| 1 | The LTTng Documentation |
| 2 | ======================= |
| 3 | Philippe Proulx <pproulx@efficios.com> |
| 4 | v2.12, 3 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 | getting 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 components |
| 50 | of the LTTng machinery, like the daemons, the libraries, and the |
| 51 | command-line interface. |
| 52 | * **<<instrumenting,Instrumentation>>** shows different ways to |
| 53 | instrument user applications and the Linux kernel. |
| 54 | + |
| 55 | Instrumenting source code is essential to provide a meaningful |
| 56 | source of events. |
| 57 | + |
| 58 | Skip this section if you don't have a programming background. |
| 59 | |
| 60 | * **<<controlling-tracing,Tracing control>>** is divided into topics |
| 61 | which demonstrate how to use the vast array of features that |
| 62 | LTTng{nbsp}{revision} offers. |
| 63 | * **<<reference,Reference>>** contains reference tables. |
| 64 | * **<<glossary,Glossary>>** is a specialized dictionary of terms related |
| 65 | to LTTng or to the field of software tracing. |
| 66 | |
| 67 | |
| 68 | include::../common/convention.txt[] |
| 69 | |
| 70 | |
| 71 | include::../common/acknowledgements.txt[] |
| 72 | |
| 73 | |
| 74 | [[whats-new]] |
| 75 | == What's new in LTTng{nbsp}{revision}? |
| 76 | |
| 77 | LTTng{nbsp}{revision} bears the name _Ta Meilleure_, a Northeast IPA |
| 78 | beer brewed by https://lagabiere.com/[Lagabière]. Translating to ``Your |
| 79 | best one'', this beer gives out strong aromas of passion fruit, lemon, |
| 80 | and peaches. Tastewise, expect a lot of fruit, a creamy texture, and a |
| 81 | smooth lingering hop bitterness. |
| 82 | |
| 83 | New features and changes in LTTng{nbsp}{revision}: |
| 84 | |
| 85 | Tracing control:: |
| 86 | + |
| 87 | * Clear the contents of one or more <<tracing-session,tracing sessions>> |
| 88 | without having to destroy and reconfigure them |
| 89 | with the new man:lttng-clear(1) command. |
| 90 | + |
| 91 | This is especially useful to clear the tracing data of a tracing session |
| 92 | between attempts to reproduce a problem. |
| 93 | + |
| 94 | See <<clear,Clear a tracing session>>. |
| 95 | |
| 96 | * Before LTTng{nbsp}{revision}, the man:lttng-track(1) and |
| 97 | man:lttng-untrack(1) commands used to add and remove process IDs |
| 98 | (PIDs) to a whitelist so that LTTng would only trace processes with |
| 99 | specific PIDs. |
| 100 | + |
| 101 | LTTng{nbsp}{revision} adds Unix user IDs (UIDs) and Unix group IDs |
| 102 | (GIDs) to the available <<pid-tracking,process attributes to track>>. |
| 103 | You can specify numeric user/group IDs and user/group names to track, |
| 104 | for example: |
| 105 | + |
| 106 | [role="term"] |
| 107 | ---- |
| 108 | $ lttng track --userspace --vuid=http,999 --vgid=mysql,9 |
| 109 | ---- |
| 110 | + |
| 111 | While you can also track UIDs and GIDs with the |
| 112 | opt:lttng-enable-event(1):--filter option of the `enable-event` command, |
| 113 | this dedicated process attribute tracking approach reduces tracing |
| 114 | overhead and prevents the creation of <<def-sub-buffer,sub-buffers>> for |
| 115 | the users and groups which LTTng doesn't track. |
| 116 | + |
| 117 | In the command manual pages, the term ``whitelist'' is renamed to |
| 118 | ``inclusion set'' to clarify the concept. |
| 119 | |
| 120 | * The <<lttng-relayd,relay daemon>> can now maintain many files |
| 121 | virtually opened without using as many file descriptors (FD). It does |
| 122 | so by closing and reopening FDs as needed. |
| 123 | + |
| 124 | This feature is meant as a workaround for users who can't bump the |
| 125 | system limit because of permission restrictions. |
| 126 | + |
| 127 | The new opt:lttng-relayd(8):--fd-pool-size relay daemon option |
| 128 | sets the maximum number of simultaneously opened file descriptors |
| 129 | (using the soft `RLIMIT_NOFILE` resource limit of the process by |
| 130 | default; see man:getrlimit(2)). |
| 131 | |
| 132 | * By default, the relay daemon writes its traces under a predefined |
| 133 | directory hierarchy, |
| 134 | +$LTTNG_HOME/lttng-traces/__host__/__session__/__domain__+, with: |
| 135 | + |
| 136 | -- |
| 137 | +__host__+:: |
| 138 | Remote hostname. |
| 139 | |
| 140 | +__session__+:: |
| 141 | <<tracing-session,Tracing session>> name. |
| 142 | |
| 143 | +__domain__+:: |
| 144 | <<domain,Tracing domain>> name (`ust` or `kernel`). |
| 145 | -- |
| 146 | + |
| 147 | Change this hierarchy to group traces by tracing session name rather |
| 148 | than by hostname |
| 149 | (+$LTTNG_HOME/lttng-traces/__session__/__host__/__domain__+) with the |
| 150 | new opt:lttng-relayd(8):--group-output-by-session option of the |
| 151 | relay daemon. |
| 152 | + |
| 153 | This feature is especially useful if you're tracing two or more hosts, |
| 154 | having different hostnames, which share the same tracing session name as |
| 155 | part of their configuration. In this scenario, you can use a descriptive |
| 156 | tracing session name (for example, `connection-hang`) across a fleet of |
| 157 | machines streaming to a single relay daemon. |
| 158 | |
| 159 | * The relay daemon has a new opt:lttng-relayd(8):--working-directory |
| 160 | option to override its working directory. |
| 161 | |
| 162 | Linux kernel tracing:: |
| 163 | + |
| 164 | * New instrumentation hooks to trace the entry and exit tracepoints of |
| 165 | the network reception code paths of the Linux kernel. |
| 166 | + |
| 167 | Use the resulting event records to identify the bounds of a network |
| 168 | reception and link the events that occur in the interim (for example, |
| 169 | wake-ups) to a specific network reception instance. You can also |
| 170 | analyze the latency of the network stack thanks to those event records. |
| 171 | |
| 172 | * The `thread` field of the `irqaction` structure, which specifies the |
| 173 | process to wake up when a threaded interrupt request (IRQ) occurs, is |
| 174 | now part of the `lttng_statedump_interrupt` event record. |
| 175 | + |
| 176 | Use this information to discover which processes handle the various |
| 177 | IRQs. You can also associate the events occurring in the context of |
| 178 | those processes with their respective IRQ. |
| 179 | |
| 180 | * New `lttng_statedump_cpu_topology` tracepoint to record the active |
| 181 | CPU/NUMA topology. |
| 182 | + |
| 183 | Use this information to discover which CPUs are SMT siblings or part of |
| 184 | the same socket. As of LTTng{nbsp}{revision}, only the x86 architecture |
| 185 | is supported since all architectures describe their topologies |
| 186 | differently. |
| 187 | + |
| 188 | The `architecture` field of the tracepoint is statically defined and |
| 189 | exists for all architecture implementations. Analysis tools can |
| 190 | therefore anticipate the layout of the event record. |
| 191 | + |
| 192 | Event record example: |
| 193 | + |
| 194 | [source,yaml] |
| 195 | ---- |
| 196 | lttng_statedump_cpu_topology: |
| 197 | architecture: x86 |
| 198 | cpu_id: 0 |
| 199 | vendor: GenuineIntel |
| 200 | family: 6 |
| 201 | model: 142 |
| 202 | model_name: Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz |
| 203 | physical_id: 0 |
| 204 | core_id: 0 |
| 205 | cores: 2 |
| 206 | ---- |
| 207 | |
| 208 | * New product UUID metadata environment field, `product_uuid`, |
| 209 | which LTTng copies from the |
| 210 | https://en.wikipedia.org/wiki/Desktop_Management_Interface[Desktop |
| 211 | Management Interface] (DMI). |
| 212 | + |
| 213 | Use this environment field to uniquely identify a machine (virtual or |
| 214 | physical) in order to correlate traces from multiple virtual machines. |
| 215 | |
| 216 | |
| 217 | [[nuts-and-bolts]] |
| 218 | == Nuts and bolts |
| 219 | |
| 220 | What is LTTng? As its name suggests, the _Linux Trace Toolkit: next |
| 221 | generation_ is a modern toolkit for tracing Linux systems and |
| 222 | applications. So your first question might be: |
| 223 | **what is tracing?** |
| 224 | |
| 225 | |
| 226 | [[what-is-tracing]] |
| 227 | === What is tracing? |
| 228 | |
| 229 | As the history of software engineering progressed and led to what |
| 230 | we now take for granted--complex, numerous and |
| 231 | interdependent software applications running in parallel on |
| 232 | sophisticated operating systems like Linux--the authors of such |
| 233 | components, software developers, began feeling a natural |
| 234 | urge to have tools that would ensure the robustness and good performance |
| 235 | of their masterpieces. |
| 236 | |
| 237 | One major achievement in this field is, inarguably, the |
| 238 | https://www.gnu.org/software/gdb/[GNU debugger (GDB)], |
| 239 | an essential tool for developers to find and fix bugs. But even the best |
| 240 | debugger won't help make your software run faster, and nowadays, faster |
| 241 | software means either more work done by the same hardware, or cheaper |
| 242 | hardware for the same work. |
| 243 | |
| 244 | A _profiler_ is often the tool of choice to identify performance |
| 245 | bottlenecks. Profiling is suitable to identify _where_ performance is |
| 246 | lost in a given software. The profiler outputs a profile, a statistical |
| 247 | summary of observed events, which you may use to discover which |
| 248 | functions took the most time to execute. However, a profiler won't |
| 249 | report _why_ some identified functions are the bottleneck. Bottlenecks |
| 250 | might only occur when specific conditions are met, conditions that are |
| 251 | sometimes impossible to capture by a statistical profiler, or impossible |
| 252 | to reproduce with an application altered by the overhead of an |
| 253 | event-based profiler. For a thorough investigation of software |
| 254 | performance issues, a history of execution is essential, with the |
| 255 | recorded values of variables and context fields you choose, and |
| 256 | with as little influence as possible on the instrumented software. This |
| 257 | is where tracing comes in handy. |
| 258 | |
| 259 | _Tracing_ is a technique used to understand what goes on in a running |
| 260 | software system. The software used for tracing is called a _tracer_, |
| 261 | which is conceptually similar to a tape recorder. When recording, |
| 262 | specific instrumentation points placed in the software source code |
| 263 | generate events that are saved on a giant tape: a _trace_ file. You |
| 264 | can trace user applications and the operating system at the same time, |
| 265 | opening the possibility of resolving a wide range of problems that would |
| 266 | otherwise be extremely challenging. |
| 267 | |
| 268 | Tracing is often compared to _logging_. However, tracers and loggers are |
| 269 | two different tools, serving two different purposes. Tracers are |
| 270 | designed to record much lower-level events that occur much more |
| 271 | frequently than log messages, often in the range of thousands per |
| 272 | second, with very little execution overhead. Logging is more appropriate |
| 273 | for a very high-level analysis of less frequent events: user accesses, |
| 274 | exceptional conditions (errors and warnings, for example), database |
| 275 | transactions, instant messaging communications, and such. Simply put, |
| 276 | logging is one of the many use cases that can be satisfied with tracing. |
| 277 | |
| 278 | The list of recorded events inside a trace file can be read manually |
| 279 | like a log file for the maximum level of detail, but it is generally |
| 280 | much more interesting to perform application-specific analyses to |
| 281 | produce reduced statistics and graphs that are useful to resolve a |
| 282 | given problem. Trace viewers and analyzers are specialized tools |
| 283 | designed to do this. |
| 284 | |
| 285 | In the end, this is what LTTng is: a powerful, open source set of |
| 286 | tools to trace the Linux kernel and user applications at the same time. |
| 287 | LTTng is composed of several components actively maintained and |
| 288 | developed by its link:/community/#where[community]. |
| 289 | |
| 290 | |
| 291 | [[lttng-alternatives]] |
| 292 | === Alternatives to noch:{LTTng} |
| 293 | |
| 294 | Excluding proprietary solutions, a few competing software tracers |
| 295 | exist for Linux: |
| 296 | |
| 297 | https://github.com/dtrace4linux/linux[dtrace4linux]:: |
| 298 | A port of Sun Microsystems' DTrace to Linux. |
| 299 | + |
| 300 | The cmd:dtrace tool interprets user scripts and is responsible for |
| 301 | loading code into the Linux kernel for further execution and collecting |
| 302 | the outputted data. |
| 303 | |
| 304 | https://en.wikipedia.org/wiki/Berkeley_Packet_Filter[eBPF]:: |
| 305 | A subsystem in the Linux kernel in which a virtual machine can |
| 306 | execute programs passed from the user space to the kernel. |
| 307 | + |
| 308 | You can attach such programs to tracepoints and kprobes thanks to a |
| 309 | system call, and they can output data to the user space when executed |
| 310 | thanks to different mechanisms (pipe, VM register values, and eBPF maps, |
| 311 | to name a few). |
| 312 | |
| 313 | https://www.kernel.org/doc/Documentation/trace/ftrace.txt[ftrace]:: |
| 314 | The de facto function tracer of the Linux kernel. |
| 315 | + |
| 316 | Its user interface is a set of special files in sysfs. |
| 317 | |
| 318 | https://perf.wiki.kernel.org/[perf]:: |
| 319 | A performance analysis tool for Linux which supports hardware |
| 320 | performance counters, tracepoints, as well as other counters and |
| 321 | types of probes. |
| 322 | + |
| 323 | The controlling utility of perf is the cmd:perf command line/text UI |
| 324 | tool. |
| 325 | |
| 326 | http://linux.die.net/man/1/strace[strace]:: |
| 327 | A command-line utility which records system calls made by a |
| 328 | user process, as well as signal deliveries and changes of process |
| 329 | state. |
| 330 | + |
| 331 | strace makes use of https://en.wikipedia.org/wiki/Ptrace[ptrace] to |
| 332 | fulfill its function. |
| 333 | |
| 334 | http://www.sysdig.org/[sysdig]:: |
| 335 | Like SystemTap, uses scripts to analyze Linux kernel events. |
| 336 | + |
| 337 | You write scripts, or _chisels_ in the jargon of sysdig, in Lua and |
| 338 | sysdig executes them while it traces the system or afterwards. The |
| 339 | interface of sysdig is the cmd:sysdig command-line tool as well as the |
| 340 | text UI-based cmd:csysdig tool. |
| 341 | |
| 342 | https://sourceware.org/systemtap/[SystemTap]:: |
| 343 | A Linux kernel and user space tracer which uses custom user scripts |
| 344 | to produce plain text traces. |
| 345 | + |
| 346 | SystemTap converts the scripts to the C language, and then compiles them |
| 347 | as Linux kernel modules which are loaded to produce trace data. The |
| 348 | primary user interface of SystemTap is the cmd:stap command-line tool. |
| 349 | |
| 350 | The main distinctive features of LTTng is that it produces correlated |
| 351 | kernel and user space traces, as well as doing so with the lowest |
| 352 | overhead amongst other solutions. It produces trace files in the |
| 353 | http://diamon.org/ctf[CTF] format, a file format optimized |
| 354 | for the production and analyses of multi-gigabyte data. |
| 355 | |
| 356 | LTTng is the result of more than 10{nbsp}years of active open source |
| 357 | development by a community of passionate developers. LTTng is currently |
| 358 | available on major desktop and server Linux distributions. |
| 359 | |
| 360 | The main interface for tracing control is a single command-line tool |
| 361 | named cmd:lttng. The latter can create several tracing sessions, enable |
| 362 | and disable events on the fly, filter events efficiently with custom |
| 363 | user expressions, start and stop tracing, and much more. LTTng can |
| 364 | record the traces on the file system or send them over the network, and |
| 365 | keep them totally or partially. You can view the traces once tracing |
| 366 | becomes inactive or in real-time. |
| 367 | |
| 368 | <<installing-lttng,Install LTTng now>> and |
| 369 | <<getting-started,start tracing>>! |
| 370 | |
| 371 | |
| 372 | [[installing-lttng]] |
| 373 | == Installation |
| 374 | |
| 375 | **LTTng** is a set of software <<plumbing,components>> which interact to |
| 376 | <<instrumenting,instrument>> the Linux kernel and user applications, and |
| 377 | to <<controlling-tracing,control tracing>> (start and stop |
| 378 | tracing, enable and disable event rules, and the rest). Those |
| 379 | components are bundled into the following packages: |
| 380 | |
| 381 | LTTng-tools:: |
| 382 | Libraries and command-line interface to control tracing. |
| 383 | |
| 384 | LTTng-modules:: |
| 385 | Linux kernel modules to instrument and trace the kernel. |
| 386 | |
| 387 | LTTng-UST:: |
| 388 | Libraries and Java/Python packages to instrument and trace user |
| 389 | applications. |
| 390 | |
| 391 | Most distributions mark the LTTng-modules and LTTng-UST packages as |
| 392 | optional when installing LTTng-tools (which is always required). In the |
| 393 | following sections, we always provide the steps to install all three, |
| 394 | but note that: |
| 395 | |
| 396 | * You only need to install LTTng-modules if you intend to trace the |
| 397 | Linux kernel. |
| 398 | * You only need to install LTTng-UST if you intend to trace user |
| 399 | applications. |
| 400 | |
| 401 | [role="growable"] |
| 402 | .Availability of LTTng{nbsp}{revision} for major Linux distributions as of 3{nbsp}November{nbsp}2023. |
| 403 | |==== |
| 404 | |Distribution |Available in releases |
| 405 | |
| 406 | |https://www.ubuntu.com/[Ubuntu] |
| 407 | |Ubuntu{nbsp}16.04 _Xenial Xerus_, Ubuntu{nbsp}18.04 _Bionic Beaver_, |
| 408 | Ubuntu{nbsp}20.04 _Focal Fossa_, and Ubuntu{nbsp}22.04 _Jammy Jellyfish_: |
| 409 | <<ubuntu-ppa,use the LTTng Stable{nbsp}{revision} PPA>>. |
| 410 | |
| 411 | |https://www.debian.org/[Debian] |
| 412 | |<<debian,Debian{nbsp}11 _bullseye_>>. |
| 413 | |
| 414 | |https://www.redhat.com/[RHEL] and https://www.suse.com/[SLES] |
| 415 | |See http://packages.efficios.com/[EfficiOS Enterprise Packages]. |
| 416 | |
| 417 | |https://alpinelinux.org/[Alpine Linux] |
| 418 | |xref:alpine-linux[Alpine Linux{nbsp}3.12, Alpine Linux{nbsp}3.13, |
| 419 | Alpine Linux{nbsp}3.14, and Alpine Linux{nbsp}3.15]. |
| 420 | |
| 421 | |https://buildroot.org/[Buildroot] |
| 422 | |xref:buildroot[Buildroot{nbsp}2020.08, Buildroot{nbsp}2020.11, |
| 423 | Builroot{nbsp}2021.02, Buildroot{nbsp}2021.05, Buildroot{nbsp}2021.08, |
| 424 | and Builroot{nbsp}2021.11]. |
| 425 | |
| 426 | |https://www.openembedded.org/wiki/Main_Page[OpenEmbedded] and |
| 427 | https://www.yoctoproject.org/[Yocto] |
| 428 | |xref:oe-yocto[Yocto Project{nbsp}3.2 _Gatesgarth_ and Yocto Project{nbsp}3.3 _Hardknott_]. |
| 429 | |==== |
| 430 | |
| 431 | |
| 432 | [[ubuntu-ppa]] |
| 433 | === Ubuntu: noch:{LTTng} Stable {revision} PPA |
| 434 | |
| 435 | The https://launchpad.net/~lttng/+archive/ubuntu/stable-{revision}[LTTng |
| 436 | Stable{nbsp}{revision} PPA] offers the latest stable |
| 437 | LTTng{nbsp}{revision} packages for Ubuntu{nbsp}16.04 _Xenial Xerus_, |
| 438 | Ubuntu{nbsp}18.04 _Bionic Beaver_, Ubuntu{nbsp}20.04 _Focal Fossa_, |
| 439 | and Ubuntu{nbsp}22.04 _Jammy Jellyfish_. |
| 440 | |
| 441 | To install LTTng{nbsp}{revision} from the LTTng Stable{nbsp}{revision} |
| 442 | PPA: |
| 443 | |
| 444 | . Add the LTTng Stable{nbsp}{revision} PPA repository and update the |
| 445 | list of packages: |
| 446 | + |
| 447 | -- |
| 448 | [role="term"] |
| 449 | ---- |
| 450 | # apt-add-repository ppa:lttng/stable-2.12 |
| 451 | # apt-get update |
| 452 | ---- |
| 453 | -- |
| 454 | |
| 455 | . Install the main LTTng{nbsp}{revision} packages: |
| 456 | + |
| 457 | -- |
| 458 | [role="term"] |
| 459 | ---- |
| 460 | # apt-get install lttng-tools |
| 461 | # apt-get install lttng-modules-dkms |
| 462 | # apt-get install liblttng-ust-dev |
| 463 | ---- |
| 464 | -- |
| 465 | |
| 466 | . **If you need to instrument and trace |
| 467 | <<java-application,Java applications>>**, install the LTTng-UST |
| 468 | Java agent: |
| 469 | + |
| 470 | -- |
| 471 | [role="term"] |
| 472 | ---- |
| 473 | # apt-get install liblttng-ust-agent-java |
| 474 | ---- |
| 475 | -- |
| 476 | |
| 477 | . **If you need to instrument and trace |
| 478 | <<python-application,Python{nbsp}3 applications>>**, install the |
| 479 | LTTng-UST Python agent: |
| 480 | + |
| 481 | -- |
| 482 | [role="term"] |
| 483 | ---- |
| 484 | # apt-get install python3-lttngust |
| 485 | ---- |
| 486 | -- |
| 487 | |
| 488 | |
| 489 | [[debian]] |
| 490 | === Debian |
| 491 | |
| 492 | To install LTTng{nbsp}{revision} on Debian{nbsp}11 _bullseye_: |
| 493 | |
| 494 | . Install the main LTTng{nbsp}{revision} packages: |
| 495 | + |
| 496 | -- |
| 497 | [role="term"] |
| 498 | ---- |
| 499 | # apt-get install lttng-modules-dkms |
| 500 | # apt-get install liblttng-ust-dev |
| 501 | # apt-get install lttng-tools |
| 502 | ---- |
| 503 | -- |
| 504 | |
| 505 | . **If you need to instrument and trace <<java-application,Java |
| 506 | applications>>**, install the LTTng-UST Java agent: |
| 507 | + |
| 508 | -- |
| 509 | [role="term"] |
| 510 | ---- |
| 511 | # apt-get install liblttng-ust-agent-java |
| 512 | ---- |
| 513 | -- |
| 514 | |
| 515 | . **If you need to instrument and trace <<python-application,Python |
| 516 | applications>>**, install the LTTng-UST Python agent: |
| 517 | + |
| 518 | -- |
| 519 | [role="term"] |
| 520 | ---- |
| 521 | # apt-get install python3-lttngust |
| 522 | ---- |
| 523 | -- |
| 524 | |
| 525 | [[alpine-linux]] |
| 526 | === Alpine Linux |
| 527 | |
| 528 | To install LTTng-tools{nbsp}{revision} and LTTng-UST{nbsp}{revision} on |
| 529 | Alpine Linux{nbsp}3.12, Alpine Linux{nbsp}3.13, Alpine Linux{nbsp}3.14, |
| 530 | or Alpine Linux{nbsp}3.15: |
| 531 | |
| 532 | . Add the LTTng packages: |
| 533 | + |
| 534 | -- |
| 535 | [role="term"] |
| 536 | ---- |
| 537 | # apk add lttng-tools |
| 538 | # apk add lttng-ust-dev |
| 539 | ---- |
| 540 | -- |
| 541 | |
| 542 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: |
| 543 | + |
| 544 | -- |
| 545 | [role="term"] |
| 546 | ---- |
| 547 | $ cd $(mktemp -d) && |
| 548 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.12.tar.bz2 && |
| 549 | tar -xf lttng-modules-latest-2.12.tar.bz2 && |
| 550 | cd lttng-modules-2.12.* && |
| 551 | make && |
| 552 | sudo make modules_install && |
| 553 | sudo depmod -a |
| 554 | ---- |
| 555 | -- |
| 556 | |
| 557 | |
| 558 | [[buildroot]] |
| 559 | === Buildroot |
| 560 | |
| 561 | To install LTTng{nbsp}{revision} on Buildroot{nbsp}2020.08, Buildroot{nbsp}2020.11, |
| 562 | Buildroot{nbsp}2021.02, Buildroot{nbsp}2021.05, Buildroot{nbsp}2021.08, or |
| 563 | Buildroot{nbsp}2021.11: |
| 564 | |
| 565 | . Launch the Buildroot configuration tool: |
| 566 | + |
| 567 | -- |
| 568 | [role="term"] |
| 569 | ---- |
| 570 | $ make menuconfig |
| 571 | ---- |
| 572 | -- |
| 573 | |
| 574 | . In **Kernel**, check **Linux kernel**. |
| 575 | . In **Toolchain**, check **Enable WCHAR support**. |
| 576 | . In **Target packages**{nbsp}→ **Debugging, profiling and benchmark**, |
| 577 | check **lttng-modules** and **lttng-tools**. |
| 578 | . In **Target packages**{nbsp}→ **Libraries**{nbsp}→ |
| 579 | **Other**, check **lttng-libust**. |
| 580 | |
| 581 | |
| 582 | [[oe-yocto]] |
| 583 | === OpenEmbedded and Yocto |
| 584 | |
| 585 | LTTng{nbsp}{revision} recipes are available in the |
| 586 | https://layers.openembedded.org/layerindex/branch/master/layer/openembedded-core/[`openembedded-core`] |
| 587 | layer for Yocto Project{nbsp}3.2 _Gatesgarth_ and Yocto Project{nbsp}3.3 _Hardknott_ |
| 588 | under the following names: |
| 589 | |
| 590 | * `lttng-tools` |
| 591 | * `lttng-modules` |
| 592 | * `lttng-ust` |
| 593 | |
| 594 | With BitBake, the simplest way to include LTTng recipes in your target |
| 595 | image is to add them to `IMAGE_INSTALL_append` in path:{conf/local.conf}: |
| 596 | |
| 597 | ---- |
| 598 | IMAGE_INSTALL_append = " lttng-tools lttng-modules lttng-ust" |
| 599 | ---- |
| 600 | |
| 601 | If you use Hob: |
| 602 | |
| 603 | . Select a machine and an image recipe. |
| 604 | . Click **Edit image recipe**. |
| 605 | . Under the **All recipes** tab, search for **lttng**. |
| 606 | . Check the desired LTTng recipes. |
| 607 | |
| 608 | |
| 609 | [[building-from-source]] |
| 610 | === Build from source |
| 611 | |
| 612 | To build and install LTTng{nbsp}{revision} from source: |
| 613 | |
| 614 | . Using the package manager of your distribution, or from source, |
| 615 | install the following dependencies of LTTng-tools and LTTng-UST: |
| 616 | + |
| 617 | -- |
| 618 | * https://sourceforge.net/projects/libuuid/[libuuid] |
| 619 | * http://directory.fsf.org/wiki/Popt[popt] |
| 620 | * http://liburcu.org/[Userspace RCU] |
| 621 | * http://www.xmlsoft.org/[libxml2] |
| 622 | * **Optional**: https://github.com/numactl/numactl[numactl] |
| 623 | -- |
| 624 | |
| 625 | . Download, build, and install the latest LTTng-modules{nbsp}{revision}: |
| 626 | + |
| 627 | -- |
| 628 | [role="term"] |
| 629 | ---- |
| 630 | $ cd $(mktemp -d) && |
| 631 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.12.tar.bz2 && |
| 632 | tar -xf lttng-modules-latest-2.12.tar.bz2 && |
| 633 | cd lttng-modules-2.12.* && |
| 634 | make && |
| 635 | sudo make modules_install && |
| 636 | sudo depmod -a |
| 637 | ---- |
| 638 | -- |
| 639 | |
| 640 | . Download, build, and install the latest LTTng-UST{nbsp}{revision}: |
| 641 | + |
| 642 | -- |
| 643 | [role="term"] |
| 644 | ---- |
| 645 | $ cd $(mktemp -d) && |
| 646 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.12.tar.bz2 && |
| 647 | tar -xf lttng-ust-latest-2.12.tar.bz2 && |
| 648 | cd lttng-ust-2.12.* && |
| 649 | ./configure && |
| 650 | make && |
| 651 | sudo make install && |
| 652 | sudo ldconfig |
| 653 | ---- |
| 654 | -- |
| 655 | + |
| 656 | Add `--disable-numa` to `./configure` if you don't have |
| 657 | https://github.com/numactl/numactl[numactl]. |
| 658 | + |
| 659 | -- |
| 660 | [IMPORTANT] |
| 661 | .Java and Python application tracing |
| 662 | ==== |
| 663 | If you need to instrument and trace <<java-application,Java |
| 664 | applications>>, pass the `--enable-java-agent-jul`, |
| 665 | `--enable-java-agent-log4j`, or `--enable-java-agent-all` options to the |
| 666 | `configure` script, depending on which Java logging framework you use. |
| 667 | |
| 668 | If you need to instrument and trace <<python-application,Python |
| 669 | applications>>, pass the `--enable-python-agent` option to the |
| 670 | `configure` script. You can set the `PYTHON` environment variable to the |
| 671 | path to the Python interpreter for which to install the LTTng-UST Python |
| 672 | agent package. |
| 673 | ==== |
| 674 | -- |
| 675 | + |
| 676 | -- |
| 677 | [NOTE] |
| 678 | ==== |
| 679 | By default, LTTng-UST libraries are installed to |
| 680 | dir:{/usr/local/lib}, which is the de facto directory in which to |
| 681 | keep self-compiled and third-party libraries. |
| 682 | |
| 683 | When <<building-tracepoint-providers-and-user-application,linking an |
| 684 | instrumented user application with `liblttng-ust`>>: |
| 685 | |
| 686 | * Append `/usr/local/lib` to the env:LD_LIBRARY_PATH environment |
| 687 | variable. |
| 688 | * Pass the `-L/usr/local/lib` and `-Wl,-rpath,/usr/local/lib` options to |
| 689 | man:gcc(1), man:g++(1), or man:clang(1). |
| 690 | ==== |
| 691 | -- |
| 692 | |
| 693 | . Download, build, and install the latest LTTng-tools{nbsp}{revision}: |
| 694 | + |
| 695 | -- |
| 696 | [role="term"] |
| 697 | ---- |
| 698 | $ cd $(mktemp -d) && |
| 699 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.12.tar.bz2 && |
| 700 | tar -xf lttng-tools-latest-2.12.tar.bz2 && |
| 701 | cd lttng-tools-2.12.* && |
| 702 | ./configure && |
| 703 | make && |
| 704 | sudo make install && |
| 705 | sudo ldconfig |
| 706 | ---- |
| 707 | -- |
| 708 | |
| 709 | TIP: The https://github.com/eepp/vlttng[vlttng tool] can do all the |
| 710 | previous steps automatically for a given version of LTTng and confine |
| 711 | the installed files in a specific directory. This can be useful to test |
| 712 | LTTng without installing it on your system. |
| 713 | |
| 714 | |
| 715 | [[getting-started]] |
| 716 | == Quick start |
| 717 | |
