man:lttng-enable-channel(1) command to create simple to more complex |
| 6659 | channels within the <<cur-tracing-session,current recording session>>. |
| 6660 | |
| 6661 | .Create a Linux kernel channel with default attributes. |
| 6662 | ==== |
| 6663 | [role="term"] |
| 6664 | ---- |
| 6665 | # lttng enable-channel --kernel my-channel |
| 6666 | ---- |
| 6667 | ==== |
| 6668 | |
| 6669 | .Create a user space channel with four sub-buffers or 1{nbsp}MiB each, per CPU, per instrumented process. |
| 6670 | ==== |
| 6671 | [role="term"] |
| 6672 | ---- |
| 6673 | $ lttng enable-channel --userspace --num-subbuf=4 --subbuf-size=1M \ |
| 6674 | --buffers-pid my-channel |
| 6675 | ---- |
| 6676 | ==== |
| 6677 | |
| 6678 | .[[blocking-timeout-example]]Create a default user space channel with an infinite blocking timeout. |
| 6679 | ==== |
| 6680 | <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 6681 | create the channel, <<enabling-disabling-events,create a recording event |
| 6682 | rule>>, and <<basic-tracing-session-control,start recording>>: |
| 6683 | |
| 6684 | [role="term"] |
| 6685 | ---- |
| 6686 | $ lttng create |
| 6687 | $ lttng enable-channel --userspace --blocking-timeout=inf blocking-chan |
| 6688 | $ lttng enable-event --userspace --channel=blocking-chan --all |
| 6689 | $ lttng start |
| 6690 | ---- |
| 6691 | |
| 6692 | Run an application instrumented with LTTng-UST tracepoints and allow it |
| 6693 | to block: |
| 6694 | |
| 6695 | [role="term"] |
| 6696 | ---- |
| 6697 | $ LTTNG_UST_ALLOW_BLOCKING=1 my-app |
| 6698 | ---- |
| 6699 | ==== |
| 6700 | |
| 6701 | .Create a Linux kernel channel which rotates eight trace files of 4{nbsp}MiB each for each stream. |
| 6702 | ==== |
| 6703 | [role="term"] |
| 6704 | ---- |
| 6705 | # lttng enable-channel --kernel --tracefile-count=8 \ |
| 6706 | --tracefile-size=4194304 my-channel |
| 6707 | ---- |
| 6708 | ==== |
| 6709 | |
| 6710 | .Create a user space channel in <<overwrite-mode,overwrite>> (or ``flight recorder'') mode. |
| 6711 | ==== |
| 6712 | [role="term"] |
| 6713 | ---- |
| 6714 | $ lttng enable-channel --userspace --overwrite my-channel |
| 6715 | ---- |
| 6716 | ==== |
| 6717 | |
| 6718 | .<<enabling-disabling-events,Create>> the same <<event,recording event rule>> attached to two different channels. |
| 6719 | ==== |
| 6720 | [role="term"] |
| 6721 | ---- |
| 6722 | $ lttng enable-event --userspace --channel=my-channel app:tp |
| 6723 | $ lttng enable-event --userspace --channel=other-channel app:tp |
| 6724 | ---- |
| 6725 | |
| 6726 | When a CPU executes the `app:tp` <<c-application,user space |
| 6727 | tracepoint>>, the two recording event rules above match the created |
| 6728 | event, making LTTng emit the event. Because the recording event rules |
| 6729 | are not attached to the same channel, LTTng records the event twice. |
| 6730 | ==== |
| 6731 | |
| 6732 | |
| 6733 | [[disable-channel]] |
| 6734 | === Disable a channel |
| 6735 | |
| 6736 | To disable a specific channel that you |
| 6737 | <<enabling-disabling-channels,created>> previously, use the |
| 6738 | man:lttng-disable-channel(1) command. |
| 6739 | |
| 6740 | .Disable a specific Linux kernel channel (<<cur-tracing-session,current recording session>>). |
| 6741 | ==== |
| 6742 | [role="term"] |
| 6743 | ---- |
| 6744 | # lttng disable-channel --kernel my-channel |
| 6745 | ---- |
| 6746 | ==== |
| 6747 | |
| 6748 | An enabled channel is an implicit <<event,recording event rule>> |
| 6749 | condition. |
| 6750 | |
| 6751 | NOTE: As of LTTng{nbsp}{revision}, you may _not_ enable a disabled |
| 6752 | channel once its recording session has been |
| 6753 | <<basic-tracing-session-control,started>> at least once. |
| 6754 | |
| 6755 | |
| 6756 | [[adding-context]] |
| 6757 | === Add context fields to be recorded to the event records of a channel |
| 6758 | |
| 6759 | <<event,Event record>> fields in trace files provide important |
| 6760 | information about previously emitted events, but sometimes some external |
| 6761 | context may help you solve a problem faster. |
| 6762 | |
| 6763 | Examples of context fields are: |
| 6764 | |
| 6765 | * The **process ID**, **thread ID**, **process name**, and |
| 6766 | **process priority** of the thread from which LTTng emits the event. |
| 6767 | |
| 6768 | * The **hostname** of the system on which LTTng emits the event. |
| 6769 | |
| 6770 | * The Linux kernel and user call stacks (since LTTng{nbsp}2.11). |
| 6771 | |
| 6772 | * The current values of many possible **performance counters** using |
| 6773 | perf, for example: |
| 6774 | |
| 6775 | ** CPU cycles, stalled cycles, idle cycles, and the other cycle types. |
| 6776 | ** Cache misses. |
| 6777 | ** Branch instructions, misses, and loads. |
| 6778 | ** CPU faults. |
| 6779 | |
| 6780 | * Any state defined at the application level (supported for the |
| 6781 | `java.util.logging` and Apache log4j <<domain,tracing domains>>). |
| 6782 | |
| 6783 | To get the full list of available context fields: |
| 6784 | |
| 6785 | * Use the opt:lttng-add-context(1):--list option of the |
| 6786 | man:lttng-add-context(1) command: |
| 6787 | + |
| 6788 | [role="term"] |
| 6789 | ---- |
| 6790 | $ lttng add-context --list |
| 6791 | ---- |
| 6792 | |
| 6793 | .Add context fields to be recorded to the event records of all the <<channel,channels>> of the <<cur-tracing-session,current recording session>>. |
| 6794 | ==== |
| 6795 | The following command line adds the virtual process identifier and the |
| 6796 | per-thread CPU cycles count fields to all the user space channels of the |
| 6797 | current recording session. |
| 6798 | |
| 6799 | [role="term"] |
| 6800 | ---- |
| 6801 | $ lttng add-context --userspace --type=vpid --type=perf:thread:cpu-cycles |
| 6802 | ---- |
| 6803 | ==== |
| 6804 | |
| 6805 | .Add performance counter context fields by raw ID |
| 6806 | ==== |
| 6807 | See man:lttng-add-context(1) for the exact format of the context field |
| 6808 | type, which is partly compatible with the format used in |
| 6809 | man:perf-record(1). |
| 6810 | |
| 6811 | [role="term"] |
| 6812 | ---- |
| 6813 | # lttng add-context --userspace --type=perf:thread:raw:r0110:test |
| 6814 | # lttng add-context --kernel --type=perf:cpu:raw:r0013c:x86unhalted |
| 6815 | ---- |
| 6816 | ==== |
| 6817 | |
| 6818 | .Add context fields to be recorded to the event records of a specific channel. |
| 6819 | ==== |
| 6820 | The following command line adds the thread identifier and user call |
| 6821 | stack context fields to the Linux kernel channel named `my-channel` of |
| 6822 | the <<cur-tracing-session,current recording session>>. |
| 6823 | |
| 6824 | [role="term"] |
| 6825 | ---- |
| 6826 | # lttng add-context --kernel --channel=my-channel \ |
| 6827 | --type=tid --type=callstack-user |
| 6828 | ---- |
| 6829 | ==== |
| 6830 | |
| 6831 | .Add an <<java-application-context,application-specific context field>> to be recorded to the event records of a specific channel. |
| 6832 | ==== |
| 6833 | The following command line makes sure LTTng writes the `cur_msg_id` |
| 6834 | context field of the `retriever` context retriever to all the Java |
| 6835 | logging <<event,event records>> of the channel named `my-channel`: |
| 6836 | |
| 6837 | [role="term"] |
| 6838 | ---- |
| 6839 | # lttng add-context --kernel --channel=my-channel \ |
| 6840 | --type='$app:retriever:cur_msg_id' |
| 6841 | ---- |
| 6842 | |
| 6843 | IMPORTANT: Make sure to always single-quote the `$` character when you |
| 6844 | run man:lttng-add-context(1) from a shell. |
| 6845 | ==== |
| 6846 | |
| 6847 | NOTE: You can't undo what the man:lttng-add-context(1) command does. |
| 6848 | |
| 6849 | |
| 6850 | [role="since-2.7"] |
| 6851 | [[pid-tracking]] |
| 6852 | === Allow specific processes to record events |
| 6853 | |
| 6854 | It's often useful to only allow processes with specific attributes to |
| 6855 | record events. For example, you may wish to record all the system calls |
| 6856 | which a given process makes (à la man:strace(1)). |
| 6857 | |
| 6858 | The man:lttng-track(1) and man:lttng-untrack(1) commands serve this |
| 6859 | purpose. Both commands operate on _inclusion sets_ of process |
| 6860 | attributes. The available process attribute types are: |
| 6861 | |
| 6862 | Linux kernel <<domain,tracing domain>>:: |
| 6863 | + |
| 6864 | * Process ID (PID). |
| 6865 | |
| 6866 | * Virtual process ID (VPID). |
| 6867 | + |
| 6868 | This is the PID as seen by the application. |
| 6869 | |
| 6870 | * Unix user ID (UID). |
| 6871 | |
| 6872 | * Virtual Unix user ID (VUID). |
| 6873 | + |
| 6874 | This is the UID as seen by the application. |
| 6875 | |
| 6876 | * Unix group ID (GID). |
| 6877 | |
| 6878 | * Virtual Unix group ID (VGID). |
| 6879 | + |
| 6880 | This is the GID as seen by the application. |
| 6881 | |
| 6882 | User space tracing domain:: |
| 6883 | + |
| 6884 | * VPID |
| 6885 | * VUID |
| 6886 | * VGID |
| 6887 | |
| 6888 | A <<tracing-session,recording session>> has nine process |
| 6889 | attribute inclusion sets: six for the Linux kernel <<domain,tracing domain>> |
| 6890 | and three for the user space tracing domain. |
| 6891 | |
| 6892 | For a given recording session, a process{nbsp}__P__ is allowed to record |
| 6893 | LTTng events for a given <<domain,tracing domain>>{nbsp}__D__ if _all_ |
| 6894 | the attributes of{nbsp}__P__ are part of the inclusion sets |
| 6895 | of{nbsp}__D__. |
| 6896 | |
| 6897 | Whether a process is allowed or not to record LTTng events is an |
| 6898 | implicit condition of all <<event,recording event rules>>. Therefore, if |
| 6899 | LTTng creates an event{nbsp}__E__ for a given process, but this process |
| 6900 | may not record events, then no recording event rule matches{nbsp}__E__, |
| 6901 | which means LTTng won't emit and record{nbsp}__E__. |
| 6902 | |
| 6903 | When you <<creating-destroying-tracing-sessions,create a recording |
| 6904 | session>>, all its process attribute inclusion sets contain all the |
| 6905 | possible values. In other words, all processes are allowed to record |
| 6906 | events. |
| 6907 | |
| 6908 | Add values to an inclusion set with the man:lttng-track(1) command and |
| 6909 | remove values with the man:lttng-untrack(1) command. |
| 6910 | |
| 6911 | [NOTE] |
| 6912 | ==== |
| 6913 | The process attribute values are _numeric_. |
| 6914 | |
| 6915 | Should a process with a given ID (part of an inclusion set), for |
| 6916 | example, exit, and then a new process be given this same ID, then the |
| 6917 | latter would also be allowed to record events. |
| 6918 | |
| 6919 | With the man:lttng-track(1) command, you can add Unix user and group |
| 6920 | _names_ to the user and group inclusion sets: the |
| 6921 | <<lttng-sessiond,session daemon>> finds the corresponding UID, VUID, |
| 6922 | GID, or VGID once on _addition_ to the inclusion set. This means that if |
| 6923 | you rename the user or group after you run the man:lttng-track(1) |
| 6924 | command, its user/group ID remains part of the inclusion sets. |
| 6925 | ==== |
| 6926 | |
| 6927 | .Allow processes to record events based on their virtual process ID (VPID). |
| 6928 | ==== |
| 6929 | For the sake of the following example, assume the target system has |
| 6930 | 16{nbsp}possible VPIDs. |
| 6931 | |
| 6932 | When you |
| 6933 | <<creating-destroying-tracing-sessions,create a recording session>>, |
| 6934 | the user space VPID inclusion set contains _all_ the possible VPIDs: |
| 6935 | |
| 6936 | [role="img-100"] |
| 6937 | .The VPID inclusion set is full. |
| 6938 | image::track-all.png[] |
| 6939 | |
| 6940 | When the inclusion set is full and you run the man:lttng-track(1) |
| 6941 | command to specify some VPIDs, LTTng: |
| 6942 | |
| 6943 | . Clears the inclusion set. |
| 6944 | . Adds the specific VPIDs to the inclusion set. |
| 6945 | |
| 6946 | After: |
| 6947 | |
| 6948 | [role="term"] |
| 6949 | ---- |
| 6950 | $ lttng track --userspace --vpid=3,4,7,10,13 |