| 718 | This is a short guide to get started quickly with LTTng kernel and user |
| 719 | space tracing. |
| 720 | |
| 721 | Before you follow this guide, make sure to <<installing-lttng,install>> |
| 722 | LTTng. |
| 723 | |
| 724 | This tutorial walks you through the steps to: |
| 725 | |
| 726 | . <<tracing-the-linux-kernel,Trace the Linux kernel>>. |
| 727 | . <<tracing-your-own-user-application,Trace a user application>> written |
| 728 | in C. |
| 729 | . <<viewing-and-analyzing-your-traces,View and analyze the |
| 730 | recorded events>>. |
| 731 | |
| 732 | |
| 733 | [[tracing-the-linux-kernel]] |
| 734 | === Trace the Linux kernel |
| 735 | |
| 736 | The following command lines start with the `#` prompt because you need |
| 737 | root privileges to trace the Linux kernel. You can also trace the kernel |
| 738 | as a regular user if your Unix user is a member of the |
| 739 | <<tracing-group,tracing group>>. |
| 740 | |
| 741 | . Create a <<tracing-session,tracing session>> which writes its traces |
| 742 | to dir:{/tmp/my-kernel-trace}: |
| 743 | + |
| 744 | -- |
| 745 | [role="term"] |
| 746 | ---- |
| 747 | # lttng create my-kernel-session --output=/tmp/my-kernel-trace |
| 748 | ---- |
| 749 | -- |
| 750 | |
| 751 | . List the available kernel tracepoints and system calls: |
| 752 | + |
| 753 | -- |
| 754 | [role="term"] |
| 755 | ---- |
| 756 | # lttng list --kernel |
| 757 | # lttng list --kernel --syscall |
| 758 | ---- |
| 759 | -- |
| 760 | |
| 761 | . Create <<event,event rules>> which match the desired instrumentation |
| 762 | point names, for example the `sched_switch` and `sched_process_fork` |
| 763 | tracepoints, and the man:open(2) and man:close(2) system calls: |
| 764 | + |
| 765 | -- |
| 766 | [role="term"] |
| 767 | ---- |
| 768 | # lttng enable-event --kernel sched_switch,sched_process_fork |
| 769 | # lttng enable-event --kernel --syscall open,close |
| 770 | ---- |
| 771 | -- |
| 772 | + |
| 773 | Create an event rule which matches _all_ the Linux kernel |
| 774 | tracepoints with the opt:lttng-enable-event(1):--all option |
| 775 | (this will generate a lot of data when tracing): |
| 776 | + |
| 777 | -- |
| 778 | [role="term"] |
| 779 | ---- |
| 780 | # lttng enable-event --kernel --all |
| 781 | ---- |
| 782 | -- |
| 783 | |
| 784 | . <<basic-tracing-session-control,Start tracing>>: |
| 785 | + |
| 786 | -- |
| 787 | [role="term"] |
| 788 | ---- |
| 789 | # lttng start |
| 790 | ---- |
| 791 | -- |
| 792 | |
| 793 | . Do some operation on your system for a few seconds. For example, |
| 794 | load a website, or list the files of a directory. |
| 795 | . <<creating-destroying-tracing-sessions,Destroy>> the current |
| 796 | tracing session: |
| 797 | + |
| 798 | -- |
| 799 | [role="term"] |
| 800 | ---- |
| 801 | # lttng destroy |
| 802 | ---- |
| 803 | -- |
| 804 | + |
| 805 | The man:lttng-destroy(1) command doesn't destroy the trace data; it |
| 806 | only destroys the state of the tracing session. |
| 807 | + |
| 808 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) command |
| 809 | implicitly (see <<basic-tracing-session-control,Start and stop a tracing |
| 810 | session>>). You need to stop tracing to make LTTng flush the remaining |
| 811 | trace data and make the trace readable. |
| 812 | |
| 813 | . For the sake of this example, make the recorded trace accessible to |
| 814 | the non-root users: |
| 815 | + |
| 816 | -- |
| 817 | [role="term"] |
| 818 | ---- |
| 819 | # chown -R $(whoami) /tmp/my-kernel-trace |
| 820 | ---- |
| 821 | -- |
| 822 | |
| 823 | See <<viewing-and-analyzing-your-traces,View and analyze the |
| 824 | recorded events>> to view the recorded events. |
| 825 | |
| 826 | |
| 827 | [[tracing-your-own-user-application]] |
| 828 | === Trace a user application |
| 829 | |
| 830 | This section steps you through a simple example to trace a |
| 831 | _Hello world_ program written in C. |
| 832 | |
| 833 | To create the traceable user application: |
| 834 | |
| 835 | . Create the tracepoint provider header file, which defines the |
| 836 | tracepoints and the events they can generate: |
| 837 | + |
| 838 | -- |
| 839 | [source,c] |
| 840 | .path:{hello-tp.h} |
| 841 | ---- |
| 842 | #undef TRACEPOINT_PROVIDER |
| 843 | #define TRACEPOINT_PROVIDER hello_world |
| 844 | |
| 845 | #undef TRACEPOINT_INCLUDE |
| 846 | #define TRACEPOINT_INCLUDE "./hello-tp.h" |
| 847 | |
| 848 | #if !defined(_HELLO_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) |
| 849 | #define _HELLO_TP_H |
| 850 | |
| 851 | #include <lttng/tracepoint.h> |
| 852 | |
| 853 | TRACEPOINT_EVENT( |
| 854 | hello_world, |
| 855 | my_first_tracepoint, |
| 856 | TP_ARGS( |
| 857 | int, my_integer_arg, |
| 858 | char*, my_string_arg |
| 859 | ), |
| 860 | TP_FIELDS( |
| 861 | ctf_string(my_string_field, my_string_arg) |
| 862 | ctf_integer(int, my_integer_field, my_integer_arg) |
| 863 | ) |
| 864 | ) |
| 865 | |
| 866 | #endif /* _HELLO_TP_H */ |
| 867 | |
| 868 | #include <lttng/tracepoint-event.h> |
| 869 | ---- |
| 870 | -- |
| 871 | |
| 872 | . Create the tracepoint provider package source file: |
| 873 | + |
| 874 | -- |
| 875 | [source,c] |
| 876 | .path:{hello-tp.c} |
| 877 | ---- |
| 878 | #define TRACEPOINT_CREATE_PROBES |
| 879 | #define TRACEPOINT_DEFINE |
| 880 | |
| 881 | #include "hello-tp.h" |
| 882 | ---- |
| 883 | -- |
| 884 | |
| 885 | . Build the tracepoint provider package: |
| 886 | + |
| 887 | -- |
| 888 | [role="term"] |
| 889 | ---- |
| 890 | $ gcc -c -I. hello-tp.c |
| 891 | ---- |
| 892 | -- |
| 893 | |
| 894 | . Create the _Hello World_ application source file: |
| 895 | + |
| 896 | -- |
| 897 | [source,c] |
| 898 | .path:{hello.c} |
| 899 | ---- |
| 900 | #include <stdio.h> |
| 901 | #include "hello-tp.h" |
| 902 | |
| 903 | int main(int argc, char *argv[]) |
| 904 | { |
| 905 | int x; |
| 906 | |
| 907 | puts("Hello, World!\nPress Enter to continue..."); |
| 908 | |
| 909 | /* |
| 910 | * The following getchar() call is only placed here for the purpose |
| 911 | * of this demonstration, to pause the application in order for |
| 912 | * you to have time to list its tracepoints. It's not needed |
| 913 | * otherwise. |
| 914 | */ |
| 915 | getchar(); |
| 916 | |
| 917 | /* |
| 918 | * A tracepoint() call. |
| 919 | * |
| 920 | * Arguments, as defined in hello-tp.h: |
| 921 | * |
| 922 | * 1. Tracepoint provider name (required) |
| 923 | * 2. Tracepoint name (required) |
| 924 | * 3. my_integer_arg (first user-defined argument) |
| 925 | * 4. my_string_arg (second user-defined argument) |
| 926 | * |
| 927 | * Notice the tracepoint provider and tracepoint names are |
| 928 | * NOT strings: they are in fact parts of variables that the |
| 929 | * macros in hello-tp.h create. |
| 930 | */ |
| 931 | tracepoint(hello_world, my_first_tracepoint, 23, "hi there!"); |
| 932 | |
| 933 | for (x = 0; x < argc; ++x) { |
| 934 | tracepoint(hello_world, my_first_tracepoint, x, argv[x]); |
| 935 | } |
| 936 | |
| 937 | puts("Quitting now!"); |
| 938 | tracepoint(hello_world, my_first_tracepoint, x * x, "x^2"); |
| 939 | |
| 940 | return 0; |
| 941 | } |
| 942 | ---- |
| 943 | -- |
| 944 | |
| 945 | . Build the application: |
| 946 | + |
| 947 | -- |
| 948 | [role="term"] |
| 949 | ---- |
| 950 | $ gcc -c hello.c |
| 951 | ---- |
| 952 | -- |
| 953 | |
| 954 | . Link the application with the tracepoint provider package, |
| 955 | `liblttng-ust`, and `libdl`: |
| 956 | + |
| 957 | -- |
| 958 | [role="term"] |
| 959 | ---- |
| 960 | $ gcc -o hello hello.o hello-tp.o -llttng-ust -ldl |
| 961 | ---- |
| 962 | -- |
| 963 | |
| 964 | Here's the whole build process: |
| 965 | |
| 966 | [role="img-100"] |
| 967 | .Build steps of the user space tracing tutorial. |
| 968 | image::ust-flow.png[] |
| 969 | |
| 970 | To trace the user application: |
| 971 | |
| 972 | . Run the application with a few arguments: |
| 973 | + |
| 974 | -- |
| 975 | [role="term"] |
| 976 | ---- |
| 977 | $ ./hello world and beyond |
| 978 | ---- |
| 979 | -- |
| 980 | + |
| 981 | You see: |
| 982 | + |
| 983 | -- |
| 984 | ---- |
| 985 | Hello, World! |
| 986 | Press Enter to continue... |
| 987 | ---- |
| 988 | -- |
| 989 | |
| 990 | . Start an LTTng <<lttng-sessiond,session daemon>>: |
| 991 | + |
| 992 | -- |
| 993 | [role="term"] |
| 994 | ---- |
| 995 | $ lttng-sessiond --daemonize |
| 996 | ---- |
| 997 | -- |
| 998 | + |
| 999 | Note that a session daemon might already be running, for example as a |
| 1000 | service that the service manager of the distribution started. |
| 1001 | |
| 1002 | . List the available user space tracepoints: |
| 1003 | + |
| 1004 | -- |
| 1005 | [role="term"] |
| 1006 | ---- |
| 1007 | $ lttng list --userspace |
| 1008 | ---- |
| 1009 | -- |
| 1010 | + |
| 1011 | You see the `hello_world:my_first_tracepoint` tracepoint listed |
| 1012 | under the `./hello` process. |
| 1013 | |
| 1014 | . Create a <<tracing-session,tracing session>>: |
| 1015 | + |
| 1016 | -- |
| 1017 | [role="term"] |
| 1018 | ---- |
| 1019 | $ lttng create my-user-space-session |
| 1020 | ---- |
| 1021 | -- |
| 1022 | |
| 1023 | . Create an <<event,event rule>> which matches the |
| 1024 | `hello_world:my_first_tracepoint` event name: |
| 1025 | + |
| 1026 | -- |
| 1027 | [role="term"] |
| 1028 | ---- |
| 1029 | $ lttng enable-event --userspace hello_world:my_first_tracepoint |
| 1030 | ---- |
| 1031 | -- |
| 1032 | |
| 1033 | . <<basic-tracing-session-control,Start tracing>>: |
| 1034 | + |
| 1035 | -- |
| 1036 | [role="term"] |
| 1037 | ---- |
| 1038 | $ lttng start |
| 1039 | ---- |
| 1040 | -- |
| 1041 | |
| 1042 | . Go back to the running `hello` application and press Enter. The |
| 1043 | program executes all `tracepoint()` instrumentation points and exits. |
| 1044 | . <<creating-destroying-tracing-sessions,Destroy>> the current |
| 1045 | tracing session: |
| 1046 | + |
| 1047 | -- |
| 1048 | [role="term"] |
| 1049 | ---- |
| 1050 | $ lttng destroy |
| 1051 | ---- |
| 1052 | -- |
| 1053 | + |
| 1054 | The man:lttng-destroy(1) command doesn't destroy the trace data; it |
| 1055 | only destroys the state of the tracing session. |
| 1056 | + |
| 1057 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) command |
| 1058 | implicitly (see <<basic-tracing-session-control,Start and stop a tracing |
| 1059 | session>>). You need to stop tracing to make LTTng flush the remaining |
| 1060 | trace data and make the trace readable. |
| 1061 | |
| 1062 | By default, LTTng saves the traces in |
| 1063 | +$LTTNG_HOME/lttng-traces/__name__-__date__-__time__+, |
| 1064 | where +__name__+ is the tracing session name. The |
| 1065 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. |
| 1066 | |
| 1067 | See <<viewing-and-analyzing-your-traces,View and analyze the |
| 1068 | recorded events>> to view the recorded events. |
| 1069 | |
| 1070 | |
| 1071 | [[viewing-and-analyzing-your-traces]] |
| 1072 | === View and analyze the recorded events |
| 1073 | |
| 1074 | Once you have completed the <<tracing-the-linux-kernel,Trace the Linux |
| 1075 | kernel>> and <<tracing-your-own-user-application,Trace a user |
| 1076 | application>> tutorials, you can inspect the recorded events. |
| 1077 | |
| 1078 | There are many tools you can use to read LTTng traces: |
| 1079 | |
| 1080 | https://babeltrace.org/[Babeltrace{nbsp}2]:: |
| 1081 | A rich, flexible trace manipulation toolkit which includes |
| 1082 | a versatile command-line interface |
| 1083 | (https://babeltrace.org/docs/v2.0/man1/babeltrace2.1/[cmd:babeltrace2]), |
| 1084 | a https://babeltrace.org/docs/v2.0/libbabeltrace2/[C library], |
| 1085 | and https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings] |
| 1086 | so that you can easily process or convert an LTTng trace with |
| 1087 | your own script. |
| 1088 | + |
| 1089 | The Babeltrace{nbsp}2 project ships with a |
| 1090 | https://babeltrace.org/docs/v2.0/man7/babeltrace2-plugin-ctf.7/[plugin] |
| 1091 | which supports the format of the traces which LTTng produces, |
| 1092 | https://diamon.org/ctf/[CTF]. |
| 1093 | |
| 1094 | http://tracecompass.org/[Trace Compass]:: |
| 1095 | A graphical user interface for viewing and analyzing any type of |
| 1096 | logs or traces, including those of LTTng. |
| 1097 | |
| 1098 | https://github.com/lttng/lttng-analyses[**LTTng analyses**]:: |
| 1099 | An experimental project which includes many high-level analyses of |
| 1100 | LTTng kernel traces, like scheduling statistics, interrupt |
| 1101 | frequency distribution, top CPU usage, and more. |
| 1102 | |
| 1103 | NOTE: This section assumes that LTTng saved the traces it recorded |
| 1104 | during the previous tutorials to their default location, in the |
| 1105 | dir:{$LTTNG_HOME/lttng-traces} directory. The env:LTTNG_HOME |
| 1106 | environment variable defaults to `$HOME` if not set. |
| 1107 | |
| 1108 | |
| 1109 | [[viewing-and-analyzing-your-traces-bt]] |
| 1110 | ==== Use the cmd:babeltrace2 command-line tool |
| 1111 | |
| 1112 | The simplest way to list all the recorded events of an LTTng trace is to |
| 1113 | pass its path to |
| 1114 | https://babeltrace.org/docs/v2.0/man1/babeltrace2.1/[cmd:babeltrace2] |
| 1115 | without options: |
| 1116 | |
| 1117 | [role="term"] |
| 1118 | ---- |
| 1119 | $ babeltrace2 ~/lttng-traces/my-user-space-session* |
| 1120 | ---- |
| 1121 | |
| 1122 | cmd:babeltrace2 finds all traces recursively within the given path and |
| 1123 | prints all their events, sorting them chronologically. |
| 1124 | |
| 1125 | Pipe the output of cmd:babeltrace2 into a tool like man:grep(1) for |
| 1126 | further filtering: |
| 1127 | |
| 1128 | [role="term"] |
| 1129 | ---- |
| 1130 | $ babeltrace2 /tmp/my-kernel-trace | grep _switch |
| 1131 | ---- |
| 1132 | |
| 1133 | Pipe the output of cmd:babeltrace2 into a tool like man:wc(1) to count |
| 1134 | the recorded events: |
| 1135 | |
| 1136 | [role="term"] |
| 1137 | ---- |
| 1138 | $ babeltrace2 /tmp/my-kernel-trace | grep _open | wc --lines |
| 1139 | ---- |
| 1140 | |
| 1141 | |
| 1142 | [[viewing-and-analyzing-your-traces-bt-python]] |
| 1143 | ==== Use the Babeltrace{nbsp}2 Python bindings |
| 1144 | |
| 1145 | The <<viewing-and-analyzing-your-traces-bt,text output of |
| 1146 | cmd:babeltrace2>> is useful to isolate events by simple matching using |
| 1147 | man:grep(1) and similar utilities. However, more elaborate filters, such |
| 1148 | as keeping only event records with a field value falling within a |
| 1149 | specific range, are not trivial to write using a shell. Moreover, |
| 1150 | reductions and even the most basic computations involving multiple event |
| 1151 | records are virtually impossible to implement. |
| 1152 | |
| 1153 | Fortunately, Babeltrace{nbsp}2 ships with |
| 1154 | https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings] |
| 1155 | which make it easy to read the event records of an LTTng trace |
| 1156 | sequentially and compute the desired information. |
| 1157 | |
| 1158 | The following script accepts an LTTng Linux kernel trace path as its |
| 1159 | first argument and prints the short names of the top five running |
| 1160 | processes on CPU{nbsp}0 during the whole trace: |
| 1161 | |
| 1162 | [source,python] |
| 1163 | .path:{top5proc.py} |
| 1164 | ---- |
| 1165 | import bt2 |
| 1166 | import sys |
| 1167 | import collections |
| 1168 | |
| 1169 | def top5proc(): |
| 1170 | # Get the trace path from the first command-line argument. |
| 1171 | it = bt2.TraceCollectionMessageIterator(sys.argv[1]) |
| 1172 | |
| 1173 | # This counter dictionary will hold execution times: |
| 1174 | # |
| 1175 | # Task command name -> Total execution time (ns) |
| 1176 | exec_times = collections.Counter() |
| 1177 | |
| 1178 | # This holds the last `sched_switch` timestamp. |
| 1179 | last_ts = None |
| 1180 | |
| 1181 | for msg in it: |
| 1182 | # We only care about event messages. |
| 1183 | if type(msg) is not bt2._EventMessageConst: |
| 1184 | continue |
| 1185 | |
| 1186 | # Event of the event message. |
| 1187 | event = msg.event |
| 1188 | |
| 1189 | # Keep only `sched_switch` events. |
| 1190 | if event.cls.name != 'sched_switch': |
| 1191 | continue |
| 1192 | |
| 1193 | # Keep only events which occurred on CPU 0. |
| 1194 | if event.packet.context_field['cpu_id'] != 0: |
| 1195 | continue |
| 1196 | |
| 1197 | # Event timestamp (ns). |
| 1198 | cur_ts = msg.default_clock_snapshot.ns_from_origin |
| 1199 | |
| 1200 | if last_ts is None: |
| 1201 | # We start here. |
| 1202 | last_ts = cur_ts |
| 1203 | |
| 1204 | # (Short) name of the previous task command. |
| 1205 | prev_comm = str(event.payload_field['prev_comm']) |
| 1206 | |
| 1207 | # Initialize an entry in our dictionary if not yet done. |
| 1208 | if prev_comm not in exec_times: |
| 1209 | exec_times[prev_comm] = 0 |
| 1210 | |
| 1211 | # Compute previous command execution time. |
| 1212 | diff = cur_ts - last_ts |
| 1213 | |
| 1214 | # Update execution time of this command. |
| 1215 | exec_times[prev_comm] += diff |
| 1216 | |
| 1217 | # Update last timestamp. |
| 1218 | last_ts = cur_ts |
| 1219 | |
| 1220 | # Print top 5. |
| 1221 | for name, ns in exec_times.most_common(5): |
| 1222 | print('{:20}{} s'.format(name, ns / 1e9)) |
| 1223 | |
| 1224 | |
| 1225 | if __name__ == '__main__': |
| 1226 | top5proc() |
| 1227 | ---- |
| 1228 | |
| 1229 | Run this script: |
| 1230 | |
| 1231 | [role="term"] |
| 1232 | ---- |
| 1233 | $ python3 top5proc.py /tmp/my-kernel-trace/kernel |
| 1234 | ---- |
| 1235 | |
| 1236 | Output example: |
| 1237 | |
| 1238 | ---- |
| 1239 | swapper/0 48.607245889 s |
| 1240 | chromium 7.192738188 s |
| 1241 | pavucontrol 0.709894415 s |
| 1242 | Compositor 0.660867933 s |
| 1243 | Xorg.bin 0.616753786 s |
| 1244 | ---- |
| 1245 | |
| 1246 | Note that `swapper/0` is the ``idle'' process of CPU{nbsp}0 on Linux; |
| 1247 | since we weren't using the CPU that much when tracing, its first |
| 1248 | position in the list makes sense. |
| 1249 | |
| 1250 | |
| 1251 | [[core-concepts]] |
| 1252 | == [[understanding-lttng]]Core concepts |
| 1253 | |
| 1254 | From a user's perspective, the LTTng system is built on a few concepts, |
| 1255 | or objects, on which the <<lttng-cli,cmd:lttng command-line tool>> |
| 1256 | operates by sending commands to the <<lttng-sessiond,session daemon>>. |
| 1257 | Understanding how those objects relate to eachother is key in mastering |
| 1258 | the toolkit. |
| 1259 | |
| 1260 | The core concepts are: |
| 1261 | |
| 1262 | * <<tracing-session,Tracing session>> |
| 1263 | * <<domain,Tracing domain>> |
| 1264 | * <<channel,Channel and ring buffer>> |
| 1265 | * <<"event","Instrumentation point, event rule, event, and event record">> |
| 1266 | |
| 1267 | |
| 1268 | [[tracing-session]] |
| 1269 | === Tracing session |
| 1270 | |
| 1271 | A _tracing session_ is a stateful dialogue between you and |
| 1272 | a <<lttng-sessiond,session daemon>>. You can |
| 1273 | <<creating-destroying-tracing-sessions,create a new tracing |
| 1274 | session>> with the `lttng create` command. |
| 1275 | |
| 1276 | Most of what you do when you control LTTng tracers happens within a |
| 1277 | tracing session. In particular, a tracing session: |
| 1278 | |
| 1279 | * Has its own name. |
| 1280 | * Has its own set of trace files. |
| 1281 | * Has its own state of activity (started or stopped). |
| 1282 | * Has its own <<tracing-session-mode,mode>> (local, network streaming, |
| 1283 | snapshot, or live). |
| 1284 | * Has its own <<channel,channels>> to which are associated their own |
| 1285 | <<event,event rules>>. |
| 1286 | * Has its own <<pid-tracking,process attribute tracking>> inclusion |
| 1287 | sets. |
| 1288 | |
| 1289 | [role="img-100"] |
| 1290 | .A _tracing session_ contains <<channel,channels>> that are members of <<domain,tracing domains>> and contain <<event,event rules>>. |
| 1291 | image::concepts.png[] |
| 1292 | |
| 1293 | Those attributes and objects are completely isolated between different |
| 1294 | tracing sessions. |
| 1295 | |
| 1296 | A tracing session is analogous to a cash machine session: |
| 1297 | the operations you do on the banking system through the cash machine do |
| 1298 | not alter the data of other users of the same system. In the case of |
| 1299 | the cash machine, a session lasts as long as your bank card is inside. |
| 1300 | In the case of LTTng, a tracing session lasts from the `lttng create` |
| 1301 | command to the `lttng destroy` command. |
| 1302 | |
| 1303 | [role="img-100"] |
| 1304 | .Each Unix user has its own set of tracing sessions. |
| 1305 | image::many-sessions.png[] |
| 1306 | |
| 1307 | |
| 1308 | [[tracing-session-mode]] |
| 1309 | ==== Tracing session mode |
| 1310 | |
| 1311 | LTTng can send the generated trace data to different locations. The |
| 1312 | _tracing session mode_ dictates where to send it. The following modes |
| 1313 | are available in LTTng{nbsp}{revision}: |
| 1314 | |
| 1315 | [[local-mode]]Local mode:: |
| 1316 | LTTng writes the traces to the file system of the machine it traces |
| 1317 | (target system). |
| 1318 | |
| 1319 | [[net-streaming-mode]]Network streaming mode:: |
| 1320 | LTTng sends the traces over the network to a |
| 1321 | <<lttng-relayd,relay daemon>> running on a remote system. |
| 1322 | |
| 1323 | Snapshot mode:: |
| 1324 | LTTng doesn't write the traces by default. |
| 1325 | + |
| 1326 | Instead, you can request LTTng to <<taking-a-snapshot,take a snapshot>>, |
| 1327 | that is, a copy of the current sub-buffers of the tracing session, and |
| 1328 | to write it to the file system of the target or to send it over the |
| 1329 | network to a <<lttng-relayd,relay daemon>> running on a remote system. |
| 1330 | |
| 1331 | [[live-mode]]Live mode:: |
| 1332 | This mode is similar to the network streaming mode, but a live |
| 1333 | trace viewer can connect to the distant relay daemon to |
| 1334 | <<lttng-live,view event records as LTTng generates them>>. |
| 1335 | |
| 1336 | |
| 1337 | [[domain]] |
| 1338 | === Tracing domain |
| 1339 | |
| 1340 | A _tracing domain_ is a namespace for event sources. A tracing domain |
| 1341 | has its own properties and features. |
| 1342 | |
| 1343 | There are currently five available tracing domains: |
| 1344 | |
| 1345 | * Linux kernel |
| 1346 | * User space |
| 1347 | * `java.util.logging` (JUL) |
| 1348 | * log4j |
| 1349 | * Python |
| 1350 | |
| 1351 | You must specify a tracing domain when using some commands to avoid |
| 1352 | ambiguity. For example, since all the domains support named tracepoints |
| 1353 | as event sources (instrumentation points that you manually insert in the |
| 1354 | source code), you need to specify a tracing domain when |
| 1355 | <<enabling-disabling-events,creating an event rule>> because all the |
| 1356 | tracing domains could have tracepoints with the same names. |
| 1357 | |
| 1358 | You can create <<channel,channels>> in the Linux kernel and user space |
| 1359 | tracing domains. The other tracing domains have a single default |
| 1360 | channel. |
| 1361 | |
| 1362 | |
| 1363 | [[channel]] |
| 1364 | === Channel and ring buffer |
| 1365 | |
| 1366 | A _channel_ is an object which is responsible for a set of ring buffers. |
| 1367 | Each ring buffer is divided into multiple sub-buffers. When an LTTng |
| 1368 | tracer emits an event, it can record it to one or more |
| 1369 | sub-buffers. The attributes of a channel determine what to do when |
| 1370 | there's no space left for a new event record because all sub-buffers |
| 1371 | are full, where to send a full sub-buffer, and other behaviours. |
| 1372 | |
| 1373 | A channel is always associated to a <<domain,tracing domain>>. The |
| 1374 | `java.util.logging` (JUL), log4j, and Python tracing domains each have |
| 1375 | a default channel which you can't configure. |
| 1376 | |
| 1377 | A channel also owns <<event,event rules>>. When an LTTng tracer emits |
| 1378 | an event, it records it to the sub-buffers of all |
| 1379 | the enabled channels with a satisfied event rule, as long as those |
| 1380 | channels are part of active <<tracing-session,tracing sessions>>. |
| 1381 | |
| 1382 | |
| 1383 | [[channel-buffering-schemes]] |
| 1384 | ==== Per-user vs. per-process buffering schemes |
| 1385 | |
| 1386 | A channel has at least one ring buffer _per CPU_. LTTng always |
| 1387 | records an event to the ring buffer associated to the CPU on which it |
| 1388 | occurs. |
| 1389 | |
| 1390 | Two _buffering schemes_ are available when you |
| 1391 | <<enabling-disabling-channels,create a channel>> in the |
| 1392 | user space <<domain,tracing domain>>: |
| 1393 | |
| 1394 | Per-user buffering:: |
| 1395 | Allocate one set of ring buffers--one per CPU--shared by all the |
| 1396 | instrumented processes of each Unix user. |
| 1397 | + |
| 1398 | -- |
| 1399 | [role="img-100"] |
| 1400 | .Per-user buffering scheme. |
| 1401 | image::per-user-buffering.png[] |
| 1402 | -- |
| 1403 | |
| 1404 | Per-process buffering:: |
| 1405 | Allocate one set of ring buffers--one per CPU--for each |
| 1406 | instrumented process. |
| 1407 | + |
| 1408 | -- |
| 1409 | [role="img-100"] |
| 1410 | .Per-process buffering scheme. |
| 1411 | image::per-process-buffering.png[] |
| 1412 | -- |
| 1413 | + |
| 1414 | The per-process buffering scheme tends to consume more memory than the |
| 1415 | per-user option because systems generally have more instrumented |
| 1416 | processes than Unix users running instrumented processes. However, the |
| 1417 | per-process buffering scheme ensures that one process having a high |
| 1418 | event throughput won't fill all the shared sub-buffers of the same |
| 1419 | user, only its own. |
| 1420 | |
| 1421 | The Linux kernel tracing domain has only one available buffering scheme |
| 1422 | which is to allocate a single set of ring buffers for the whole system. |
| 1423 | This scheme is similar to the per-user option, but with a single, global |
| 1424 | user ``running'' the kernel. |
| 1425 | |
| 1426 | |
| 1427 | [[channel-overwrite-mode-vs-discard-mode]] |
| 1428 | ==== Overwrite vs. discard event record loss modes |
| 1429 | |
| 1430 | When an event occurs, LTTng records it to a specific sub-buffer (yellow |
| 1431 | arc in the following animations) of the ring buffer of a specific |
| 1432 | channel. When there's no space left in a sub-buffer, the tracer marks it |
| 1433 | as consumable (red) and another, empty sub-buffer starts receiving the |
| 1434 | following event records. A <<lttng-consumerd,consumer daemon>> |
| 1435 | eventually consumes the marked sub-buffer (returns to white). |
| 1436 | |
| 1437 | [NOTE] |
| 1438 | [role="docsvg-channel-subbuf-anim"] |
| 1439 | ==== |
| 1440 | {note-no-anim} |
| 1441 | ==== |
| 1442 | |
| 1443 | In an ideal world, sub-buffers are consumed faster than they are filled, |
| 1444 | as it is the case in the previous animation. In the real world, |
| 1445 | however, all sub-buffers can be full at some point, leaving no space to |
| 1446 | record the following events. |
| 1447 | |
| 1448 | By default, LTTng-modules and LTTng-UST are _non-blocking_ tracers: when |
| 1449 | no empty sub-buffer is available, it is acceptable to lose event records |
| 1450 | when the alternative would be to cause substantial delays in the |
| 1451 | execution of the instrumented application. LTTng privileges performance |
| 1452 | over integrity; it aims at perturbing the target system as little as |
| 1453 | possible in order to make tracing of subtle race conditions and rare |
| 1454 | interrupt cascades possible. |
| 1455 | |
| 1456 | Since LTTng{nbsp}2.10, the LTTng user space tracer, LTTng-UST, supports |
| 1457 | a _blocking mode_. See the <<blocking-timeout-example,blocking timeout |
| 1458 | example>> to learn how to use the blocking mode. |
| 1459 | |
| 1460 | When it comes to losing event records because no empty sub-buffer is |
| 1461 | available, or because the <<opt-blocking-timeout,blocking timeout>> is |
| 1462 | reached, the _event record loss mode_ of the channel determines what to |
| 1463 | do. The available event record loss modes are: |
| 1464 | |
| 1465 | Discard mode:: |
| 1466 | Drop the newest event records until the tracer releases a sub-buffer. |
| 1467 | + |
| 1468 | This is the only available mode when you specify a |
| 1469 | <<opt-blocking-timeout,blocking timeout>>. |
| 1470 | |
| 1471 | Overwrite mode:: |
| 1472 | Clear the sub-buffer containing the oldest event records and start |
| 1473 | writing the newest event records there. |
| 1474 | + |
| 1475 | This mode is sometimes called _flight recorder mode_ because it's |
| 1476 | similar to a |
| 1477 | https://en.wikipedia.org/wiki/Flight_recorder[flight recorder]: |
| 1478 | always keep a fixed amount of the latest data. |
| 1479 | |
| 1480 | Which mechanism you should choose depends on your context: prioritize |
| 1481 | the newest or the oldest event records in the ring buffer? |
| 1482 | |
| 1483 | Beware that, in overwrite mode, the tracer abandons a _whole sub-buffer_ |
| 1484 | as soon as a there's no space left for a new event record, whereas in |
| 1485 | discard mode, the tracer only discards the event record that doesn't |
| 1486 | fit. |
| 1487 | |
| 1488 | In discard mode, LTTng increments a count of lost event records when an |
| 1489 | event record is lost and saves this count to the trace. Since |
| 1490 | LTTng{nbsp}2.8, in overwrite mode, LTTng writes to a given sub-buffer |
| 1491 | its sequence number within its data stream. With a <<local-mode,local>>, |
| 1492 | <<net-streaming-mode,network streaming>>, or <<live-mode,live>> |
| 1493 | <<tracing-session,tracing session>>, a trace reader can use such |
| 1494 | sequence numbers to report lost packets. In overwrite mode, LTTng |
| 1495 | doesn't write to the trace the exact number of lost event records in |
| 1496 | those lost sub-buffers. |
| 1497 | |
| 1498 | Trace analyses can use saved discarded event record and sub-buffer |
| 1499 | (packet) counts of the trace to decide whether or not to perform the |
| 1500 | analyses even if trace data is known to be missing. |
| 1501 | |
| 1502 | There are a few ways to decrease your probability of losing event |
| 1503 | records. |
| 1504 | <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>> shows |
| 1505 | how to fine-tune the sub-buffer count and size of a channel to virtually |
| 1506 | stop losing event records, though at the cost of greater memory usage. |
| 1507 | |
| 1508 | |
| 1509 | [[channel-subbuf-size-vs-subbuf-count]] |
| 1510 | ==== Sub-buffer count and size |
| 1511 | |
| 1512 | When you <<enabling-disabling-channels,create a channel>>, you can |
| 1513 | set its number of sub-buffers and their size. |
| 1514 | |
| 1515 | Note that there is noticeable CPU overhead introduced when |
| 1516 | switching sub-buffers (marking a full one as consumable and switching |
| 1517 | to an empty one for the following events to be recorded). Knowing this, |
| 1518 | the following list presents a few practical situations along with how |
| 1519 | to configure the sub-buffer count and size for them: |
| 1520 | |
| 1521 | * **High event throughput**: In general, prefer bigger sub-buffers to |
| 1522 | lower the risk of losing event records. |
| 1523 | + |
| 1524 | Having bigger sub-buffers also ensures a lower |
| 1525 | <<channel-switch-timer,sub-buffer switching frequency>>. |
| 1526 | + |
| 1527 | The number of sub-buffers is only meaningful if you create the channel |
| 1528 | in overwrite mode: in this case, if a sub-buffer overwrite happens, the |
| 1529 | other sub-buffers are left unaltered. |
| 1530 | |
| 1531 | * **Low event throughput**: In general, prefer smaller sub-buffers |
| 1532 | since the risk of losing event records is low. |
| 1533 | + |
| 1534 | Because events occur less frequently, the sub-buffer switching frequency |
| 1535 | should remain low and thus the overhead of the tracer shouldn't be a |
| 1536 | problem. |
| 1537 | |
| 1538 | * **Low memory system**: If your target system has a low memory |
| 1539 | limit, prefer fewer first, then smaller sub-buffers. |
| 1540 | + |
| 1541 | Even if the system is limited in memory, you want to keep the |
| 1542 | sub-buffers as big as possible to avoid a high sub-buffer switching |
| 1543 | frequency. |
| 1544 | |
| 1545 | Note that LTTng uses http://diamon.org/ctf/[CTF] as its trace format, |
| 1546 | which means event data is very compact. For example, the average |
| 1547 | LTTng kernel event record weights about 32{nbsp}bytes. Thus, a |
| 1548 | sub-buffer size of 1{nbsp}MiB is considered big. |
| 1549 | |
| 1550 | The previous situations highlight the major trade-off between a few big |
| 1551 | sub-buffers and more, smaller sub-buffers: sub-buffer switching |
| 1552 | frequency vs. how much data is lost in overwrite mode. Assuming a |
| 1553 | constant event throughput and using the overwrite mode, the two |
| 1554 | following configurations have the same ring buffer total size: |
| 1555 | |
| 1556 | [NOTE] |
| 1557 | [role="docsvg-channel-subbuf-size-vs-count-anim"] |
| 1558 | ==== |
| 1559 | {note-no-anim} |
| 1560 | ==== |
| 1561 | |
| 1562 | * **Two sub-buffers of 4{nbsp}MiB each**: Expect a very low sub-buffer |
| 1563 | switching frequency, but if a sub-buffer overwrite happens, half of |
| 1564 | the event records so far (4{nbsp}MiB) are definitely lost. |
| 1565 | * **Eight sub-buffers of 1{nbsp}MiB each**: Expect four times the |
| 1566 | overhead of the tracer as the previous configuration, but if a |
| 1567 | sub-buffer overwrite happens, only the eighth of event records so far |
| 1568 | are definitely lost. |
| 1569 | |
| 1570 | In discard mode, the sub-buffers count parameter is pointless: use two |
| 1571 | sub-buffers and set their size according to the requirements of your |
| 1572 | situation. |
| 1573 | |
| 1574 | |
| 1575 | [[channel-switch-timer]] |
| 1576 | ==== Switch timer period |
| 1577 | |
| 1578 | The _switch timer period_ is an important configurable attribute of |
| 1579 | a channel to ensure periodic sub-buffer flushing. |
| 1580 | |
| 1581 | When the _switch timer_ expires, a sub-buffer switch happens. Set |
| 1582 | the switch timer period attribute when you |
| 1583 | <<enabling-disabling-channels,create a channel>> to ensure that LTTng |
| 1584 | consumes and commits trace data to trace files or to a distant relay |
| 1585 | daemon periodically in case of a low event throughput. |
| 1586 | |
| 1587 | [NOTE] |
| 1588 | [role="docsvg-channel-switch-timer"] |
| 1589 | ==== |
| 1590 | {note-no-anim} |
| 1591 | ==== |
| 1592 | |
| 1593 | This attribute is also convenient when you use big sub-buffers to cope |
| 1594 | with a sporadic high event throughput, even if the throughput is |
| 1595 | normally low. |
| 1596 | |
| 1597 | |
| 1598 | [[channel-read-timer]] |
| 1599 | ==== Read timer period |
| 1600 | |
| 1601 | By default, the LTTng tracers use a notification mechanism to signal a |
| 1602 | full sub-buffer so that a consumer daemon can consume it. When such |
| 1603 | notifications must be avoided, for example in real-time applications, |
| 1604 | use the _read timer_ of the channel instead. When the read timer fires, |
| 1605 | the <<lttng-consumerd,consumer daemon>> checks for full, consumable |
| 1606 | sub-buffers. |
| 1607 | |
| 1608 | |
| 1609 | [[tracefile-rotation]] |
| 1610 | ==== Trace file count and size |
| 1611 | |
| 1612 | By default, trace files can grow as large as needed. Set the maximum |
| 1613 | size of each trace file that a channel writes when you |
| 1614 | <<enabling-disabling-channels,create a channel>>. When the size of a |
| 1615 | trace file reaches the fixed maximum size of the channel, LTTng creates |
| 1616 | another file to contain the next event records. LTTng appends a file |
| 1617 | count to each trace file name in this case. |
| 1618 | |
| 1619 | If you set the trace file size attribute when you create a channel, the |
| 1620 | maximum number of trace files that LTTng creates is _unlimited_ by |
| 1621 | default. To limit them, set a maximum number of trace files. When the |
| 1622 | number of trace files reaches the fixed maximum count of the channel, |
| 1623 | the oldest trace file is overwritten. This mechanism is called _trace |
| 1624 | file rotation_. |
| 1625 | |
| 1626 | [IMPORTANT] |
| 1627 | ==== |
| 1628 | Even if you don't limit the trace file count, you can't assume that |
| 1629 | LTTng doesn't manage any trace file. |
| 1630 | |
| 1631 | In other words, there is no safe way to know if LTTng still holds a |
| 1632 | given trace file open with the trace file rotation feature. |
| 1633 | |
| 1634 | The only way to obtain an unmanaged, self-contained LTTng trace before |
| 1635 | you <<creating-destroying-tracing-sessions,destroy>> the tracing session |
| 1636 | is with the <<session-rotation,tracing session rotation>> feature |
| 1637 | (available since LTTng{nbsp}2.11). |
| 1638 | ==== |
| 1639 | |
| 1640 | |
| 1641 | [[event]] |
| 1642 | === Instrumentation point, event rule, event, and event record |
| 1643 | |
| 1644 | An _event rule_ is a set of conditions which must be **all** satisfied |
| 1645 | for LTTng to record an occuring event. |
| 1646 | |
| 1647 | You set the conditions when you <<enabling-disabling-events,create |
| 1648 | an event rule>>. |
| 1649 | |
| 1650 | You always attach an event rule to a <<channel,channel>> when you create |
| 1651 | it. |
| 1652 | |
| 1653 | When an event passes the conditions of an event rule, LTTng records it |
| 1654 | in one of the sub-buffers of the attached channel. |
| 1655 | |
| 1656 | The available conditions, as of LTTng{nbsp}{revision}, are: |
| 1657 | |
| 1658 | * The event rule _is enabled_. |
| 1659 | * The type of the instrumentation point _is{nbsp}T_. |
| 1660 | * The name of the instrumentation point (sometimes called _event name_) |
| 1661 | _matches{nbsp}N_, but _isn't{nbsp}E_. |
| 1662 | * The log level of the instrumentation point _is as severe as{nbsp}L_, or |
| 1663 | _is exactly{nbsp}L_. |
| 1664 | * The fields of the payload of the event _satisfy_ a filter |
| 1665 | expression{nbsp}__F__. |
| 1666 | |
| 1667 | As you can see, all the conditions but the dynamic filter are related to |
| 1668 | the status of the event rule or to the instrumentation point, not to the |
| 1669 | occurring events. This is why, without a filter, checking if an event |
| 1670 | passes an event rule isn't a dynamic task: when you create or modify an |
| 1671 | event rule, all the tracers of its tracing domain enable or disable the |
| 1672 | instrumentation points themselves once. This is possible because the |
| 1673 | attributes of an instrumentation point (type, name, and log level) are |
| 1674 | defined statically. In other words, without a dynamic filter, the tracer |
| 1675 | _doesn't evaluate_ the arguments of an instrumentation point unless it |
| 1676 | matches an enabled event rule. |
| 1677 | |
| 1678 | Note that, for LTTng to record an event, the <<channel,channel>> to |
| 1679 | which a matching event rule is attached must also be enabled, and the |
| 1680 | <<tracing-session,tracing session>> owning this channel must be active |
| 1681 | (started). |
| 1682 | |
| 1683 | [role="img-100"] |
| 1684 | .Logical path from an instrumentation point to an event record. |
| 1685 | image::event-rule.png[] |
| 1686 | |
| 1687 | .Event, event record, or event rule? |
| 1688 | **** |
| 1689 | With so many similar terms, it's easy to get confused. |
| 1690 | |
| 1691 | An **event** is the consequence of the execution of an _instrumentation |
| 1692 | point_, like a tracepoint that you manually place in some source code, |
| 1693 | or a Linux kernel kprobe. An event is said to _occur_ at a specific |
| 1694 | time. Different actions can be taken upon the occurrence of an event, |
| 1695 | like record the payload of the event to a buffer. |
| 1696 | |
| 1697 | An **event record** is the representation of an event in a sub-buffer. A |
| 1698 | tracer is responsible for capturing the payload of an event, current |
| 1699 | context variables, the ID of the event, and its timestamp. LTTng |
| 1700 | can append this sub-buffer to a trace file. |
| 1701 | |
| 1702 | An **event rule** is a set of conditions which must _all_ be satisfied |
| 1703 | for LTTng to record an occuring event. Events still occur without |
| 1704 | satisfying event rules, but LTTng doesn't record them. |
| 1705 | **** |
| 1706 | |
| 1707 | |
| 1708 | [[plumbing]] |
| 1709 | == Components of noch:{LTTng} |
| 1710 | |
| 1711 | The second _T_ in _LTTng_ stands for _toolkit_: it would be wrong |
| 1712 | to call LTTng a simple _tool_ since it is composed of multiple |
| 1713 | interacting components. This section describes those components, |
| 1714 | explains their respective roles, and shows how they connect together to |
| 1715 | form the LTTng ecosystem. |
| 1716 | |
| 1717 | The following diagram shows how the most important components of LTTng |
| 1718 | interact with user applications, the Linux kernel, and you: |
| 1719 | |
| 1720 | [role="img-100"] |
| 1721 | .Control and trace data paths between LTTng components. |
| 1722 | image::plumbing.png[] |
| 1723 | |
| 1724 | The LTTng project incorporates: |
| 1725 | |
| 1726 | * **LTTng-tools**: Libraries and command-line interface to |
| 1727 | control tracing sessions. |
| 1728 | ** <<lttng-sessiond,Session daemon>> (man:lttng-sessiond(8)). |
| 1729 | ** <<lttng-consumerd,Consumer daemon>> (cmd:lttng-consumerd). |
| 1730 | ** <<lttng-relayd,Relay daemon>> (man:lttng-relayd(8)). |
| 1731 | ** <<liblttng-ctl-lttng,Tracing control library>> (`liblttng-ctl`). |
| 1732 | ** <<lttng-cli,Tracing control command-line tool>> (man:lttng(1)). |
| 1733 | * **LTTng-UST**: Libraries and Java/Python packages to trace user |
| 1734 | applications. |
| 1735 | ** <<lttng-ust,User space tracing library>> (`liblttng-ust`) and its |
| 1736 | headers to instrument and trace any native user application. |
| 1737 | ** <<prebuilt-ust-helpers,Preloadable user space tracing helpers>>: |
| 1738 | *** `liblttng-ust-libc-wrapper` |
| 1739 | *** `liblttng-ust-pthread-wrapper` |
| 1740 | *** `liblttng-ust-cyg-profile` |
| 1741 | *** `liblttng-ust-cyg-profile-fast` |
| 1742 | *** `liblttng-ust-dl` |
| 1743 | ** User space tracepoint provider source files generator command-line |
| 1744 | tool (man:lttng-gen-tp(1)). |
| 1745 | ** <<lttng-ust-agents,LTTng-UST Java agent>> to instrument and trace |
| 1746 | Java applications using `java.util.logging` or |
| 1747 | Apache log4j{nbsp}1.2 logging. |
| 1748 | ** <<lttng-ust-agents,LTTng-UST Python agent>> to instrument |
| 1749 | Python applications using the standard `logging` package. |
| 1750 | * **LTTng-modules**: <<lttng-modules,Linux kernel modules>> to trace |
| 1751 | the kernel. |
| 1752 | ** LTTng kernel tracer module. |
| 1753 | ** Tracing ring buffer kernel modules. |
| 1754 | ** Probe kernel modules. |
| 1755 | ** LTTng logger kernel module. |
| 1756 | |
| 1757 | |
| 1758 | [[lttng-cli]] |
| 1759 | === Tracing control command-line interface |
| 1760 | |
| 1761 | [role="img-100"] |
| 1762 | .The tracing control command-line interface. |
| 1763 | image::plumbing-lttng-cli.png[] |
| 1764 | |
| 1765 | The _man:lttng(1) command-line tool_ is the standard user interface to |
| 1766 | control LTTng <<tracing-session,tracing sessions>>. The cmd:lttng tool |
| 1767 | is part of LTTng-tools. |
| 1768 | |
| 1769 | The cmd:lttng tool is linked with |
| 1770 | <<liblttng-ctl-lttng,`liblttng-ctl`>> to communicate with |
| 1771 | one or more <<lttng-sessiond,session daemons>> behind the scenes. |
| 1772 | |
| 1773 | The cmd:lttng tool has a Git-like interface: |
| 1774 | |
| 1775 | [role="term"] |
| 1776 | ---- |
| 1777 | $ lttng <GENERAL OPTIONS> <COMMAND> <COMMAND OPTIONS> |
| 1778 | ---- |
| 1779 | |
| 1780 | The <<controlling-tracing,Tracing control>> section explores the |
| 1781 | available features of LTTng using the cmd:lttng tool. |
| 1782 | |
| 1783 | |
| 1784 | [[liblttng-ctl-lttng]] |
| 1785 | === Tracing control library |
| 1786 | |
| 1787 | [role="img-100"] |
| 1788 | .The tracing control library. |
| 1789 | image::plumbing-liblttng-ctl.png[] |
| 1790 | |
| 1791 | The _LTTng control library_, `liblttng-ctl`, is used to communicate |
| 1792 | with a <<lttng-sessiond,session daemon>> using a C API that hides the |
| 1793 | underlying details of the protocol. `liblttng-ctl` is part of LTTng-tools. |
| 1794 | |
| 1795 | The <<lttng-cli,cmd:lttng command-line tool>> |
| 1796 | is linked with `liblttng-ctl`. |
| 1797 | |
| 1798 | Use `liblttng-ctl` in C or $$C++$$ source code by including its |
| 1799 | ``master'' header: |
| 1800 | |
| 1801 | [source,c] |
| 1802 | ---- |
| 1803 | #include <lttng/lttng.h> |
| 1804 | ---- |
| 1805 | |
| 1806 | Some objects are referenced by name (C string), such as tracing |
| 1807 | sessions, but most of them require to create a handle first using |
| 1808 | `lttng_create_handle()`. |
| 1809 | |
| 1810 | As of LTTng{nbsp}{revision}, the best available developer documentation for |
| 1811 | `liblttng-ctl` is its installed header files. Every function and structure is |
| 1812 | thoroughly documented. |
| 1813 | |
| 1814 | |
| 1815 | [[lttng-ust]] |
| 1816 | === User space tracing library |
| 1817 | |
| 1818 | [role="img-100"] |
| 1819 | .The user space tracing library. |
| 1820 | image::plumbing-liblttng-ust.png[] |
| 1821 | |
| 1822 | The _user space tracing library_, `liblttng-ust` (see man:lttng-ust(3)), |
| 1823 | is the LTTng user space tracer. It receives commands from a |
| 1824 | <<lttng-sessiond,session daemon>>, for example to |
| 1825 | enable and disable specific instrumentation points, and writes event |
| 1826 | records to ring buffers shared with a |
| 1827 | <<lttng-consumerd,consumer daemon>>. |
| 1828 | `liblttng-ust` is part of LTTng-UST. |
| 1829 | |
| 1830 | Public C header files are installed beside `liblttng-ust` to |
| 1831 | instrument any <<c-application,C or $$C++$$ application>>. |
| 1832 | |
| 1833 | <<lttng-ust-agents,LTTng-UST agents>>, which are regular Java and Python |
| 1834 | packages, use their own library providing tracepoints which is |
| 1835 | linked with `liblttng-ust`. |
| 1836 | |
| 1837 | An application or library doesn't have to initialize `liblttng-ust` |
| 1838 | manually: its constructor does the necessary tasks to properly register |
| 1839 | to a session daemon. The initialization phase also enables the |
| 1840 | instrumentation points matching the <<event,event rules>> that you |
| 1841 | already created. |
| 1842 | |
| 1843 | |
| 1844 | [[lttng-ust-agents]] |
| 1845 | === User space tracing agents |
| 1846 | |
| 1847 | [role="img-100"] |
| 1848 | .The user space tracing agents. |
| 1849 | image::plumbing-lttng-ust-agents.png[] |
| 1850 | |
| 1851 | The _LTTng-UST Java and Python agents_ are regular Java and Python |
| 1852 | packages which add LTTng tracing capabilities to the |
| 1853 | native logging frameworks. The LTTng-UST agents are part of LTTng-UST. |
| 1854 | |
| 1855 | In the case of Java, the |
| 1856 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[`java.util.logging` |
| 1857 | core logging facilities] and |
| 1858 | https://logging.apache.org/log4j/1.2/[Apache log4j{nbsp}1.2] are supported. |
| 1859 | Note that Apache Log4{nbsp}2 isn't supported. |
| 1860 | |
| 1861 | In the case of Python, the standard |
| 1862 | https://docs.python.org/3/library/logging.html[`logging`] package |
| 1863 | is supported. Both Python{nbsp}2 and Python{nbsp}3 modules can import the |
| 1864 | LTTng-UST Python agent package. |
| 1865 | |
| 1866 | The applications using the LTTng-UST agents are in the |
| 1867 | `java.util.logging` (JUL), |
| 1868 | log4j, and Python <<domain,tracing domains>>. |
| 1869 | |
| 1870 | Both agents use the same mechanism to trace the log statements. When an |
| 1871 | agent initializes, it creates a log handler that attaches to the root |
| 1872 | logger. The agent also registers to a <<lttng-sessiond,session daemon>>. |
| 1873 | When the application executes a log statement, the root logger passes it |
| 1874 | to the log handler of the agent. The log handler of the agent calls a |
| 1875 | native function in a tracepoint provider package shared library linked |
| 1876 | with <<lttng-ust,`liblttng-ust`>>, passing the formatted log message and |
| 1877 | other fields, like its logger name and its log level. This native |
| 1878 | function contains a user space instrumentation point, hence tracing the |
| 1879 | log statement. |
| 1880 | |
| 1881 | The log level condition of an |
| 1882 | <<event,event rule>> is considered when tracing |
| 1883 | a Java or a Python application, and it's compatible with the standard |
| 1884 | JUL, log4j, and Python log levels. |
| 1885 | |
| 1886 | |
| 1887 | [[lttng-modules]] |
| 1888 | === LTTng kernel modules |
| 1889 | |
| 1890 | [role="img-100"] |
| 1891 | .The LTTng kernel modules. |
| 1892 | image::plumbing-lttng-modules.png[] |
| 1893 | |
| 1894 | The _LTTng kernel modules_ are a set of Linux kernel modules |
| 1895 | which implement the kernel tracer of the LTTng project. The LTTng |
| 1896 | kernel modules are part of LTTng-modules. |
| 1897 | |
| 1898 | The LTTng kernel modules include: |
| 1899 | |
| 1900 | * A set of _probe_ modules. |
| 1901 | + |
| 1902 | Each module attaches to a specific subsystem |
| 1903 | of the Linux kernel using its tracepoint instrument points. There are |
| 1904 | also modules to attach to the entry and return points of the Linux |
| 1905 | system call functions. |
| 1906 | |
| 1907 | * _Ring buffer_ modules. |
| 1908 | + |
| 1909 | A ring buffer implementation is provided as kernel modules. The LTTng |
| 1910 | kernel tracer writes to the ring buffer; a |
| 1911 | <<lttng-consumerd,consumer daemon>> reads from the ring buffer. |
| 1912 | |
| 1913 | * The _LTTng kernel tracer_ module. |
| 1914 | * The _LTTng logger_ module. |
| 1915 | + |
| 1916 | The LTTng logger module implements the special path:{/proc/lttng-logger} |
| 1917 | (and path:{/dev/lttng-logger} since LTTng{nbsp}2.11) files so that any |
| 1918 | executable can generate LTTng events by opening and writing to those |
| 1919 | files. |
| 1920 | + |
| 1921 | See <<proc-lttng-logger-abi,LTTng logger>>. |
| 1922 | |
| 1923 | Generally, you don't have to load the LTTng kernel modules manually |
| 1924 | (using man:modprobe(8), for example): a root <<lttng-sessiond,session |
| 1925 | daemon>> loads the necessary modules when starting. If you have extra |
| 1926 | probe modules, you can specify to load them to the session daemon on |
| 1927 | the command line. |
| 1928 | |
| 1929 | The LTTng kernel modules are installed in |
| 1930 | +/usr/lib/modules/__release__/extra+ by default, where +__release__+ is |
| 1931 | the kernel release (see `uname --kernel-release`). |
| 1932 | |
| 1933 | |
| 1934 | [[lttng-sessiond]] |
| 1935 | === Session daemon |
| 1936 | |
| 1937 | [role="img-100"] |
| 1938 | .The session daemon. |
| 1939 | image::plumbing-sessiond.png[] |
| 1940 | |
| 1941 | The _session daemon_, man:lttng-sessiond(8), is a daemon responsible for |
| 1942 | managing tracing sessions and for controlling the various components of |
| 1943 | LTTng. The session daemon is part of LTTng-tools. |
| 1944 | |
| 1945 | The session daemon sends control requests to and receives control |
| 1946 | responses from: |
| 1947 | |
| 1948 | * The <<lttng-ust,user space tracing library>>. |
| 1949 | + |
| 1950 | Any instance of the user space tracing library first registers to |
| 1951 | a session daemon. Then, the session daemon can send requests to |
| 1952 | this instance, such as: |
| 1953 | + |
| 1954 | -- |
| 1955 | ** Get the list of tracepoints. |
| 1956 | ** Share an <<event,event rule>> so that the user space tracing library |
| 1957 | can enable or disable tracepoints. Amongst the possible conditions |
| 1958 | of an event rule is a filter expression which `liblttng-ust` evalutes |
| 1959 | when an event occurs. |
| 1960 | ** Share <<channel,channel>> attributes and ring buffer locations. |
| 1961 | -- |
| 1962 | + |
| 1963 | The session daemon and the user space tracing library use a Unix |
| 1964 | domain socket for their communication. |
| 1965 | |
| 1966 | * The <<lttng-ust-agents,user space tracing agents>>. |
| 1967 | + |
| 1968 | Any instance of a user space tracing agent first registers to |
| 1969 | a session daemon. Then, the session daemon can send requests to |
| 1970 | this instance, such as: |
| 1971 | + |
| 1972 | -- |
| 1973 | ** Get the list of loggers. |
| 1974 | ** Enable or disable a specific logger. |
| 1975 | -- |
| 1976 | + |
| 1977 | The session daemon and the user space tracing agent use a TCP connection |
| 1978 | for their communication. |
| 1979 | |
| 1980 | * The <<lttng-modules,LTTng kernel tracer>>. |
| 1981 | * The <<lttng-consumerd,consumer daemon>>. |
| 1982 | + |
| 1983 | The session daemon sends requests to the consumer daemon to instruct |
| 1984 | it where to send the trace data streams, amongst other information. |
| 1985 | |
| 1986 | * The <<lttng-relayd,relay daemon>>. |
| 1987 | |
| 1988 | The session daemon receives commands from the |
| 1989 | <<liblttng-ctl-lttng,tracing control library>>. |
| 1990 | |
| 1991 | The root session daemon loads the appropriate |
| 1992 | <<lttng-modules,LTTng kernel modules>> on startup. It also spawns |
| 1993 | a <<lttng-consumerd,consumer daemon>> as soon as you create |
| 1994 | an <<event,event rule>>. |
| 1995 | |
| 1996 | The session daemon doesn't send and receive trace data: this is the |
| 1997 | role of the <<lttng-consumerd,consumer daemon>> and |
| 1998 | <<lttng-relayd,relay daemon>>. It does, however, generate the |
| 1999 | http://diamon.org/ctf/[CTF] metadata stream. |
| 2000 | |
| 2001 | Each Unix user can have its own session daemon instance. The |
| 2002 | tracing sessions which different session daemons manage are completely |
| 2003 | independent. |
| 2004 | |
| 2005 | The root user's session daemon is the only one which is |
| 2006 | allowed to control the LTTng kernel tracer, and its spawned consumer |
| 2007 | daemon is the only one which is allowed to consume trace data from the |
| 2008 | LTTng kernel tracer. Note, however, that any Unix user which is a member |
| 2009 | of the <<tracing-group,tracing group>> is allowed |
| 2010 | to create <<channel,channels>> in the |
| 2011 | Linux kernel <<domain,tracing domain>>, and thus to trace the Linux |
| 2012 | kernel. |
| 2013 | |
| 2014 | The <<lttng-cli,cmd:lttng command-line tool>> automatically starts a |
| 2015 | session daemon when using its `create` command if none is currently |
| 2016 | running. You can also start the session daemon manually. |
| 2017 | |
| 2018 | |
| 2019 | [[lttng-consumerd]] |
| 2020 | === Consumer daemon |
| 2021 | |
| 2022 | [role="img-100"] |
| 2023 | .The consumer daemon. |
| 2024 | image::plumbing-consumerd.png[] |
| 2025 | |
| 2026 | The _consumer daemon_, cmd:lttng-consumerd, is a daemon which shares |
| 2027 | ring buffers with user applications or with the LTTng kernel modules to |
| 2028 | collect trace data and send it to some location (on disk or to a |
| 2029 | <<lttng-relayd,relay daemon>> over the network). The consumer daemon |
| 2030 | is part of LTTng-tools. |
| 2031 | |
| 2032 | You don't start a consumer daemon manually: a consumer daemon is always |
| 2033 | spawned by a <<lttng-sessiond,session daemon>> as soon as you create an |
| 2034 | <<event,event rule>>, that is, before you start tracing. When you kill |
| 2035 | its owner session daemon, the consumer daemon also exits because it is |
| 2036 | the child process of the session daemon. Command-line options of |
| 2037 | man:lttng-sessiond(8) target the consumer daemon process. |
| 2038 | |
| 2039 | There are up to two running consumer daemons per Unix user, whereas only |
| 2040 | one session daemon can run per user. This is because each process can be |
| 2041 | either 32-bit or 64-bit: if the target system runs a mixture of 32-bit |
| 2042 | and 64-bit processes, it is more efficient to have separate |
| 2043 | corresponding 32-bit and 64-bit consumer daemons. The root user is an |
| 2044 | exception: it can have up to _three_ running consumer daemons: 32-bit |
| 2045 | and 64-bit instances for its user applications, and one more |
| 2046 | reserved for collecting kernel trace data. |
| 2047 | |
| 2048 | |
| 2049 | [[lttng-relayd]] |
| 2050 | === Relay daemon |
| 2051 | |
| 2052 | [role="img-100"] |
| 2053 | .The relay daemon. |
| 2054 | image::plumbing-relayd.png[] |
| 2055 | |
| 2056 | The _relay daemon_, man:lttng-relayd(8), is a daemon acting as a bridge |
| 2057 | between remote session and consumer daemons, local trace files, and a |
| 2058 | remote live trace viewer. The relay daemon is part of LTTng-tools. |
| 2059 | |
| 2060 | The main purpose of the relay daemon is to implement a receiver of |