| 6951 | ---- |
| 6952 | |
| 6953 | the VPID inclusion set is: |
| 6954 | |
| 6955 | [role="img-100"] |
| 6956 | .The VPID inclusion set contains the VPIDs 3, 4, 7, 10, and 13. |
| 6957 | image::track-3-4-7-10-13.png[] |
| 6958 | |
| 6959 | Add more VPIDs to the inclusion set afterwards: |
| 6960 | |
| 6961 | [role="term"] |
| 6962 | ---- |
| 6963 | $ lttng track --userspace --vpid=1,15,16 |
| 6964 | ---- |
| 6965 | |
| 6966 | The result is: |
| 6967 | |
| 6968 | [role="img-100"] |
| 6969 | .VPIDs 1, 15, and 16 are added to the inclusion set. |
| 6970 | image::track-1-3-4-7-10-13-15-16.png[] |
| 6971 | |
| 6972 | The man:lttng-untrack(1) command removes entries from process attribute |
| 6973 | inclusion sets. Given the previous example, the following command: |
| 6974 | |
| 6975 | [role="term"] |
| 6976 | ---- |
| 6977 | $ lttng untrack --userspace --vpid=3,7,10,13 |
| 6978 | ---- |
| 6979 | |
| 6980 | leads to this VPID inclusion set: |
| 6981 | |
| 6982 | [role="img-100"] |
| 6983 | .VPIDs 3, 7, 10, and 13 are removed from the inclusion set. |
| 6984 | image::track-1-4-15-16.png[] |
| 6985 | |
| 6986 | You can make the VPID inclusion set full again with the |
| 6987 | opt:lttng-track(1):--all option: |
| 6988 | |
| 6989 | [role="term"] |
| 6990 | ---- |
| 6991 | $ lttng track --userspace --vpid --all |
| 6992 | ---- |
| 6993 | |
| 6994 | The result is, again: |
| 6995 | |
| 6996 | [role="img-100"] |
| 6997 | .The VPID inclusion set is full. |
| 6998 | image::track-all.png[] |
| 6999 | ==== |
| 7000 | |
| 7001 | .Allow specific processes to record events based on their user ID (UID). |
| 7002 | ==== |
| 7003 | A typical use case with process attribute inclusion sets is to start |
| 7004 | with an empty inclusion set, then <<basic-tracing-session-control,start |
| 7005 | the tracers>>, and finally add values manually while the tracers are |
| 7006 | active. |
| 7007 | |
| 7008 | Use the opt:lttng-untrack(1):--all option of the |
| 7009 | man:lttng-untrack(1) command to clear the inclusion set after you |
| 7010 | <<creating-destroying-tracing-sessions,create a recording session>>, for |
| 7011 | example (with UIDs): |
| 7012 | |
| 7013 | [role="term"] |
| 7014 | ---- |
| 7015 | # lttng untrack --kernel --uid --all |
| 7016 | ---- |
| 7017 | |
| 7018 | gives: |
| 7019 | |
| 7020 | [role="img-100"] |
| 7021 | .The UID inclusion set is empty. |
| 7022 | image::untrack-all.png[] |
| 7023 | |
| 7024 | If the LTTng tracer runs with this inclusion set configuration, it |
| 7025 | records no events within the <<cur-tracing-session,current recording |
| 7026 | session>> because no processes is allowed to do so. Use the |
| 7027 | man:lttng-track(1) command as usual to add specific values to the UID |
| 7028 | inclusion set when you need to, for example: |
| 7029 | |
| 7030 | [role="term"] |
| 7031 | ---- |
| 7032 | # lttng track --kernel --uid=http,11 |
| 7033 | ---- |
| 7034 | |
| 7035 | Result: |
| 7036 | |
| 7037 | [role="img-100"] |
| 7038 | .UIDs 6 (`http`) and 11 are part of the UID inclusion set. |
| 7039 | image::track-6-11.png[] |
| 7040 | ==== |
| 7041 | |
| 7042 | |
| 7043 | [role="since-2.5"] |
| 7044 | [[saving-loading-tracing-session]] |
| 7045 | === Save and load recording session configurations |
| 7046 | |
| 7047 | Configuring a <<tracing-session,recording session>> can be long. Some of |
| 7048 | the tasks involved are: |
| 7049 | |
| 7050 | * <<enabling-disabling-channels,Create channels>> with |
| 7051 | specific attributes. |
| 7052 | |
| 7053 | * <<adding-context,Add context fields>> to be recorded to the |
| 7054 | <<event,event records>> of specific channels. |
| 7055 | |
| 7056 | * <<enabling-disabling-events,Create recording event rules>> with |
| 7057 | specific log level, filter, and other conditions. |
| 7058 | |
| 7059 | If you use LTTng to solve real world problems, chances are you have to |
| 7060 | record events using the same recording session setup over and over, |
| 7061 | modifying a few variables each time in your instrumented program or |
| 7062 | environment. |
| 7063 | |
| 7064 | To avoid constant recording session reconfiguration, the man:lttng(1) |
| 7065 | command-line tool can save and load recording session configurations |
| 7066 | to/from XML files. |
| 7067 | |
| 7068 | To save a given recording session configuration: |
| 7069 | |
| 7070 | * Use the man:lttng-save(1) command: |
| 7071 | + |
| 7072 | -- |
| 7073 | [role="term"] |
| 7074 | ---- |
| 7075 | $ lttng save SESSION |
| 7076 | ---- |
| 7077 | -- |
| 7078 | + |
| 7079 | Replace +__SESSION__+ with the name of the recording session to save. |
| 7080 | |
| 7081 | LTTng saves recording session configurations to |
| 7082 | dir:{$LTTNG_HOME/.lttng/sessions} by default. Note that the |
| 7083 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. See |
| 7084 | man:lttng-save(1) to learn more about the recording session configuration |
| 7085 | output path. |
| 7086 | |
| 7087 | LTTng saves all configuration parameters, for example: |
| 7088 | |
| 7089 | * The recording session name. |
| 7090 | * The trace data output path. |
| 7091 | * The <<channel,channels>>, with their state and all their attributes. |
| 7092 | * The context fields you added to channels. |
| 7093 | * The <<event,recording event rules>> with their state and conditions. |
| 7094 | |
| 7095 | To load a recording session: |
| 7096 | |
| 7097 | * Use the man:lttng-load(1) command: |
| 7098 | + |
| 7099 | -- |
| 7100 | [role="term"] |
| 7101 | ---- |
| 7102 | $ lttng load SESSION |
| 7103 | ---- |
| 7104 | -- |
| 7105 | + |
| 7106 | Replace +__SESSION__+ with the name of the recording session to load. |
| 7107 | |
| 7108 | When LTTng loads a configuration, it restores your saved recording session |
| 7109 | as if you just configured it manually. |
| 7110 | |
| 7111 | You can also save and load many sessions at a time; see |
| 7112 | man:lttng-save(1) and man:lttng-load(1) to learn more. |
| 7113 | |
| 7114 | |
| 7115 | [[sending-trace-data-over-the-network]] |
| 7116 | === Send trace data over the network |
| 7117 | |
| 7118 | LTTng can send the recorded trace data of a <<tracing-session,recording |
| 7119 | session>> to a remote system over the network instead of writing it to |
| 7120 | the local file system. |
| 7121 | |
| 7122 | To send the trace data over the network: |
| 7123 | |
| 7124 | . On the _remote_ system (which can also be the target system), |
| 7125 | start an LTTng <<lttng-relayd,relay daemon>> (man:lttng-relayd(8)): |
| 7126 | + |
| 7127 | -- |
| 7128 | [role="term"] |
| 7129 | ---- |
| 7130 | $ lttng-relayd |
| 7131 | ---- |
| 7132 | -- |
| 7133 | |
| 7134 | . On the _target_ system, create a recording session |
| 7135 | <<net-streaming-mode,configured>> to send trace data over the network: |
| 7136 | + |
| 7137 | -- |
| 7138 | [role="term"] |
| 7139 | ---- |
| 7140 | $ lttng create my-session --set-url=net://remote-system |
| 7141 | ---- |
| 7142 | -- |
| 7143 | + |
| 7144 | Replace +__remote-system__+ with the host name or IP address of the |
| 7145 | remote system. See man:lttng-create(1) for the exact URL format. |
| 7146 | |
| 7147 | . On the target system, use the man:lttng(1) command-line tool as usual. |
| 7148 | + |
| 7149 | When recording is <<basic-tracing-session-control,active>>, the |
| 7150 | <<lttng-consumerd,consumer daemon>> of the target sends the contents of |
| 7151 | <<channel,sub-buffers>> to the remote relay daemon instead of flushing |
| 7152 | them to the local file system. The relay daemon writes the received |
| 7153 | packets to its local file system. |
| 7154 | |
| 7155 | See the ``Output directory'' section of man:lttng-relayd(8) to learn |
| 7156 | where a relay daemon writes its received trace data. |
| 7157 | |
| 7158 | |
| 7159 | [role="since-2.4"] |
| 7160 | [[lttng-live]] |
| 7161 | === View events as LTTng records them (noch:{LTTng} live) |
| 7162 | |
| 7163 | _LTTng live_ is a network protocol implemented by the |
| 7164 | <<lttng-relayd,relay daemon>> (man:lttng-relayd(8)) to allow compatible |
| 7165 | trace readers to display or analyze <<event,event records>> as LTTng |
| 7166 | records events on the target system while recording is |
| 7167 | <<basic-tracing-session-control,active>>. |
| 7168 | |
| 7169 | The relay daemon creates a _tee_: it forwards the trace data to both the |
| 7170 | local file system and to connected live readers: |
| 7171 | |
| 7172 | [role="img-90"] |
| 7173 | .The relay daemon creates a _tee_, forwarding the trace data to both trace files and a connected live reader. |
| 7174 | image::live.png[] |
| 7175 | |
| 7176 | To use LTTng live: |
| 7177 | |
| 7178 | . On the _target system_, create a <<tracing-session,recording session>> |
| 7179 | in _live mode_: |
| 7180 | + |
| 7181 | -- |
| 7182 | [role="term"] |
| 7183 | ---- |
| 7184 | $ lttng create my-session --live |
| 7185 | ---- |
| 7186 | -- |
| 7187 | + |
| 7188 | This operation spawns a local relay daemon. |
| 7189 | |
| 7190 | . Start the live reader and configure it to connect to the relay daemon. |
| 7191 | + |
| 7192 | For example, with man:babeltrace2(1): |
| 7193 | + |
| 7194 | -- |
| 7195 | [role="term"] |
| 7196 | ---- |
| 7197 | $ babeltrace2 net://localhost/host/HOSTNAME/my-session |
| 7198 | ---- |
| 7199 | -- |
| 7200 | + |
| 7201 | Replace +__HOSTNAME__+ with the host name of the target system. |
| 7202 | |
| 7203 | . Configure the recording session as usual with the man:lttng(1) |
| 7204 | command-line tool, and <<basic-tracing-session-control,start recording>>. |
| 7205 | |
| 7206 | List the available live recording sessions with man:babeltrace2(1): |
| 7207 | |
| 7208 | [role="term"] |
| 7209 | ---- |
| 7210 | $ babeltrace2 net://localhost |
| 7211 | ---- |
| 7212 | |
| 7213 | You can start the relay daemon on another system. In this case, you need |
| 7214 | to specify the URL of the relay daemon when you |
| 7215 | <<creating-destroying-tracing-sessions,create the recording session>> with |
| 7216 | the opt:lttng-create(1):--set-url option of the man:lttng-create(1) |
| 7217 | command. You also need to replace +__localhost__+ in the procedure above |
| 7218 | with the host name of the system on which the relay daemon runs. |
| 7219 | |
| 7220 | |
| 7221 | [role="since-2.3"] |
| 7222 | [[taking-a-snapshot]] |
| 7223 | === Take a snapshot of the current sub-buffers of a recording session |
| 7224 | |
| 7225 | The normal behavior of LTTng is to append full sub-buffers to growing |
| 7226 | trace data files. This is ideal to keep a full history of the events |
| 7227 | which the target system emitted, but it can represent too much data in |
| 7228 | some situations. |
| 7229 | |
| 7230 | For example, you may wish to have LTTng record your application |
| 7231 | continuously until some critical situation happens, in which case you |
| 7232 | only need the latest few recorded events to perform the desired |
| 7233 | analysis, not multi-gigabyte trace files. |
| 7234 | |
| 7235 | With the man:lttng-snapshot(1) command, you can take a _snapshot_ of the |
| 7236 | current <<channel,sub-buffers>> of a given <<tracing-session,recording |
| 7237 | session>>. LTTng can write the snapshot to the local file system or send |
| 7238 | it over the network. |
| 7239 | |
| 7240 | [role="img-100"] |
| 7241 | .A snapshot is a copy of the current sub-buffers, which LTTng does _not_ clear after the operation. |
| 7242 | image::snapshot.png[] |
| 7243 | |
| 7244 | The snapshot feature of LTTng is similar to how a |
| 7245 | https://en.wikipedia.org/wiki/Flight_recorder[flight recorder] or the |
| 7246 | ``roll'' mode of an oscilloscope work. |
| 7247 | |
| 7248 | TIP: If you wish to create unmanaged, self-contained, non-overlapping |
| 7249 | trace chunk archives instead of a simple copy of the current |
| 7250 | sub-buffers, see the <<session-rotation,recording session rotation>> |
| 7251 | feature (available since LTTng{nbsp}2.11). |
| 7252 | |