| 2061 | <<sending-trace-data-over-the-network,trace data over the network>>. |
| 2062 | This is useful when the target system doesn't have much file system |
| 2063 | space to record trace files locally. |
| 2064 | |
| 2065 | The relay daemon is also a server to which a |
| 2066 | <<lttng-live,live trace viewer>> can |
| 2067 | connect. The live trace viewer sends requests to the relay daemon to |
| 2068 | receive trace data as the target system emits events. The |
| 2069 | communication protocol is named _LTTng live_; it is used over TCP |
| 2070 | connections. |
| 2071 | |
| 2072 | Note that you can start the relay daemon on the target system directly. |
| 2073 | This is the setup of choice when the use case is to view events as |
| 2074 | the target system emits them without the need of a remote system. |
| 2075 | |
| 2076 | |
| 2077 | [[instrumenting]] |
| 2078 | == [[using-lttng]]Instrumentation |
| 2079 | |
| 2080 | There are many examples of tracing and monitoring in our everyday life: |
| 2081 | |
| 2082 | * You have access to real-time and historical weather reports and |
| 2083 | forecasts thanks to weather stations installed around the country. |
| 2084 | * You know your heart is safe thanks to an electrocardiogram. |
| 2085 | * You make sure not to drive your car too fast and to have enough fuel |
| 2086 | to reach your destination thanks to gauges visible on your dashboard. |
| 2087 | |
| 2088 | All the previous examples have something in common: they rely on |
| 2089 | **instruments**. Without the electrodes attached to the surface of your |
| 2090 | body skin, cardiac monitoring is futile. |
| 2091 | |
| 2092 | LTTng, as a tracer, is no different from those real life examples. If |
| 2093 | you're about to trace a software system or, in other words, record its |
| 2094 | history of execution, you better have **instrumentation points** in the |
| 2095 | subject you're tracing, that is, the actual software. |
| 2096 | |
| 2097 | Various ways were developed to instrument a piece of software for LTTng |
| 2098 | tracing. The most straightforward one is to manually place |
| 2099 | instrumentation points, called _tracepoints_, in the source code of the |
| 2100 | software. It is also possible to add instrumentation points dynamically |
| 2101 | in the Linux kernel <<domain,tracing domain>>. |
| 2102 | |
| 2103 | If you're only interested in tracing the Linux kernel, your |
| 2104 | instrumentation needs are probably already covered by the built-in |
| 2105 | <<lttng-modules,Linux kernel tracepoints>> of LTTng. You may also wish |
| 2106 | to trace a user application which is already instrumented for LTTng |
| 2107 | tracing. In such cases, skip this whole section and read the topics of |
| 2108 | the <<controlling-tracing,Tracing control>> section. |
| 2109 | |
| 2110 | Many methods are available to instrument a piece of software for LTTng |
| 2111 | tracing. They are: |
| 2112 | |
| 2113 | * <<c-application,User space instrumentation for C and $$C++$$ |
| 2114 | applications>>. |
| 2115 | * <<prebuilt-ust-helpers,Prebuilt user space tracing helpers>>. |
| 2116 | * <<java-application,User space Java agent>>. |
| 2117 | * <<python-application,User space Python agent>>. |
| 2118 | * <<proc-lttng-logger-abi,LTTng logger>>. |
| 2119 | * <<instrumenting-linux-kernel,LTTng kernel tracepoints>>. |
| 2120 | |
| 2121 | |
| 2122 | [[c-application]] |
| 2123 | === [[cxx-application]]User space instrumentation for C and $$C++$$ applications |
| 2124 | |
| 2125 | The procedure to instrument a C or $$C++$$ user application with |
| 2126 | the <<lttng-ust,LTTng user space tracing library>>, `liblttng-ust`, is: |
| 2127 | |
| 2128 | . <<tracepoint-provider,Create the source files of a tracepoint provider |
| 2129 | package>>. |
| 2130 | . <<probing-the-application-source-code,Add tracepoints to |
| 2131 | the source code of the application>>. |
| 2132 | . <<building-tracepoint-providers-and-user-application,Build and link |
| 2133 | a tracepoint provider package and the user application>>. |
| 2134 | |
| 2135 | If you need quick, man:printf(3)-like instrumentation, skip |
| 2136 | those steps and use <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> |
| 2137 | instead. |
| 2138 | |
| 2139 | IMPORTANT: You need to <<installing-lttng,install>> LTTng-UST to |
| 2140 | instrument a user application with `liblttng-ust`. |
| 2141 | |
| 2142 | |
| 2143 | [[tracepoint-provider]] |
| 2144 | ==== Create the source files of a tracepoint provider package |
| 2145 | |
| 2146 | A _tracepoint provider_ is a set of compiled functions which provide |
| 2147 | **tracepoints** to an application, the type of instrumentation point |
| 2148 | supported by LTTng-UST. Those functions can emit events with |
| 2149 | user-defined fields and serialize those events as event records to one |
| 2150 | or more LTTng-UST <<channel,channel>> sub-buffers. The `tracepoint()` |
| 2151 | macro, which you <<probing-the-application-source-code,insert in the |
| 2152 | source code of a user application>>, calls those functions. |
| 2153 | |
| 2154 | A _tracepoint provider package_ is an object file (`.o`) or a shared |
| 2155 | library (`.so`) which contains one or more tracepoint providers. |
| 2156 | Its source files are: |
| 2157 | |
| 2158 | * One or more <<tpp-header,tracepoint provider header>> (`.h`). |
| 2159 | * A <<tpp-source,tracepoint provider package source>> (`.c`). |
| 2160 | |
| 2161 | A tracepoint provider package is dynamically linked with `liblttng-ust`, |
| 2162 | the LTTng user space tracer, at run time. |
| 2163 | |
| 2164 | [role="img-100"] |
| 2165 | .User application linked with `liblttng-ust` and containing a tracepoint provider. |
| 2166 | image::ust-app.png[] |
| 2167 | |
| 2168 | NOTE: If you need quick, man:printf(3)-like instrumentation, |
| 2169 | skip creating and using a tracepoint provider and use |
| 2170 | <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> instead. |
| 2171 | |
| 2172 | |
| 2173 | [[tpp-header]] |
| 2174 | ===== Create a tracepoint provider header file template |
| 2175 | |
| 2176 | A _tracepoint provider header file_ contains the tracepoint |
| 2177 | definitions of a tracepoint provider. |
| 2178 | |
| 2179 | To create a tracepoint provider header file: |
| 2180 | |
| 2181 | . Start from this template: |
| 2182 | + |
| 2183 | -- |
| 2184 | [source,c] |
| 2185 | .Tracepoint provider header file template (`.h` file extension). |
| 2186 | ---- |
| 2187 | #undef TRACEPOINT_PROVIDER |
| 2188 | #define TRACEPOINT_PROVIDER provider_name |
| 2189 | |
| 2190 | #undef TRACEPOINT_INCLUDE |
| 2191 | #define TRACEPOINT_INCLUDE "./tp.h" |
| 2192 | |
| 2193 | #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ) |
| 2194 | #define _TP_H |
| 2195 | |
| 2196 | #include <lttng/tracepoint.h> |
| 2197 | |
| 2198 | /* |
| 2199 | * Use TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(), |
| 2200 | * TRACEPOINT_EVENT_INSTANCE(), and TRACEPOINT_LOGLEVEL() here. |
| 2201 | */ |
| 2202 | |
| 2203 | #endif /* _TP_H */ |
| 2204 | |
| 2205 | #include <lttng/tracepoint-event.h> |
| 2206 | ---- |
| 2207 | -- |
| 2208 | |
| 2209 | . Replace: |
| 2210 | + |
| 2211 | * `provider_name` with the name of your tracepoint provider. |
| 2212 | * `"tp.h"` with the name of your tracepoint provider header file. |
| 2213 | |
| 2214 | . Below the `#include <lttng/tracepoint.h>` line, put your |
| 2215 | <<defining-tracepoints,tracepoint definitions>>. |
| 2216 | |
| 2217 | Your tracepoint provider name must be unique amongst all the possible |
| 2218 | tracepoint provider names used on the same target system. We |
| 2219 | suggest to include the name of your project or company in the name, |
| 2220 | for example, `org_lttng_my_project_tpp`. |
| 2221 | |
| 2222 | TIP: [[lttng-gen-tp]]Use the man:lttng-gen-tp(1) tool to create |
| 2223 | this boilerplate for you. When using cmd:lttng-gen-tp, all you need to |
| 2224 | write are the <<defining-tracepoints,tracepoint definitions>>. |
| 2225 | |
| 2226 | |
| 2227 | [[defining-tracepoints]] |
| 2228 | ===== Create a tracepoint definition |
| 2229 | |
| 2230 | A _tracepoint definition_ defines, for a given tracepoint: |
| 2231 | |
| 2232 | * Its **input arguments**. They are the macro parameters that the |
| 2233 | `tracepoint()` macro accepts for this particular tracepoint |
| 2234 | in the source code of the user application. |
| 2235 | * Its **output event fields**. They are the sources of event fields |
| 2236 | that form the payload of any event that the execution of the |
| 2237 | `tracepoint()` macro emits for this particular tracepoint. |
| 2238 | |
| 2239 | Create a tracepoint definition by using the |
| 2240 | `TRACEPOINT_EVENT()` macro below the `#include <lttng/tracepoint.h>` |
| 2241 | line in the |
| 2242 | <<tpp-header,tracepoint provider header file template>>. |
| 2243 | |
| 2244 | The syntax of the `TRACEPOINT_EVENT()` macro is: |
| 2245 | |
| 2246 | [source,c] |
| 2247 | .`TRACEPOINT_EVENT()` macro syntax. |
| 2248 | ---- |
| 2249 | TRACEPOINT_EVENT( |
| 2250 | /* Tracepoint provider name */ |
| 2251 | provider_name, |
| 2252 | |
| 2253 | /* Tracepoint name */ |
| 2254 | tracepoint_name, |
| 2255 | |
| 2256 | /* Input arguments */ |
| 2257 | TP_ARGS( |
| 2258 | arguments |
| 2259 | ), |
| 2260 | |
| 2261 | /* Output event fields */ |
| 2262 | TP_FIELDS( |
| 2263 | fields |
| 2264 | ) |
| 2265 | ) |
| 2266 | ---- |
| 2267 | |
| 2268 | Replace: |
| 2269 | |
| 2270 | * `provider_name` with your tracepoint provider name. |
| 2271 | * `tracepoint_name` with your tracepoint name. |
| 2272 | * `arguments` with the <<tpp-def-input-args,input arguments>>. |
| 2273 | * `fields` with the <<tpp-def-output-fields,output event field>> |
| 2274 | definitions. |
| 2275 | |
| 2276 | This tracepoint emits events named `provider_name:tracepoint_name`. |
| 2277 | |
| 2278 | [IMPORTANT] |
| 2279 | .Event name length limitation |
| 2280 | ==== |
| 2281 | The concatenation of the tracepoint provider name and the |
| 2282 | tracepoint name must not exceed **254{nbsp}characters**. If it does, the |
| 2283 | instrumented application compiles and runs, but LTTng throws multiple |
| 2284 | warnings and you could experience serious issues. |
| 2285 | ==== |
| 2286 | |
| 2287 | [[tpp-def-input-args]]The syntax of the `TP_ARGS()` macro is: |
| 2288 | |
| 2289 | [source,c] |
| 2290 | .`TP_ARGS()` macro syntax. |
| 2291 | ---- |
| 2292 | TP_ARGS( |
| 2293 | type, arg_name |
| 2294 | ) |
| 2295 | ---- |
| 2296 | |
| 2297 | Replace: |
| 2298 | |
| 2299 | * `type` with the C type of the argument. |
| 2300 | * `arg_name` with the argument name. |
| 2301 | |
| 2302 | You can repeat `type` and `arg_name` up to 10{nbsp}times to have more |
| 2303 | than one argument. |
| 2304 | |
| 2305 | .`TP_ARGS()` usage with three arguments. |
| 2306 | ==== |
| 2307 | [source,c] |
| 2308 | ---- |
| 2309 | TP_ARGS( |
| 2310 | int, count, |
| 2311 | float, ratio, |
| 2312 | const char*, query |
| 2313 | ) |
| 2314 | ---- |
| 2315 | ==== |
| 2316 | |
| 2317 | The `TP_ARGS()` and `TP_ARGS(void)` forms are valid to create a |
| 2318 | tracepoint definition with no input arguments. |
| 2319 | |
| 2320 | [[tpp-def-output-fields]]The `TP_FIELDS()` macro contains a list of |
| 2321 | `ctf_*()` macros. Each `ctf_*()` macro defines one event field. See |
| 2322 | man:lttng-ust(3) for a complete description of the available `ctf_*()` |
| 2323 | macros. A `ctf_*()` macro specifies the type, size, and byte order of |
| 2324 | one event field. |
| 2325 | |
| 2326 | Each `ctf_*()` macro takes an _argument expression_ parameter. This is a |
| 2327 | C expression that the tracer evalutes at the `tracepoint()` macro site |
| 2328 | in the source code of the application. This expression provides the |
| 2329 | source of data of a field. The argument expression can include input |
| 2330 | argument names listed in the `TP_ARGS()` macro. |
| 2331 | |
| 2332 | Each `ctf_*()` macro also takes a _field name_ parameter. Field names |
| 2333 | must be unique within a given tracepoint definition. |
| 2334 | |
| 2335 | Here's a complete tracepoint definition example: |
| 2336 | |
| 2337 | .Tracepoint definition. |
| 2338 | ==== |
| 2339 | The following tracepoint definition defines a tracepoint which takes |
| 2340 | three input arguments and has four output event fields. |
| 2341 | |
| 2342 | [source,c] |
| 2343 | ---- |
| 2344 | #include "my-custom-structure.h" |
| 2345 | |
| 2346 | TRACEPOINT_EVENT( |
| 2347 | my_provider, |
| 2348 | my_tracepoint, |
| 2349 | TP_ARGS( |
| 2350 | const struct my_custom_structure*, my_custom_structure, |
| 2351 | float, ratio, |
| 2352 | const char*, query |
| 2353 | ), |
| 2354 | TP_FIELDS( |
| 2355 | ctf_string(query_field, query) |
| 2356 | ctf_float(double, ratio_field, ratio) |
| 2357 | ctf_integer(int, recv_size, my_custom_structure->recv_size) |
| 2358 | ctf_integer(int, send_size, my_custom_structure->send_size) |
| 2359 | ) |
| 2360 | ) |
| 2361 | ---- |
| 2362 | |
| 2363 | Refer to this tracepoint definition with the `tracepoint()` macro in |
| 2364 | the source code of your application like this: |
| 2365 | |
| 2366 | [source,c] |
| 2367 | ---- |
| 2368 | tracepoint(my_provider, my_tracepoint, |
| 2369 | my_structure, some_ratio, the_query); |
| 2370 | ---- |
| 2371 | ==== |
| 2372 | |
| 2373 | NOTE: The LTTng tracer only evaluates tracepoint arguments at run time |
| 2374 | if they satisfy an enabled <<event,event rule>>. |
| 2375 | |
| 2376 | |
| 2377 | [[using-tracepoint-classes]] |
| 2378 | ===== Use a tracepoint class |
| 2379 | |
| 2380 | A _tracepoint class_ is a class of tracepoints which share the same |
| 2381 | output event field definitions. A _tracepoint instance_ is one |
| 2382 | instance of such a defined tracepoint class, with its own tracepoint |
| 2383 | name. |
| 2384 | |
| 2385 | The <<defining-tracepoints,`TRACEPOINT_EVENT()` macro>> is actually a |
| 2386 | shorthand which defines both a tracepoint class and a tracepoint |
| 2387 | instance at the same time. |
| 2388 | |
| 2389 | When you build a tracepoint provider package, the C or $$C++$$ compiler |
| 2390 | creates one serialization function for each **tracepoint class**. A |
| 2391 | serialization function is responsible for serializing the event fields |
| 2392 | of a tracepoint to a sub-buffer when tracing. |
| 2393 | |
| 2394 | For various performance reasons, when your situation requires multiple |
| 2395 | tracepoint definitions with different names, but with the same event |
| 2396 | fields, we recommend that you manually create a tracepoint class |
| 2397 | and instantiate as many tracepoint instances as needed. One positive |
| 2398 | effect of such a design, amongst other advantages, is that all |
| 2399 | tracepoint instances of the same tracepoint class reuse the same |
| 2400 | serialization function, thus reducing |
| 2401 | https://en.wikipedia.org/wiki/Cache_pollution[cache pollution]. |
| 2402 | |
| 2403 | .Use a tracepoint class and tracepoint instances. |
| 2404 | ==== |
| 2405 | Consider the following three tracepoint definitions: |
| 2406 | |
| 2407 | [source,c] |
| 2408 | ---- |
| 2409 | TRACEPOINT_EVENT( |
| 2410 | my_app, |
| 2411 | get_account, |
| 2412 | TP_ARGS( |
| 2413 | int, userid, |
| 2414 | size_t, len |
| 2415 | ), |
| 2416 | TP_FIELDS( |
| 2417 | ctf_integer(int, userid, userid) |
| 2418 | ctf_integer(size_t, len, len) |
| 2419 | ) |
| 2420 | ) |
| 2421 | |
| 2422 | TRACEPOINT_EVENT( |
| 2423 | my_app, |
| 2424 | get_settings, |
| 2425 | TP_ARGS( |
| 2426 | int, userid, |
| 2427 | size_t, len |
| 2428 | ), |
| 2429 | TP_FIELDS( |
| 2430 | ctf_integer(int, userid, userid) |
| 2431 | ctf_integer(size_t, len, len) |
| 2432 | ) |
| 2433 | ) |
| 2434 | |
| 2435 | TRACEPOINT_EVENT( |
| 2436 | my_app, |
| 2437 | get_transaction, |
| 2438 | TP_ARGS( |
| 2439 | int, userid, |
| 2440 | size_t, len |
| 2441 | ), |
| 2442 | TP_FIELDS( |
| 2443 | ctf_integer(int, userid, userid) |
| 2444 | ctf_integer(size_t, len, len) |
| 2445 | ) |
| 2446 | ) |
| 2447 | ---- |
| 2448 | |
| 2449 | In this case, we create three tracepoint classes, with one implicit |
| 2450 | tracepoint instance for each of them: `get_account`, `get_settings`, and |
| 2451 | `get_transaction`. However, they all share the same event field names |
| 2452 | and types. Hence three identical, yet independent serialization |
| 2453 | functions are created when you build the tracepoint provider package. |
| 2454 | |
| 2455 | A better design choice is to define a single tracepoint class and three |
| 2456 | tracepoint instances: |
| 2457 | |
| 2458 | [source,c] |
| 2459 | ---- |
| 2460 | /* The tracepoint class */ |
| 2461 | TRACEPOINT_EVENT_CLASS( |
| 2462 | /* Tracepoint provider name */ |
| 2463 | my_app, |
| 2464 | |
| 2465 | /* Tracepoint class name */ |
| 2466 | my_class, |
| 2467 | |
| 2468 | /* Input arguments */ |
| 2469 | TP_ARGS( |
| 2470 | int, userid, |
| 2471 | size_t, len |
| 2472 | ), |
| 2473 | |
| 2474 | /* Output event fields */ |
| 2475 | TP_FIELDS( |
| 2476 | ctf_integer(int, userid, userid) |
| 2477 | ctf_integer(size_t, len, len) |
| 2478 | ) |
| 2479 | ) |
| 2480 | |
| 2481 | /* The tracepoint instances */ |
| 2482 | TRACEPOINT_EVENT_INSTANCE( |
| 2483 | /* Tracepoint provider name */ |
| 2484 | my_app, |
| 2485 | |
| 2486 | /* Tracepoint class name */ |
| 2487 | my_class, |
| 2488 | |
| 2489 | /* Tracepoint name */ |
| 2490 | get_account, |
| 2491 | |
| 2492 | /* Input arguments */ |
| 2493 | TP_ARGS( |
| 2494 | int, userid, |
| 2495 | size_t, len |
| 2496 | ) |
| 2497 | ) |
| 2498 | TRACEPOINT_EVENT_INSTANCE( |
| 2499 | my_app, |
| 2500 | my_class, |
| 2501 | get_settings, |
| 2502 | TP_ARGS( |
| 2503 | int, userid, |
| 2504 | size_t, len |
| 2505 | ) |
| 2506 | ) |
| 2507 | TRACEPOINT_EVENT_INSTANCE( |
| 2508 | my_app, |
| 2509 | my_class, |
| 2510 | get_transaction, |
| 2511 | TP_ARGS( |
| 2512 | int, userid, |
| 2513 | size_t, len |
| 2514 | ) |
| 2515 | ) |
| 2516 | ---- |
| 2517 | ==== |
| 2518 | |
| 2519 | |
| 2520 | [[assigning-log-levels]] |
| 2521 | ===== Assign a log level to a tracepoint definition |
| 2522 | |
| 2523 | Assign a _log level_ to a <<defining-tracepoints,tracepoint definition>> |
| 2524 | with the `TRACEPOINT_LOGLEVEL()` macro. |
| 2525 | |
| 2526 | Assigning different levels of severity to tracepoint definitions can |
| 2527 | be useful: when you <<enabling-disabling-events,create an event rule>>, |
| 2528 | you can target tracepoints having a log level as severe as a specific |
| 2529 | value. |
| 2530 | |
| 2531 | The concept of LTTng-UST log levels is similar to the levels found |
| 2532 | in typical logging frameworks: |
| 2533 | |
| 2534 | * In a logging framework, the log level is given by the function |
| 2535 | or method name you use at the log statement site: `debug()`, |
| 2536 | `info()`, `warn()`, `error()`, and so on. |
| 2537 | * In LTTng-UST, you statically assign the log level to a tracepoint |
| 2538 | definition; any `tracepoint()` macro invocation which refers to |
| 2539 | this definition has this log level. |
| 2540 | |
| 2541 | You must use `TRACEPOINT_LOGLEVEL()` _after_ the |
| 2542 | <<defining-tracepoints,`TRACEPOINT_EVENT()`>> or |
| 2543 | <<using-tracepoint-classes,`TRACEPOINT_INSTANCE()`>> macro for a given |
| 2544 | tracepoint. |
| 2545 | |
| 2546 | The syntax of the `TRACEPOINT_LOGLEVEL()` macro is: |
| 2547 | |
| 2548 | [source,c] |
| 2549 | .`TRACEPOINT_LOGLEVEL()` macro syntax. |
| 2550 | ---- |
| 2551 | TRACEPOINT_LOGLEVEL(provider_name, tracepoint_name, log_level) |
| 2552 | ---- |
| 2553 | |
| 2554 | Replace: |
| 2555 | |
| 2556 | * `provider_name` with the tracepoint provider name. |
| 2557 | * `tracepoint_name` with the tracepoint name. |
| 2558 | * `log_level` with the log level to assign to the tracepoint |
| 2559 | definition named `tracepoint_name` in the `provider_name` |
| 2560 | tracepoint provider. |
| 2561 | + |
| 2562 | See man:lttng-ust(3) for a list of available log level names. |
| 2563 | |
| 2564 | .Assign the `TRACE_DEBUG_UNIT` log level to a tracepoint definition. |
| 2565 | ==== |
| 2566 | [source,c] |
| 2567 | ---- |
| 2568 | /* Tracepoint definition */ |
| 2569 | TRACEPOINT_EVENT( |
| 2570 | my_app, |
| 2571 | get_transaction, |
| 2572 | TP_ARGS( |
| 2573 | int, userid, |
| 2574 | size_t, len |
| 2575 | ), |
| 2576 | TP_FIELDS( |
| 2577 | ctf_integer(int, userid, userid) |
| 2578 | ctf_integer(size_t, len, len) |
| 2579 | ) |
| 2580 | ) |
| 2581 | |
| 2582 | /* Log level assignment */ |
| 2583 | TRACEPOINT_LOGLEVEL(my_app, get_transaction, TRACE_DEBUG_UNIT) |
| 2584 | ---- |
| 2585 | ==== |
| 2586 | |
| 2587 | |
| 2588 | [[tpp-source]] |
| 2589 | ===== Create a tracepoint provider package source file |
| 2590 | |
| 2591 | A _tracepoint provider package source file_ is a C source file which |
| 2592 | includes a <<tpp-header,tracepoint provider header file>> to expand its |
| 2593 | macros into event serialization and other functions. |
| 2594 | |
| 2595 | Use the following tracepoint provider package source file template: |
| 2596 | |
| 2597 | [source,c] |
| 2598 | .Tracepoint provider package source file template. |
| 2599 | ---- |
| 2600 | #define TRACEPOINT_CREATE_PROBES |
| 2601 | |
| 2602 | #include "tp.h" |
| 2603 | ---- |
| 2604 | |
| 2605 | Replace `tp.h` with the name of your <<tpp-header,tracepoint provider |
| 2606 | header file>> name. You may also include more than one tracepoint |
| 2607 | provider header file here to create a tracepoint provider package |
| 2608 | holding more than one tracepoint providers. |
| 2609 | |
| 2610 | |
| 2611 | [[probing-the-application-source-code]] |
| 2612 | ==== Add tracepoints to the source code of an application |
| 2613 | |
| 2614 | Once you <<tpp-header,create a tracepoint provider header file>>, use |
| 2615 | the `tracepoint()` macro in the source code of your application to |
| 2616 | insert the tracepoints that this header |
| 2617 | <<defining-tracepoints,defines>>. |
| 2618 | |
| 2619 | The `tracepoint()` macro takes at least two parameters: the tracepoint |
| 2620 | provider name and the tracepoint name. The corresponding tracepoint |
| 2621 | definition defines the other parameters. |
| 2622 | |
| 2623 | .`tracepoint()` usage. |
| 2624 | ==== |
| 2625 | The following <<defining-tracepoints,tracepoint definition>> defines a |
| 2626 | tracepoint which takes two input arguments and has two output event |
| 2627 | fields. |
| 2628 | |
| 2629 | [source,c] |
| 2630 | .Tracepoint provider header file. |
| 2631 | ---- |
| 2632 | #include "my-custom-structure.h" |
| 2633 | |
| 2634 | TRACEPOINT_EVENT( |
| 2635 | my_provider, |
| 2636 | my_tracepoint, |
| 2637 | TP_ARGS( |
| 2638 | int, argc, |
| 2639 | const char*, cmd_name |
| 2640 | ), |
| 2641 | TP_FIELDS( |
| 2642 | ctf_string(cmd_name, cmd_name) |
| 2643 | ctf_integer(int, number_of_args, argc) |
| 2644 | ) |
| 2645 | ) |
| 2646 | ---- |
| 2647 | |
| 2648 | Refer to this tracepoint definition with the `tracepoint()` macro in |
| 2649 | the source code of your application like this: |
| 2650 | |
| 2651 | [source,c] |
| 2652 | .Application source file. |
| 2653 | ---- |
| 2654 | #include "tp.h" |
| 2655 | |
| 2656 | int main(int argc, char* argv[]) |
| 2657 | { |
| 2658 | tracepoint(my_provider, my_tracepoint, argc, argv[0]); |
| 2659 | |
| 2660 | return 0; |
| 2661 | } |
| 2662 | ---- |
| 2663 | |
| 2664 | Note how the source code of the application includes |
| 2665 | the tracepoint provider header file containing the tracepoint |
| 2666 | definitions to use, path:{tp.h}. |
| 2667 | ==== |
| 2668 | |
| 2669 | .`tracepoint()` usage with a complex tracepoint definition. |
| 2670 | ==== |
| 2671 | Consider this complex tracepoint definition, where multiple event |
| 2672 | fields refer to the same input arguments in their argument expression |
| 2673 | parameter: |
| 2674 | |
| 2675 | [source,c] |
| 2676 | .Tracepoint provider header file. |
| 2677 | ---- |
| 2678 | /* For `struct stat` */ |
| 2679 | #include <sys/types.h> |
| 2680 | #include <sys/stat.h> |
| 2681 | #include <unistd.h> |
| 2682 | |
| 2683 | TRACEPOINT_EVENT( |
| 2684 | my_provider, |
| 2685 | my_tracepoint, |
| 2686 | TP_ARGS( |
| 2687 | int, my_int_arg, |
| 2688 | char*, my_str_arg, |
| 2689 | struct stat*, st |
| 2690 | ), |
| 2691 | TP_FIELDS( |
| 2692 | ctf_integer(int, my_constant_field, 23 + 17) |
| 2693 | ctf_integer(int, my_int_arg_field, my_int_arg) |
| 2694 | ctf_integer(int, my_int_arg_field2, my_int_arg * my_int_arg) |
| 2695 | ctf_integer(int, sum4_field, my_str_arg[0] + my_str_arg[1] + |
| 2696 | my_str_arg[2] + my_str_arg[3]) |
| 2697 | ctf_string(my_str_arg_field, my_str_arg) |
| 2698 | ctf_integer_hex(off_t, size_field, st->st_size) |
| 2699 | ctf_float(double, size_dbl_field, (double) st->st_size) |
| 2700 | ctf_sequence_text(char, half_my_str_arg_field, my_str_arg, |
| 2701 | size_t, strlen(my_str_arg) / 2) |
| 2702 | ) |
| 2703 | ) |
| 2704 | ---- |
| 2705 | |
| 2706 | Refer to this tracepoint definition with the `tracepoint()` macro in |
| 2707 | the source code of your application like this: |
| 2708 | |
| 2709 | [source,c] |
| 2710 | .Application source file. |
| 2711 | ---- |
| 2712 | #define TRACEPOINT_DEFINE |
| 2713 | #include "tp.h" |
| 2714 | |
| 2715 | int main(void) |
| 2716 | { |
| 2717 | struct stat s; |
| 2718 | |
| 2719 | stat("/etc/fstab", &s); |
| 2720 | tracepoint(my_provider, my_tracepoint, 23, "Hello, World!", &s); |
| 2721 | |
| 2722 | return 0; |
| 2723 | } |
| 2724 | ---- |
| 2725 | |
| 2726 | If you look at the event record that LTTng writes when tracing this |
| 2727 | program, assuming the file size of path:{/etc/fstab} is 301{nbsp}bytes, |
| 2728 | it should look like this: |
| 2729 | |
| 2730 | .Event record fields |
| 2731 | |==== |
| 2732 | |Field name |Field value |
| 2733 | |`my_constant_field` |40 |
| 2734 | |`my_int_arg_field` |23 |
| 2735 | |`my_int_arg_field2` |529 |
| 2736 | |`sum4_field` |389 |
| 2737 | |`my_str_arg_field` |`Hello, World!` |
| 2738 | |`size_field` |0x12d |
| 2739 | |`size_dbl_field` |301.0 |
| 2740 | |`half_my_str_arg_field` |`Hello,` |
| 2741 | |==== |
| 2742 | ==== |
| 2743 | |
| 2744 | Sometimes, the arguments you pass to `tracepoint()` are expensive to |
| 2745 | compute--they use the call stack, for example. To avoid this computation |
| 2746 | when the tracepoint is disabled, use the `tracepoint_enabled()` and |
| 2747 | `do_tracepoint()` macros. |
| 2748 | |
| 2749 | The syntax of the `tracepoint_enabled()` and `do_tracepoint()` macros |
| 2750 | is: |
| 2751 | |
| 2752 | [source,c] |
| 2753 | .`tracepoint_enabled()` and `do_tracepoint()` macros syntax. |
| 2754 | ---- |
| 2755 | tracepoint_enabled(provider_name, tracepoint_name) |
| 2756 | do_tracepoint(provider_name, tracepoint_name, ...) |
| 2757 | ---- |
| 2758 | |
| 2759 | Replace: |
| 2760 | |
| 2761 | * `provider_name` with the tracepoint provider name. |
| 2762 | * `tracepoint_name` with the tracepoint name. |
| 2763 | |
| 2764 | `tracepoint_enabled()` returns a non-zero value if the tracepoint named |
| 2765 | `tracepoint_name` from the provider named `provider_name` is enabled |
| 2766 | **at run time**. |
| 2767 | |
| 2768 | `do_tracepoint()` is like `tracepoint()`, except that it doesn't check |
| 2769 | if the tracepoint is enabled. Using `tracepoint()` with |
| 2770 | `tracepoint_enabled()` is dangerous since `tracepoint()` also contains |
| 2771 | the `tracepoint_enabled()` check, thus a race condition is |
| 2772 | possible in this situation: |
| 2773 | |
| 2774 | [source,c] |
| 2775 | .Possible race condition when using `tracepoint_enabled()` with `tracepoint()`. |
| 2776 | ---- |
| 2777 | if (tracepoint_enabled(my_provider, my_tracepoint)) { |
| 2778 | stuff = prepare_stuff(); |
| 2779 | } |
| 2780 | |
| 2781 | tracepoint(my_provider, my_tracepoint, stuff); |
| 2782 | ---- |
| 2783 | |
| 2784 | If the tracepoint is enabled after the condition, then `stuff` isn't |
| 2785 | prepared: the emitted event will either contain wrong data, or the whole |
| 2786 | application could crash (segmentation fault, for example). |
| 2787 | |
| 2788 | NOTE: Neither `tracepoint_enabled()` nor `do_tracepoint()` have an |
| 2789 | `STAP_PROBEV()` call. If you need it, you must emit |
| 2790 | this call yourself. |
| 2791 | |
| 2792 | |
| 2793 | [[building-tracepoint-providers-and-user-application]] |
| 2794 | ==== Build and link a tracepoint provider package and an application |
| 2795 | |
| 2796 | Once you have one or more <<tpp-header,tracepoint provider header |
| 2797 | files>> and a <<tpp-source,tracepoint provider package source file>>, |
| 2798 | create the tracepoint provider package by compiling its source |
| 2799 | file. From here, multiple build and run scenarios are possible. The |
| 2800 | following table shows common application and library configurations |
| 2801 | along with the required command lines to achieve them. |
| 2802 | |
| 2803 | In the following diagrams, we use the following file names: |
| 2804 | |
| 2805 | `app`:: |
| 2806 | Executable application. |
| 2807 | |
| 2808 | `app.o`:: |
| 2809 | Application object file. |
| 2810 | |
| 2811 | `tpp.o`:: |
| 2812 | Tracepoint provider package object file. |
| 2813 | |
| 2814 | `tpp.a`:: |
| 2815 | Tracepoint provider package archive file. |
| 2816 | |
| 2817 | `libtpp.so`:: |
| 2818 | Tracepoint provider package shared object file. |
| 2819 | |
| 2820 | `emon.o`:: |
| 2821 | User library object file. |
| 2822 | |
| 2823 | `libemon.so`:: |
| 2824 | User library shared object file. |
| 2825 | |
| 2826 | We use the following symbols in the diagrams of table below: |
| 2827 | |
| 2828 | [role="img-100"] |
| 2829 | .Symbols used in the build scenario diagrams. |
| 2830 | image::ust-sit-symbols.png[] |
| 2831 | |
| 2832 | We assume that path:{.} is part of the env:LD_LIBRARY_PATH environment |
| 2833 | variable in the following instructions. |
| 2834 | |
| 2835 | [role="growable ust-scenarios",cols="asciidoc,asciidoc"] |
| 2836 | .Common tracepoint provider package scenarios. |
| 2837 | |==== |
| 2838 | |Scenario |Instructions |
| 2839 | |
| 2840 | | |
| 2841 | The instrumented application is statically linked with |
| 2842 | the tracepoint provider package object. |
| 2843 | |
| 2844 | image::ust-sit+app-linked-with-tp-o+app-instrumented.png[] |
| 2845 | |
| 2846 | | |
| 2847 | include::../common/ust-sit-step-tp-o.txt[] |
| 2848 | |
| 2849 | To build the instrumented application: |
| 2850 | |
| 2851 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 2852 | + |
| 2853 | -- |
| 2854 | [source,c] |
| 2855 | ---- |
| 2856 | #define TRACEPOINT_DEFINE |
| 2857 | ---- |
| 2858 | -- |
| 2859 | |
| 2860 | . Compile the application source file: |
| 2861 | + |
| 2862 | -- |
| 2863 | [role="term"] |
| 2864 | ---- |
| 2865 | $ gcc -c app.c |
| 2866 | ---- |
| 2867 | -- |
| 2868 | |
| 2869 | . Build the application: |
| 2870 | + |
| 2871 | -- |
| 2872 | [role="term"] |
| 2873 | ---- |
| 2874 | $ gcc -o app app.o tpp.o -llttng-ust -ldl |
| 2875 | ---- |
| 2876 | -- |
| 2877 | |
| 2878 | To run the instrumented application: |
| 2879 | |
| 2880 | * Start the application: |
| 2881 | + |
| 2882 | -- |
| 2883 | [role="term"] |
| 2884 | ---- |
| 2885 | $ ./app |
| 2886 | ---- |
| 2887 | -- |
| 2888 | |
| 2889 | | |
| 2890 | The instrumented application is statically linked with the |
| 2891 | tracepoint provider package archive file. |
| 2892 | |
| 2893 | image::ust-sit+app-linked-with-tp-a+app-instrumented.png[] |
| 2894 | |
| 2895 | | |
| 2896 | To create the tracepoint provider package archive file: |
| 2897 | |
| 2898 | . Compile the <<tpp-source,tracepoint provider package source file>>: |
| 2899 | + |
| 2900 | -- |
| 2901 | [role="term"] |
| 2902 | ---- |
| 2903 | $ gcc -I. -c tpp.c |
| 2904 | ---- |
| 2905 | -- |
| 2906 | |
| 2907 | . Create the tracepoint provider package archive file: |
| 2908 | + |
| 2909 | -- |
| 2910 | [role="term"] |
| 2911 | ---- |
| 2912 | $ ar rcs tpp.a tpp.o |
| 2913 | ---- |
| 2914 | -- |
| 2915 | |
| 2916 | To build the instrumented application: |
| 2917 | |
| 2918 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 2919 | + |
| 2920 | -- |
| 2921 | [source,c] |
| 2922 | ---- |
| 2923 | #define TRACEPOINT_DEFINE |
| 2924 | ---- |
| 2925 | -- |
| 2926 | |
| 2927 | . Compile the application source file: |
| 2928 | + |
| 2929 | -- |
| 2930 | [role="term"] |
| 2931 | ---- |
| 2932 | $ gcc -c app.c |
| 2933 | ---- |
| 2934 | -- |
| 2935 | |
| 2936 | . Build the application: |
| 2937 | + |
| 2938 | -- |
| 2939 | [role="term"] |
| 2940 | ---- |
| 2941 | $ gcc -o app app.o tpp.a -llttng-ust -ldl |
| 2942 | ---- |
| 2943 | -- |
| 2944 | |
| 2945 | To run the instrumented application: |
| 2946 | |
| 2947 | * Start the application: |
| 2948 | + |
| 2949 | -- |
| 2950 | [role="term"] |
| 2951 | ---- |
| 2952 | $ ./app |
| 2953 | ---- |
| 2954 | -- |
| 2955 | |
| 2956 | | |
| 2957 | The instrumented application is linked with the tracepoint provider |
| 2958 | package shared object. |
| 2959 | |
| 2960 | image::ust-sit+app-linked-with-tp-so+app-instrumented.png[] |
| 2961 | |
| 2962 | | |
| 2963 | include::../common/ust-sit-step-tp-so.txt[] |
| 2964 | |
| 2965 | To build the instrumented application: |
| 2966 | |
| 2967 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 2968 | + |
| 2969 | -- |
| 2970 | [source,c] |
| 2971 | ---- |
| 2972 | #define TRACEPOINT_DEFINE |
| 2973 | ---- |
| 2974 | -- |
| 2975 | |
| 2976 | . Compile the application source file: |
| 2977 | + |
| 2978 | -- |
| 2979 | [role="term"] |
| 2980 | ---- |
| 2981 | $ gcc -c app.c |
| 2982 | ---- |
| 2983 | -- |
| 2984 | |
| 2985 | . Build the application: |
| 2986 | + |
| 2987 | -- |
| 2988 | [role="term"] |
| 2989 | ---- |
| 2990 | $ gcc -o app app.o -ldl -L. -ltpp |
| 2991 | ---- |
| 2992 | -- |
| 2993 | |
| 2994 | To run the instrumented application: |
| 2995 | |
| 2996 | * Start the application: |
| 2997 | + |
| 2998 | -- |
| 2999 | [role="term"] |
| 3000 | ---- |
| 3001 | $ ./app |
| 3002 | ---- |
| 3003 | -- |
| 3004 | |
| 3005 | | |
| 3006 | The tracepoint provider package shared object is preloaded before the |
| 3007 | instrumented application starts. |
| 3008 | |
| 3009 | image::ust-sit+tp-so-preloaded+app-instrumented.png[] |
| 3010 | |
| 3011 | | |
| 3012 | include::../common/ust-sit-step-tp-so.txt[] |
| 3013 | |
| 3014 | To build the instrumented application: |
| 3015 | |
| 3016 | . In path:{app.c}, before including path:{tpp.h}, add the |
| 3017 | following lines: |
| 3018 | + |
| 3019 | -- |
| 3020 | [source,c] |
| 3021 | ---- |
| 3022 | #define TRACEPOINT_DEFINE |
| 3023 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3024 | ---- |
| 3025 | -- |
| 3026 | |
| 3027 | . Compile the application source file: |
| 3028 | + |
| 3029 | -- |
| 3030 | [role="term"] |
| 3031 | ---- |
| 3032 | $ gcc -c app.c |
| 3033 | ---- |
| 3034 | -- |
| 3035 | |
| 3036 | . Build the application: |
| 3037 | + |
| 3038 | -- |
| 3039 | [role="term"] |
| 3040 | ---- |
| 3041 | $ gcc -o app app.o -ldl |
| 3042 | ---- |
| 3043 | -- |
| 3044 | |
| 3045 | To run the instrumented application with tracing support: |
| 3046 | |
| 3047 | * Preload the tracepoint provider package shared object and |
| 3048 | start the application: |
| 3049 | + |
| 3050 | -- |
| 3051 | [role="term"] |
| 3052 | ---- |
| 3053 | $ LD_PRELOAD=./libtpp.so ./app |
| 3054 | ---- |
| 3055 | -- |
| 3056 | |
| 3057 | To run the instrumented application without tracing support: |
| 3058 | |
| 3059 | * Start the application: |
| 3060 | + |
| 3061 | -- |
| 3062 | [role="term"] |
| 3063 | ---- |
| 3064 | $ ./app |
| 3065 | ---- |
| 3066 | -- |
| 3067 | |
| 3068 | | |
| 3069 | The instrumented application dynamically loads the tracepoint provider |
| 3070 | package shared object. |
| 3071 | |
| 3072 | image::ust-sit+app-dlopens-tp-so+app-instrumented.png[] |
| 3073 | |
| 3074 | | |
| 3075 | include::../common/ust-sit-step-tp-so.txt[] |
| 3076 | |
| 3077 | To build the instrumented application: |
| 3078 | |
| 3079 | . In path:{app.c}, before including path:{tpp.h}, add the |
| 3080 | following lines: |
| 3081 | + |
| 3082 | -- |
| 3083 | [source,c] |
| 3084 | ---- |
| 3085 | #define TRACEPOINT_DEFINE |
| 3086 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3087 | ---- |
| 3088 | -- |
| 3089 | |
| 3090 | . Compile the application source file: |
| 3091 | + |
| 3092 | -- |
| 3093 | [role="term"] |
| 3094 | ---- |
| 3095 | $ gcc -c app.c |
| 3096 | ---- |
| 3097 | -- |
| 3098 | |
| 3099 | . Build the application: |
| 3100 | + |
| 3101 | -- |
| 3102 | [role="term"] |
| 3103 | ---- |
| 3104 | $ gcc -o app app.o -ldl |
| 3105 | ---- |
| 3106 | -- |
| 3107 | |
| 3108 | To run the instrumented application: |
| 3109 | |
| 3110 | * Start the application: |
| 3111 | + |
| 3112 | -- |
| 3113 | [role="term"] |
| 3114 | ---- |
| 3115 | $ ./app |
| 3116 | ---- |
| 3117 | -- |
| 3118 | |
| 3119 | | |
| 3120 | The application is linked with the instrumented user library. |
| 3121 | |
| 3122 | The instrumented user library is statically linked with the tracepoint |
| 3123 | provider package object file. |
| 3124 | |
| 3125 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-o+lib-instrumented.png[] |
| 3126 | |
| 3127 | | |
| 3128 | include::../common/ust-sit-step-tp-o-fpic.txt[] |
| 3129 | |
| 3130 | To build the instrumented user library: |
| 3131 | |
| 3132 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3133 | following line: |
| 3134 | + |
| 3135 | -- |
| 3136 | [source,c] |
| 3137 | ---- |
| 3138 | #define TRACEPOINT_DEFINE |
| 3139 | ---- |
| 3140 | -- |
| 3141 | |
| 3142 | . Compile the user library source file: |
| 3143 | + |
| 3144 | -- |
| 3145 | [role="term"] |
| 3146 | ---- |
| 3147 | $ gcc -I. -fpic -c emon.c |
| 3148 | ---- |
| 3149 | -- |
| 3150 | |
| 3151 | . Build the user library shared object: |
| 3152 | + |
| 3153 | -- |
| 3154 | [role="term"] |
| 3155 | ---- |
| 3156 | $ gcc -shared -o libemon.so emon.o tpp.o -llttng-ust -ldl |
| 3157 | ---- |
| 3158 | -- |
| 3159 | |
| 3160 | To build the application: |
| 3161 | |
| 3162 | . Compile the application source file: |
| 3163 | + |
| 3164 | -- |
| 3165 | [role="term"] |
| 3166 | ---- |
| 3167 | $ gcc -c app.c |
| 3168 | ---- |
| 3169 | -- |
| 3170 | |
| 3171 | . Build the application: |
| 3172 | + |
| 3173 | -- |
| 3174 | [role="term"] |
| 3175 | ---- |
| 3176 | $ gcc -o app app.o -L. -lemon |
| 3177 | ---- |
| 3178 | -- |
| 3179 | |
| 3180 | To run the application: |
| 3181 | |
| 3182 | * Start the application: |
| 3183 | + |
| 3184 | -- |
| 3185 | [role="term"] |
| 3186 | ---- |
| 3187 | $ ./app |
| 3188 | ---- |
| 3189 | -- |
| 3190 | |
| 3191 | | |
| 3192 | The application is linked with the instrumented user library. |
| 3193 | |
| 3194 | The instrumented user library is linked with the tracepoint provider |
| 3195 | package shared object. |
| 3196 | |
| 3197 | image::ust-sit+app-linked-with-lib+lib-linked-with-tp-so+lib-instrumented.png[] |
| 3198 | |
| 3199 | | |
| 3200 | include::../common/ust-sit-step-tp-so.txt[] |
| 3201 | |
| 3202 | To build the instrumented user library: |
| 3203 | |
| 3204 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3205 | following line: |
| 3206 | + |
| 3207 | -- |
| 3208 | [source,c] |
| 3209 | ---- |
| 3210 | #define TRACEPOINT_DEFINE |
| 3211 | ---- |
| 3212 | -- |
| 3213 | |
| 3214 | . Compile the user library source file: |
| 3215 | + |
| 3216 | -- |
| 3217 | [role="term"] |
| 3218 | ---- |
| 3219 | $ gcc -I. -fpic -c emon.c |
| 3220 | ---- |
| 3221 | -- |
| 3222 | |
| 3223 | . Build the user library shared object: |
| 3224 | + |
| 3225 | -- |
| 3226 | [role="term"] |
| 3227 | ---- |
| 3228 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
| 3229 | ---- |
| 3230 | -- |
| 3231 | |
| 3232 | To build the application: |
| 3233 | |
| 3234 | . Compile the application source file: |
| 3235 | + |
| 3236 | -- |
| 3237 | [role="term"] |
| 3238 | ---- |
| 3239 | $ gcc -c app.c |
| 3240 | ---- |
| 3241 | -- |
| 3242 | |
| 3243 | . Build the application: |
| 3244 | + |
| 3245 | -- |
| 3246 | [role="term"] |
| 3247 | ---- |
| 3248 | $ gcc -o app app.o -L. -lemon |
| 3249 | ---- |
| 3250 | -- |
| 3251 | |
| 3252 | To run the application: |
| 3253 | |
| 3254 | * Start the application: |
| 3255 | + |
| 3256 | -- |
| 3257 | [role="term"] |
| 3258 | ---- |
| 3259 | $ ./app |
| 3260 | ---- |
| 3261 | -- |
| 3262 | |
| 3263 | | |
| 3264 | The tracepoint provider package shared object is preloaded before the |
| 3265 | application starts. |
| 3266 | |
| 3267 | The application is linked with the instrumented user library. |
| 3268 | |
| 3269 | image::ust-sit+tp-so-preloaded+app-linked-with-lib+lib-instrumented.png[] |
| 3270 | |
| 3271 | | |
| 3272 | include::../common/ust-sit-step-tp-so.txt[] |
| 3273 | |
| 3274 | To build the instrumented user library: |
| 3275 | |
| 3276 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3277 | following lines: |
| 3278 | + |
| 3279 | -- |
| 3280 | [source,c] |
| 3281 | ---- |
| 3282 | #define TRACEPOINT_DEFINE |
| 3283 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3284 | ---- |
| 3285 | -- |
| 3286 | |
| 3287 | . Compile the user library source file: |
| 3288 | + |
| 3289 | -- |
| 3290 | [role="term"] |
| 3291 | ---- |
| 3292 | $ gcc -I. -fpic -c emon.c |
| 3293 | ---- |
| 3294 | -- |
| 3295 | |
| 3296 | . Build the user library shared object: |
| 3297 | + |
| 3298 | -- |
| 3299 | [role="term"] |
| 3300 | ---- |
| 3301 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3302 | ---- |
| 3303 | -- |
| 3304 | |
| 3305 | To build the application: |
| 3306 | |
| 3307 | . Compile the application source file: |
| 3308 | + |
| 3309 | -- |
| 3310 | [role="term"] |
| 3311 | ---- |
| 3312 | $ gcc -c app.c |
| 3313 | ---- |
| 3314 | -- |
| 3315 | |
| 3316 | . Build the application: |
| 3317 | + |
| 3318 | -- |
| 3319 | [role="term"] |
| 3320 | ---- |
| 3321 | $ gcc -o app app.o -L. -lemon |
| 3322 | ---- |
| 3323 | -- |
| 3324 | |
| 3325 | To run the application with tracing support: |
| 3326 | |
| 3327 | * Preload the tracepoint provider package shared object and |
| 3328 | start the application: |
| 3329 | + |
| 3330 | -- |
| 3331 | [role="term"] |
| 3332 | ---- |
| 3333 | $ LD_PRELOAD=./libtpp.so ./app |
| 3334 | ---- |
| 3335 | -- |
| 3336 | |
| 3337 | To run the application without tracing support: |
| 3338 | |
| 3339 | * Start the application: |
| 3340 | + |
| 3341 | -- |
| 3342 | [role="term"] |
| 3343 | ---- |
| 3344 | $ ./app |
| 3345 | ---- |
| 3346 | -- |
| 3347 | |
| 3348 | | |
| 3349 | The application is linked with the instrumented user library. |
| 3350 | |
| 3351 | The instrumented user library dynamically loads the tracepoint provider |
| 3352 | package shared object. |
| 3353 | |
| 3354 | image::ust-sit+app-linked-with-lib+lib-dlopens-tp-so+lib-instrumented.png[] |
| 3355 | |
| 3356 | | |
| 3357 | include::../common/ust-sit-step-tp-so.txt[] |
| 3358 | |
| 3359 | To build the instrumented user library: |
| 3360 | |
| 3361 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3362 | following lines: |
| 3363 | + |
| 3364 | -- |
| 3365 | [source,c] |
| 3366 | ---- |
| 3367 | #define TRACEPOINT_DEFINE |
| 3368 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3369 | ---- |
| 3370 | -- |
| 3371 | |
| 3372 | . Compile the user library source file: |
| 3373 | + |
| 3374 | -- |
| 3375 | [role="term"] |
| 3376 | ---- |
| 3377 | $ gcc -I. -fpic -c emon.c |
| 3378 | ---- |
| 3379 | -- |
| 3380 | |
| 3381 | . Build the user library shared object: |
| 3382 | + |
| 3383 | -- |
| 3384 | [role="term"] |
| 3385 | ---- |
| 3386 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3387 | ---- |
| 3388 | -- |
| 3389 | |
| 3390 | To build the application: |
| 3391 | |
| 3392 | . Compile the application source file: |
| 3393 | + |
| 3394 | -- |
| 3395 | [role="term"] |
| 3396 | ---- |
| 3397 | $ gcc -c app.c |
| 3398 | ---- |
| 3399 | -- |
| 3400 | |
| 3401 | . Build the application: |
| 3402 | + |
| 3403 | -- |
| 3404 | [role="term"] |
| 3405 | ---- |
| 3406 | $ gcc -o app app.o -L. -lemon |
| 3407 | ---- |
| 3408 | -- |
| 3409 | |
| 3410 | To run the application: |
| 3411 | |
| 3412 | * Start the application: |
| 3413 | + |
| 3414 | -- |
| 3415 | [role="term"] |
| 3416 | ---- |
| 3417 | $ ./app |
| 3418 | ---- |
| 3419 | -- |
| 3420 | |
| 3421 | | |
| 3422 | The application dynamically loads the instrumented user library. |
| 3423 | |
| 3424 | The instrumented user library is linked with the tracepoint provider |
| 3425 | package shared object. |
| 3426 | |
| 3427 | image::ust-sit+app-dlopens-lib+lib-linked-with-tp-so+lib-instrumented.png[] |
| 3428 | |
| 3429 | | |
| 3430 | include::../common/ust-sit-step-tp-so.txt[] |
| 3431 | |
| 3432 | To build the instrumented user library: |
| 3433 | |
| 3434 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3435 | following line: |
| 3436 | + |
| 3437 | -- |
| 3438 | [source,c] |
| 3439 | ---- |
| 3440 | #define TRACEPOINT_DEFINE |
| 3441 | ---- |
| 3442 | -- |
| 3443 | |
| 3444 | . Compile the user library source file: |
| 3445 | + |
| 3446 | -- |
| 3447 | [role="term"] |
| 3448 | ---- |
| 3449 | $ gcc -I. -fpic -c emon.c |
| 3450 | ---- |
| 3451 | -- |
| 3452 | |
| 3453 | . Build the user library shared object: |
| 3454 | + |
| 3455 | -- |
| 3456 | [role="term"] |
| 3457 | ---- |
| 3458 | $ gcc -shared -o libemon.so emon.o -ldl -L. -ltpp |
| 3459 | ---- |
| 3460 | -- |
| 3461 | |
| 3462 | To build the application: |
| 3463 | |
| 3464 | . Compile the application source file: |
| 3465 | + |
| 3466 | -- |
| 3467 | [role="term"] |
| 3468 | ---- |
| 3469 | $ gcc -c app.c |
| 3470 | ---- |
| 3471 | -- |
| 3472 | |
| 3473 | . Build the application: |
| 3474 | + |
| 3475 | -- |
| 3476 | [role="term"] |
| 3477 | ---- |
| 3478 | $ gcc -o app app.o -ldl -L. -lemon |
| 3479 | ---- |
| 3480 | -- |
| 3481 | |
| 3482 | To run the application: |
| 3483 | |
| 3484 | * Start the application: |
| 3485 | + |
| 3486 | -- |
| 3487 | [role="term"] |
| 3488 | ---- |
| 3489 | $ ./app |
| 3490 | ---- |
| 3491 | -- |
| 3492 | |
| 3493 | | |
| 3494 | The application dynamically loads the instrumented user library. |
| 3495 | |
| 3496 | The instrumented user library dynamically loads the tracepoint provider |
| 3497 | package shared object. |
| 3498 | |
| 3499 | image::ust-sit+app-dlopens-lib+lib-dlopens-tp-so+lib-instrumented.png[] |
| 3500 | |
| 3501 | | |
| 3502 | include::../common/ust-sit-step-tp-so.txt[] |
| 3503 | |
| 3504 | To build the instrumented user library: |
| 3505 | |
| 3506 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3507 | following lines: |
| 3508 | + |
| 3509 | -- |
| 3510 | [source,c] |
| 3511 | ---- |
| 3512 | #define TRACEPOINT_DEFINE |
| 3513 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3514 | ---- |
| 3515 | -- |
| 3516 | |
| 3517 | . Compile the user library source file: |
| 3518 | + |
| 3519 | -- |
| 3520 | [role="term"] |
| 3521 | ---- |
| 3522 | $ gcc -I. -fpic -c emon.c |
| 3523 | ---- |
| 3524 | -- |
| 3525 | |
| 3526 | . Build the user library shared object: |
| 3527 | + |
| 3528 | -- |
| 3529 | [role="term"] |
| 3530 | ---- |
| 3531 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3532 | ---- |
| 3533 | -- |
| 3534 | |
| 3535 | To build the application: |
| 3536 | |
| 3537 | . Compile the application source file: |
| 3538 | + |
| 3539 | -- |
| 3540 | [role="term"] |
| 3541 | ---- |
| 3542 | $ gcc -c app.c |
| 3543 | ---- |
| 3544 | -- |
| 3545 | |
| 3546 | . Build the application: |
| 3547 | + |
| 3548 | -- |
| 3549 | [role="term"] |
| 3550 | ---- |
| 3551 | $ gcc -o app app.o -ldl -L. -lemon |
| 3552 | ---- |
| 3553 | -- |
| 3554 | |
| 3555 | To run the application: |
| 3556 | |
| 3557 | * Start the application: |
| 3558 | + |
| 3559 | -- |
| 3560 | [role="term"] |
| 3561 | ---- |
| 3562 | $ ./app |
| 3563 | ---- |
| 3564 | -- |
| 3565 | |
| 3566 | | |
| 3567 | The tracepoint provider package shared object is preloaded before the |
| 3568 | application starts. |
| 3569 | |
| 3570 | The application dynamically loads the instrumented user library. |
| 3571 | |
| 3572 | image::ust-sit+tp-so-preloaded+app-dlopens-lib+lib-instrumented.png[] |
| 3573 | |
| 3574 | | |
| 3575 | include::../common/ust-sit-step-tp-so.txt[] |
| 3576 | |
| 3577 | To build the instrumented user library: |
| 3578 | |
| 3579 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3580 | following lines: |
| 3581 | + |
| 3582 | -- |
| 3583 | [source,c] |
| 3584 | ---- |
| 3585 | #define TRACEPOINT_DEFINE |
| 3586 | #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE |
| 3587 | ---- |
| 3588 | -- |
| 3589 | |
| 3590 | . Compile the user library source file: |
| 3591 | + |
| 3592 | -- |
| 3593 | [role="term"] |
| 3594 | ---- |
| 3595 | $ gcc -I. -fpic -c emon.c |
| 3596 | ---- |
| 3597 | -- |
| 3598 | |
| 3599 | . Build the user library shared object: |
| 3600 | + |
| 3601 | -- |
| 3602 | [role="term"] |
| 3603 | ---- |
| 3604 | $ gcc -shared -o libemon.so emon.o -ldl |
| 3605 | ---- |
| 3606 | -- |
| 3607 | |
| 3608 | To build the application: |
| 3609 | |
| 3610 | . Compile the application source file: |
| 3611 | + |
| 3612 | -- |
| 3613 | [role="term"] |
| 3614 | ---- |
| 3615 | $ gcc -c app.c |
| 3616 | ---- |
| 3617 | -- |
| 3618 | |
| 3619 | . Build the application: |
| 3620 | + |
| 3621 | -- |
| 3622 | [role="term"] |
| 3623 | ---- |
| 3624 | $ gcc -o app app.o -L. -lemon |
| 3625 | ---- |
| 3626 | -- |
| 3627 | |
| 3628 | To run the application with tracing support: |
| 3629 | |
| 3630 | * Preload the tracepoint provider package shared object and |
| 3631 | start the application: |
| 3632 | + |
| 3633 | -- |
| 3634 | [role="term"] |
| 3635 | ---- |
| 3636 | $ LD_PRELOAD=./libtpp.so ./app |
| 3637 | ---- |
| 3638 | -- |
| 3639 | |
| 3640 | To run the application without tracing support: |
| 3641 | |
| 3642 | * Start the application: |
| 3643 | + |
| 3644 | -- |
| 3645 | [role="term"] |
| 3646 | ---- |
| 3647 | $ ./app |
| 3648 | ---- |
| 3649 | -- |
| 3650 | |
| 3651 | | |
| 3652 | The application is statically linked with the tracepoint provider |
| 3653 | package object file. |
| 3654 | |
| 3655 | The application is linked with the instrumented user library. |
| 3656 | |
| 3657 | image::ust-sit+app-linked-with-tp-o+app-linked-with-lib+lib-instrumented.png[] |
| 3658 | |
| 3659 | | |
| 3660 | include::../common/ust-sit-step-tp-o.txt[] |
| 3661 | |
| 3662 | To build the instrumented user library: |
| 3663 | |
| 3664 | . In path:{emon.c}, before including path:{tpp.h}, add the |
| 3665 | following line: |
| 3666 | + |
| 3667 | -- |
| 3668 | [source,c] |
| 3669 | ---- |
| 3670 | #define TRACEPOINT_DEFINE |
| 3671 | ---- |
| 3672 | -- |
| 3673 | |
| 3674 | . Compile the user library source file: |
| 3675 | + |
| 3676 | -- |
| 3677 | [role="term"] |
| 3678 | ---- |
| 3679 | $ gcc -I. -fpic -c emon.c |
| 3680 | ---- |
| 3681 | -- |
| 3682 | |
| 3683 | . Build the user library shared object: |
| 3684 | + |
| 3685 | -- |
| 3686 | [role="term"] |
| 3687 | ---- |
| 3688 | $ gcc -shared -o libemon.so emon.o |
| 3689 | ---- |
| 3690 | -- |
| 3691 | |
| 3692 | To build the application: |
| 3693 | |
| 3694 | . Compile the application source file: |
| 3695 | + |
| 3696 | -- |
| 3697 | [role="term"] |
| 3698 | ---- |
| 3699 | $ gcc -c app.c |
| 3700 | ---- |
| 3701 | -- |
| 3702 | |
| 3703 | . Build the application: |
| 3704 | + |
| 3705 | -- |
| 3706 | [role="term"] |
| 3707 | ---- |
| 3708 | $ gcc -o app app.o tpp.o -llttng-ust -ldl -L. -lemon |
| 3709 | ---- |
| 3710 | -- |
| 3711 | |
| 3712 | To run the instrumented application: |
| 3713 | |
| 3714 | * Start the application: |
| 3715 | + |
| 3716 | -- |
| 3717 | [role="term"] |
| 3718 | ---- |
| 3719 | $ ./app |
| 3720 | ---- |
| 3721 | -- |
| 3722 | |
| 3723 | | |
| 3724 | The application is statically linked with the tracepoint provider |
| 3725 | package object file. |
| 3726 | |
| 3727 | The application dynamically loads the instrumented user library. |
| 3728 | |
| 3729 | image::ust-sit+app-linked-with-tp-o+app-dlopens-lib+lib-instrumented.png[] |
| 3730 | |
| 3731 | | |
| 3732 | include::../common/ust-sit-step-tp-o.txt[] |
| 3733 | |
| 3734 | To build the application: |
| 3735 | |
| 3736 | . In path:{app.c}, before including path:{tpp.h}, add the following line: |
| 3737 | + |
| 3738 | -- |
| 3739 | [source,c] |
| 3740 | ---- |
| 3741 | #define TRACEPOINT_DEFINE |
| 3742 | ---- |
| 3743 | -- |
| 3744 | |
| 3745 | . Compile the application source file: |
| 3746 | + |
| 3747 | -- |
| 3748 | [role="term"] |
| 3749 | ---- |
| 3750 | $ gcc -c app.c |
| 3751 | ---- |
| 3752 | -- |
| 3753 | |
| 3754 | . Build the application: |
| 3755 | + |
| 3756 | -- |
| 3757 | [role="term"] |
| 3758 | ---- |
| 3759 | $ gcc -Wl,--export-dynamic -o app app.o tpp.o \ |
| 3760 | -llttng-ust -ldl |
| 3761 | ---- |
| 3762 | -- |
| 3763 | + |
| 3764 | The `--export-dynamic` option passed to the linker is necessary for the |
| 3765 | dynamically loaded library to ``see'' the tracepoint symbols defined in |
| 3766 | the application. |
| 3767 | |
| 3768 | To build the instrumented user library: |
| 3769 | |
| 3770 | . Compile the user library source file: |
| 3771 | + |
| 3772 | -- |
| 3773 | [role="term"] |
| 3774 | ---- |
| 3775 | $ gcc -I. -fpic -c emon.c |
| 3776 | ---- |
| 3777 | -- |
| 3778 | |
| 3779 | . Build the user library shared object: |
| 3780 | + |
| 3781 | -- |
| 3782 | [role="term"] |
| 3783 | ---- |
| 3784 | $ gcc -shared -o libemon.so emon.o |
| 3785 | ---- |
| 3786 | -- |
| 3787 | |
| 3788 | To run the application: |
| 3789 | |
| 3790 | * Start the application: |
| 3791 | + |
| 3792 | -- |
| 3793 | [role="term"] |
| 3794 | ---- |
| 3795 | $ ./app |
| 3796 | ---- |
| 3797 | -- |
| 3798 | |==== |
| 3799 | |
| 3800 | |
| 3801 | [[using-lttng-ust-with-daemons]] |
| 3802 | ===== Use noch:{LTTng-UST} with daemons |
| 3803 | |
| 3804 | If your instrumented application calls man:fork(2), man:clone(2), |
| 3805 | or BSD's man:rfork(2), without a following man:exec(3)-family |
| 3806 | system call, you must preload the path:{liblttng-ust-fork.so} shared |
| 3807 | object when you start the application. |
| 3808 | |
| 3809 | [role="term"] |
| 3810 | ---- |
| 3811 | $ LD_PRELOAD=liblttng-ust-fork.so ./my-app |
| 3812 | ---- |
| 3813 | |
| 3814 | If your tracepoint provider package is |
| 3815 | a shared library which you also preload, you must put both |
| 3816 | shared objects in env:LD_PRELOAD: |
| 3817 | |
| 3818 | [role="term"] |
| 3819 | ---- |
| 3820 | $ LD_PRELOAD=liblttng-ust-fork.so:/path/to/tp.so ./my-app |
| 3821 | ---- |
| 3822 | |
| 3823 | |
| 3824 | [role="since-2.9"] |
| 3825 | [[liblttng-ust-fd]] |
| 3826 | ===== Use noch:{LTTng-UST} with applications which close file descriptors that don't belong to them |
| 3827 | |
| 3828 | If your instrumented application closes one or more file descriptors |
| 3829 | which it did not open itself, you must preload the |
| 3830 | path:{liblttng-ust-fd.so} shared object when you start the application: |
| 3831 | |
| 3832 | [role="term"] |
| 3833 | ---- |
| 3834 | $ LD_PRELOAD=liblttng-ust-fd.so ./my-app |
| 3835 | ---- |
| 3836 | |
| 3837 | Typical use cases include closing all the file descriptors after |
| 3838 | man:fork(2) or man:rfork(2) and buggy applications doing |
| 3839 | ``double closes''. |
| 3840 | |
| 3841 | |
| 3842 | [[lttng-ust-pkg-config]] |
| 3843 | ===== Use noch:{pkg-config} |
| 3844 | |
| 3845 | On some distributions, LTTng-UST ships with a |
| 3846 | https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config] |
| 3847 | metadata file. If this is your case, then use cmd:pkg-config to |
| 3848 | build an application on the command line: |
| 3849 | |
| 3850 | [role="term"] |
| 3851 | ---- |
| 3852 | $ gcc -o my-app my-app.o tp.o $(pkg-config --cflags --libs lttng-ust) |
| 3853 | ---- |
| 3854 | |
| 3855 | |
| 3856 | [[instrumenting-32-bit-app-on-64-bit-system]] |
| 3857 | ===== [[advanced-instrumenting-techniques]]Build a 32-bit instrumented application for a 64-bit target system |
| 3858 | |
| 3859 | In order to trace a 32-bit application running on a 64-bit system, |
| 3860 | LTTng must use a dedicated 32-bit |
| 3861 | <<lttng-consumerd,consumer daemon>>. |
| 3862 | |
| 3863 | The following steps show how to build and install a 32-bit consumer |
| 3864 | daemon, which is _not_ part of the default 64-bit LTTng build, how to |
| 3865 | build and install the 32-bit LTTng-UST libraries, and how to build and |
| 3866 | link an instrumented 32-bit application in that context. |
| 3867 | |
| 3868 | To build a 32-bit instrumented application for a 64-bit target system, |
| 3869 | assuming you have a fresh target system with no installed Userspace RCU |
| 3870 | or LTTng packages: |
| 3871 | |
| 3872 | . Download, build, and install a 32-bit version of Userspace RCU: |
| 3873 | + |
| 3874 | -- |
| 3875 | [role="term"] |
| 3876 | ---- |
| 3877 | $ cd $(mktemp -d) && |