| 7253 | To take a snapshot of the <<cur-tracing-session,current recording |
| 7254 | session>>: |
| 7255 | |
| 7256 | . Create a recording session in <<snapshot-mode,snapshot mode>>: |
| 7257 | + |
| 7258 | -- |
| 7259 | [role="term"] |
| 7260 | ---- |
| 7261 | $ lttng create my-session --snapshot |
| 7262 | ---- |
| 7263 | -- |
| 7264 | + |
| 7265 | The <<channel-overwrite-mode-vs-discard-mode,event record loss mode>> of |
| 7266 | <<channel,channels>> created in this mode is automatically set to |
| 7267 | <<overwrite-mode,_overwrite_>>. |
| 7268 | |
| 7269 | . Configure the recording session as usual with the man:lttng(1) |
| 7270 | command-line tool, and <<basic-tracing-session-control,start |
| 7271 | recording>>. |
| 7272 | |
| 7273 | . **Optional**: When you need to take a snapshot, |
| 7274 | <<basic-tracing-session-control,stop recording>>. |
| 7275 | + |
| 7276 | You can take a snapshot when the tracers are active, but if you stop |
| 7277 | them first, you're guaranteed that the trace data in the sub-buffers |
| 7278 | doesn't change before you actually take the snapshot. |
| 7279 | |
| 7280 | . Take a snapshot: |
| 7281 | + |
| 7282 | -- |
| 7283 | [role="term"] |
| 7284 | ---- |
| 7285 | $ lttng snapshot record --name=my-first-snapshot |
| 7286 | ---- |
| 7287 | -- |
| 7288 | + |
| 7289 | LTTng writes the current sub-buffers of all the channels of the |
| 7290 | <<cur-tracing-session,current recording session>> to |
| 7291 | trace files on the local file system. Those trace files have |
| 7292 | `my-first-snapshot` in their name. |
| 7293 | |
| 7294 | There's no difference between the format of a normal trace file and the |
| 7295 | format of a snapshot: LTTng trace readers also support LTTng snapshots. |
| 7296 | |
| 7297 | By default, LTTng writes snapshot files to the path shown by |
| 7298 | |
| 7299 | [role="term"] |
| 7300 | ---- |
| 7301 | $ lttng snapshot list-output |
| 7302 | ---- |
| 7303 | |
| 7304 | You can change this path or decide to send snapshots over the network |
| 7305 | using either: |
| 7306 | |
| 7307 | . An output path or URL that you specify when you |
| 7308 | <<creating-destroying-tracing-sessions,create the recording session>>. |
| 7309 | |
| 7310 | . A snapshot output path or URL that you add using the |
| 7311 | `add-output` action of the man:lttng-snapshot(1) command. |
| 7312 | |
| 7313 | . An output path or URL that you provide directly to the |
| 7314 | `record` action of the man:lttng-snapshot(1) command. |
| 7315 | |
| 7316 | Method{nbsp}3 overrides method{nbsp}2, which overrides method 1. When |
| 7317 | you specify a URL, a <<lttng-relayd,relay daemon>> must listen on a |
| 7318 | remote system (see ``<<sending-trace-data-over-the-network,Send trace |
| 7319 | data over the network>>''). |
| 7320 | |
| 7321 | The `snapshot-session` <<trigger,trigger>> action can also take |
| 7322 | a recording session snapshot. |
| 7323 | |
| 7324 | |
| 7325 | [role="since-2.11"] |
| 7326 | [[session-rotation]] |
| 7327 | === Archive the current trace chunk (rotate a recording session) |
| 7328 | |
| 7329 | The <<taking-a-snapshot,snapshot user guide>> shows how to dump the |
| 7330 | current sub-buffers of a recording session to the file system or send them |
| 7331 | over the network. When you take a snapshot, LTTng doesn't clear the ring |
| 7332 | buffers of the recording session: if you take another snapshot immediately |
| 7333 | after, both snapshots could contain overlapping trace data. |
| 7334 | |
| 7335 | Inspired by https://en.wikipedia.org/wiki/Log_rotation[log rotation], |
| 7336 | _recording session rotation_ is a feature which appends the content of the |
| 7337 | ring buffers to what's already on the file system or sent over the |
| 7338 | network since the creation of the recording session or since the last |
| 7339 | rotation, and then clears those ring buffers to avoid trace data |
| 7340 | overlaps. |
| 7341 | |
| 7342 | What LTTng is about to write when performing a recording session rotation |
| 7343 | is called the _current trace chunk_. When LTTng writes or sends over the |
| 7344 | network this current trace chunk, it becomes a _trace chunk archive_. |
| 7345 | Therefore, a recording session rotation operation _archives_ the current |
| 7346 | trace chunk. |
| 7347 | |
| 7348 | [role="img-100"] |
| 7349 | .A recording session rotation operation _archives_ the current trace chunk. |
| 7350 | image::rotation.png[] |
| 7351 | |
| 7352 | A trace chunk archive is a self-contained LTTng trace which LTTng |
| 7353 | doesn't manage anymore: you can read it, modify it, move it, or remove |
| 7354 | it. |
| 7355 | |
| 7356 | As of LTTng{nbsp}{revision}, there are three methods to perform a |
| 7357 | recording session rotation: |
| 7358 | |
| 7359 | * <<immediate-rotation,Immediately>>. |
| 7360 | |
| 7361 | * With a <<rotation-schedule,rotation schedule>>. |
| 7362 | |
| 7363 | * Through the execution of a `rotate-session` <<trigger,trigger>> |
| 7364 | action. |
| 7365 | |
| 7366 | [[immediate-rotation]]To perform an immediate rotation of the |
| 7367 | <<cur-tracing-session,current recording session>>: |
| 7368 | |
| 7369 | . <<creating-destroying-tracing-sessions,Create a recording session>> in |
| 7370 | <<local-mode,local mode>> or <<net-streaming-mode,network streaming |
| 7371 | mode>> (only those two recording session modes support recording session |
| 7372 | rotation): |
| 7373 | + |
| 7374 | -- |
| 7375 | [role="term"] |
| 7376 | ---- |
| 7377 | # lttng create my-session |
| 7378 | ---- |
| 7379 | -- |
| 7380 | |
| 7381 | . <<enabling-disabling-events,Create one or more recording event rules>> |
| 7382 | and <<basic-tracing-session-control,start recording>>: |
| 7383 | + |
| 7384 | -- |
| 7385 | [role="term"] |
| 7386 | ---- |
| 7387 | # lttng enable-event --kernel sched_'*' |
| 7388 | # lttng start |
| 7389 | ---- |
| 7390 | -- |
| 7391 | |
| 7392 | . When needed, immediately rotate the current recording session: |
| 7393 | + |
| 7394 | -- |
| 7395 | [role="term"] |
| 7396 | ---- |
| 7397 | # lttng rotate |
| 7398 | ---- |
| 7399 | -- |
| 7400 | + |
| 7401 | The man:lttng-rotate(1) command prints the path to the created trace |
| 7402 | chunk archive. See its manual page to learn about the format of trace |
| 7403 | chunk archive directory names. |
| 7404 | + |
| 7405 | Perform other immediate rotations while the recording session is active. |
| 7406 | It's guaranteed that all the trace chunk archives don't contain |
| 7407 | overlapping trace data. You can also perform an immediate rotation once |
| 7408 | you have <<basic-tracing-session-control,stopped>> the recording session. |
| 7409 | |
| 7410 | . When you're done recording, |
| 7411 | <<creating-destroying-tracing-sessions,destroy the current recording |
| 7412 | session>>: |
| 7413 | + |
| 7414 | -- |
| 7415 | [role="term"] |
| 7416 | ---- |
| 7417 | # lttng destroy |
| 7418 | ---- |
| 7419 | -- |
| 7420 | + |
| 7421 | The recording session destruction operation creates one last trace chunk |
| 7422 | archive from the current trace chunk. |
| 7423 | |
| 7424 | [[rotation-schedule]]A recording session rotation schedule is a planned |
| 7425 | rotation which LTTng performs automatically based on one of the |
| 7426 | following conditions: |
| 7427 | |
| 7428 | * A timer with a configured period expires. |
| 7429 | |
| 7430 | * The total size of the _flushed_ part of the current trace chunk |
| 7431 | becomes greater than or equal to a configured value. |
| 7432 | |
| 7433 | To schedule a rotation of the <<cur-tracing-session,current recording |
| 7434 | session>>, set a _rotation schedule_: |
| 7435 | |
| 7436 | . <<creating-destroying-tracing-sessions,Create a recording session>> in |
| 7437 | <<local-mode,local mode>> or <<net-streaming-mode,network streaming |
| 7438 | mode>> (only those two creation modes support recording session |
| 7439 | rotation): |
| 7440 | + |
| 7441 | -- |
| 7442 | [role="term"] |
| 7443 | ---- |
| 7444 | # lttng create my-session |
| 7445 | ---- |
| 7446 | -- |
| 7447 | |
| 7448 | . <<enabling-disabling-events,Create one or more recording event rules>>: |
| 7449 | + |
| 7450 | -- |
| 7451 | [role="term"] |
| 7452 | ---- |
| 7453 | # lttng enable-event --kernel sched_'*' |
| 7454 | ---- |
| 7455 | -- |
| 7456 | |
| 7457 | . Set a recording session rotation schedule: |
| 7458 | + |
| 7459 | -- |
| 7460 | [role="term"] |
| 7461 | ---- |
| 7462 | # lttng enable-rotation --timer=10s |
| 7463 | ---- |
| 7464 | -- |
| 7465 | + |
| 7466 | In this example, we set a rotation schedule so that LTTng performs a |
| 7467 | recording session rotation every ten seconds. |
| 7468 | + |
| 7469 | See man:lttng-enable-rotation(1) to learn more about other ways to set a |
| 7470 | rotation schedule. |
| 7471 | |
| 7472 | . <<basic-tracing-session-control,Start recording>>: |
| 7473 | + |
| 7474 | -- |
| 7475 | [role="term"] |
| 7476 | ---- |
| 7477 | # lttng start |
| 7478 | ---- |
| 7479 | -- |
| 7480 | + |
| 7481 | LTTng performs recording session rotations automatically while the |
| 7482 | recording session is active thanks to the rotation schedule. |
| 7483 | |
| 7484 | . When you're done recording, |
| 7485 | <<creating-destroying-tracing-sessions,destroy the current recording |
| 7486 | session>>: |
| 7487 | + |
| 7488 | -- |
| 7489 | [role="term"] |
| 7490 | ---- |
| 7491 | # lttng destroy |
| 7492 | ---- |
| 7493 | -- |
| 7494 | + |
| 7495 | The recording session destruction operation creates one last trace chunk |
| 7496 | archive from the current trace chunk. |
| 7497 | |
| 7498 | Unset a recording session rotation schedule with the |
| 7499 | man:lttng-disable-rotation(1) command. |
| 7500 | |
| 7501 | |
| 7502 | [role="since-2.13"] |
| 7503 | [[add-event-rule-matches-trigger]] |
| 7504 | === Add an ``event rule matches'' trigger to a session daemon |
| 7505 | |
| 7506 | With the man:lttng-add-trigger(1) command, you can add a |
| 7507 | <<trigger,trigger>> to a <<lttng-sessiond,session daemon>>. |
| 7508 | |
| 7509 | A trigger associates an LTTng tracing condition to one or more actions: |
| 7510 | when the condition is satisfied, LTTng attempts to execute the actions. |
| 7511 | |
| 7512 | A trigger doesn't need any <<tracing-session,recording session>> to exist: |
| 7513 | it belongs to a session daemon. |
| 7514 | |
| 7515 | As of LTTng{nbsp}{revision}, many condition types are available through |
| 7516 | the <<liblttng-ctl-lttng,`liblttng-ctl`>> C{nbsp}API, but the |
| 7517 | man:lttng-add-trigger(1) command only accepts the ``event rule matches'' |
| 7518 | condition. |
| 7519 | |
| 7520 | An ``event rule matches'' condition is satisfied when its event rule |
| 7521 | matches an event. |
| 7522 | |
| 7523 | Unlike a <<event,recording event rule>>, the event rule of an |
| 7524 | ``event rule matches'' trigger condition has no implicit conditions, |
| 7525 | that is: |
| 7526 | |
| 7527 | * It has no enabled/disabled state. |
| 7528 | * It has no attached <<channel,channel>>. |
| 7529 | * It doesn't belong to a <<tracing-session,recording session>>. |
| 7530 | |
| 7531 | Both the man:lttng-add-trigger(1) and man:lttng-enable-event(1) commands |
| 7532 | accept command-line arguments to specify an <<event-rule,event rule>>. |
| 7533 | That being said, the former is a more recent command and therefore |
| 7534 | follows the common event rule specification format (see |
| 7535 | man:lttng-event-rule(7)). |
| 7536 | |
| 7537 | .Start a <<tracing-session,recording session>> when an event rule matches. |
| 7538 | ==== |
| 7539 | This example shows how to add the following trigger to the root |
| 7540 | <<lttng-sessiond,session daemon>>: |
| 7541 | |
| 7542 | Condition:: |
| 7543 | An event rule matches a Linux kernel system call event of which the |
| 7544 | name starts with `exec` and `*/ls` matches the `filename` payload |
| 7545 | field. |
| 7546 | + |
| 7547 | With such an event rule, LTTng emits an event when the cmd:ls program |
| 7548 | starts. |
| 7549 | |
| 7550 | Action:: |
| 7551 | <<basic-tracing-session-control,Start the recording session>> |
| 7552 | named `pitou`. |
| 7553 | |
| 7554 | To add such a trigger to the root session daemon: |
| 7555 | |
| 7556 | . **If there's no currently running LTTng root session daemon**, start |
| 7557 | one: |
| 7558 | + |
| 7559 | [role="term"] |
| 7560 | ---- |
| 7561 | # lttng-sessiond --daemonize |
| 7562 | ---- |
| 7563 | |
| 7564 | . <<creating-destroying-tracing-sessions,Create a recording session>> |
| 7565 | named `pitou` and |
| 7566 | <<enabling-disabling-events,create a recording event rule>> matching |
| 7567 | all the system call events: |
| 7568 | + |
| 7569 | [role="term"] |
| 7570 | ---- |
| 7571 | # lttng create pitou |
| 7572 | # lttng enable-event --kernel --syscall --all |
| 7573 | ---- |
| 7574 | |
| 7575 | . Add the trigger to the root session daemon: |
| 7576 | + |
| 7577 | [role="term"] |
| 7578 | ---- |
| 7579 | # lttng add-trigger --condition=event-rule-matches \ |
| 7580 | --type=syscall --name='exec*' \ |
| 7581 | --filter='filename == "*/ls"' \ |
| 7582 | --action=start-session pitou |
| 7583 | ---- |
| 7584 | + |
| 7585 | Confirm that the trigger exists with the man:lttng-list-triggers(1) |
| 7586 | command: |
| 7587 | + |
| 7588 | [role="term"] |
| 7589 | ---- |
| 7590 | # lttng list-triggers |
| 7591 | ---- |
| 7592 | |
| 7593 | . Make sure the `pitou` recording session is still inactive (stopped): |
| 7594 | + |
| 7595 | [role="term"] |
| 7596 | ---- |
| 7597 | # lttng list pitou |
| 7598 | ---- |
| 7599 | + |
| 7600 | The first line should be something like: |
| 7601 | + |
| 7602 | ---- |
| 7603 | Recording session pitou: [inactive] |
| 7604 | ---- |
| 7605 | |
| 7606 | Run the cmd:ls program to fire the LTTng trigger above: |
| 7607 | |
| 7608 | [role="term"] |
| 7609 | ---- |
| 7610 | $ ls ~ |
| 7611 | ---- |
| 7612 | |
| 7613 | At this point, the `pitou` recording session should be active |
| 7614 | (started). Confirm this with the man:lttng-list(1) command again: |
| 7615 | |
| 7616 | [role="term"] |
| 7617 | ---- |
| 7618 | # lttng list pitou |
| 7619 | ---- |
| 7620 | |
| 7621 | The first line should now look like: |
| 7622 | |
| 7623 | ---- |
| 7624 | Recording session pitou: [active] |
| 7625 | ---- |
| 7626 | |
| 7627 | This line confirms that the LTTng trigger you added fired, therefore |
| 7628 | starting the `pitou` recording session. |
| 7629 | ==== |
| 7630 | |
| 7631 | .[[trigger-event-notif]]Send a notification to a user application when an event rule matches. |
| 7632 | ==== |
| 7633 | This example shows how to add the following trigger to the root |
| 7634 | <<lttng-sessiond,session daemon>>: |
| 7635 | |
| 7636 | Condition:: |
| 7637 | An event rule matches a Linux kernel tracepoint event named |
| 7638 | `sched_switch` and of which the value of the `next_comm` payload |
| 7639 | field is `bash`. |
| 7640 | + |
| 7641 | With such an event rule, LTTng emits an event when Linux gives access to |
| 7642 | the processor to a process named `bash`. |
| 7643 | |
| 7644 | Action:: |
| 7645 | Send an LTTng notification to a user application. |
| 7646 | |
| 7647 | Moreover, we'll specify a _capture descriptor_ with the |
| 7648 | `event-rule-matches` trigger condition so that the user application can |
| 7649 | get the value of a specific `sched_switch` event payload field. |
| 7650 | |
| 7651 | First, write and build the user application: |
| 7652 | |
| 7653 | . Create the C{nbsp}source file of the application: |
| 7654 | + |
| 7655 | -- |
| 7656 | [source,c] |
| 7657 | .path:{notif-app.c} |
| 7658 | ---- |
| 7659 | #include <stdlib.h> |
| 7660 | #include <stdio.h> |
| 7661 | #include <stdbool.h> |
| 7662 | #include <assert.h> |
| 7663 | #include <string.h> |
| 7664 | #include <lttng/lttng.h> |
| 7665 | |
| 7666 | /* |
| 7667 | * Subscribes to notifications, through the notification channel |
| 7668 | * `notification_channel`, which match the condition of the trigger |
| 7669 | * named `trigger_name`. |
| 7670 | * |
| 7671 | * Returns `true` on success. |
| 7672 | */ |
| 7673 | static bool subscribe(struct lttng_notification_channel *notification_channel, |
| 7674 | const char *trigger_name) |
| 7675 | { |
| 7676 | const struct lttng_condition *condition = NULL; |
| 7677 | struct lttng_triggers *triggers = NULL; |
| 7678 | unsigned int trigger_count; |
| 7679 | unsigned int i; |
| 7680 | enum lttng_error_code error_code; |
| 7681 | enum lttng_trigger_status trigger_status; |
| 7682 | bool ret = false; |
| 7683 | |
| 7684 | /* Get all LTTng triggers */ |
| 7685 | error_code = lttng_list_triggers(&triggers); |
| 7686 | assert(error_code == LTTNG_OK); |
| 7687 | |
| 7688 | /* Get the number of triggers */ |
| 7689 | trigger_status = lttng_triggers_get_count(triggers, &trigger_count); |
| 7690 | assert(trigger_status == LTTNG_TRIGGER_STATUS_OK); |
| 7691 | |
| 7692 | /* Find the trigger named `trigger_name` */ |
| 7693 | for (i = 0; i < trigger_count; i++) { |
| 7694 | const struct lttng_trigger *trigger; |
| 7695 | const char *this_trigger_name; |
| 7696 | |
| 7697 | trigger = lttng_triggers_get_at_index(triggers, i); |
| 7698 | trigger_status = lttng_trigger_get_name(trigger, &this_trigger_name); |
| 7699 | assert(trigger_status == LTTNG_TRIGGER_STATUS_OK); |
| 7700 | |
| 7701 | if (strcmp(this_trigger_name, trigger_name) == 0) { |
| 7702 | /* Trigger found: subscribe with its condition */ |
| 7703 | enum lttng_notification_channel_status notification_channel_status; |
| 7704 | |
| 7705 | notification_channel_status = lttng_notification_channel_subscribe( |
| 7706 | notification_channel, |
| 7707 | lttng_trigger_get_const_condition(trigger)); |
| 7708 | assert(notification_channel_status == |
| 7709 | LTTNG_NOTIFICATION_CHANNEL_STATUS_OK); |
| 7710 | ret = true; |
| 7711 | break; |
| 7712 | } |
| 7713 | } |
| 7714 | |
| 7715 | lttng_triggers_destroy(triggers); |
| 7716 | return ret; |
| 7717 | } |
| 7718 | |
| 7719 | /* |
| 7720 | * Handles the evaluation `evaluation` of a single notification. |
| 7721 | */ |
| 7722 | static void handle_evaluation(const struct lttng_evaluation *evaluation) |
| 7723 | { |
| 7724 | enum lttng_evaluation_status evaluation_status; |
| 7725 | const struct lttng_event_field_value *array_field_value; |
| 7726 | const struct lttng_event_field_value *string_field_value; |
| 7727 | enum lttng_event_field_value_status event_field_value_status; |
| 7728 | const char *string_field_string_value; |
| 7729 | |
| 7730 | /* Get the value of the first captured (string) field */ |
| 7731 | evaluation_status = lttng_evaluation_event_rule_matches_get_captured_values( |
| 7732 | evaluation, &array_field_value); |
| 7733 | assert(evaluation_status == LTTNG_EVALUATION_STATUS_OK); |
| 7734 | event_field_value_status = |
| 7735 | lttng_event_field_value_array_get_element_at_index( |
| 7736 | array_field_value, 0, &string_field_value); |
| 7737 | assert(event_field_value_status == LTTNG_EVENT_FIELD_VALUE_STATUS_OK); |
| 7738 | assert(lttng_event_field_value_get_type(string_field_value) == |
| 7739 | LTTNG_EVENT_FIELD_VALUE_TYPE_STRING); |
| 7740 | event_field_value_status = lttng_event_field_value_string_get_value( |
| 7741 | string_field_value, &string_field_string_value); |
| 7742 | assert(event_field_value_status == LTTNG_EVENT_FIELD_VALUE_STATUS_OK); |
| 7743 | |
| 7744 | /* Print the string value of the field */ |
| 7745 | puts(string_field_string_value); |
| 7746 | } |
| 7747 | |
| 7748 | int main(int argc, char *argv[]) |
| 7749 | { |
| 7750 | int exit_status = EXIT_SUCCESS; |
| 7751 | struct lttng_notification_channel *notification_channel; |
| 7752 | enum lttng_notification_channel_status notification_channel_status; |
| 7753 | const struct lttng_condition *condition; |
| 7754 | const char *trigger_name; |
| 7755 | bool subscribe_res; |
| 7756 | |
| 7757 | assert(argc >= 2); |
| 7758 | trigger_name = argv[1]; |
| 7759 | |
| 7760 | /* |
| 7761 | * Create a notification channel. |
| 7762 | * |
| 7763 | * A notification channel connects the user application to the LTTng |
| 7764 | * session daemon. |
| 7765 | * |
| 7766 | * You can use this notification channel to listen to various types |
| 7767 | * of notifications. |
| 7768 | */ |
| 7769 | notification_channel = lttng_notification_channel_create( |
| 7770 | lttng_session_daemon_notification_endpoint); |
| 7771 | assert(notification_channel); |
| 7772 | |
| 7773 | /* |
| 7774 | * Subscribe to notifications which match the condition of the |
| 7775 | * trigger named `trigger_name`. |
| 7776 | */ |
| 7777 | if (!subscribe(notification_channel, trigger_name)) { |
| 7778 | fprintf(stderr, |
| 7779 | "Error: Failed to subscribe to notifications (trigger `%s`).\n", |
| 7780 | trigger_name); |
| 7781 | exit_status = EXIT_FAILURE; |
| 7782 | goto end; |
| 7783 | } |
| 7784 | |
| 7785 | /* |
| 7786 | * Notification loop. |
| 7787 | * |
| 7788 | * Put this in a dedicated thread to avoid blocking the main thread. |
| 7789 | */ |
| 7790 | while (true) { |
| 7791 | struct lttng_notification *notification; |
| 7792 | enum lttng_notification_channel_status status; |
| 7793 | const struct lttng_evaluation *notification_evaluation; |
| 7794 | |
| 7795 | /* Receive the next notification */ |
| 7796 | status = lttng_notification_channel_get_next_notification( |
| 7797 | notification_channel, ¬ification); |
| 7798 | |
| 7799 | switch (status) { |
| 7800 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_OK: |
| 7801 | break; |
| 7802 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED: |
| 7803 | /* |
| 7804 | * The session daemon can drop notifications if a receiving |
| 7805 | * application doesn't consume the notifications fast |
| 7806 | * enough. |
| 7807 | */ |
| 7808 | continue; |
| 7809 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_CLOSED: |
| 7810 | /* |
| 7811 | * The session daemon closed the notification channel. |
| 7812 | * |
| 7813 | * This is typically caused by a session daemon shutting |
| 7814 | * down. |
| 7815 | */ |
| 7816 | goto end; |
| 7817 | default: |
| 7818 | /* Unhandled conditions or errors */ |
| 7819 | exit_status = EXIT_FAILURE; |
| 7820 | goto end; |
| 7821 | } |
| 7822 | |
| 7823 | /* |
| 7824 | * Handle the condition evaluation. |
| 7825 | * |
| 7826 | * A notification provides, amongst other things: |
| 7827 | * |
| 7828 | * * The condition that caused LTTng to send this notification. |
| 7829 | * |
| 7830 | * * The condition evaluation, which provides more specific |
| 7831 | * information on the evaluation of the condition. |
| 7832 | */ |
| 7833 | handle_evaluation(lttng_notification_get_evaluation(notification)); |
| 7834 | |
| 7835 | /* Destroy the notification object */ |
| 7836 | lttng_notification_destroy(notification); |
| 7837 | } |
| 7838 | |
| 7839 | end: |
| 7840 | lttng_notification_channel_destroy(notification_channel); |
| 7841 | return exit_status; |
| 7842 | } |
| 7843 | ---- |
| 7844 | -- |
| 7845 | + |
| 7846 | This application prints the first captured string field value of the |
| 7847 | condition evaluation of each LTTng notification it receives. |
| 7848 | |
| 7849 | . Build the `notif-app` application, |
| 7850 | using https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config] |
| 7851 | to provide the right compiler and linker flags: |
| 7852 | + |
| 7853 | -- |
| 7854 | [role="term"] |
| 7855 | ---- |
| 7856 | $ gcc -o notif-app notif-app.c $(pkg-config --cflags --libs lttng-ctl) |
| 7857 | ---- |
| 7858 | -- |
| 7859 | |
| 7860 | Now, to add the trigger to the root session daemon: |
| 7861 | |
| 7862 | [start=3] |
| 7863 | . **If there's no currently running LTTng root session daemon**, start |
| 7864 | one: |
| 7865 | + |
| 7866 | [role="term"] |
| 7867 | ---- |
| 7868 | # lttng-sessiond --daemonize |
| 7869 | ---- |
| 7870 | |
| 7871 | . Add the trigger, naming it `sched-switch-notif`, to the root |
| 7872 | session daemon: |
| 7873 | + |
| 7874 | [role="term"] |
| 7875 | ---- |
| 7876 | # lttng add-trigger --name=sched-switch-notif \ |