| 3878 | wget http://lttng.org/files/urcu/userspace-rcu-latest-0.9.tar.bz2 && |
| 3879 | tar -xf userspace-rcu-latest-0.9.tar.bz2 && |
| 3880 | cd userspace-rcu-0.9.* && |
| 3881 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 && |
| 3882 | make && |
| 3883 | sudo make install && |
| 3884 | sudo ldconfig |
| 3885 | ---- |
| 3886 | -- |
| 3887 | |
| 3888 | . Using the package manager of your distribution, or from source, |
| 3889 | install the following 32-bit versions of the following dependencies of |
| 3890 | LTTng-tools and LTTng-UST: |
| 3891 | + |
| 3892 | -- |
| 3893 | * https://sourceforge.net/projects/libuuid/[libuuid] |
| 3894 | * http://directory.fsf.org/wiki/Popt[popt] |
| 3895 | * http://www.xmlsoft.org/[libxml2] |
| 3896 | -- |
| 3897 | |
| 3898 | . Download, build, and install a 32-bit version of the latest |
| 3899 | LTTng-UST{nbsp}{revision}: |
| 3900 | + |
| 3901 | -- |
| 3902 | [role="term"] |
| 3903 | ---- |
| 3904 | $ cd $(mktemp -d) && |
| 3905 | wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.12.tar.bz2 && |
| 3906 | tar -xf lttng-ust-latest-2.12.tar.bz2 && |
| 3907 | cd lttng-ust-2.12.* && |
| 3908 | ./configure --libdir=/usr/local/lib32 \ |
| 3909 | CFLAGS=-m32 CXXFLAGS=-m32 \ |
| 3910 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' && |
| 3911 | make && |
| 3912 | sudo make install && |
| 3913 | sudo ldconfig |
| 3914 | ---- |
| 3915 | -- |
| 3916 | + |
| 3917 | [NOTE] |
| 3918 | ==== |
| 3919 | Depending on your distribution, |
| 3920 | 32-bit libraries could be installed at a different location than |
| 3921 | `/usr/lib32`. For example, Debian is known to install |
| 3922 | some 32-bit libraries in `/usr/lib/i386-linux-gnu`. |
| 3923 | |
| 3924 | In this case, make sure to set `LDFLAGS` to all the |
| 3925 | relevant 32-bit library paths, for example: |
| 3926 | |
| 3927 | [role="term"] |
| 3928 | ---- |
| 3929 | $ LDFLAGS='-L/usr/lib/i386-linux-gnu -L/usr/lib32' |
| 3930 | ---- |
| 3931 | ==== |
| 3932 | |
| 3933 | . Download the latest LTTng-tools{nbsp}{revision}, build, and install |
| 3934 | the 32-bit consumer daemon: |
| 3935 | + |
| 3936 | -- |
| 3937 | [role="term"] |
| 3938 | ---- |
| 3939 | $ cd $(mktemp -d) && |
| 3940 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.12.tar.bz2 && |
| 3941 | tar -xf lttng-tools-latest-2.12.tar.bz2 && |
| 3942 | cd lttng-tools-2.12.* && |
| 3943 | ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 CXXFLAGS=-m32 \ |
| 3944 | LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' \ |
| 3945 | --disable-bin-lttng --disable-bin-lttng-crash \ |
| 3946 | --disable-bin-lttng-relayd --disable-bin-lttng-sessiond && |
| 3947 | make && |
| 3948 | cd src/bin/lttng-consumerd && |
| 3949 | sudo make install && |
| 3950 | sudo ldconfig |
| 3951 | ---- |
| 3952 | -- |
| 3953 | |
| 3954 | . From your distribution or from source, |
| 3955 | <<installing-lttng,install>> the 64-bit versions of |
| 3956 | LTTng-UST and Userspace RCU. |
| 3957 | . Download, build, and install the 64-bit version of the |
| 3958 | latest LTTng-tools{nbsp}{revision}: |
| 3959 | + |
| 3960 | -- |
| 3961 | [role="term"] |
| 3962 | ---- |
| 3963 | $ cd $(mktemp -d) && |
| 3964 | wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.12.tar.bz2 && |
| 3965 | tar -xf lttng-tools-latest-2.12.tar.bz2 && |
| 3966 | cd lttng-tools-2.12.* && |
| 3967 | ./configure --with-consumerd32-libdir=/usr/local/lib32 \ |
| 3968 | --with-consumerd32-bin=/usr/local/lib32/lttng/libexec/lttng-consumerd && |
| 3969 | make && |
| 3970 | sudo make install && |
| 3971 | sudo ldconfig |
| 3972 | ---- |
| 3973 | -- |
| 3974 | |
| 3975 | . Pass the following options to man:gcc(1), man:g++(1), or man:clang(1) |
| 3976 | when linking your 32-bit application: |
| 3977 | + |
| 3978 | ---- |
| 3979 | -m32 -L/usr/lib32 -L/usr/local/lib32 \ |
| 3980 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 |
| 3981 | ---- |
| 3982 | + |
| 3983 | For example, let's rebuild the quick start example in |
| 3984 | <<tracing-your-own-user-application,Trace a user application>> as an |
| 3985 | instrumented 32-bit application: |
| 3986 | + |
| 3987 | -- |
| 3988 | [role="term"] |
| 3989 | ---- |
| 3990 | $ gcc -m32 -c -I. hello-tp.c |
| 3991 | $ gcc -m32 -c hello.c |
| 3992 | $ gcc -m32 -o hello hello.o hello-tp.o \ |
| 3993 | -L/usr/lib32 -L/usr/local/lib32 \ |
| 3994 | -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 \ |
| 3995 | -llttng-ust -ldl |
| 3996 | ---- |
| 3997 | -- |
| 3998 | |
| 3999 | No special action is required to execute the 32-bit application and |
| 4000 | to trace it: use the command-line man:lttng(1) tool as usual. |
| 4001 | |
| 4002 | |
| 4003 | [role="since-2.5"] |
| 4004 | [[tracef]] |
| 4005 | ==== Use `tracef()` |
| 4006 | |
| 4007 | man:tracef(3) is a small LTTng-UST API designed for quick, |
| 4008 | man:printf(3)-like instrumentation without the burden of |
| 4009 | <<tracepoint-provider,creating>> and |
| 4010 | <<building-tracepoint-providers-and-user-application,building>> |
| 4011 | a tracepoint provider package. |
| 4012 | |
| 4013 | To use `tracef()` in your application: |
| 4014 | |
| 4015 | . In the C or C++ source files where you need to use `tracef()`, |
| 4016 | include `<lttng/tracef.h>`: |
| 4017 | + |
| 4018 | -- |
| 4019 | [source,c] |
| 4020 | ---- |
| 4021 | #include <lttng/tracef.h> |
| 4022 | ---- |
| 4023 | -- |
| 4024 | |
| 4025 | . In the source code of the application, use `tracef()` like you would |
| 4026 | use man:printf(3): |
| 4027 | + |
| 4028 | -- |
| 4029 | [source,c] |
| 4030 | ---- |
| 4031 | /* ... */ |
| 4032 | |
| 4033 | tracef("my message: %d (%s)", my_integer, my_string); |
| 4034 | |
| 4035 | /* ... */ |
| 4036 | ---- |
| 4037 | -- |
| 4038 | |
| 4039 | . Link your application with `liblttng-ust`: |
| 4040 | + |
| 4041 | -- |
| 4042 | [role="term"] |
| 4043 | ---- |
| 4044 | $ gcc -o app app.c -llttng-ust |
| 4045 | ---- |
| 4046 | -- |
| 4047 | |
| 4048 | To trace the events that `tracef()` calls emit: |
| 4049 | |
| 4050 | * <<enabling-disabling-events,Create an event rule>> which matches the |
| 4051 | `lttng_ust_tracef:*` event name: |
| 4052 | + |
| 4053 | -- |
| 4054 | [role="term"] |
| 4055 | ---- |
| 4056 | $ lttng enable-event --userspace 'lttng_ust_tracef:*' |
| 4057 | ---- |
| 4058 | -- |
| 4059 | |
| 4060 | [IMPORTANT] |
| 4061 | .Limitations of `tracef()` |
| 4062 | ==== |
| 4063 | The `tracef()` utility function was developed to make user space tracing |
| 4064 | super simple, albeit with notable disadvantages compared to |
| 4065 | <<defining-tracepoints,user-defined tracepoints>>: |
| 4066 | |
| 4067 | * All the emitted events have the same tracepoint provider and |
| 4068 | tracepoint names, respectively `lttng_ust_tracef` and `event`. |
| 4069 | * There is no static type checking. |
| 4070 | * The only event record field you actually get, named `msg`, is a string |
| 4071 | potentially containing the values you passed to `tracef()` |
| 4072 | using your own format string. This also means that you can't filter |
| 4073 | events with a custom expression at run time because there are no |
| 4074 | isolated fields. |
| 4075 | * Since `tracef()` uses the man:vasprintf(3) function of the |
| 4076 | C{nbsp}standard library behind the scenes to format the strings at run |
| 4077 | time, its expected performance is lower than with user-defined |
| 4078 | tracepoints, which don't require a conversion to a string. |
| 4079 | |
| 4080 | Taking this into consideration, `tracef()` is useful for some quick |
| 4081 | prototyping and debugging, but you shouldn't consider it for any |
| 4082 | permanent and serious applicative instrumentation. |
| 4083 | ==== |
| 4084 | |
| 4085 | |
| 4086 | [role="since-2.7"] |
| 4087 | [[tracelog]] |
| 4088 | ==== Use `tracelog()` |
| 4089 | |
| 4090 | The man:tracelog(3) API is very similar to <<tracef,`tracef()`>>, with |
| 4091 | the difference that it accepts an additional log level parameter. |
| 4092 | |
| 4093 | The goal of `tracelog()` is to ease the migration from logging to |
| 4094 | tracing. |
| 4095 | |
| 4096 | To use `tracelog()` in your application: |
| 4097 | |
| 4098 | . In the C or C++ source files where you need to use `tracelog()`, |
| 4099 | include `<lttng/tracelog.h>`: |
| 4100 | + |
| 4101 | -- |
| 4102 | [source,c] |
| 4103 | ---- |
| 4104 | #include <lttng/tracelog.h> |
| 4105 | ---- |
| 4106 | -- |
| 4107 | |
| 4108 | . In the source code of the application, use `tracelog()` like you would |
| 4109 | use man:printf(3), except for the first parameter which is the log |
| 4110 | level: |
| 4111 | + |
| 4112 | -- |
| 4113 | [source,c] |
| 4114 | ---- |
| 4115 | /* ... */ |
| 4116 | |
| 4117 | tracelog(TRACE_WARNING, "my message: %d (%s)", |
| 4118 | my_integer, my_string); |
| 4119 | |
| 4120 | /* ... */ |
| 4121 | ---- |
| 4122 | -- |
| 4123 | + |
| 4124 | See man:lttng-ust(3) for a list of available log level names. |
| 4125 | |
| 4126 | . Link your application with `liblttng-ust`: |
| 4127 | + |
| 4128 | -- |
| 4129 | [role="term"] |
| 4130 | ---- |
| 4131 | $ gcc -o app app.c -llttng-ust |
| 4132 | ---- |
| 4133 | -- |
| 4134 | |
| 4135 | To trace the events that `tracelog()` calls emit with a log level |
| 4136 | _as severe as_ a specific log level: |
| 4137 | |
| 4138 | * <<enabling-disabling-events,Create an event rule>> which matches the |
| 4139 | `lttng_ust_tracelog:*` event name and a minimum level |
| 4140 | of severity: |
| 4141 | + |
| 4142 | -- |
| 4143 | [role="term"] |
| 4144 | ---- |
| 4145 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' |
| 4146 | --loglevel=TRACE_WARNING |
| 4147 | ---- |
| 4148 | -- |
| 4149 | |
| 4150 | To trace the events that `tracelog()` calls emit with a |
| 4151 | _specific log level_: |
| 4152 | |
| 4153 | * Create an event rule which matches the `lttng_ust_tracelog:*` |
| 4154 | event name and a specific log level: |
| 4155 | + |
| 4156 | -- |
| 4157 | [role="term"] |
| 4158 | ---- |
| 4159 | $ lttng enable-event --userspace 'lttng_ust_tracelog:*' |
| 4160 | --loglevel-only=TRACE_INFO |
| 4161 | ---- |
| 4162 | -- |
| 4163 | |
| 4164 | |
| 4165 | [[prebuilt-ust-helpers]] |
| 4166 | === Prebuilt user space tracing helpers |
| 4167 | |
| 4168 | The LTTng-UST package provides a few helpers in the form of preloadable |
| 4169 | shared objects which automatically instrument system functions and |
| 4170 | calls. |
| 4171 | |
| 4172 | The helper shared objects are normally found in dir:{/usr/lib}. If you |
| 4173 | built LTTng-UST <<building-from-source,from source>>, they are probably |
| 4174 | located in dir:{/usr/local/lib}. |
| 4175 | |
| 4176 | The installed user space tracing helpers in LTTng-UST{nbsp}{revision} |
| 4177 | are: |
| 4178 | |
| 4179 | path:{liblttng-ust-libc-wrapper.so}:: |
| 4180 | path:{liblttng-ust-pthread-wrapper.so}:: |
| 4181 | <<liblttng-ust-libc-pthread-wrapper,C{nbsp}standard library |
| 4182 | memory and POSIX threads function tracing>>. |
| 4183 | |
| 4184 | path:{liblttng-ust-cyg-profile.so}:: |
| 4185 | path:{liblttng-ust-cyg-profile-fast.so}:: |
| 4186 | <<liblttng-ust-cyg-profile,Function entry and exit tracing>>. |
| 4187 | |
| 4188 | path:{liblttng-ust-dl.so}:: |
| 4189 | <<liblttng-ust-dl,Dynamic linker tracing>>. |
| 4190 | |
| 4191 | To use a user space tracing helper with any user application: |
| 4192 | |
| 4193 | * Preload the helper shared object when you start the application: |
| 4194 | + |
| 4195 | -- |
| 4196 | [role="term"] |
| 4197 | ---- |
| 4198 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so my-app |
| 4199 | ---- |
| 4200 | -- |
| 4201 | + |
| 4202 | You can preload more than one helper: |
| 4203 | + |
| 4204 | -- |
| 4205 | [role="term"] |
| 4206 | ---- |
| 4207 | $ LD_PRELOAD=liblttng-ust-libc-wrapper.so:liblttng-ust-dl.so my-app |
| 4208 | ---- |
| 4209 | -- |
| 4210 | |
| 4211 | |
| 4212 | [role="since-2.3"] |
| 4213 | [[liblttng-ust-libc-pthread-wrapper]] |
| 4214 | ==== Instrument C standard library memory and POSIX threads functions |
| 4215 | |
| 4216 | The path:{liblttng-ust-libc-wrapper.so} and |
| 4217 | path:{liblttng-ust-pthread-wrapper.so} helpers |
| 4218 | add instrumentation to some C standard library and POSIX |
| 4219 | threads functions. |
| 4220 | |
| 4221 | [role="growable"] |
| 4222 | .Functions instrumented by preloading path:{liblttng-ust-libc-wrapper.so}. |
| 4223 | |==== |
| 4224 | |TP provider name |TP name |Instrumented function |
| 4225 | |
| 4226 | .6+|`lttng_ust_libc` |`malloc` |man:malloc(3) |
| 4227 | |`calloc` |man:calloc(3) |
| 4228 | |`realloc` |man:realloc(3) |
| 4229 | |`free` |man:free(3) |
| 4230 | |`memalign` |man:memalign(3) |
| 4231 | |`posix_memalign` |man:posix_memalign(3) |
| 4232 | |==== |
| 4233 | |
| 4234 | [role="growable"] |
| 4235 | .Functions instrumented by preloading path:{liblttng-ust-pthread-wrapper.so}. |
| 4236 | |==== |
| 4237 | |TP provider name |TP name |Instrumented function |
| 4238 | |
| 4239 | .4+|`lttng_ust_pthread` |`pthread_mutex_lock_req` |man:pthread_mutex_lock(3p) (request time) |
| 4240 | |`pthread_mutex_lock_acq` |man:pthread_mutex_lock(3p) (acquire time) |
| 4241 | |`pthread_mutex_trylock` |man:pthread_mutex_trylock(3p) |
| 4242 | |`pthread_mutex_unlock` |man:pthread_mutex_unlock(3p) |
| 4243 | |==== |
| 4244 | |
| 4245 | When you preload the shared object, it replaces the functions listed |
| 4246 | in the previous tables by wrappers which contain tracepoints and call |
| 4247 | the replaced functions. |
| 4248 | |
| 4249 | |
| 4250 | [[liblttng-ust-cyg-profile]] |
| 4251 | ==== Instrument function entry and exit |
| 4252 | |
| 4253 | The path:{liblttng-ust-cyg-profile*.so} helpers can add instrumentation |
| 4254 | to the entry and exit points of functions. |
| 4255 | |
| 4256 | man:gcc(1) and man:clang(1) have an option named |
| 4257 | https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html[`-finstrument-functions`] |
| 4258 | which generates instrumentation calls for entry and exit to functions. |
| 4259 | The LTTng-UST function tracing helpers, |
| 4260 | path:{liblttng-ust-cyg-profile.so} and |
| 4261 | path:{liblttng-ust-cyg-profile-fast.so}, take advantage of this feature |
| 4262 | to add tracepoints to the two generated functions (which contain |
| 4263 | `cyg_profile` in their names, hence the name of the helper). |
| 4264 | |
| 4265 | To use the LTTng-UST function tracing helper, the source files to |
| 4266 | instrument must be built using the `-finstrument-functions` compiler |
| 4267 | flag. |
| 4268 | |
| 4269 | There are two versions of the LTTng-UST function tracing helper: |
| 4270 | |
| 4271 | * **path:{liblttng-ust-cyg-profile-fast.so}** is a lightweight variant |
| 4272 | that you should only use when it can be _guaranteed_ that the |
| 4273 | complete event stream is recorded without any lost event record. |
| 4274 | Any kind of duplicate information is left out. |
| 4275 | + |
| 4276 | Assuming no event record is lost, having only the function addresses on |
| 4277 | entry is enough to create a call graph, since an event record always |
| 4278 | contains the ID of the CPU that generated it. |
| 4279 | + |
| 4280 | Use a tool like man:addr2line(1) to convert function addresses back to |
| 4281 | source file names and line numbers. |
| 4282 | |
| 4283 | * **path:{liblttng-ust-cyg-profile.so}** is a more robust variant |
| 4284 | which also works in use cases where event records might get discarded or |
| 4285 | not recorded from application startup. |
| 4286 | In these cases, the trace analyzer needs more information to be |
| 4287 | able to reconstruct the program flow. |
| 4288 | |
| 4289 | See man:lttng-ust-cyg-profile(3) to learn more about the instrumentation |
| 4290 | points of this helper. |
| 4291 | |
| 4292 | All the tracepoints that this helper provides have the |
| 4293 | log level `TRACE_DEBUG_FUNCTION` (see man:lttng-ust(3)). |
| 4294 | |
| 4295 | TIP: It's sometimes a good idea to limit the number of source files that |
| 4296 | you compile with the `-finstrument-functions` option to prevent LTTng |
| 4297 | from writing an excessive amount of trace data at run time. When using |
| 4298 | man:gcc(1), use the |
| 4299 | `-finstrument-functions-exclude-function-list` option to avoid |
| 4300 | instrument entries and exits of specific function names. |
| 4301 | |
| 4302 | |
| 4303 | [role="since-2.4"] |
| 4304 | [[liblttng-ust-dl]] |
| 4305 | ==== Instrument the dynamic linker |
| 4306 | |
| 4307 | The path:{liblttng-ust-dl.so} helper adds instrumentation to the |
| 4308 | man:dlopen(3) and man:dlclose(3) function calls. |
| 4309 | |
| 4310 | See man:lttng-ust-dl(3) to learn more about the instrumentation points |
| 4311 | of this helper. |
| 4312 | |
| 4313 | |
| 4314 | [role="since-2.4"] |
| 4315 | [[java-application]] |
| 4316 | === User space Java agent |
| 4317 | |
| 4318 | You can instrument any Java application which uses one of the following |
| 4319 | logging frameworks: |
| 4320 | |
| 4321 | * The https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[**`java.util.logging`**] |
| 4322 | (JUL) core logging facilities. |
| 4323 | * http://logging.apache.org/log4j/1.2/[**Apache log4j{nbsp}1.2**], since |
| 4324 | LTTng{nbsp}2.6. Note that Apache Log4j{nbsp}2 isn't supported. |
| 4325 | |
| 4326 | [role="img-100"] |
| 4327 | .LTTng-UST Java agent imported by a Java application. |
| 4328 | image::java-app.png[] |
| 4329 | |
| 4330 | Note that the methods described below are new in LTTng{nbsp}2.8. |
| 4331 | Previous LTTng versions use another technique. |
| 4332 | |
| 4333 | NOTE: We use http://openjdk.java.net/[OpenJDK]{nbsp}8 for development |
| 4334 | and https://ci.lttng.org/[continuous integration], thus this version is |
| 4335 | directly supported. However, the LTTng-UST Java agent is also tested |
| 4336 | with OpenJDK{nbsp}7. |
| 4337 | |
| 4338 | |
| 4339 | [role="since-2.8"] |
| 4340 | [[jul]] |
| 4341 | ==== Use the LTTng-UST Java agent for `java.util.logging` |
| 4342 | |
| 4343 | To use the LTTng-UST Java agent in a Java application which uses |
| 4344 | `java.util.logging` (JUL): |
| 4345 | |
| 4346 | . In the source code of the Java application, import the LTTng-UST log |
| 4347 | handler package for `java.util.logging`: |
| 4348 | + |
| 4349 | -- |
| 4350 | [source,java] |
| 4351 | ---- |
| 4352 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 4353 | ---- |
| 4354 | -- |
| 4355 | |
| 4356 | . Create an LTTng-UST JUL log handler: |
| 4357 | + |
| 4358 | -- |
| 4359 | [source,java] |
| 4360 | ---- |
| 4361 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 4362 | ---- |
| 4363 | -- |
| 4364 | |
| 4365 | . Add this handler to the JUL loggers which should emit LTTng events: |
| 4366 | + |
| 4367 | -- |
| 4368 | [source,java] |
| 4369 | ---- |
| 4370 | Logger myLogger = Logger.getLogger("some-logger"); |
| 4371 | |
| 4372 | myLogger.addHandler(lttngUstLogHandler); |
| 4373 | ---- |
| 4374 | -- |
| 4375 | |
| 4376 | . Use `java.util.logging` log statements and configuration as usual. |
| 4377 | The loggers with an attached LTTng-UST log handler can emit |
| 4378 | LTTng events. |
| 4379 | |
| 4380 | . Before exiting the application, remove the LTTng-UST log handler from |
| 4381 | the loggers attached to it and call its `close()` method: |
| 4382 | + |
| 4383 | -- |
| 4384 | [source,java] |
| 4385 | ---- |
| 4386 | myLogger.removeHandler(lttngUstLogHandler); |
| 4387 | lttngUstLogHandler.close(); |
| 4388 | ---- |
| 4389 | -- |
| 4390 | + |
| 4391 | This isn't strictly necessary, but it is recommended for a clean |
| 4392 | disposal of the resources of the handler. |
| 4393 | |
| 4394 | . Include the common and JUL-specific JAR files of the LTTng-UST Java agent, |
| 4395 | path:{lttng-ust-agent-common.jar} and path:{lttng-ust-agent-jul.jar}, |
| 4396 | in the |
| 4397 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class |
| 4398 | path] when you build the Java application. |
| 4399 | + |
| 4400 | The JAR files are typically located in dir:{/usr/share/java}. |
| 4401 | + |
| 4402 | IMPORTANT: The LTTng-UST Java agent must be |
| 4403 | <<installing-lttng,installed>> for the logging framework your |
| 4404 | application uses. |
| 4405 | |
| 4406 | .Use the LTTng-UST Java agent for `java.util.logging`. |
| 4407 | ==== |
| 4408 | [source,java] |
| 4409 | .path:{Test.java} |
| 4410 | ---- |
| 4411 | import java.io.IOException; |
| 4412 | import java.util.logging.Handler; |
| 4413 | import java.util.logging.Logger; |
| 4414 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 4415 | |
| 4416 | public class Test |
| 4417 | { |
| 4418 | private static final int answer = 42; |
| 4419 | |
| 4420 | public static void main(String[] argv) throws Exception |
| 4421 | { |
| 4422 | // Create a logger |
| 4423 | Logger logger = Logger.getLogger("jello"); |
| 4424 | |
| 4425 | // Create an LTTng-UST log handler |
| 4426 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 4427 | |
| 4428 | // Add the LTTng-UST log handler to our logger |
| 4429 | logger.addHandler(lttngUstLogHandler); |
| 4430 | |
| 4431 | // Log at will! |
| 4432 | logger.info("some info"); |
| 4433 | logger.warning("some warning"); |
| 4434 | Thread.sleep(500); |
| 4435 | logger.finer("finer information; the answer is " + answer); |
| 4436 | Thread.sleep(123); |
| 4437 | logger.severe("error!"); |
| 4438 | |
| 4439 | // Not mandatory, but cleaner |
| 4440 | logger.removeHandler(lttngUstLogHandler); |
| 4441 | lttngUstLogHandler.close(); |
| 4442 | } |
| 4443 | } |
| 4444 | ---- |
| 4445 | |
| 4446 | Build this example: |
| 4447 | |
| 4448 | [role="term"] |
| 4449 | ---- |
| 4450 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
| 4451 | ---- |
| 4452 | |
| 4453 | <<creating-destroying-tracing-sessions,Create a tracing session>>, |
| 4454 | <<enabling-disabling-events,create an event rule>> matching the |
| 4455 | `jello` JUL logger, and <<basic-tracing-session-control,start tracing>>: |
| 4456 | |
| 4457 | [role="term"] |
| 4458 | ---- |
| 4459 | $ lttng create |
| 4460 | $ lttng enable-event --jul jello |
| 4461 | $ lttng start |
| 4462 | ---- |
| 4463 | |
| 4464 | Run the compiled class: |
| 4465 | |
| 4466 | [role="term"] |
| 4467 | ---- |
| 4468 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
| 4469 | ---- |
| 4470 | |
| 4471 | <<basic-tracing-session-control,Stop tracing>> and inspect the |
| 4472 | recorded events: |
| 4473 | |
| 4474 | [role="term"] |
| 4475 | ---- |
| 4476 | $ lttng stop |
| 4477 | $ lttng view |
| 4478 | ---- |
| 4479 | ==== |
| 4480 | |
| 4481 | In the resulting trace, an <<event,event record>> generated by a Java |
| 4482 | application using `java.util.logging` is named `lttng_jul:event` and |
| 4483 | has the following fields: |
| 4484 | |
| 4485 | `msg`:: |
| 4486 | Log record message. |
| 4487 | |
| 4488 | `logger_name`:: |
| 4489 | Logger name. |
| 4490 | |
| 4491 | `class_name`:: |
| 4492 | Name of the class in which the log statement was executed. |
| 4493 | |
| 4494 | `method_name`:: |
| 4495 | Name of the method in which the log statement was executed. |
| 4496 | |
| 4497 | `long_millis`:: |
| 4498 | Logging time (timestamp in milliseconds). |
| 4499 | |
| 4500 | `int_loglevel`:: |
| 4501 | Log level integer value. |
| 4502 | |
| 4503 | `int_threadid`:: |
| 4504 | ID of the thread in which the log statement was executed. |
| 4505 | |
| 4506 | Use the opt:lttng-enable-event(1):--loglevel or |
| 4507 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 4508 | man:lttng-enable-event(1) command to target a range of JUL log levels |
| 4509 | or a specific JUL log level. |
| 4510 | |
| 4511 | |
| 4512 | [role="since-2.8"] |
| 4513 | [[log4j]] |
| 4514 | ==== Use the LTTng-UST Java agent for Apache log4j |
| 4515 | |
| 4516 | To use the LTTng-UST Java agent in a Java application which uses |
| 4517 | Apache log4j{nbsp}1.2: |
| 4518 | |
| 4519 | . In the source code of the Java application, import the LTTng-UST log |
| 4520 | appender package for Apache log4j: |
| 4521 | + |
| 4522 | -- |
| 4523 | [source,java] |
| 4524 | ---- |
| 4525 | import org.lttng.ust.agent.log4j.LttngLogAppender; |
| 4526 | ---- |
| 4527 | -- |
| 4528 | |
| 4529 | . Create an LTTng-UST log4j log appender: |
| 4530 | + |
| 4531 | -- |
| 4532 | [source,java] |
| 4533 | ---- |
| 4534 | Appender lttngUstLogAppender = new LttngLogAppender(); |
| 4535 | ---- |
| 4536 | -- |
| 4537 | |
| 4538 | . Add this appender to the log4j loggers which should emit LTTng events: |
| 4539 | + |
| 4540 | -- |
| 4541 | [source,java] |
| 4542 | ---- |
| 4543 | Logger myLogger = Logger.getLogger("some-logger"); |
| 4544 | |
| 4545 | myLogger.addAppender(lttngUstLogAppender); |
| 4546 | ---- |
| 4547 | -- |
| 4548 | |
| 4549 | . Use Apache log4j log statements and configuration as usual. The |
| 4550 | loggers with an attached LTTng-UST log appender can emit LTTng events. |
| 4551 | |
| 4552 | . Before exiting the application, remove the LTTng-UST log appender from |
| 4553 | the loggers attached to it and call its `close()` method: |
| 4554 | + |
| 4555 | -- |
| 4556 | [source,java] |
| 4557 | ---- |
| 4558 | myLogger.removeAppender(lttngUstLogAppender); |
| 4559 | lttngUstLogAppender.close(); |
| 4560 | ---- |
| 4561 | -- |
| 4562 | + |
| 4563 | This isn't strictly necessary, but it is recommended for a clean |
| 4564 | disposal of the resources of the appender. |
| 4565 | |
| 4566 | . Include the common and log4j-specific JAR |
| 4567 | files of the LTTng-UST Java agent, path:{lttng-ust-agent-common.jar} and |
| 4568 | path:{lttng-ust-agent-log4j.jar}, in the |
| 4569 | https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class |
| 4570 | path] when you build the Java application. |
| 4571 | + |
| 4572 | The JAR files are typically located in dir:{/usr/share/java}. |
| 4573 | + |
| 4574 | IMPORTANT: The LTTng-UST Java agent must be |
| 4575 | <<installing-lttng,installed>> for the logging framework your |
| 4576 | application uses. |
| 4577 | |
| 4578 | .Use the LTTng-UST Java agent for Apache log4j. |
| 4579 | ==== |
| 4580 | [source,java] |
| 4581 | .path:{Test.java} |
| 4582 | ---- |
| 4583 | import org.apache.log4j.Appender; |
| 4584 | import org.apache.log4j.Logger; |
| 4585 | import org.lttng.ust.agent.log4j.LttngLogAppender; |
| 4586 | |
| 4587 | public class Test |
| 4588 | { |
| 4589 | private static final int answer = 42; |
| 4590 | |
| 4591 | public static void main(String[] argv) throws Exception |
| 4592 | { |
| 4593 | // Create a logger |
| 4594 | Logger logger = Logger.getLogger("jello"); |
| 4595 | |
| 4596 | // Create an LTTng-UST log appender |
| 4597 | Appender lttngUstLogAppender = new LttngLogAppender(); |
| 4598 | |
| 4599 | // Add the LTTng-UST log appender to our logger |
| 4600 | logger.addAppender(lttngUstLogAppender); |
| 4601 | |
| 4602 | // Log at will! |
| 4603 | logger.info("some info"); |
| 4604 | logger.warn("some warning"); |
| 4605 | Thread.sleep(500); |
| 4606 | logger.debug("debug information; the answer is " + answer); |
| 4607 | Thread.sleep(123); |
| 4608 | logger.fatal("error!"); |
| 4609 | |
| 4610 | // Not mandatory, but cleaner |
| 4611 | logger.removeAppender(lttngUstLogAppender); |
| 4612 | lttngUstLogAppender.close(); |
| 4613 | } |
| 4614 | } |
| 4615 | |
| 4616 | ---- |
| 4617 | |
| 4618 | Build this example (`$LOG4JPATH` is the path to the Apache log4j JAR |
| 4619 | file): |
| 4620 | |
| 4621 | [role="term"] |
| 4622 | ---- |
| 4623 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH Test.java |
| 4624 | ---- |
| 4625 | |
| 4626 | <<creating-destroying-tracing-sessions,Create a tracing session>>, |
| 4627 | <<enabling-disabling-events,create an event rule>> matching the |
| 4628 | `jello` log4j logger, and <<basic-tracing-session-control,start tracing>>: |
| 4629 | |
| 4630 | [role="term"] |
| 4631 | ---- |
| 4632 | $ lttng create |
| 4633 | $ lttng enable-event --log4j jello |
| 4634 | $ lttng start |
| 4635 | ---- |
| 4636 | |
| 4637 | Run the compiled class: |
| 4638 | |
| 4639 | [role="term"] |
| 4640 | ---- |
| 4641 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-log4j.jar:$LOG4JPATH:. Test |
| 4642 | ---- |
| 4643 | |
| 4644 | <<basic-tracing-session-control,Stop tracing>> and inspect the |
| 4645 | recorded events: |
| 4646 | |
| 4647 | [role="term"] |
| 4648 | ---- |
| 4649 | $ lttng stop |
| 4650 | $ lttng view |
| 4651 | ---- |
| 4652 | ==== |
| 4653 | |
| 4654 | In the resulting trace, an <<event,event record>> generated by a Java |
| 4655 | application using log4j is named `lttng_log4j:event` and |
| 4656 | has the following fields: |
| 4657 | |
| 4658 | `msg`:: |
| 4659 | Log record message. |
| 4660 | |
| 4661 | `logger_name`:: |
| 4662 | Logger name. |
| 4663 | |
| 4664 | `class_name`:: |
| 4665 | Name of the class in which the log statement was executed. |
| 4666 | |
| 4667 | `method_name`:: |
| 4668 | Name of the method in which the log statement was executed. |
| 4669 | |
| 4670 | `filename`:: |
| 4671 | Name of the file in which the executed log statement is located. |
| 4672 | |
| 4673 | `line_number`:: |
| 4674 | Line number at which the log statement was executed. |
| 4675 | |
| 4676 | `timestamp`:: |
| 4677 | Logging timestamp. |
| 4678 | |
| 4679 | `int_loglevel`:: |
| 4680 | Log level integer value. |
| 4681 | |
| 4682 | `thread_name`:: |
| 4683 | Name of the Java thread in which the log statement was executed. |
| 4684 | |
| 4685 | Use the opt:lttng-enable-event(1):--loglevel or |
| 4686 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 4687 | man:lttng-enable-event(1) command to target a range of Apache log4j |
| 4688 | log levels or a specific log4j log level. |
| 4689 | |
| 4690 | |
| 4691 | [role="since-2.8"] |
| 4692 | [[java-application-context]] |
| 4693 | ==== Provide application-specific context fields in a Java application |
| 4694 | |
| 4695 | A Java application-specific context field is a piece of state provided |
| 4696 | by the application which <<adding-context,you can add>>, using the |
| 4697 | man:lttng-add-context(1) command, to each <<event,event record>> |
| 4698 | produced by the log statements of this application. |
| 4699 | |
| 4700 | For example, a given object might have a current request ID variable. |
| 4701 | You can create a context information retriever for this object and |
| 4702 | assign a name to this current request ID. You can then, using the |
| 4703 | man:lttng-add-context(1) command, add this context field by name to |
| 4704 | the JUL or log4j <<channel,channel>>. |
| 4705 | |
| 4706 | To provide application-specific context fields in a Java application: |
| 4707 | |
| 4708 | . In the source code of the Java application, import the LTTng-UST |
| 4709 | Java agent context classes and interfaces: |
| 4710 | + |
| 4711 | -- |
| 4712 | [source,java] |
| 4713 | ---- |
| 4714 | import org.lttng.ust.agent.context.ContextInfoManager; |
| 4715 | import org.lttng.ust.agent.context.IContextInfoRetriever; |
| 4716 | ---- |
| 4717 | -- |
| 4718 | |
| 4719 | . Create a context information retriever class, that is, a class which |
| 4720 | implements the `IContextInfoRetriever` interface: |
| 4721 | + |
| 4722 | -- |
| 4723 | [source,java] |
| 4724 | ---- |
| 4725 | class MyContextInfoRetriever implements IContextInfoRetriever |
| 4726 | { |
| 4727 | @Override |
| 4728 | public Object retrieveContextInfo(String key) |
| 4729 | { |
| 4730 | if (key.equals("intCtx")) { |
| 4731 | return (short) 17; |
| 4732 | } else if (key.equals("strContext")) { |
| 4733 | return "context value!"; |
| 4734 | } else { |
| 4735 | return null; |
| 4736 | } |
| 4737 | } |
| 4738 | } |
| 4739 | ---- |
| 4740 | -- |
| 4741 | + |
| 4742 | This `retrieveContextInfo()` method is the only member of the |
| 4743 | `IContextInfoRetriever` interface. Its role is to return the current |
| 4744 | value of a state by name to create a context field. The names of the |
| 4745 | context fields and which state variables they return depends on your |
| 4746 | specific scenario. |
| 4747 | + |
| 4748 | All primitive types and objects are supported as context fields. |
| 4749 | When `retrieveContextInfo()` returns an object, the context field |
| 4750 | serializer calls its `toString()` method to add a string field to |
| 4751 | event records. The method can also return `null`, which means that |
| 4752 | no context field is available for the required name. |
| 4753 | |
| 4754 | . Register an instance of your context information retriever class to |
| 4755 | the context information manager singleton: |
| 4756 | + |
| 4757 | -- |
| 4758 | [source,java] |
| 4759 | ---- |
| 4760 | IContextInfoRetriever cir = new MyContextInfoRetriever(); |
| 4761 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 4762 | cim.registerContextInfoRetriever("retrieverName", cir); |
| 4763 | ---- |
| 4764 | -- |
| 4765 | |
| 4766 | . Before exiting the application, remove your context information |
| 4767 | retriever from the context information manager singleton: |
| 4768 | + |
| 4769 | -- |
| 4770 | [source,java] |
| 4771 | ---- |
| 4772 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 4773 | cim.unregisterContextInfoRetriever("retrieverName"); |
| 4774 | ---- |
| 4775 | -- |
| 4776 | + |
| 4777 | This isn't strictly necessary, but it is recommended for a clean |
| 4778 | disposal of some resources of the manager. |
| 4779 | |
| 4780 | . Build your Java application with LTTng-UST Java agent support as |
| 4781 | usual, following the procedure for either the <<jul,JUL>> or |
| 4782 | <<log4j,Apache log4j>> framework. |
| 4783 | |
| 4784 | |
| 4785 | .Provide application-specific context fields in a Java application. |
| 4786 | ==== |
| 4787 | [source,java] |
| 4788 | .path:{Test.java} |
| 4789 | ---- |
| 4790 | import java.util.logging.Handler; |
| 4791 | import java.util.logging.Logger; |
| 4792 | import org.lttng.ust.agent.jul.LttngLogHandler; |
| 4793 | import org.lttng.ust.agent.context.ContextInfoManager; |
| 4794 | import org.lttng.ust.agent.context.IContextInfoRetriever; |
| 4795 | |
| 4796 | public class Test |
| 4797 | { |
| 4798 | // Our context information retriever class |
| 4799 | private static class MyContextInfoRetriever |
| 4800 | implements IContextInfoRetriever |
| 4801 | { |
| 4802 | @Override |
| 4803 | public Object retrieveContextInfo(String key) { |
| 4804 | if (key.equals("intCtx")) { |
| 4805 | return (short) 17; |
| 4806 | } else if (key.equals("strContext")) { |
| 4807 | return "context value!"; |
| 4808 | } else { |
| 4809 | return null; |
| 4810 | } |
| 4811 | } |
| 4812 | } |
| 4813 | |
| 4814 | private static final int answer = 42; |
| 4815 | |
| 4816 | public static void main(String args[]) throws Exception |
| 4817 | { |
| 4818 | // Get the context information manager instance |
| 4819 | ContextInfoManager cim = ContextInfoManager.getInstance(); |
| 4820 | |
| 4821 | // Create and register our context information retriever |
| 4822 | IContextInfoRetriever cir = new MyContextInfoRetriever(); |
| 4823 | cim.registerContextInfoRetriever("myRetriever", cir); |
| 4824 | |
| 4825 | // Create a logger |
| 4826 | Logger logger = Logger.getLogger("jello"); |
| 4827 | |
| 4828 | // Create an LTTng-UST log handler |
| 4829 | Handler lttngUstLogHandler = new LttngLogHandler(); |
| 4830 | |
| 4831 | // Add the LTTng-UST log handler to our logger |
| 4832 | logger.addHandler(lttngUstLogHandler); |
| 4833 | |
| 4834 | // Log at will! |
| 4835 | logger.info("some info"); |
| 4836 | logger.warning("some warning"); |
| 4837 | Thread.sleep(500); |
| 4838 | logger.finer("finer information; the answer is " + answer); |
| 4839 | Thread.sleep(123); |
| 4840 | logger.severe("error!"); |
| 4841 | |
| 4842 | // Not mandatory, but cleaner |
| 4843 | logger.removeHandler(lttngUstLogHandler); |
| 4844 | lttngUstLogHandler.close(); |
| 4845 | cim.unregisterContextInfoRetriever("myRetriever"); |
| 4846 | } |
| 4847 | } |
| 4848 | ---- |
| 4849 | |
| 4850 | Build this example: |
| 4851 | |
| 4852 | [role="term"] |
| 4853 | ---- |
| 4854 | $ javac -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar Test.java |
| 4855 | ---- |
| 4856 | |
| 4857 | <<creating-destroying-tracing-sessions,Create a tracing session>> |
| 4858 | and <<enabling-disabling-events,create an event rule>> matching the |
| 4859 | `jello` JUL logger: |
| 4860 | |
| 4861 | [role="term"] |
| 4862 | ---- |
| 4863 | $ lttng create |
| 4864 | $ lttng enable-event --jul jello |
| 4865 | ---- |
| 4866 | |
| 4867 | <<adding-context,Add the application-specific context fields>> to the |
| 4868 | JUL channel: |
| 4869 | |
| 4870 | [role="term"] |
| 4871 | ---- |
| 4872 | $ lttng add-context --jul --type='$app.myRetriever:intCtx' |
| 4873 | $ lttng add-context --jul --type='$app.myRetriever:strContext' |
| 4874 | ---- |
| 4875 | |
| 4876 | <<basic-tracing-session-control,Start tracing>>: |
| 4877 | |
| 4878 | [role="term"] |
| 4879 | ---- |
| 4880 | $ lttng start |
| 4881 | ---- |
| 4882 | |
| 4883 | Run the compiled class: |
| 4884 | |
| 4885 | [role="term"] |
| 4886 | ---- |
| 4887 | $ java -cp /usr/share/java/jarpath/lttng-ust-agent-common.jar:/usr/share/java/jarpath/lttng-ust-agent-jul.jar:. Test |
| 4888 | ---- |
| 4889 | |
| 4890 | <<basic-tracing-session-control,Stop tracing>> and inspect the |
| 4891 | recorded events: |
| 4892 | |
| 4893 | [role="term"] |
| 4894 | ---- |
| 4895 | $ lttng stop |
| 4896 | $ lttng view |
| 4897 | ---- |
| 4898 | ==== |
| 4899 | |
| 4900 | |
| 4901 | [role="since-2.7"] |
| 4902 | [[python-application]] |
| 4903 | === User space Python agent |
| 4904 | |
| 4905 | You can instrument a Python{nbsp}2 or Python{nbsp}3 application which |
| 4906 | uses the standard |
| 4907 | https://docs.python.org/3/library/logging.html[`logging`] package. |
| 4908 | |
| 4909 | Each log statement emits an LTTng event once the |
| 4910 | application module imports the |
| 4911 | <<lttng-ust-agents,LTTng-UST Python agent>> package. |
| 4912 | |
| 4913 | [role="img-100"] |
| 4914 | .A Python application importing the LTTng-UST Python agent. |
| 4915 | image::python-app.png[] |
| 4916 | |
| 4917 | To use the LTTng-UST Python agent: |
| 4918 | |
| 4919 | . In the source code of the Python application, import the LTTng-UST |
| 4920 | Python agent: |
| 4921 | + |
| 4922 | -- |
| 4923 | [source,python] |
| 4924 | ---- |
| 4925 | import lttngust |
| 4926 | ---- |
| 4927 | -- |
| 4928 | + |
| 4929 | The LTTng-UST Python agent automatically adds its logging handler to the |
| 4930 | root logger at import time. |
| 4931 | + |
| 4932 | Any log statement that the application executes before this import does |
| 4933 | not emit an LTTng event. |
| 4934 | + |
| 4935 | IMPORTANT: The LTTng-UST Python agent must be |
| 4936 | <<installing-lttng,installed>>. |
| 4937 | |
| 4938 | . Use log statements and logging configuration as usual. |
| 4939 | Since the LTTng-UST Python agent adds a handler to the _root_ |
| 4940 | logger, you can trace any log statement from any logger. |
| 4941 | |
| 4942 | .Use the LTTng-UST Python agent. |
| 4943 | ==== |
| 4944 | [source,python] |
| 4945 | .path:{test.py} |
| 4946 | ---- |
| 4947 | import lttngust |
| 4948 | import logging |
| 4949 | import time |
| 4950 | |
| 4951 | |
| 4952 | def example(): |
| 4953 | logging.basicConfig() |
| 4954 | logger = logging.getLogger('my-logger') |
| 4955 | |
| 4956 | while True: |
| 4957 | logger.debug('debug message') |
| 4958 | logger.info('info message') |
| 4959 | logger.warn('warn message') |
| 4960 | logger.error('error message') |
| 4961 | logger.critical('critical message') |
| 4962 | time.sleep(1) |
| 4963 | |
| 4964 | |
| 4965 | if __name__ == '__main__': |
| 4966 | example() |
| 4967 | ---- |
| 4968 | |
| 4969 | NOTE: `logging.basicConfig()`, which adds to the root logger a basic |
| 4970 | logging handler which prints to the standard error stream, isn't |
| 4971 | strictly required for LTTng-UST tracing to work, but in versions of |
| 4972 | Python preceding{nbsp}3.2, you could see a warning message which indicates |
| 4973 | that no handler exists for the logger `my-logger`. |
| 4974 | |
| 4975 | <<creating-destroying-tracing-sessions,Create a tracing session>>, |
| 4976 | <<enabling-disabling-events,create an event rule>> matching the |
| 4977 | `my-logger` Python logger, and <<basic-tracing-session-control,start |
| 4978 | tracing>>: |
| 4979 | |
| 4980 | [role="term"] |
| 4981 | ---- |
| 4982 | $ lttng create |
| 4983 | $ lttng enable-event --python my-logger |
| 4984 | $ lttng start |
| 4985 | ---- |
| 4986 | |
| 4987 | Run the Python script: |
| 4988 | |
| 4989 | [role="term"] |
| 4990 | ---- |
| 4991 | $ python test.py |
| 4992 | ---- |
| 4993 | |
| 4994 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded |
| 4995 | events: |
| 4996 | |
| 4997 | [role="term"] |
| 4998 | ---- |
| 4999 | $ lttng stop |
| 5000 | $ lttng view |
| 5001 | ---- |
| 5002 | ==== |
| 5003 | |
| 5004 | In the resulting trace, an <<event,event record>> generated by a Python |
| 5005 | application is named `lttng_python:event` and has the following fields: |
| 5006 | |
| 5007 | `asctime`:: |
| 5008 | Logging time (string). |
| 5009 | |
| 5010 | `msg`:: |
| 5011 | Log record message. |
| 5012 | |
| 5013 | `logger_name`:: |
| 5014 | Logger name. |
| 5015 | |
| 5016 | `funcName`:: |
| 5017 | Name of the function in which the log statement was executed. |
| 5018 | |
| 5019 | `lineno`:: |
| 5020 | Line number at which the log statement was executed. |
| 5021 | |
| 5022 | `int_loglevel`:: |
| 5023 | Log level integer value. |
| 5024 | |
| 5025 | `thread`:: |
| 5026 | ID of the Python thread in which the log statement was executed. |
| 5027 | |
| 5028 | `threadName`:: |
| 5029 | Name of the Python thread in which the log statement was executed. |
| 5030 | |
| 5031 | Use the opt:lttng-enable-event(1):--loglevel or |
| 5032 | opt:lttng-enable-event(1):--loglevel-only option of the |
| 5033 | man:lttng-enable-event(1) command to target a range of Python log levels |
| 5034 | or a specific Python log level. |
| 5035 | |
| 5036 | When an application imports the LTTng-UST Python agent, the agent tries |
| 5037 | to register to a <<lttng-sessiond,session daemon>>. Note that you must |
| 5038 | <<start-sessiond,start the session daemon>> _before_ you run the Python |
| 5039 | application. If a session daemon is found, the agent tries to register |
| 5040 | to it during five seconds, after which the application continues |
| 5041 | without LTTng tracing support. Override this timeout value with |
| 5042 | the env:LTTNG_UST_PYTHON_REGISTER_TIMEOUT environment variable |
| 5043 | (milliseconds). |
| 5044 | |
| 5045 | If the session daemon stops while a Python application with an imported |
| 5046 | LTTng-UST Python agent runs, the agent retries to connect and to |
| 5047 | register to a session daemon every three seconds. Override this |
| 5048 | delay with the env:LTTNG_UST_PYTHON_REGISTER_RETRY_DELAY environment |
| 5049 | variable. |
| 5050 | |
| 5051 | |
| 5052 | [role="since-2.5"] |
| 5053 | [[proc-lttng-logger-abi]] |
| 5054 | === LTTng logger |
| 5055 | |
| 5056 | The `lttng-tracer` Linux kernel module, part of |
| 5057 | <<lttng-modules,LTTng-modules>>, creates the special LTTng logger files |
| 5058 | path:{/proc/lttng-logger} and path:{/dev/lttng-logger} (since |
| 5059 | LTTng{nbsp}2.11) when it's loaded. Any application can write text data |
| 5060 | to any of those files to emit an LTTng event. |
| 5061 | |
| 5062 | [role="img-100"] |
| 5063 | .An application writes to the LTTng logger file to emit an LTTng event. |
| 5064 | image::lttng-logger.png[] |
| 5065 | |
| 5066 | The LTTng logger is the quickest method--not the most efficient, |
| 5067 | however--to add instrumentation to an application. It is designed |
| 5068 | mostly to instrument shell scripts: |
| 5069 | |
| 5070 | [role="term"] |
| 5071 | ---- |
| 5072 | $ echo "Some message, some $variable" > /dev/lttng-logger |
| 5073 | ---- |
| 5074 | |
| 5075 | Any event that the LTTng logger emits is named `lttng_logger` and |
| 5076 | belongs to the Linux kernel <<domain,tracing domain>>. However, unlike |
| 5077 | other instrumentation points in the kernel tracing domain, **any Unix |
| 5078 | user** can <<enabling-disabling-events,create an event rule>> which |
| 5079 | matches its event name, not only the root user or users in the |
| 5080 | <<tracing-group,tracing group>>. |
| 5081 | |
| 5082 | To use the LTTng logger: |
| 5083 | |
| 5084 | * From any application, write text data to the path:{/dev/lttng-logger} |
| 5085 | file. |
| 5086 | |
| 5087 | The `msg` field of `lttng_logger` event records contains the |
| 5088 | recorded message. |
| 5089 | |
| 5090 | NOTE: The maximum message length of an LTTng logger event is |
| 5091 | 1024{nbsp}bytes. Writing more than this makes the LTTng logger emit more |
| 5092 | than one event to contain the remaining data. |
| 5093 | |
| 5094 | You shouldn't use the LTTng logger to trace a user application which |
| 5095 | can be instrumented in a more efficient way, namely: |
| 5096 | |
| 5097 | * <<c-application,C and $$C++$$ applications>>. |
| 5098 | * <<java-application,Java applications>>. |
| 5099 | * <<python-application,Python applications>>. |
| 5100 | |
| 5101 | .Use the LTTng logger. |
| 5102 | ==== |
| 5103 | [source,bash] |
| 5104 | .path:{test.bash} |
| 5105 | ---- |
| 5106 | echo 'Hello, World!' > /dev/lttng-logger |
| 5107 | sleep 2 |
| 5108 | df --human-readable --print-type / > /dev/lttng-logger |
| 5109 | ---- |
| 5110 | |
| 5111 | <<creating-destroying-tracing-sessions,Create a tracing session>>, |
| 5112 | <<enabling-disabling-events,create an event rule>> matching the |
| 5113 | `lttng_logger` Linux kernel tracepoint, and |
| 5114 | <<basic-tracing-session-control,start tracing>>: |
| 5115 | |
| 5116 | [role="term"] |
| 5117 | ---- |
| 5118 | $ lttng create |
| 5119 | $ lttng enable-event --kernel lttng_logger |
| 5120 | $ lttng start |
| 5121 | ---- |
| 5122 | |
| 5123 | Run the Bash script: |
| 5124 | |
| 5125 | [role="term"] |
| 5126 | ---- |
| 5127 | $ bash test.bash |
| 5128 | ---- |
| 5129 | |
| 5130 | <<basic-tracing-session-control,Stop tracing>> and inspect the recorded |
| 5131 | events: |
| 5132 | |
| 5133 | [role="term"] |
| 5134 | ---- |
| 5135 | $ lttng stop |
| 5136 | $ lttng view |
| 5137 | ---- |
| 5138 | ==== |
| 5139 | |
| 5140 | |
| 5141 | [[instrumenting-linux-kernel]] |
| 5142 | === LTTng kernel tracepoints |
| 5143 | |
| 5144 | NOTE: This section shows how to _add_ instrumentation points to the |
| 5145 | Linux kernel. The subsystems of the kernel are already thoroughly |
| 5146 | instrumented at strategic places for LTTng when you |
| 5147 | <<installing-lttng,install>> the <<lttng-modules,LTTng-modules>> |
| 5148 | package. |
| 5149 | |
| 5150 | //// |
| 5151 | There are two methods to instrument the Linux kernel: |
| 5152 | |
| 5153 | . <<linux-add-lttng-layer,Add an LTTng layer>> over an existing ftrace |
| 5154 | tracepoint which uses the `TRACE_EVENT()` API. |
| 5155 | + |
| 5156 | Choose this if you want to instrumentation a Linux kernel tree with an |
| 5157 | instrumentation point compatible with ftrace, perf, and SystemTap. |
| 5158 | |
| 5159 | . Use an <<linux-lttng-tracepoint-event,LTTng-only approach>> to |
| 5160 | instrument an out-of-tree kernel module. |
| 5161 | + |
| 5162 | Choose this if you don't need ftrace, perf, or SystemTap support. |
| 5163 | //// |
| 5164 | |
| 5165 | |
| 5166 | [[linux-add-lttng-layer]] |
| 5167 | ==== [[instrumenting-linux-kernel-itself]][[mainline-trace-event]][[lttng-adaptation-layer]]Add an LTTng layer to an existing ftrace tracepoint |
| 5168 | |
| 5169 | This section shows how to add an LTTng layer to existing ftrace |
| 5170 | instrumentation using the `TRACE_EVENT()` API. |
| 5171 | |
| 5172 | This section doesn't document the `TRACE_EVENT()` macro. Read the |
| 5173 | following articles to learn more about this API: |
| 5174 | |
| 5175 | * http://lwn.net/Articles/379903/[Using the TRACE_EVENT() macro (Part{nbsp}1)] |
| 5176 | * http://lwn.net/Articles/381064/[Using the TRACE_EVENT() macro (Part{nbsp}2)] |
| 5177 | * http://lwn.net/Articles/383362/[Using the TRACE_EVENT() macro (Part{nbsp}3)] |
| 5178 | |
| 5179 | The following procedure assumes that your ftrace tracepoints are |
| 5180 | correctly defined in their own header and that they are created in |
| 5181 | one source file using the `CREATE_TRACE_POINTS` definition. |
| 5182 | |
| 5183 | To add an LTTng layer over an existing ftrace tracepoint: |
| 5184 | |
| 5185 | . Make sure the following kernel configuration options are |
| 5186 | enabled: |
| 5187 | + |
| 5188 | -- |
| 5189 | * `CONFIG_MODULES` |
| 5190 | * `CONFIG_KALLSYMS` |
| 5191 | * `CONFIG_HIGH_RES_TIMERS` |
| 5192 | * `CONFIG_TRACEPOINTS` |
| 5193 | -- |
| 5194 | |
| 5195 | . Build the Linux source tree with your custom ftrace tracepoints. |
| 5196 | . Boot the resulting Linux image on your target system. |
| 5197 | + |
| 5198 | Confirm that the tracepoints exist by looking for their names in the |
| 5199 | dir:{/sys/kernel/debug/tracing/events/subsys} directory, where `subsys` |
| 5200 | is your subsystem name. |
| 5201 | |
| 5202 | . Get a copy of the latest LTTng-modules{nbsp}{revision}: |
| 5203 | + |
| 5204 | -- |
| 5205 | [role="term"] |
| 5206 | ---- |
| 5207 | $ cd $(mktemp -d) && |
| 5208 | wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.12.tar.bz2 && |
| 5209 | tar -xf lttng-modules-latest-2.12.tar.bz2 && |
| 5210 | cd lttng-modules-2.12.* |
| 5211 | ---- |
| 5212 | -- |
| 5213 | |
| 5214 | . In dir:{instrumentation/events/lttng-module}, relative to the root |
| 5215 | of the LTTng-modules source tree, create a header file named |
| 5216 | +__subsys__.h+ for your custom subsystem +__subsys__+ and write your |
| 5217 | LTTng-modules tracepoint definitions using the LTTng-modules |
| 5218 | macros in it. |
| 5219 | + |
| 5220 | Start with this template: |
| 5221 | + |
| 5222 | -- |
| 5223 | [source,c] |
| 5224 | .path:{instrumentation/events/lttng-module/my_subsys.h} |
| 5225 | ---- |
| 5226 | #undef TRACE_SYSTEM |
| 5227 | #define TRACE_SYSTEM my_subsys |
| 5228 | |
| 5229 | #if !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) |
| 5230 | #define _LTTNG_MY_SUBSYS_H |
| 5231 | |
| 5232 | #include "../../../probes/lttng-tracepoint-event.h" |
| 5233 | #include <linux/tracepoint.h> |
| 5234 | |
| 5235 | LTTNG_TRACEPOINT_EVENT( |
| 5236 | /* |
| 5237 | * Format is identical to the TRACE_EVENT() version for the three |
| 5238 | * following macro parameters: |
| 5239 | */ |
| 5240 | my_subsys_my_event, |
| 5241 | TP_PROTO(int my_int, const char *my_string), |
| 5242 | TP_ARGS(my_int, my_string), |
| 5243 | |
| 5244 | /* LTTng-modules specific macros */ |
| 5245 | TP_FIELDS( |
| 5246 | ctf_integer(int, my_int_field, my_int) |
| 5247 | ctf_string(my_bar_field, my_bar) |
| 5248 | ) |
| 5249 | ) |
| 5250 | |
| 5251 | #endif /* !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) */ |
| 5252 | |
| 5253 | #include "../../../probes/define_trace.h" |
| 5254 | ---- |
| 5255 | -- |
| 5256 | + |
| 5257 | The entries in the `TP_FIELDS()` section are the list of fields for the |
| 5258 | LTTng tracepoint. This is similar to the `TP_STRUCT__entry()` part of |
| 5259 | the `TRACE_EVENT()` ftrace macro. |
| 5260 | + |
| 5261 | See <<lttng-modules-tp-fields,Tracepoint fields macros>> for a |
| 5262 | complete description of the available `ctf_*()` macros. |
| 5263 | |
| 5264 | . Create the kernel module C{nbsp}source file of the LTTng-modules |
| 5265 | probe, +probes/lttng-probe-__subsys__.c+, where +__subsys__+ is your |
| 5266 | subsystem name: |
| 5267 | + |
| 5268 | -- |
| 5269 | [source,c] |
| 5270 | .path:{probes/lttng-probe-my-subsys.c} |
| 5271 | ---- |
| 5272 | #include <linux/module.h> |
| 5273 | #include "../lttng-tracer.h" |
| 5274 | |
| 5275 | /* |
| 5276 | * Build-time verification of mismatch between mainline |
| 5277 | * TRACE_EVENT() arguments and the LTTng-modules adaptation |
| 5278 | * layer LTTNG_TRACEPOINT_EVENT() arguments. |
| 5279 | */ |
| 5280 | #include <trace/events/my_subsys.h> |
| 5281 | |
| 5282 | /* Create LTTng tracepoint probes */ |
| 5283 | #define LTTNG_PACKAGE_BUILD |
| 5284 | #define CREATE_TRACE_POINTS |
| 5285 | #define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module |
| 5286 | |
| 5287 | #include "../instrumentation/events/lttng-module/my_subsys.h" |
| 5288 | |
| 5289 | MODULE_LICENSE("GPL and additional rights"); |
| 5290 | MODULE_AUTHOR("Your name <your-email>"); |
| 5291 | MODULE_DESCRIPTION("LTTng my_subsys probes"); |
| 5292 | MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "." |
| 5293 | __stringify(LTTNG_MODULES_MINOR_VERSION) "." |
| 5294 | __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION) |
| 5295 | LTTNG_MODULES_EXTRAVERSION); |
| 5296 | ---- |
| 5297 | -- |
| 5298 | |
| 5299 | . Edit path:{probes/KBuild} and add your new kernel module object |
| 5300 | next to the existing ones: |
| 5301 | + |
| 5302 | -- |
| 5303 | [source,make] |
| 5304 | .path:{probes/KBuild} |
| 5305 | ---- |
| 5306 | # ... |
| 5307 | |
| 5308 | obj-m += lttng-probe-module.o |
| 5309 | obj-m += lttng-probe-power.o |
| 5310 | |
| 5311 | obj-m += lttng-probe-my-subsys.o |
| 5312 | |
| 5313 | # ... |
| 5314 | ---- |
| 5315 | -- |
| 5316 | |
| 5317 | . Build and install the LTTng kernel modules: |
| 5318 | + |
| 5319 | -- |
| 5320 | [role="term"] |
| 5321 | ---- |
| 5322 | $ make KERNELDIR=/path/to/linux |
| 5323 | # make modules_install && depmod -a |
| 5324 | ---- |
| 5325 | -- |
| 5326 | + |
| 5327 | Replace `/path/to/linux` with the path to the Linux source tree where |
| 5328 | you defined and used tracepoints with the `TRACE_EVENT()` ftrace macro. |
| 5329 | |
| 5330 | Note that you can also use the |
| 5331 | <<lttng-tracepoint-event-code,`LTTNG_TRACEPOINT_EVENT_CODE()` macro>> |
| 5332 | instead of `LTTNG_TRACEPOINT_EVENT()` to use custom local variables and |
| 5333 | C code that need to be executed before the event fields are recorded. |
| 5334 | |
| 5335 | The best way to learn how to use the previous LTTng-modules macros is to |
| 5336 | inspect the existing LTTng-modules tracepoint definitions in the |
| 5337 | dir:{instrumentation/events/lttng-module} header files. Compare them |
| 5338 | with the Linux kernel mainline versions in the |
| 5339 | dir:{include/trace/events} directory of the Linux source tree. |
| 5340 | |
| 5341 | |
| 5342 | [role="since-2.7"] |
| 5343 | [[lttng-tracepoint-event-code]] |
| 5344 | ===== Use custom C code to access the data for tracepoint fields |
| 5345 | |
| 5346 | Although we recommended to always use the |
| 5347 | <<lttng-adaptation-layer,`LTTNG_TRACEPOINT_EVENT()`>> macro to describe |
| 5348 | the arguments and fields of an LTTng-modules tracepoint when possible, |
| 5349 | sometimes you need a more complex process to access the data that the |
| 5350 | tracer records as event record fields. In other words, you need local |
| 5351 | variables and multiple C{nbsp}statements instead of simple |
| 5352 | argument-based expressions that you pass to the |
| 5353 | <<lttng-modules-tp-fields,`ctf_*()` macros of `TP_FIELDS()`>>. |
| 5354 | |
| 5355 | Use the `LTTNG_TRACEPOINT_EVENT_CODE()` macro instead of |
| 5356 | `LTTNG_TRACEPOINT_EVENT()` to declare custom local variables and define |
| 5357 | a block of C{nbsp}code to be executed before LTTng records the fields. |
| 5358 | The structure of this macro is: |
| 5359 | |
| 5360 | [source,c] |
| 5361 | .`LTTNG_TRACEPOINT_EVENT_CODE()` macro syntax. |
| 5362 | ---- |
| 5363 | LTTNG_TRACEPOINT_EVENT_CODE( |
| 5364 | /* |
| 5365 | * Format identical to the LTTNG_TRACEPOINT_EVENT() |
| 5366 | * version for the following three macro parameters: |
| 5367 | */ |
| 5368 | my_subsys_my_event, |
| 5369 | TP_PROTO(int my_int, const char *my_string), |
| 5370 | TP_ARGS(my_int, my_string), |
| 5371 | |
| 5372 | /* Declarations of custom local variables */ |
| 5373 | TP_locvar( |
| 5374 | int a = 0; |
| 5375 | unsigned long b = 0; |
| 5376 | const char *name = "(undefined)"; |
| 5377 | struct my_struct *my_struct; |
| 5378 | ), |
| 5379 | |
| 5380 | /* |
| 5381 | * Custom code which uses both tracepoint arguments |
| 5382 | * (in TP_ARGS()) and local variables (in TP_locvar()). |
| 5383 | * |
| 5384 | * Local variables are actually members of a structure pointed |
| 5385 | * to by the special variable tp_locvar. |
| 5386 | */ |
| 5387 | TP_code( |
| 5388 | if (my_int) { |
| 5389 | tp_locvar->a = my_int + 17; |
| 5390 | tp_locvar->my_struct = get_my_struct_at(tp_locvar->a); |
| 5391 | tp_locvar->b = my_struct_compute_b(tp_locvar->my_struct); |
| 5392 | tp_locvar->name = my_struct_get_name(tp_locvar->my_struct); |
| 5393 | put_my_struct(tp_locvar->my_struct); |
| 5394 | |
| 5395 | if (tp_locvar->b) { |
| 5396 | tp_locvar->a = 1; |
| 5397 | } |
| 5398 | } |
| 5399 | ), |
| 5400 | |
| 5401 | /* |
| 5402 | * Format identical to the LTTNG_TRACEPOINT_EVENT() |
| 5403 | * version for this, except that tp_locvar members can be |