| 7877 | --condition=event-rule-matches \ |
| 7878 | --type=kernel --name=sched_switch \ |
| 7879 | --filter='next_comm == "bash"' --capture=prev_comm \ |
| 7880 | --action=notify |
| 7881 | ---- |
| 7882 | + |
| 7883 | Confirm that the `sched-switch-notif` trigger exists with the |
| 7884 | man:lttng-list-triggers(1) command: |
| 7885 | + |
| 7886 | [role="term"] |
| 7887 | ---- |
| 7888 | # lttng list-triggers |
| 7889 | ---- |
| 7890 | |
| 7891 | Run the cmd:notif-app application, passing the name of the trigger |
| 7892 | of which to watch the notifications: |
| 7893 | |
| 7894 | [role="term"] |
| 7895 | ---- |
| 7896 | # ./notif-app sched-switch-notif |
| 7897 | ---- |
| 7898 | |
| 7899 | Now, in an interactive Bash, type a few keys to fire the |
| 7900 | `sched-switch-notif` trigger. Watch the `notif-app` application print |
| 7901 | the previous process names. |
| 7902 | ==== |
| 7903 | |
| 7904 | [role="since-2.6"] |
| 7905 | [[mi]] |
| 7906 | === Use the machine interface |
| 7907 | |
| 7908 | With any command of the man:lttng(1) command-line tool, set the |
| 7909 | opt:lttng(1):--mi option to `xml` (before the command name) to get an |
| 7910 | XML machine interface output, for example: |
| 7911 | |
| 7912 | [role="term"] |
| 7913 | ---- |
| 7914 | $ lttng --mi=xml list my-session |
| 7915 | ---- |
| 7916 | |
| 7917 | A schema definition (XSD) is |
| 7918 | https://github.com/lttng/lttng-tools/blob/stable-{revision}/src/common/mi-lttng-4.0.xsd[available] |
| 7919 | to ease the integration with external tools as much as possible. |
| 7920 | |
| 7921 | |
| 7922 | [role="since-2.8"] |
| 7923 | [[metadata-regenerate]] |
| 7924 | === Regenerate the metadata of an LTTng trace |
| 7925 | |
| 7926 | An LTTng trace, which is a https://diamon.org/ctf[CTF] trace, has both |
| 7927 | data stream files and a metadata stream file. This metadata file |
| 7928 | contains, amongst other things, information about the offset of the |
| 7929 | clock sources which LTTng uses to assign timestamps to <<event,event |
| 7930 | records>> when recording. |
| 7931 | |
| 7932 | If, once a <<tracing-session,recording session>> is |
| 7933 | <<basic-tracing-session-control,started>>, a major |
| 7934 | https://en.wikipedia.org/wiki/Network_Time_Protocol[NTP] correction |
| 7935 | happens, the clock offset of the trace also needs to be updated. Use |
| 7936 | the `metadata` item of the man:lttng-regenerate(1) command to do so. |
| 7937 | |
| 7938 | The main use case of this command is to allow a system to boot with |
| 7939 | an incorrect wall time and have LTTng trace it before its wall time |
| 7940 | is corrected. Once the system is known to be in a state where its |
| 7941 | wall time is correct, you can run `lttng regenerate metadata`. |
| 7942 | |
| 7943 | To regenerate the metadata stream files of the |
| 7944 | <<cur-tracing-session,current recording session>>: |
| 7945 | |
| 7946 | * Use the `metadata` item of the man:lttng-regenerate(1) command: |
| 7947 | + |
| 7948 | -- |
| 7949 | [role="term"] |
| 7950 | ---- |
| 7951 | $ lttng regenerate metadata |
| 7952 | ---- |
| 7953 | -- |
| 7954 | |
| 7955 | |
| 7956 | [role="since-2.9"] |
| 7957 | [[regenerate-statedump]] |
| 7958 | === Regenerate the state dump event records of a recording session |
| 7959 | |
| 7960 | The LTTng kernel and user space tracers generate state dump |
| 7961 | <<event,event records>> when the application starts or when you |
| 7962 | <<basic-tracing-session-control,start a recording session>>. |
| 7963 | |
| 7964 | An analysis can use the state dump event records to set an initial state |
| 7965 | before it builds the rest of the state from the subsequent event |
| 7966 | records. http://tracecompass.org/[Trace Compass] is a notable |
| 7967 | example of an application which uses the state dump of an LTTng trace. |
| 7968 | |
| 7969 | When you <<taking-a-snapshot,take a snapshot>>, it's possible that the |
| 7970 | state dump event records aren't included in the snapshot trace files |
| 7971 | because they were recorded to a <<channel,sub-buffer>> that has been |
| 7972 | consumed or <<overwrite-mode,overwritten>> already. |
| 7973 | |
| 7974 | Use the `statedump` item of the man:lttng-regenerate(1) command to emit |
| 7975 | and record the state dump events again. |
| 7976 | |
| 7977 | To regenerate the state dump of the <<cur-tracing-session,current |
| 7978 | recording session>>, provided you created it in <<snapshot-mode,snapshot |
| 7979 | mode>>, before you take a snapshot: |
| 7980 | |
| 7981 | . Use the `statedump` item of the man:lttng-regenerate(1) command: |
| 7982 | + |
| 7983 | -- |
| 7984 | [role="term"] |
| 7985 | ---- |
| 7986 | $ lttng regenerate statedump |
| 7987 | ---- |
| 7988 | -- |
| 7989 | |
| 7990 | . <<basic-tracing-session-control,Stop the recording session>>: |
| 7991 | + |
| 7992 | -- |
| 7993 | [role="term"] |
| 7994 | ---- |
| 7995 | $ lttng stop |
| 7996 | ---- |
| 7997 | -- |
| 7998 | |
| 7999 | . <<taking-a-snapshot,Take a snapshot>>: |
| 8000 | + |
| 8001 | -- |
| 8002 | [role="term"] |
| 8003 | ---- |
| 8004 | $ lttng snapshot record --name=my-snapshot |
| 8005 | ---- |
| 8006 | -- |
| 8007 | |
| 8008 | Depending on the event throughput, you should run steps{nbsp}1 |
| 8009 | and{nbsp}2 as closely as possible. |
| 8010 | |
| 8011 | [NOTE] |
| 8012 | ==== |
| 8013 | To record the state dump events, you need to |
| 8014 | <<enabling-disabling-events,create recording event rules>> which enable |
| 8015 | them: |
| 8016 | |
| 8017 | * The names of LTTng-UST state dump tracepoints start with |
| 8018 | `lttng_ust_statedump:`. |
| 8019 | |
| 8020 | * The names of LTTng-modules state dump tracepoints start with |
| 8021 | `lttng_statedump_`. |
| 8022 | ==== |
| 8023 | |
| 8024 | |
| 8025 | [role="since-2.7"] |
| 8026 | [[persistent-memory-file-systems]] |
| 8027 | === Record trace data on persistent memory file systems |
| 8028 | |
| 8029 | https://en.wikipedia.org/wiki/Non-volatile_random-access_memory[Non-volatile |
| 8030 | random-access memory] (NVRAM) is random-access memory that retains its |
| 8031 | information when power is turned off (non-volatile). Systems with such |
| 8032 | memory can store data structures in RAM and retrieve them after a |
| 8033 | reboot, without flushing to typical _storage_. |
| 8034 | |
| 8035 | Linux supports NVRAM file systems thanks to either |
| 8036 | https://www.kernel.org/doc/Documentation/filesystems/dax.txt[DAX]{nbsp}+{nbsp}http://lkml.iu.edu/hypermail/linux/kernel/1504.1/03463.html[pmem] |
| 8037 | (requires Linux{nbsp}4.1+) or http://pramfs.sourceforge.net/[PRAMFS] (requires Linux{nbsp}<{nbsp}4). |
| 8038 | |
| 8039 | This section doesn't describe how to operate such file systems; we |
| 8040 | assume that you have a working persistent memory file system. |
| 8041 | |
| 8042 | When you <<creating-destroying-tracing-sessions,create a recording |
| 8043 | session>>, you can specify the path of the shared memory holding the |
| 8044 | sub-buffers. If you specify a location on an NVRAM file system, then you |
| 8045 | can retrieve the latest recorded trace data when the system reboots |
| 8046 | after a crash. |
| 8047 | |
| 8048 | To record trace data on a persistent memory file system and retrieve the |
| 8049 | trace data after a system crash: |
| 8050 | |
| 8051 | . Create a recording session with a <<channel,sub-buffer>> shared memory |
| 8052 | path located on an NVRAM file system: |
| 8053 | + |
| 8054 | -- |
| 8055 | [role="term"] |
| 8056 | ---- |
| 8057 | $ lttng create my-session --shm-path=/path/to/shm/on/nvram |
| 8058 | ---- |
| 8059 | -- |
| 8060 | |
| 8061 | . Configure the recording session as usual with the man:lttng(1) |
| 8062 | command-line tool, and <<basic-tracing-session-control,start |
| 8063 | recording>>. |
| 8064 | |
| 8065 | . After a system crash, use the man:lttng-crash(1) command-line tool to |
| 8066 | read the trace data recorded on the NVRAM file system: |
| 8067 | + |
| 8068 | -- |
| 8069 | [role="term"] |
| 8070 | ---- |
| 8071 | $ lttng-crash /path/to/shm/on/nvram |
| 8072 | ---- |
| 8073 | -- |
| 8074 | |
| 8075 | The binary layout of the ring buffer files isn't exactly the same as the |
| 8076 | trace files layout. This is why you need to use man:lttng-crash(1) |
| 8077 | instead of some standard LTTng trace reader. |
| 8078 | |
| 8079 | To convert the ring buffer files to LTTng trace files: |
| 8080 | |
| 8081 | * Use the opt:lttng-crash(1):--extract option of man:lttng-crash(1): |
| 8082 | + |
| 8083 | -- |
| 8084 | [role="term"] |
| 8085 | ---- |
| 8086 | $ lttng-crash --extract=/path/to/trace /path/to/shm/on/nvram |
| 8087 | ---- |
| 8088 | -- |
| 8089 | |
| 8090 | |
| 8091 | [role="since-2.10"] |
| 8092 | [[notif-trigger-api]] |
| 8093 | === Get notified when the buffer usage of a channel is too high or too low |
| 8094 | |
| 8095 | With the notification and <<trigger,trigger>> C{nbsp}API of |
| 8096 | <<liblttng-ctl-lttng,`liblttng-ctl`>>, LTTng can notify your user |
| 8097 | application when the buffer usage of one or more <<channel,channels>> |
| 8098 | becomes too low or too high. |
| 8099 | |
| 8100 | Use this API and enable or disable <<event,recording event rules>> while |
| 8101 | a recording session <<basic-tracing-session-control,is active>> to avoid |
| 8102 | <<channel-overwrite-mode-vs-discard-mode,discarded event records>>, for |
| 8103 | example. |
| 8104 | |
| 8105 | .Send a notification to a user application when the buffer usage of an LTTng channel is too high. |
| 8106 | ==== |
| 8107 | In this example, we create and build an application which gets notified |
| 8108 | when the buffer usage of a specific LTTng channel is higher than |
| 8109 | 75{nbsp}%. |
| 8110 | |
| 8111 | We only print that it's the case in this example, but we could as well |
| 8112 | use the `liblttng-ctl` C{nbsp}API to <<enabling-disabling-events,disable |
| 8113 | recording event rules>> when this happens, for example. |
| 8114 | |
| 8115 | . Create the C{nbsp}source file of the application: |
| 8116 | + |
| 8117 | -- |
| 8118 | [source,c] |
| 8119 | .path:{notif-app.c} |
| 8120 | ---- |
| 8121 | #include <stdlib.h> |
| 8122 | #include <stdio.h> |
| 8123 | #include <assert.h> |
| 8124 | #include <lttng/lttng.h> |
| 8125 | |
| 8126 | int main(int argc, char *argv[]) |
| 8127 | { |
| 8128 | int exit_status = EXIT_SUCCESS; |
| 8129 | struct lttng_notification_channel *notification_channel; |
| 8130 | struct lttng_condition *condition; |
| 8131 | struct lttng_action *action; |
| 8132 | struct lttng_trigger *trigger; |
| 8133 | const char *recording_session_name; |
| 8134 | const char *channel_name; |
| 8135 | |
| 8136 | assert(argc >= 3); |
| 8137 | recording_session_name = argv[1]; |
| 8138 | channel_name = argv[2]; |
| 8139 | |
| 8140 | /* |
| 8141 | * Create a notification channel. |
| 8142 | * |
| 8143 | * A notification channel connects the user application to the LTTng |
| 8144 | * session daemon. |
| 8145 | * |
| 8146 | * You can use this notification channel to listen to various types |
| 8147 | * of notifications. |
| 8148 | */ |
| 8149 | notification_channel = lttng_notification_channel_create( |
| 8150 | lttng_session_daemon_notification_endpoint); |
| 8151 | |
| 8152 | /* |
| 8153 | * Create a "buffer usage becomes greater than" condition. |
| 8154 | * |
| 8155 | * In this case, the condition is satisfied when the buffer usage |
| 8156 | * becomes greater than or equal to 75 %. |
| 8157 | * |
| 8158 | * We create the condition for a specific recording session name, |
| 8159 | * channel name, and for the user space tracing domain. |
| 8160 | * |
| 8161 | * The following condition types also exist: |
| 8162 | * |
| 8163 | * * The buffer usage of a channel becomes less than a given value. |
| 8164 | * |
| 8165 | * * The consumed data size of a recording session becomes greater |
| 8166 | * than a given value. |
| 8167 | * |
| 8168 | * * A recording session rotation becomes ongoing. |
| 8169 | * |
| 8170 | * * A recording session rotation becomes completed. |
| 8171 | * |
| 8172 | * * A given event rule matches an event. |
| 8173 | */ |
| 8174 | condition = lttng_condition_buffer_usage_high_create(); |
| 8175 | lttng_condition_buffer_usage_set_threshold_ratio(condition, .75); |
| 8176 | lttng_condition_buffer_usage_set_session_name(condition, |
| 8177 | recording_session_name); |
| 8178 | lttng_condition_buffer_usage_set_channel_name(condition, |
| 8179 | channel_name); |
| 8180 | lttng_condition_buffer_usage_set_domain_type(condition, |
| 8181 | LTTNG_DOMAIN_UST); |
| 8182 | |
| 8183 | /* |
| 8184 | * Create an action (receive a notification) to execute when the |
| 8185 | * condition created above is satisfied. |
| 8186 | */ |
| 8187 | action = lttng_action_notify_create(); |
| 8188 | |
| 8189 | /* |
| 8190 | * Create a trigger. |
| 8191 | * |
| 8192 | * A trigger associates a condition to an action: LTTng executes |
| 8193 | * the action when the condition is satisfied. |
| 8194 | */ |
| 8195 | trigger = lttng_trigger_create(condition, action); |
| 8196 | |
| 8197 | /* Register the trigger to the LTTng session daemon. */ |
| 8198 | lttng_register_trigger(trigger); |
| 8199 | |
| 8200 | /* |
| 8201 | * Now that we have registered a trigger, LTTng will send a |
| 8202 | * notification every time its condition is met through a |
| 8203 | * notification channel. |
| 8204 | * |
| 8205 | * To receive this notification, we must subscribe to notifications |
| 8206 | * which match the same condition. |
| 8207 | */ |
| 8208 | lttng_notification_channel_subscribe(notification_channel, |
| 8209 | condition); |
| 8210 | |
| 8211 | /* |
| 8212 | * Notification loop. |
| 8213 | * |
| 8214 | * Put this in a dedicated thread to avoid blocking the main thread. |
| 8215 | */ |
| 8216 | for (;;) { |
| 8217 | struct lttng_notification *notification; |
| 8218 | enum lttng_notification_channel_status status; |
| 8219 | const struct lttng_evaluation *notification_evaluation; |
| 8220 | const struct lttng_condition *notification_condition; |
| 8221 | double buffer_usage; |
| 8222 | |
| 8223 | /* Receive the next notification. */ |
| 8224 | status = lttng_notification_channel_get_next_notification( |
| 8225 | notification_channel, ¬ification); |
| 8226 | |
| 8227 | switch (status) { |
| 8228 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_OK: |
| 8229 | break; |
| 8230 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED: |
| 8231 | /* |
| 8232 | * The session daemon can drop notifications if a monitoring |
| 8233 | * application isn't consuming the notifications fast |
| 8234 | * enough. |
| 8235 | */ |
| 8236 | continue; |
| 8237 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_CLOSED: |
| 8238 | /* |
| 8239 | * The session daemon closed the notification channel. |
| 8240 | * |
| 8241 | * This is typically caused by a session daemon shutting |
| 8242 | * down. |
| 8243 | */ |
| 8244 | goto end; |
| 8245 | default: |
| 8246 | /* Unhandled conditions or errors. */ |
| 8247 | exit_status = EXIT_FAILURE; |
| 8248 | goto end; |
| 8249 | } |
| 8250 | |
| 8251 | /* |
| 8252 | * A notification provides, amongst other things: |
| 8253 | * |
| 8254 | * * The condition that caused LTTng to send this notification. |
| 8255 | * |
| 8256 | * * The condition evaluation, which provides more specific |
| 8257 | * information on the evaluation of the condition. |
| 8258 | * |
| 8259 | * The condition evaluation provides the buffer usage |
| 8260 | * value at the moment the condition was satisfied. |
| 8261 | */ |
| 8262 | notification_condition = lttng_notification_get_condition( |
| 8263 | notification); |
| 8264 | notification_evaluation = lttng_notification_get_evaluation( |
| 8265 | notification); |
| 8266 | |
| 8267 | /* We're subscribed to only one condition. */ |
| 8268 | assert(lttng_condition_get_type(notification_condition) == |
| 8269 | LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH); |
| 8270 | |
| 8271 | /* |
| 8272 | * Get the exact sampled buffer usage from the condition |
| 8273 | * evaluation. |
| 8274 | */ |
| 8275 | lttng_evaluation_buffer_usage_get_usage_ratio( |
| 8276 | notification_evaluation, &buffer_usage); |
| 8277 | |
| 8278 | /* |
| 8279 | * At this point, instead of printing a message, we could do |
| 8280 | * something to reduce the buffer usage of the channel, like |
| 8281 | * disable specific events, for example. |
| 8282 | */ |
| 8283 | printf("Buffer usage is %f %% in recording session \"%s\", " |
| 8284 | "user space channel \"%s\".\n", buffer_usage * 100, |
| 8285 | recording_session_name, channel_name); |
| 8286 | |
| 8287 | /* Destroy the notification object. */ |
| 8288 | lttng_notification_destroy(notification); |
| 8289 | } |
| 8290 | |
| 8291 | end: |
| 8292 | lttng_action_destroy(action); |
| 8293 | lttng_condition_destroy(condition); |
| 8294 | lttng_trigger_destroy(trigger); |
| 8295 | lttng_notification_channel_destroy(notification_channel); |
| 8296 | return exit_status; |
| 8297 | } |
| 8298 | ---- |
| 8299 | -- |
| 8300 | |
| 8301 | . Build the `notif-app` application, linking it with `liblttng-ctl`: |
| 8302 | + |
| 8303 | -- |
| 8304 | [role="term"] |
| 8305 | ---- |
| 8306 | $ gcc -o notif-app notif-app.c $(pkg-config --cflags --libs lttng-ctl) |
| 8307 | ---- |
| 8308 | -- |
| 8309 | |
| 8310 | . <<creating-destroying-tracing-sessions,Create a recording session>>, |
| 8311 | <<enabling-disabling-events,create a recording event rule>> matching |
| 8312 | all the user space tracepoint events, and |
| 8313 | <<basic-tracing-session-control,start recording>>: |
| 8314 | + |
| 8315 | -- |
| 8316 | [role="term"] |
| 8317 | ---- |
| 8318 | $ lttng create my-session |
| 8319 | $ lttng enable-event --userspace --all |
| 8320 | $ lttng start |
| 8321 | ---- |
| 8322 | -- |
| 8323 | + |
| 8324 | If you create the channel manually with the man:lttng-enable-channel(1) |
| 8325 | command, you can set its <<channel-monitor-timer,monitor timer>> to |
| 8326 | control how frequently LTTng samples the current values of the channel |
| 8327 | properties to evaluate user conditions. |
| 8328 | |
| 8329 | . Run the `notif-app` application. |
| 8330 | + |
| 8331 | This program accepts the <<tracing-session,recording session>> and |
| 8332 | user space channel names as its two first arguments. The channel |
| 8333 | which LTTng automatically creates with the man:lttng-enable-event(1) |
| 8334 | command above is named `channel0`: |
| 8335 | + |
| 8336 | -- |
| 8337 | [role="term"] |
| 8338 | ---- |
| 8339 | $ ./notif-app my-session channel0 |
| 8340 | ---- |
| 8341 | -- |
| 8342 | |
| 8343 | . In another terminal, run an application with a very high event |
| 8344 | throughput so that the 75{nbsp}% buffer usage condition is reached. |
| 8345 | + |
| 8346 | In the first terminal, the application should print lines like this: |
| 8347 | + |
| 8348 | ---- |
| 8349 | Buffer usage is 81.45197 % in recording session "my-session", user space |
| 8350 | channel "channel0". |
| 8351 | ---- |
| 8352 | + |
| 8353 | If you don't see anything, try to make the threshold of the condition in |
| 8354 | path:{notif-app.c} lower (0.1{nbsp}%, for example), and then rebuild the |
| 8355 | `notif-app` application (step{nbsp}2) and run it again (step{nbsp}4). |
| 8356 | ==== |
| 8357 | |
| 8358 | |
| 8359 | [[reference]] |
| 8360 | == Reference |
| 8361 | |
| 8362 | [[lttng-modules-ref]] |
| 8363 | === noch:{LTTng-modules} |
| 8364 | |
| 8365 | |
| 8366 | [role="since-2.9"] |
| 8367 | [[lttng-tracepoint-enum]] |
| 8368 | ==== `LTTNG_TRACEPOINT_ENUM()` usage |
| 8369 | |
| 8370 | Use the `LTTNG_TRACEPOINT_ENUM()` macro to define an enumeration: |
| 8371 | |
| 8372 | [source,c] |
| 8373 | ---- |
| 8374 | LTTNG_TRACEPOINT_ENUM(name, TP_ENUM_VALUES(entries)) |
| 8375 | ---- |
| 8376 | |
| 8377 | Replace: |
| 8378 | |
| 8379 | * `name` with the name of the enumeration (C identifier, unique |
| 8380 | amongst all the defined enumerations). |
| 8381 | * `entries` with a list of enumeration entries. |
| 8382 | |
| 8383 | The available enumeration entry macros are: |
| 8384 | |
| 8385 | +ctf_enum_value(__name__, __value__)+:: |
| 8386 | Entry named +__name__+ mapped to the integral value +__value__+. |
| 8387 | |
| 8388 | +ctf_enum_range(__name__, __begin__, __end__)+:: |
| 8389 | Entry named +__name__+ mapped to the range of integral values between |
| 8390 | +__begin__+ (included) and +__end__+ (included). |
| 8391 | |
| 8392 | +ctf_enum_auto(__name__)+:: |
| 8393 | Entry named +__name__+ mapped to the integral value following the |
| 8394 | last mapping value. |
| 8395 | + |
| 8396 | The last value of a `ctf_enum_value()` entry is its +__value__+ |
| 8397 | parameter. |
| 8398 | + |
| 8399 | The last value of a `ctf_enum_range()` entry is its +__end__+ parameter. |
| 8400 | + |
| 8401 | If `ctf_enum_auto()` is the first entry in the list, its integral |
| 8402 | value is 0. |
| 8403 | |
| 8404 | Use the `ctf_enum()` <<lttng-modules-tp-fields,field definition macro>> |
| 8405 | to use a defined enumeration as a tracepoint field. |
| 8406 | |
| 8407 | .Define an enumeration with `LTTNG_TRACEPOINT_ENUM()`. |
| 8408 | ==== |
| 8409 | [source,c] |
| 8410 | ---- |
| 8411 | LTTNG_TRACEPOINT_ENUM( |
| 8412 | my_enum, |
| 8413 | TP_ENUM_VALUES( |
| 8414 | ctf_enum_auto("AUTO: EXPECT 0") |
| 8415 | ctf_enum_value("VALUE: 23", 23) |
| 8416 | ctf_enum_value("VALUE: 27", 27) |
| 8417 | ctf_enum_auto("AUTO: EXPECT 28") |
| 8418 | ctf_enum_range("RANGE: 101 TO 303", 101, 303) |
| 8419 | ctf_enum_auto("AUTO: EXPECT 304") |
| 8420 | ) |
| 8421 | ) |
| 8422 | ---- |
| 8423 | ==== |
| 8424 | |
| 8425 | |
| 8426 | [role="since-2.7"] |
| 8427 | [[lttng-modules-tp-fields]] |
| 8428 | ==== Tracepoint fields macros (for `TP_FIELDS()`) |
| 8429 | |
| 8430 | [[tp-fast-assign]][[tp-struct-entry]]The available macros to define |
| 8431 | tracepoint fields, which must be listed within `TP_FIELDS()` in |
| 8432 | `LTTNG_TRACEPOINT_EVENT()`, are: |
| 8433 | |
| 8434 | [role="func-desc growable",cols="asciidoc,asciidoc"] |
| 8435 | .Available macros to define LTTng-modules tracepoint fields |
| 8436 | |==== |
| 8437 | |Macro |Description and parameters |
| 8438 | |
| 8439 | | |
| 8440 | +ctf_integer(__t__, __n__, __e__)+ |
| 8441 | |
| 8442 | +ctf_integer_nowrite(__t__, __n__, __e__)+ |
| 8443 | |
| 8444 | +ctf_user_integer(__t__, __n__, __e__)+ |
| 8445 | |
| 8446 | +ctf_user_integer_nowrite(__t__, __n__, __e__)+ |
| 8447 | | |
| 8448 | Standard integer, displayed in base{nbsp}10. |
| 8449 | |
| 8450 | +__t__+:: |
| 8451 | Integer C type (`int`, `long`, `size_t`, ...). |
| 8452 | |
| 8453 | +__n__+:: |
| 8454 | Field name. |
| 8455 | |
| 8456 | +__e__+:: |
| 8457 | Argument expression. |
| 8458 | |
| 8459 | | |
| 8460 | +ctf_integer_hex(__t__, __n__, __e__)+ |
| 8461 | |
| 8462 | +ctf_user_integer_hex(__t__, __n__, __e__)+ |
| 8463 | | |
| 8464 | Standard integer, displayed in base{nbsp}16. |
| 8465 | |
| 8466 | +__t__+:: |
| 8467 | Integer C type. |
| 8468 | |
| 8469 | +__n__+:: |
| 8470 | Field name. |
| 8471 | |
| 8472 | +__e__+:: |
| 8473 | Argument expression. |
| 8474 | |
| 8475 | |+ctf_integer_oct(__t__, __n__, __e__)+ |
| 8476 | | |
| 8477 | Standard integer, displayed in base{nbsp}8. |
| 8478 | |
| 8479 | +__t__+:: |
| 8480 | Integer C type. |
| 8481 | |
| 8482 | +__n__+:: |
| 8483 | Field name. |
| 8484 | |
| 8485 | +__e__+:: |
| 8486 | Argument expression. |
| 8487 | |
| 8488 | | |
| 8489 | +ctf_integer_network(__t__, __n__, __e__)+ |
| 8490 | |
| 8491 | +ctf_user_integer_network(__t__, __n__, __e__)+ |
| 8492 | | |
| 8493 | Integer in network byte order (big-endian), displayed in base{nbsp}10. |
| 8494 | |
| 8495 | +__t__+:: |
| 8496 | Integer C type. |
| 8497 | |
| 8498 | +__n__+:: |
| 8499 | Field name. |
| 8500 | |
| 8501 | +__e__+:: |
| 8502 | Argument expression. |
| 8503 | |
| 8504 | | |
| 8505 | +ctf_integer_network_hex(__t__, __n__, __e__)+ |
| 8506 | |
| 8507 | +ctf_user_integer_network_hex(__t__, __n__, __e__)+ |
| 8508 | | |
| 8509 | Integer in network byte order, displayed in base{nbsp}16. |
| 8510 | |
| 8511 | +__t__+:: |
| 8512 | Integer C type. |
| 8513 | |
| 8514 | +__n__+:: |
| 8515 | Field name. |
| 8516 | |
| 8517 | +__e__+:: |
| 8518 | Argument expression. |
| 8519 | |
| 8520 | | |
| 8521 | +ctf_enum(__N__, __t__, __n__, __e__)+ |
| 8522 | |
| 8523 | +ctf_enum_nowrite(__N__, __t__, __n__, __e__)+ |
| 8524 | |
| 8525 | +ctf_user_enum(__N__, __t__, __n__, __e__)+ |
| 8526 | |
| 8527 | +ctf_user_enum_nowrite(__N__, __t__, __n__, __e__)+ |
| 8528 | | |
| 8529 | Enumeration. |
| 8530 | |
| 8531 | +__N__+:: |
| 8532 | Name of a <<lttng-tracepoint-enum,previously defined enumeration>>. |
| 8533 | |
| 8534 | +__t__+:: |
| 8535 | Integer C type (`int`, `long`, `size_t`, ...). |
| 8536 | |
| 8537 | +__n__+:: |
| 8538 | Field name. |
| 8539 | |
| 8540 | +__e__+:: |
| 8541 | Argument expression. |
| 8542 | |
| 8543 | | |
| 8544 | +ctf_string(__n__, __e__)+ |
| 8545 | |
| 8546 | +ctf_string_nowrite(__n__, __e__)+ |
| 8547 | |
| 8548 | +ctf_user_string(__n__, __e__)+ |
| 8549 | |
| 8550 | +ctf_user_string_nowrite(__n__, __e__)+ |
| 8551 | | |
| 8552 | Null-terminated string; undefined behavior if +__e__+ is `NULL`. |
| 8553 | |
| 8554 | +__n__+:: |
| 8555 | Field name. |
| 8556 | |
| 8557 | +__e__+:: |
| 8558 | Argument expression. |
| 8559 | |
| 8560 | | |
| 8561 | +ctf_array(__t__, __n__, __e__, __s__)+ |
| 8562 | |
| 8563 | +ctf_array_nowrite(__t__, __n__, __e__, __s__)+ |
| 8564 | |
| 8565 | +ctf_user_array(__t__, __n__, __e__, __s__)+ |
| 8566 | |
| 8567 | +ctf_user_array_nowrite(__t__, __n__, __e__, __s__)+ |
| 8568 | | |
| 8569 | Statically-sized array of integers. |
| 8570 | |
| 8571 | +__t__+:: |
| 8572 | Array element C type. |
| 8573 | |
| 8574 | +__n__+:: |
| 8575 | Field name. |
| 8576 | |
| 8577 | +__e__+:: |
| 8578 | Argument expression. |
| 8579 | |
| 8580 | +__s__+:: |
| 8581 | Number of elements. |
| 8582 | |
| 8583 | | |
| 8584 | +ctf_array_bitfield(__t__, __n__, __e__, __s__)+ |
| 8585 | |
| 8586 | +ctf_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ |
| 8587 | |
| 8588 | +ctf_user_array_bitfield(__t__, __n__, __e__, __s__)+ |
| 8589 | |
| 8590 | +ctf_user_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ |
| 8591 | | |
| 8592 | Statically-sized array of bits. |
| 8593 | |
| 8594 | The type of +__e__+ must be an integer type. +__s__+ is the number |
| 8595 | of elements of such type in +__e__+, not the number of bits. |
| 8596 | |
| 8597 | +__t__+:: |
| 8598 | Array element C type. |
| 8599 | |
| 8600 | +__n__+:: |
| 8601 | Field name. |
| 8602 | |
| 8603 | +__e__+:: |
| 8604 | Argument expression. |
| 8605 | |
| 8606 | +__s__+:: |
| 8607 | Number of elements. |
| 8608 | |
| 8609 | | |
| 8610 | +ctf_array_text(__t__, __n__, __e__, __s__)+ |
| 8611 | |
| 8612 | +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+ |
| 8613 | |
| 8614 | +ctf_user_array_text(__t__, __n__, __e__, __s__)+ |
| 8615 | |
| 8616 | +ctf_user_array_text_nowrite(__t__, __n__, __e__, __s__)+ |
| 8617 | | |
| 8618 | Statically-sized array, printed as text. |
| 8619 | |
| 8620 | The string doesn't need to be null-terminated. |
| 8621 | |
| 8622 | +__t__+:: |
| 8623 | Array element C type (always `char`). |
| 8624 | |
| 8625 | +__n__+:: |
| 8626 | Field name. |
| 8627 | |
| 8628 | +__e__+:: |
| 8629 | Argument expression. |
| 8630 | |
| 8631 | +__s__+:: |
| 8632 | Number of elements. |
| 8633 | |
| 8634 | | |
| 8635 | +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+ |
| 8636 | |
| 8637 | +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8638 | |
| 8639 | +ctf_user_sequence(__t__, __n__, __e__, __T__, __E__)+ |
| 8640 | |
| 8641 | +ctf_user_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8642 | | |
| 8643 | Dynamically-sized array of integers. |
| 8644 | |
| 8645 | The type of +__E__+ must be unsigned. |
| 8646 | |
| 8647 | +__t__+:: |
| 8648 | Array element C type. |
| 8649 | |
| 8650 | +__n__+:: |
| 8651 | Field name. |
| 8652 | |
| 8653 | +__e__+:: |
| 8654 | Argument expression. |
| 8655 | |
| 8656 | +__T__+:: |
| 8657 | Length expression C type. |
| 8658 | |
| 8659 | +__E__+:: |
| 8660 | Length expression. |
| 8661 | |
| 8662 | | |
| 8663 | +ctf_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ |
| 8664 | |
| 8665 | +ctf_user_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ |
| 8666 | | |
| 8667 | Dynamically-sized array of integers, displayed in base{nbsp}16. |
| 8668 | |
| 8669 | The type of +__E__+ must be unsigned. |
| 8670 | |
| 8671 | +__t__+:: |
| 8672 | Array element C type. |
| 8673 | |
| 8674 | +__n__+:: |
| 8675 | Field name. |
| 8676 | |
| 8677 | +__e__+:: |
| 8678 | Argument expression. |
| 8679 | |
| 8680 | +__T__+:: |
| 8681 | Length expression C type. |
| 8682 | |
| 8683 | +__E__+:: |
| 8684 | Length expression. |
| 8685 | |
| 8686 | |+ctf_sequence_network(__t__, __n__, __e__, __T__, __E__)+ |
| 8687 | | |
| 8688 | Dynamically-sized array of integers in network byte order (big-endian), |
| 8689 | displayed in base{nbsp}10. |
| 8690 | |
| 8691 | The type of +__E__+ must be unsigned. |
| 8692 | |
| 8693 | +__t__+:: |
| 8694 | Array element C type. |
| 8695 | |
| 8696 | +__n__+:: |
| 8697 | Field name. |
| 8698 | |
| 8699 | +__e__+:: |
| 8700 | Argument expression. |
| 8701 | |
| 8702 | +__T__+:: |
| 8703 | Length expression C type. |
| 8704 | |
| 8705 | +__E__+:: |
| 8706 | Length expression. |
| 8707 | |
| 8708 | | |
| 8709 | +ctf_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ |
| 8710 | |
| 8711 | +ctf_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8712 | |
| 8713 | +ctf_user_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ |
| 8714 | |
| 8715 | +ctf_user_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8716 | | |
| 8717 | Dynamically-sized array of bits. |
| 8718 | |
| 8719 | The type of +__e__+ must be an integer type. +__s__+ is the number |
| 8720 | of elements of such type in +__e__+, not the number of bits. |
| 8721 | |
| 8722 | The type of +__E__+ must be unsigned. |
| 8723 | |
| 8724 | +__t__+:: |
| 8725 | Array element C type. |
| 8726 | |
| 8727 | +__n__+:: |
| 8728 | Field name. |
| 8729 | |
| 8730 | +__e__+:: |
| 8731 | Argument expression. |
| 8732 | |
| 8733 | +__T__+:: |
| 8734 | Length expression C type. |
| 8735 | |
| 8736 | +__E__+:: |
| 8737 | Length expression. |
| 8738 | |
| 8739 | | |
| 8740 | +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+ |
| 8741 | |
| 8742 | +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8743 | |
| 8744 | +ctf_user_sequence_text(__t__, __n__, __e__, __T__, __E__)+ |
| 8745 | |
| 8746 | +ctf_user_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 8747 | | |
| 8748 | Dynamically-sized array, displayed as text. |
| 8749 | |
| 8750 | The string doesn't need to be null-terminated. |
| 8751 | |
| 8752 | The type of +__E__+ must be unsigned. |
| 8753 | |
| 8754 | The behaviour is undefined if +__e__+ is `NULL`. |
| 8755 | |
| 8756 | +__t__+:: |
| 8757 | Sequence element C type (always `char`). |
| 8758 | |
| 8759 | +__n__+:: |
| 8760 | Field name. |
| 8761 | |
| 8762 | +__e__+:: |
| 8763 | Argument expression. |
| 8764 | |
| 8765 | +__T__+:: |
| 8766 | Length expression C type. |
| 8767 | |
| 8768 | +__E__+:: |
| 8769 | Length expression. |
| 8770 | |==== |
| 8771 | |
| 8772 | Use the `_user` versions when the argument expression, `e`, is |
| 8773 | a user space address. In the cases of `ctf_user_integer*()` and |
| 8774 | `ctf_user_float*()`, `&e` must be a user space address, thus `e` must |
| 8775 | be addressable. |
| 8776 | |
| 8777 | The `_nowrite` versions omit themselves from the trace data, but are |
| 8778 | otherwise identical. This means LTTng won't write the `_nowrite` fields |
| 8779 | to the recorded trace. Their primary purpose is to make some of the |
| 8780 | event context available to the <<enabling-disabling-events,recording |
| 8781 | event rule filters>> without having to commit the data to |
| 8782 | <<channel,sub-buffers>>. |
| 8783 | |
| 8784 | |
| 8785 | [[glossary]] |
| 8786 | == Glossary |
| 8787 | |
| 8788 | Terms related to LTTng and to tracing in general: |
| 8789 | |
| 8790 | [[def-action]]action:: |
| 8791 | The part of a <<def-trigger,trigger>> which LTTng executes when the |
| 8792 | trigger <<def-condition,condition>> is satisfied. |
| 8793 | |
| 8794 | Babeltrace:: |
| 8795 | The https://diamon.org/babeltrace[Babeltrace] project, which includes: |
| 8796 | + |
| 8797 | * The |
| 8798 | https://babeltrace.org/docs/v2.0/man1/babeltrace2.1/[cmd:babeltrace2] |
| 8799 | command-line interface. |
| 8800 | * The libbabeltrace2 library which offers a |
| 8801 | https://babeltrace.org/docs/v2.0/libbabeltrace2/[C API]. |
| 8802 | * https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings]. |
| 8803 | * Plugins. |
| 8804 | |
| 8805 | [[def-buffering-scheme]]<<channel-buffering-schemes,buffering scheme>>:: |
| 8806 | A layout of <<def-sub-buffer,sub-buffers>> applied to a given channel. |
| 8807 | |
| 8808 | [[def-channel]]<<channel,channel>>:: |
| 8809 | An entity which is responsible for a set of |
| 8810 | <<def-ring-buffer,ring buffers>>. |
| 8811 | + |
| 8812 | <<def-recording-event-rule,Recording event rules>> are always attached |
| 8813 | to a specific channel. |
| 8814 | |
| 8815 | clock:: |
| 8816 | A source of time for a <<def-tracer,tracer>>. |
| 8817 | |
| 8818 | [[def-condition]]condition:: |
| 8819 | The part of a <<def-trigger,trigger>> which must be satisfied for |
| 8820 | LTTng to attempt to execute the trigger <<def-action,actions>>. |
| 8821 | |
| 8822 | [[def-consumer-daemon]]<<lttng-consumerd,consumer daemon>>:: |
| 8823 | A program which is responsible for consuming the full |
| 8824 | <<def-sub-buffer,sub-buffers>> and write them to a file system or |
| 8825 | send them over the network. |
| 8826 | |
| 8827 | [[def-current-trace-chunk]]current trace chunk:: |
| 8828 | A <<def-trace-chunk,trace chunk>> which includes the current content |
| 8829 | of all the <<def-sub-buffer,sub-buffers>> of the |
| 8830 | <<def-tracing-session,recording session>> and the stream files |
| 8831 | produced since the latest event amongst: |
| 8832 | + |
| 8833 | * The creation of the recording session. |
| 8834 | * The last <<def-tracing-session-rotation,recording session rotation>>, if |
| 8835 | any. |
| 8836 | |
| 8837 | <<channel-overwrite-mode-vs-discard-mode,discard mode>>:: |
| 8838 | The <<def-event-record-loss-mode,event record loss mode>> in which |
| 8839 | the <<def-tracer,tracer>> _discards_ new <<def-event-record,event |
| 8840 | records>> when there's no <<def-sub-buffer,sub-buffer>> space left to |
| 8841 | store them. |
| 8842 | |
| 8843 | [[def-event]]event:: |
| 8844 | The execution of an <<def-instrumentation-point,instrumentation |
| 8845 | point>>, like a <<def-tracepoint,tracepoint>> that you manually place |
| 8846 | in some source code, or a Linux kprobe. |
| 8847 | + |
| 8848 | When an instrumentation point is executed, LTTng creates an event. |
| 8849 | + |
| 8850 | When an <<def-event-rule,event rule>> matches the event, |
| 8851 | <<def-lttng,LTTng>> executes some action, for example: |
| 8852 | + |
| 8853 | * Record its payload to a <<def-sub-buffer,sub-buffer>> as an |
| 8854 | <<def-event-record,event record>>. |
| 8855 | * Attempt to execute the user-defined actions of a |
| 8856 | <<def-trigger,trigger>> with an |
| 8857 | <<add-event-rule-matches-trigger,``event rule matches''>> condition. |
| 8858 | |
| 8859 | [[def-event-name]]event name:: |
| 8860 | The name of an <<def-event,event>>, which is also the name of the |
| 8861 | <<def-event-record,event record>>. |
| 8862 | + |
| 8863 | This is also called the _instrumentation point name_. |
| 8864 | |
| 8865 | [[def-event-record]]event record:: |
| 8866 | A record (binary serialization), in a <<def-trace,trace>>, of the |
| 8867 | payload of an <<def-event,event>>. |
| 8868 | + |
| 8869 | The payload of an event record has zero or more _fields_. |
| 8870 | |
| 8871 | [[def-event-record-loss-mode]]<<channel-overwrite-mode-vs-discard-mode,event record loss mode>>:: |
| 8872 | The mechanism by which event records of a given |
| 8873 | <<def-channel,channel>> are lost (not recorded) when there's no |
| 8874 | <<def-sub-buffer,sub-buffer>> space left to store them. |
| 8875 | |
| 8876 | [[def-event-rule]]<<event-rule,event rule>>:: |
| 8877 | Set of conditions which an <<def-event,event>> must satisfy |
| 8878 | for LTTng to execute some action. |
| 8879 | + |
| 8880 | An event rule is said to _match_ events, like a |
| 8881 | https://en.wikipedia.org/wiki/Regular_expression[regular expression] |
| 8882 | matches strings. |
| 8883 | + |
| 8884 | A <<def-recording-event-rule,recording event rule>> is a specific type |
| 8885 | of event rule of which the action is to <<def-record,record>> the event |
| 8886 | to a <<def-sub-buffer,sub-buffer>>. |
| 8887 | |
| 8888 | [[def-incl-set]]inclusion set:: |
| 8889 | In the <<pid-tracking,process attribute inclusion set>> context: a |
| 8890 | set of <<def-proc-attr,process attributes>> of a given type. |
| 8891 | |
| 8892 | <<instrumenting,instrumentation>>:: |
| 8893 | The use of <<def-lttng,LTTng>> probes to make a kernel or |
| 8894 | <<def-user-application,user application>> traceable. |
| 8895 | |
| 8896 | [[def-instrumentation-point]]instrumentation point:: |
| 8897 | A point in the execution path of a kernel or |
| 8898 | <<def-user-application,user application>> which, when executed, |
| 8899 | create an <<def-event,event>>. |
| 8900 | |
| 8901 | instrumentation point name:: |
| 8902 | See _<<def-event-name,event name>>_. |
| 8903 | |
| 8904 | `java.util.logging`:: |
| 8905 | The |
| 8906 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[core logging facilities] |
| 8907 | of the Java platform. |
| 8908 | |
| 8909 | log4j:: |
| 8910 | A https://logging.apache.org/log4j/1.2/[logging library] for Java |
| 8911 | developed by the Apache Software Foundation. |
| 8912 | |
| 8913 | log level:: |
| 8914 | Level of severity of a log statement or user space |
| 8915 | <<def-instrumentation-point,instrumentation point>>. |
| 8916 | |
| 8917 | [[def-lttng]]LTTng:: |
| 8918 | The _Linux Trace Toolkit: next generation_ project. |
| 8919 | |
| 8920 | <<lttng-cli,cmd:lttng>>:: |
| 8921 | A command-line tool provided by the <<def-lttng-tools,LTTng-tools>> |
| 8922 | project which you can use to send and receive control messages to and |
| 8923 | from a <<def-session-daemon,session daemon>>. |
| 8924 | |
| 8925 | cmd:lttng-consumerd:: |
| 8926 | The name of the <<def-consumer-daemon,consumer daemon>> program. |
| 8927 | |
| 8928 | cmd:lttng-crash:: |
| 8929 | A utility provided by the <<def-lttng-tools,LTTng-tools>> project |
| 8930 | which can convert <<def-ring-buffer,ring buffer>> files (usually |
| 8931 | <<persistent-memory-file-systems,saved on a persistent memory file |
| 8932 | system>>) to <<def-trace,trace>> files. |
| 8933 | + |
| 8934 | See man:lttng-crash(1). |
| 8935 | |
| 8936 | LTTng Documentation:: |
| 8937 | This document. |
| 8938 | |
| 8939 | <<lttng-live,LTTng live>>:: |
| 8940 | A communication protocol between the <<lttng-relayd,relay daemon>> and |
| 8941 | live readers which makes it possible to show or analyze |
| 8942 | <<def-event-record,event records>> ``live'', as they're received by |
| 8943 | the <<def-relay-daemon,relay daemon>>. |
| 8944 | |
| 8945 | <<lttng-modules,LTTng-modules>>:: |
| 8946 | The https://github.com/lttng/lttng-modules[LTTng-modules] project, |
| 8947 | which contains the Linux kernel modules to make the Linux kernel |
| 8948 | <<def-instrumentation-point,instrumentation points>> available for |
| 8949 | <<def-lttng,LTTng>> tracing. |
| 8950 | |
| 8951 | cmd:lttng-relayd:: |
| 8952 | The name of the <<def-relay-daemon,relay daemon>> program. |
| 8953 | |
| 8954 | cmd:lttng-sessiond:: |
| 8955 | The name of the <<def-session-daemon,session daemon>> program. |
| 8956 | |
| 8957 | [[def-lttng-tools]]LTTng-tools:: |
| 8958 | The https://github.com/lttng/lttng-tools[LTTng-tools] project, which |
| 8959 | contains the various programs and libraries used to |
| 8960 | <<controlling-tracing,control tracing>>. |
| 8961 | |
| 8962 | [[def-lttng-ust]]<<lttng-ust,LTTng-UST>>:: |
| 8963 | The https://github.com/lttng/lttng-ust[LTTng-UST] project, which |
| 8964 | contains libraries to instrument |
| 8965 | <<def-user-application,user applications>>. |
| 8966 | |
| 8967 | <<lttng-ust-agents,LTTng-UST Java agent>>:: |
| 8968 | A Java package provided by the <<def-lttng-ust,LTTng-UST>> project to |
| 8969 | allow the LTTng instrumentation of `java.util.logging` and Apache |
| 8970 | log4j{nbsp}1.2 logging statements. |
| 8971 | |
| 8972 | <<lttng-ust-agents,LTTng-UST Python agent>>:: |
| 8973 | A Python package provided by the <<def-lttng-ust,LTTng-UST>> project |
| 8974 | to allow the <<def-lttng,LTTng>> instrumentation of Python logging |
| 8975 | statements. |
| 8976 | |
| 8977 | <<channel-overwrite-mode-vs-discard-mode,overwrite mode>>:: |
| 8978 | The <<def-event-record-loss-mode,event record loss mode>> in which new |
| 8979 | <<def-event-record,event records>> _overwrite_ older event records |
| 8980 | when there's no <<def-sub-buffer,sub-buffer>> space left to store |
| 8981 | them. |
| 8982 | |
| 8983 | <<channel-buffering-schemes,per-process buffering>>:: |
| 8984 | A <<def-buffering-scheme,buffering scheme>> in which each instrumented |
| 8985 | process has its own <<def-sub-buffer,sub-buffers>> for a given user |
| 8986 | space <<def-channel,channel>>. |
| 8987 | |
| 8988 | <<channel-buffering-schemes,per-user buffering>>:: |
| 8989 | A <<def-buffering-scheme,buffering scheme>> in which all the processes |
| 8990 | of a Unix user share the same <<def-sub-buffer,sub-buffers>> for a |
| 8991 | given user space <<def-channel,channel>>. |
| 8992 | |
| 8993 | [[def-proc-attr]]process attribute:: |
| 8994 | In the <<pid-tracking,process attribute inclusion set>> context: |
| 8995 | + |
| 8996 | * A process ID. |
| 8997 | * A virtual process ID. |
| 8998 | * A Unix user ID. |
| 8999 | * A virtual Unix user ID. |
| 9000 | * A Unix group ID. |
| 9001 | * A virtual Unix group ID. |
| 9002 | |
| 9003 | record (_noun_):: |
| 9004 | See <<def-event-record,_event record_>>. |
| 9005 | |
| 9006 | [[def-record]]record (_verb_):: |
| 9007 | Serialize the binary payload of an <<def-event,event>> to a |
| 9008 | <<def-sub-buffer,sub-buffer>>. |
| 9009 | |
| 9010 | [[def-recording-event-rule]]<<event,recording event rule>>:: |
| 9011 | Specific type of <<def-event-rule,event rule>> of which the action is |
| 9012 | to <<def-record,record>> the matched event to a |
| 9013 | <<def-sub-buffer,sub-buffer>>. |
| 9014 | |
| 9015 | [[def-tracing-session]][[def-recording-session]]<<tracing-session,recording session>>:: |
| 9016 | A stateful dialogue between you and a <<lttng-sessiond,session daemon>>. |
| 9017 | |
| 9018 | [[def-tracing-session-rotation]]<<session-rotation,recording session rotation>>:: |
| 9019 | The action of archiving the |
| 9020 | <<def-current-trace-chunk,current trace chunk>> of a |
| 9021 | <<def-tracing-session,recording session>>. |
| 9022 | |
| 9023 | [[def-relay-daemon]]<<lttng-relayd,relay daemon>>:: |
| 9024 | A process which is responsible for receiving the <<def-trace,trace>> |
| 9025 | data which a distant <<def-consumer-daemon,consumer daemon>> sends. |
| 9026 | |
| 9027 | [[def-ring-buffer]]ring buffer:: |
| 9028 | A set of <<def-sub-buffer,sub-buffers>>. |
| 9029 | |
| 9030 | rotation:: |
| 9031 | See _<<def-tracing-session-rotation,recording session rotation>>_. |
| 9032 | |
| 9033 | [[def-session-daemon]]<<lttng-sessiond,session daemon>>:: |
| 9034 | A process which receives control commands from you and orchestrates |
| 9035 | the <<def-tracer,tracers>> and various <<def-lttng,LTTng>> daemons. |
| 9036 | |
| 9037 | <<taking-a-snapshot,snapshot>>:: |
| 9038 | A copy of the current data of all the <<def-sub-buffer,sub-buffers>> |
| 9039 | of a given <<def-tracing-session,recording session>>, saved as |
| 9040 | <<def-trace,trace>> files. |
| 9041 | |
| 9042 | [[def-sub-buffer]]sub-buffer:: |
| 9043 | One part of an <<def-lttng,LTTng>> <<def-ring-buffer,ring buffer>> |
| 9044 | which contains <<def-event-record,event records>>. |
| 9045 | |
| 9046 | timestamp:: |
| 9047 | The time information attached to an <<def-event,event>> when LTTng |
| 9048 | creates it. |
| 9049 | |
| 9050 | [[def-trace]]trace (_noun_):: |
| 9051 | A set of: |
| 9052 | + |
| 9053 | * One https://diamon.org/ctf/[CTF] metadata stream file. |
| 9054 | * One or more CTF data stream files which are the concatenations of one |
| 9055 | or more flushed <<def-sub-buffer,sub-buffers>>. |
| 9056 | |
| 9057 | [[def-trace-verb]]trace (_verb_):: |
| 9058 | From the perspective of a <<def-tracer,tracer>>: attempt to execute |
| 9059 | one or more actions when emitting an <<def-event,event>> in an |
| 9060 | application or in a system. |
| 9061 | |
| 9062 | [[def-trace-chunk]]trace chunk:: |
| 9063 | A self-contained <<def-trace,trace>> which is part of a |
| 9064 | <<def-tracing-session,recording session>>. Each |
| 9065 | <<def-tracing-session-rotation, recording session rotation>> produces a |
| 9066 | <<def-trace-chunk-archive,trace chunk archive>>. |
| 9067 | |
| 9068 | [[def-trace-chunk-archive]]trace chunk archive:: |
| 9069 | The result of a <<def-tracing-session-rotation, recording session |
| 9070 | rotation>>. |
| 9071 | + |
| 9072 | <<def-lttng,LTTng>> doesn't manage any trace chunk archive, even if its |
| 9073 | containing <<def-tracing-session,recording session>> is still active: you |
| 9074 | are free to read it, modify it, move it, or remove it. |
| 9075 | |
| 9076 | Trace Compass:: |
| 9077 | The http://tracecompass.org[Trace Compass] project and application. |
| 9078 | |
| 9079 | [[def-tracepoint]]tracepoint:: |
| 9080 | An instrumentation point using the tracepoint mechanism of the Linux |
| 9081 | kernel or of <<def-lttng-ust,LTTng-UST>>. |
| 9082 | |
| 9083 | tracepoint definition:: |
| 9084 | The definition of a single <<def-tracepoint,tracepoint>>. |
| 9085 | |
| 9086 | tracepoint name:: |
| 9087 | The name of a <<def-tracepoint,tracepoint>>. |
| 9088 | |
| 9089 | [[def-tracepoint-provider]]tracepoint provider:: |
| 9090 | A set of functions providing <<def-tracepoint,tracepoints>> to an |
| 9091 | instrumented <<def-user-application,user application>>. |
| 9092 | + |
| 9093 | Not to be confused with a <<def-tracepoint-provider-package,tracepoint |
| 9094 | provider package>>: many tracepoint providers can exist within a |
| 9095 | tracepoint provider package. |
| 9096 | |
| 9097 | [[def-tracepoint-provider-package]]tracepoint provider package:: |
| 9098 | One or more <<def-tracepoint-provider,tracepoint providers>> compiled |
| 9099 | as an https://en.wikipedia.org/wiki/Object_file[object file] or as a |
| 9100 | link:https://en.wikipedia.org/wiki/Library_(computing)#Shared_libraries[shared |
| 9101 | library]. |
| 9102 | |
| 9103 | [[def-tracer]]tracer:: |
| 9104 | A piece of software which executes some action when it emits |
| 9105 | an <<def-event,event>>, like <<def-record,record>> it to some |
| 9106 | buffer. |
| 9107 | |
| 9108 | <<domain,tracing domain>>:: |
| 9109 | A type of LTTng <<def-tracer,tracer>>. |
| 9110 | |
| 9111 | <<tracing-group,tracing group>>:: |
| 9112 | The Unix group which a Unix user can be part of to be allowed to |
| 9113 | control the Linux kernel LTTng <<def-tracer,tracer>>. |
| 9114 | |
| 9115 | [[def-trigger]]<<trigger,trigger>>:: |
| 9116 | A <<def-condition,condition>>-<<def-action,actions>> pair; when the |
| 9117 | condition of a trigger is satisfied, LTTng attempts to execute its |
| 9118 | actions. |
| 9119 | |
| 9120 | [[def-user-application]]user application:: |
| 9121 | An application (program or library) running in user space, as opposed |
| 9122 | to a Linux kernel module, for example. |