| 5404 | * used in the argument expression parameters of |
| 5405 | * the ctf_*() macros. |
| 5406 | */ |
| 5407 | TP_FIELDS( |
| 5408 | ctf_integer(unsigned long, my_struct_b, tp_locvar->b) |
| 5409 | ctf_integer(int, my_struct_a, tp_locvar->a) |
| 5410 | ctf_string(my_string_field, my_string) |
| 5411 | ctf_string(my_struct_name, tp_locvar->name) |
| 5412 | ) |
| 5413 | ) |
| 5414 | ---- |
| 5415 | |
| 5416 | IMPORTANT: The C code defined in `TP_code()` must not have any side |
| 5417 | effects when executed. In particular, the code must not allocate |
| 5418 | memory or get resources without deallocating this memory or putting |
| 5419 | those resources afterwards. |
| 5420 | |
| 5421 | |
| 5422 | [[instrumenting-linux-kernel-tracing]] |
| 5423 | ==== Load and unload a custom probe kernel module |
| 5424 | |
| 5425 | You must load a <<lttng-adaptation-layer,created LTTng-modules probe |
| 5426 | kernel module>> in the kernel before it can emit LTTng events. |
| 5427 | |
| 5428 | To load the default probe kernel modules and a custom probe kernel |
| 5429 | module: |
| 5430 | |
| 5431 | * Use the opt:lttng-sessiond(8):--extra-kmod-probes option to give extra |
| 5432 | probe modules to load when starting a root <<lttng-sessiond,session |
| 5433 | daemon>>: |
| 5434 | + |
| 5435 | -- |
| 5436 | .Load the `my_subsys`, `usb`, and the default probe modules. |
| 5437 | ==== |
| 5438 | [role="term"] |
| 5439 | ---- |
| 5440 | # lttng-sessiond --extra-kmod-probes=my_subsys,usb |
| 5441 | ---- |
| 5442 | ==== |
| 5443 | -- |
| 5444 | + |
| 5445 | You only need to pass the subsystem name, not the whole kernel module |
| 5446 | name. |
| 5447 | |
| 5448 | To load _only_ a given custom probe kernel module: |
| 5449 | |
| 5450 | * Use the opt:lttng-sessiond(8):--kmod-probes option to give the probe |
| 5451 | modules to load when starting a root session daemon: |
| 5452 | + |
| 5453 | -- |
| 5454 | .Load only the `my_subsys` and `usb` probe modules. |
| 5455 | ==== |
| 5456 | [role="term"] |
| 5457 | ---- |
| 5458 | # lttng-sessiond --kmod-probes=my_subsys,usb |
| 5459 | ---- |
| 5460 | ==== |
| 5461 | -- |
| 5462 | |
| 5463 | To confirm that a probe module is loaded: |
| 5464 | |
| 5465 | * Use man:lsmod(8): |
| 5466 | + |
| 5467 | -- |
| 5468 | [role="term"] |
| 5469 | ---- |
| 5470 | $ lsmod | grep lttng_probe_usb |
| 5471 | ---- |
| 5472 | -- |
| 5473 | |
| 5474 | To unload the loaded probe modules: |
| 5475 | |
| 5476 | * Kill the session daemon with `SIGTERM`: |
| 5477 | + |
| 5478 | -- |
| 5479 | [role="term"] |
| 5480 | ---- |
| 5481 | # pkill lttng-sessiond |
| 5482 | ---- |
| 5483 | -- |
| 5484 | + |
| 5485 | You can also use the man:modprobe(8) `--remove` option if the session |
| 5486 | daemon terminates abnormally. |
| 5487 | |
| 5488 | |
| 5489 | [[controlling-tracing]] |
| 5490 | == Tracing control |
| 5491 | |
| 5492 | Once an application or a Linux kernel is |
| 5493 | <<instrumenting,instrumented>> for LTTng tracing, |
| 5494 | you can _trace_ it. |
| 5495 | |
| 5496 | This section is divided in topics on how to use the various |
| 5497 | <<plumbing,components of LTTng>>, in particular the <<lttng-cli,cmd:lttng |
| 5498 | command-line tool>>, to _control_ the LTTng daemons and tracers. |
| 5499 | |
| 5500 | NOTE: In the following subsections, we refer to an man:lttng(1) command |
| 5501 | using its man page name. For example, instead of _Run the `create` |
| 5502 | command to..._, we use _Run the man:lttng-create(1) command to..._. |
| 5503 | |
| 5504 | |
| 5505 | [[start-sessiond]] |
| 5506 | === Start a session daemon |
| 5507 | |
| 5508 | In some situations, you need to run a <<lttng-sessiond,session daemon>> |
| 5509 | (man:lttng-sessiond(8)) _before_ you can use the man:lttng(1) |
| 5510 | command-line tool. |
| 5511 | |
| 5512 | You will see the following error when you run a command while no session |
| 5513 | daemon is running: |
| 5514 | |
| 5515 | ---- |
| 5516 | Error: No session daemon is available |
| 5517 | ---- |
| 5518 | |
| 5519 | The only command that automatically runs a session daemon is |
| 5520 | man:lttng-create(1), which you use to |
| 5521 | <<creating-destroying-tracing-sessions,create a tracing session>>. While |
| 5522 | this is most of the time the first operation that you do, sometimes it's |
| 5523 | not. Some examples are: |
| 5524 | |
| 5525 | * <<list-instrumentation-points,List the available instrumentation points>>. |
| 5526 | * <<saving-loading-tracing-session,Load a tracing session configuration>>. |
| 5527 | |
| 5528 | [[tracing-group]] Each Unix user must have its own running session |
| 5529 | daemon to trace user applications. The session daemon that the root user |
| 5530 | starts is the only one allowed to control the LTTng kernel tracer. Users |
| 5531 | that are part of the _tracing group_ can control the root session |
| 5532 | daemon. The default tracing group name is `tracing`; set it to something |
| 5533 | else with the opt:lttng-sessiond(8):--group option when you start the |
| 5534 | root session daemon. |
| 5535 | |
| 5536 | To start a user session daemon: |
| 5537 | |
| 5538 | * Run man:lttng-sessiond(8): |
| 5539 | + |
| 5540 | -- |
| 5541 | [role="term"] |
| 5542 | ---- |
| 5543 | $ lttng-sessiond --daemonize |
| 5544 | ---- |
| 5545 | -- |
| 5546 | |
| 5547 | To start the root session daemon: |
| 5548 | |
| 5549 | * Run man:lttng-sessiond(8) as the root user: |
| 5550 | + |
| 5551 | -- |
| 5552 | [role="term"] |
| 5553 | ---- |
| 5554 | # lttng-sessiond --daemonize |
| 5555 | ---- |
| 5556 | -- |
| 5557 | |
| 5558 | In both cases, remove the opt:lttng-sessiond(8):--daemonize option to |
| 5559 | start the session daemon in foreground. |
| 5560 | |
| 5561 | To stop a session daemon, use man:kill(1) on its process ID (standard |
| 5562 | `TERM` signal). |
| 5563 | |
| 5564 | Note that some Linux distributions could manage the LTTng session daemon |
| 5565 | as a service. In this case, you should use the service manager to |
| 5566 | start, restart, and stop session daemons. |
| 5567 | |
| 5568 | |
| 5569 | [[creating-destroying-tracing-sessions]] |
| 5570 | === Create and destroy a tracing session |
| 5571 | |
| 5572 | Almost all the LTTng control operations happen in the scope of |
| 5573 | a <<tracing-session,tracing session>>, which is the dialogue between the |
| 5574 | <<lttng-sessiond,session daemon>> and you. |
| 5575 | |
| 5576 | To create a tracing session with a generated name: |
| 5577 | |
| 5578 | * Use the man:lttng-create(1) command: |
| 5579 | + |
| 5580 | -- |
| 5581 | [role="term"] |
| 5582 | ---- |
| 5583 | $ lttng create |
| 5584 | ---- |
| 5585 | -- |
| 5586 | |
| 5587 | The name of the created tracing session is `auto` followed by the |
| 5588 | creation date. |
| 5589 | |
| 5590 | To create a tracing session with a specific name: |
| 5591 | |
| 5592 | * Use the optional argument of the man:lttng-create(1) command: |
| 5593 | + |
| 5594 | -- |
| 5595 | [role="term"] |
| 5596 | ---- |
| 5597 | $ lttng create my-session |
| 5598 | ---- |
| 5599 | -- |
| 5600 | + |
| 5601 | Replace `my-session` with the specific tracing session name. |
| 5602 | |
| 5603 | LTTng appends the creation date to the name of the created tracing |
| 5604 | session. |
| 5605 | |
| 5606 | LTTng writes the traces of a tracing session in |
| 5607 | +$LTTNG_HOME/lttng-trace/__name__+ by default, where +__name__+ is the |
| 5608 | name of the tracing session. Note that the env:LTTNG_HOME environment |
| 5609 | variable defaults to `$HOME` if not set. |
| 5610 | |
| 5611 | To output LTTng traces to a non-default location: |
| 5612 | |
| 5613 | * Use the opt:lttng-create(1):--output option of the man:lttng-create(1) command: |
| 5614 | + |
| 5615 | -- |
| 5616 | [role="term"] |
| 5617 | ---- |
| 5618 | $ lttng create my-session --output=/tmp/some-directory |
| 5619 | ---- |
| 5620 | -- |
| 5621 | |
| 5622 | You may create as many tracing sessions as you wish. |
| 5623 | |
| 5624 | To list all the existing tracing sessions for your Unix user: |
| 5625 | |
| 5626 | * Use the man:lttng-list(1) command: |
| 5627 | + |
| 5628 | -- |
| 5629 | [role="term"] |
| 5630 | ---- |
| 5631 | $ lttng list |
| 5632 | ---- |
| 5633 | -- |
| 5634 | |
| 5635 | [[cur-tracing-session]]When you create a tracing session, it is set as |
| 5636 | the _current tracing session_. The following man:lttng(1) commands |
| 5637 | operate on the current tracing session when you don't specify one: |
| 5638 | |
| 5639 | [role="list-3-cols"] |
| 5640 | * man:lttng-add-context(1) |
| 5641 | * man:lttng-clear(1) |
| 5642 | * man:lttng-destroy(1) |
| 5643 | * man:lttng-disable-channel(1) |
| 5644 | * man:lttng-disable-event(1) |
| 5645 | * man:lttng-disable-rotation(1) |
| 5646 | * man:lttng-enable-channel(1) |
| 5647 | * man:lttng-enable-event(1) |
| 5648 | * man:lttng-enable-rotation(1) |
| 5649 | * man:lttng-load(1) |
| 5650 | * man:lttng-regenerate(1) |
| 5651 | * man:lttng-rotate(1) |
| 5652 | * man:lttng-save(1) |
| 5653 | * man:lttng-snapshot(1) |
| 5654 | * man:lttng-start(1) |
| 5655 | * man:lttng-status(1) |
| 5656 | * man:lttng-stop(1) |
| 5657 | * man:lttng-track(1) |
| 5658 | * man:lttng-untrack(1) |
| 5659 | * man:lttng-view(1) |
| 5660 | |
| 5661 | To change the current tracing session: |
| 5662 | |
| 5663 | * Use the man:lttng-set-session(1) command: |
| 5664 | + |
| 5665 | -- |
| 5666 | [role="term"] |
| 5667 | ---- |
| 5668 | $ lttng set-session new-session |
| 5669 | ---- |
| 5670 | -- |
| 5671 | + |
| 5672 | Replace `new-session` by the name of the new current tracing session. |
| 5673 | |
| 5674 | When you're done tracing in a given tracing session, destroy it. This |
| 5675 | operation frees the resources taken by the tracing session to destroy; |
| 5676 | it doesn't destroy the trace data that LTTng wrote for this tracing |
| 5677 | session (see <<clear,Clear a tracing session>> for one way to do this). |
| 5678 | |
| 5679 | To destroy the current tracing session: |
| 5680 | |
| 5681 | * Use the man:lttng-destroy(1) command: |
| 5682 | + |
| 5683 | -- |
| 5684 | [role="term"] |
| 5685 | ---- |
| 5686 | $ lttng destroy |
| 5687 | ---- |
| 5688 | -- |
| 5689 | |
| 5690 | The man:lttng-destroy(1) command also runs the man:lttng-stop(1) |
| 5691 | command implicitly (see <<basic-tracing-session-control,Start and stop a |
| 5692 | tracing session>>). You need to stop tracing to make LTTng flush the |
| 5693 | remaining trace data and make the trace readable. |
| 5694 | |
| 5695 | |
| 5696 | [[list-instrumentation-points]] |
| 5697 | === List the available instrumentation points |
| 5698 | |
| 5699 | The <<lttng-sessiond,session daemon>> can query the running instrumented |
| 5700 | user applications and the Linux kernel to get a list of available |
| 5701 | instrumentation points. For the Linux kernel <<domain,tracing domain>>, |
| 5702 | they are tracepoints and system calls. For the user space tracing |
| 5703 | domain, they are tracepoints. For the other tracing domains, they are |
| 5704 | logger names. |
| 5705 | |
| 5706 | To list the available instrumentation points: |
| 5707 | |
| 5708 | * Use the man:lttng-list(1) command with the option of the requested |
| 5709 | tracing domain amongst: |
| 5710 | + |
| 5711 | -- |
| 5712 | opt:lttng-list(1):--kernel:: |
| 5713 | Linux kernel tracepoints (your Unix user must be a root user, or it |
| 5714 | must be a member of the <<tracing-group,tracing group>>). |
| 5715 | |
| 5716 | opt:lttng-list(1):--kernel with opt:lttng-list(1):--syscall:: |
| 5717 | Linux kernel system calls (your Unix user must be a root user, or it |
| 5718 | must be a member of the tracing group). |
| 5719 | |
| 5720 | opt:lttng-list(1):--userspace:: |
| 5721 | User space tracepoints. |
| 5722 | |
| 5723 | opt:lttng-list(1):--jul:: |
| 5724 | `java.util.logging` loggers. |
| 5725 | |
| 5726 | opt:lttng-list(1):--log4j:: |
| 5727 | Apache log4j loggers. |
| 5728 | |
| 5729 | opt:lttng-list(1):--python:: |
| 5730 | Python loggers. |
| 5731 | -- |
| 5732 | |
| 5733 | .List the available user space tracepoints. |
| 5734 | ==== |
| 5735 | [role="term"] |
| 5736 | ---- |
| 5737 | $ lttng list --userspace |
| 5738 | ---- |
| 5739 | ==== |
| 5740 | |
| 5741 | .List the available Linux kernel system call tracepoints. |
| 5742 | ==== |
| 5743 | [role="term"] |
| 5744 | ---- |
| 5745 | $ lttng list --kernel --syscall |
| 5746 | ---- |
| 5747 | ==== |
| 5748 | |
| 5749 | |
| 5750 | [[enabling-disabling-events]] |
| 5751 | === Create and enable an event rule |
| 5752 | |
| 5753 | Once you <<creating-destroying-tracing-sessions,create a tracing |
| 5754 | session>>, you can create <<event,event rules>> with the |
| 5755 | man:lttng-enable-event(1) command. |
| 5756 | |
| 5757 | You specify each condition with a command-line option. The available |
| 5758 | condition arguments are shown in the following table. |
| 5759 | |
| 5760 | [role="growable",cols="asciidoc,asciidoc,default"] |
| 5761 | .Condition command-line arguments for the man:lttng-enable-event(1) command. |
| 5762 | |==== |
| 5763 | |Argument |Description |Applicable tracing domains |
| 5764 | |
| 5765 | | |
| 5766 | One of: |
| 5767 | |
| 5768 | . `--syscall` |
| 5769 | . +--probe=__ADDR__+ |
| 5770 | . +--function=__ADDR__+ |
| 5771 | . +--userspace-probe=__PATH__:__SYMBOL__+ |
| 5772 | . +--userspace-probe=sdt:__PATH__:__PROVIDER__:__NAME__+ |
| 5773 | |
| 5774 | | |
| 5775 | Instead of using the default _tracepoint_ instrumentation type, use: |
| 5776 | |
| 5777 | . A Linux system call (entry and exit). |
| 5778 | . A Linux https://lwn.net/Articles/132196/[kprobe] (symbol or address). |
| 5779 | . The entry and return points of a Linux function (symbol or address). |
| 5780 | . The entry point of a user application or library function (path to |
| 5781 | application/library and symbol). |
| 5782 | . A https://www.sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps[SystemTap |
| 5783 | Statically Defined Tracing] (USDT) probe (path to application/library, |
| 5784 | provider and probe names). |
| 5785 | |
| 5786 | |Linux kernel. |
| 5787 | |
| 5788 | |First positional argument. |
| 5789 | |
| 5790 | | |
| 5791 | Tracepoint or system call name. |
| 5792 | |
| 5793 | With the opt:lttng-enable-event(1):--probe, |
| 5794 | opt:lttng-enable-event(1):--function, and |
| 5795 | opt:lttng-enable-event(1):--userspace-probe options, this is a custom |
| 5796 | name given to the event rule. With the JUL, log4j, and Python domains, |
| 5797 | this is a logger name. |
| 5798 | |
| 5799 | With a tracepoint, logger, or system call name, use the special |
| 5800 | `*` globbing character to match anything (for example, `sched_*`, |
| 5801 | `my_comp*:*msg_*`). |
| 5802 | |
| 5803 | |All. |
| 5804 | |
| 5805 | | |
| 5806 | One of: |
| 5807 | |
| 5808 | . +--loglevel=__LEVEL__+ |
| 5809 | . +--loglevel-only=__LEVEL__+ |
| 5810 | |
| 5811 | | |
| 5812 | . Match only tracepoints or log statements with a logging level at |
| 5813 | least as severe as +__LEVEL__+. |
| 5814 | . Match only tracepoints or log statements with a logging level |
| 5815 | equal to +__LEVEL__+. |
| 5816 | |
| 5817 | See man:lttng-enable-event(1) for the list of available logging level |
| 5818 | names. |
| 5819 | |
| 5820 | |User space, JUL, log4j, and Python. |
| 5821 | |
| 5822 | |+--exclude=__EXCLUSIONS__+ |
| 5823 | |
| 5824 | | |
| 5825 | When you use a `*` character at the end of the tracepoint or logger |
| 5826 | name (first positional argument), exclude the specific names in the |
| 5827 | comma-delimited list +__EXCLUSIONS__+. |
| 5828 | |
| 5829 | | |
| 5830 | User space, JUL, log4j, and Python. |
| 5831 | |
| 5832 | |+--filter=__EXPR__+ |
| 5833 | |
| 5834 | | |
| 5835 | Match only events which satisfy the expression +__EXPR__+. |
| 5836 | |
| 5837 | See man:lttng-enable-event(1) to learn more about the syntax of a |
| 5838 | filter expression. |
| 5839 | |
| 5840 | |All. |
| 5841 | |
| 5842 | |==== |
| 5843 | |
| 5844 | You attach an event rule to a <<channel,channel>> on creation. If you do |
| 5845 | not specify the channel with the opt:lttng-enable-event(1):--channel |
| 5846 | option, and if the event rule to create is the first in its |
| 5847 | <<domain,tracing domain>> for a given tracing session, then LTTng |
| 5848 | creates a _default channel_ for you. This default channel is reused in |
| 5849 | subsequent invocations of the man:lttng-enable-event(1) command for the |
| 5850 | same tracing domain. |
| 5851 | |
| 5852 | An event rule is always enabled at creation time. |
| 5853 | |
| 5854 | The following examples show how to combine the previous |
| 5855 | command-line options to create simple to more complex event rules. |
| 5856 | |
| 5857 | .Create an event rule targetting a Linux kernel tracepoint (default channel). |
| 5858 | ==== |
| 5859 | [role="term"] |
| 5860 | ---- |
| 5861 | $ lttng enable-event --kernel sched_switch |
| 5862 | ---- |
| 5863 | ==== |
| 5864 | |
| 5865 | .Create an event rule matching four Linux kernel system calls (default channel). |
| 5866 | ==== |
| 5867 | [role="term"] |
| 5868 | ---- |
| 5869 | $ lttng enable-event --kernel --syscall open,write,read,close |
| 5870 | ---- |
| 5871 | ==== |
| 5872 | |
| 5873 | .Create event rules matching tracepoints with filter expressions (default channel). |
| 5874 | ==== |
| 5875 | [role="term"] |
| 5876 | ---- |
| 5877 | $ lttng enable-event --kernel sched_switch --filter='prev_comm == "bash"' |
| 5878 | ---- |
| 5879 | |
| 5880 | [role="term"] |
| 5881 | ---- |
| 5882 | $ lttng enable-event --kernel --all \ |
| 5883 | --filter='$ctx.tid == 1988 || $ctx.tid == 1534' |
| 5884 | ---- |
| 5885 | |
| 5886 | [role="term"] |
| 5887 | ---- |
| 5888 | $ lttng enable-event --jul my_logger \ |
| 5889 | --filter='$app.retriever:cur_msg_id > 3' |
| 5890 | ---- |
| 5891 | |
| 5892 | IMPORTANT: Make sure to always quote the filter string when you |
| 5893 | use man:lttng(1) from a shell. |
| 5894 | |
| 5895 | See also <<pid-tracking,Track process attributes>> which offers another, |
| 5896 | more efficient filtering mechanism for process ID, user ID, and group |
| 5897 | ID attributes. |
| 5898 | ==== |
| 5899 | |
| 5900 | .Create an event rule matching any user space tracepoint of a given tracepoint provider with a log level range (default channel). |
| 5901 | ==== |
| 5902 | [role="term"] |
| 5903 | ---- |
| 5904 | $ lttng enable-event --userspace my_app:'*' --loglevel=TRACE_INFO |
| 5905 | ---- |
| 5906 | |
| 5907 | IMPORTANT: Make sure to always quote the wildcard character when you |
| 5908 | use man:lttng(1) from a shell. |
| 5909 | ==== |
| 5910 | |
| 5911 | .Create an event rule matching multiple Python loggers with a wildcard and with exclusions (default channel). |
| 5912 | ==== |
| 5913 | [role="term"] |
| 5914 | ---- |
| 5915 | $ lttng enable-event --python my-app.'*' \ |
| 5916 | --exclude='my-app.module,my-app.hello' |
| 5917 | ---- |
| 5918 | ==== |
| 5919 | |
| 5920 | .Create an event rule matching any Apache log4j logger with a specific log level (default channel). |
| 5921 | ==== |
| 5922 | [role="term"] |
| 5923 | ---- |
| 5924 | $ lttng enable-event --log4j --all --loglevel-only=LOG4J_WARN |
| 5925 | ---- |
| 5926 | ==== |
| 5927 | |
| 5928 | .Create an event rule attached to a specific channel matching a specific user space tracepoint provider and tracepoint. |
| 5929 | ==== |
| 5930 | [role="term"] |
| 5931 | ---- |
| 5932 | $ lttng enable-event --userspace my_app:my_tracepoint --channel=my-channel |
| 5933 | ---- |
| 5934 | ==== |
| 5935 | |
| 5936 | .Create an event rule matching the `malloc` function entry in path:{/usr/lib/libc.so.6}: |
| 5937 | ==== |
| 5938 | [role="term"] |
| 5939 | ---- |
| 5940 | $ lttng enable-event --kernel --userspace-probe=/usr/lib/libc.so.6:malloc \ |
| 5941 | libc_malloc |
| 5942 | ---- |
| 5943 | ==== |
| 5944 | |
| 5945 | .Create an event rule matching the `server`/`accept_request` https://www.sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps[USDT probe] in path:{/usr/bin/serv}: |
| 5946 | ==== |
| 5947 | [role="term"] |
| 5948 | ---- |
| 5949 | $ lttng enable-event --kernel --userspace-probe=sdt:serv:server:accept_request \ |
| 5950 | server_accept_request |
| 5951 | ---- |
| 5952 | ==== |
| 5953 | |
| 5954 | The event rules of a given channel form a whitelist: as soon as an |
| 5955 | emitted event passes one of them, LTTng can record the event. For |
| 5956 | example, an event named `my_app:my_tracepoint` emitted from a user space |
| 5957 | tracepoint with a `TRACE_ERROR` log level passes both of the following |
| 5958 | rules: |
| 5959 | |
| 5960 | [role="term"] |
| 5961 | ---- |
| 5962 | $ lttng enable-event --userspace my_app:my_tracepoint |
| 5963 | $ lttng enable-event --userspace my_app:my_tracepoint \ |
| 5964 | --loglevel=TRACE_INFO |
| 5965 | ---- |
| 5966 | |
| 5967 | The second event rule is redundant: the first one includes |
| 5968 | the second one. |
| 5969 | |
| 5970 | |
| 5971 | [[disable-event-rule]] |
| 5972 | === Disable an event rule |
| 5973 | |
| 5974 | To disable an event rule that you <<enabling-disabling-events,created>> |
| 5975 | previously, use the man:lttng-disable-event(1) command. This command |
| 5976 | disables _all_ the event rules (of a given tracing domain and channel) |
| 5977 | which match an instrumentation point. The other conditions aren't |
| 5978 | supported as of LTTng{nbsp}{revision}. |
| 5979 | |
| 5980 | The LTTng tracer doesn't record an emitted event which passes |
| 5981 | a _disabled_ event rule. |
| 5982 | |
| 5983 | .Disable an event rule matching a Python logger (default channel). |
| 5984 | ==== |
| 5985 | [role="term"] |
| 5986 | ---- |
| 5987 | $ lttng disable-event --python my-logger |
| 5988 | ---- |
| 5989 | ==== |
| 5990 | |
| 5991 | .Disable an event rule matching all `java.util.logging` loggers (default channel). |
| 5992 | ==== |
| 5993 | [role="term"] |
| 5994 | ---- |
| 5995 | $ lttng disable-event --jul '*' |
| 5996 | ---- |
| 5997 | ==== |
| 5998 | |
| 5999 | .Disable _all_ the event rules of the default channel. |
| 6000 | ==== |
| 6001 | The opt:lttng-disable-event(1):--all-events option isn't, like the |
| 6002 | opt:lttng-enable-event(1):--all option of man:lttng-enable-event(1), the |
| 6003 | equivalent of the event name `*` (wildcard): it disables _all_ the event |
| 6004 | rules of a given channel. |
| 6005 | |
| 6006 | [role="term"] |
| 6007 | ---- |
| 6008 | $ lttng disable-event --jul --all-events |
| 6009 | ---- |
| 6010 | ==== |
| 6011 | |
| 6012 | NOTE: You can't delete an event rule once you create it. |
| 6013 | |
| 6014 | |
| 6015 | [[status]] |
| 6016 | === Get the status of a tracing session |
| 6017 | |
| 6018 | To get the status of the <<cur-tracing-session,current tracing |
| 6019 | session>>, that is, its parameters, its channels, event rules, and their |
| 6020 | attributes: |
| 6021 | |
| 6022 | * Use the man:lttng-status(1) command: |
| 6023 | + |
| 6024 | -- |
| 6025 | [role="term"] |
| 6026 | ---- |
| 6027 | $ lttng status |
| 6028 | ---- |
| 6029 | -- |
| 6030 | |
| 6031 | To get the status of any tracing session: |
| 6032 | |
| 6033 | * Use the man:lttng-list(1) command with the name of the tracing |
| 6034 | session: |
| 6035 | + |
| 6036 | -- |
| 6037 | [role="term"] |
| 6038 | ---- |
| 6039 | $ lttng list my-session |
| 6040 | ---- |
| 6041 | -- |
| 6042 | + |
| 6043 | Replace `my-session` with the desired tracing session name. |
| 6044 | |
| 6045 | |
| 6046 | [[basic-tracing-session-control]] |
| 6047 | === Start and stop a tracing session |
| 6048 | |
| 6049 | Once you <<creating-destroying-tracing-sessions,create a tracing |
| 6050 | session>> and |
| 6051 | <<enabling-disabling-events,create one or more event rules>>, |
| 6052 | you can start and stop the tracers for this tracing session. |
| 6053 | |
| 6054 | To start tracing in the <<cur-tracing-session,current tracing session>>: |
| 6055 | |
| 6056 | * Use the man:lttng-start(1) command: |
| 6057 | + |
| 6058 | -- |
| 6059 | [role="term"] |
| 6060 | ---- |
| 6061 | $ lttng start |
| 6062 | ---- |
| 6063 | -- |
| 6064 | |
| 6065 | LTTng is very flexible: you can launch user applications before |
| 6066 | or after the you start the tracers. The tracers only record the events |
| 6067 | if they pass enabled event rules and if they occur while the tracers are |
| 6068 | started. |
| 6069 | |
| 6070 | To stop tracing in the current tracing session: |
| 6071 | |
| 6072 | * Use the man:lttng-stop(1) command: |
| 6073 | + |
| 6074 | -- |
| 6075 | [role="term"] |
| 6076 | ---- |
| 6077 | $ lttng stop |
| 6078 | ---- |
| 6079 | -- |
| 6080 | + |
| 6081 | If there were <<channel-overwrite-mode-vs-discard-mode,lost event |
| 6082 | records>> or lost sub-buffers since the last time you ran |
| 6083 | man:lttng-start(1), warnings are printed when you run the |
| 6084 | man:lttng-stop(1) command. |
| 6085 | |
| 6086 | IMPORTANT: You need to stop tracing to make LTTng flush the remaining |
| 6087 | trace data and make the trace readable. Note that the |
| 6088 | man:lttng-destroy(1) command (see |
| 6089 | <<creating-destroying-tracing-sessions,Create and destroy a tracing |
| 6090 | session>>) also runs the man:lttng-stop(1) command implicitly. |
| 6091 | |
| 6092 | [role="since-2.12"] |
| 6093 | [[clear]] |
| 6094 | === Clear a tracing session |
| 6095 | |
| 6096 | You might need to remove all the current tracing data of one or more |
| 6097 | <<tracing-session,tracing sessions>> between multiple attempts to |
| 6098 | reproduce a problem without interrupting the LTTng tracing activity. |
| 6099 | |
| 6100 | To clear the tracing data of the |
| 6101 | <<cur-tracing-session,current tracing session>>: |
| 6102 | |
| 6103 | * Use the man:lttng-clear(1) command: |
| 6104 | + |
| 6105 | -- |
| 6106 | [role="term"] |
| 6107 | ---- |
| 6108 | $ lttng clear |
| 6109 | ---- |
| 6110 | -- |
| 6111 | |
| 6112 | To clear the tracing data of all the tracing sessions: |
| 6113 | |
| 6114 | * Use the `lttng clear` command with the opt:lttng-clear(1):--all |
| 6115 | option: |
| 6116 | + |
| 6117 | -- |
| 6118 | [role="term"] |
| 6119 | ---- |
| 6120 | $ lttng clear --all |
| 6121 | ---- |
| 6122 | -- |
| 6123 | |
| 6124 | |
| 6125 | [[enabling-disabling-channels]] |
| 6126 | === Create a channel |
| 6127 | |
| 6128 | Once you create a tracing session, you can create a <<channel,channel>> |
| 6129 | with the man:lttng-enable-channel(1) command. |
| 6130 | |
| 6131 | Note that LTTng automatically creates a default channel when, for a |
| 6132 | given <<domain,tracing domain>>, no channels exist and you |
| 6133 | <<enabling-disabling-events,create>> the first event rule. This default |
| 6134 | channel is named `channel0` and its attributes are set to reasonable |
| 6135 | values. Therefore, you only need to create a channel when you need |
| 6136 | non-default attributes. |
| 6137 | |
| 6138 | You specify each non-default channel attribute with a command-line |
| 6139 | option when you use the man:lttng-enable-channel(1) command. The |
| 6140 | available command-line options are: |
| 6141 | |
| 6142 | [role="growable",cols="asciidoc,asciidoc"] |
| 6143 | .Command-line options for the man:lttng-enable-channel(1) command. |
| 6144 | |==== |
| 6145 | |Option |Description |
| 6146 | |
| 6147 | |`--overwrite` |
| 6148 | |
| 6149 | | |
| 6150 | Use the _overwrite_ |
| 6151 | <<channel-overwrite-mode-vs-discard-mode,event record loss mode>> instead |
| 6152 | of the default _discard_ mode. |
| 6153 | |
| 6154 | |`--buffers-pid` (user space tracing domain only) |
| 6155 | |
| 6156 | | |
| 6157 | Use the per-process <<channel-buffering-schemes,buffering scheme>> |
| 6158 | instead of the default per-user buffering scheme. |
| 6159 | |
| 6160 | |+--subbuf-size=__SIZE__+ |
| 6161 | |
| 6162 | | |
| 6163 | Allocate sub-buffers of +__SIZE__+ bytes (power of two), for each CPU, |
| 6164 | either for each Unix user (default), or for each instrumented process. |
| 6165 | |
| 6166 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. |
| 6167 | |
| 6168 | |+--num-subbuf=__COUNT__+ |
| 6169 | |
| 6170 | | |
| 6171 | Allocate +__COUNT__+ sub-buffers (power of two), for each CPU, either |
| 6172 | for each Unix user (default), or for each instrumented process. |
| 6173 | |
| 6174 | See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>. |
| 6175 | |
| 6176 | |+--tracefile-size=__SIZE__+ |
| 6177 | |
| 6178 | | |
| 6179 | Set the maximum size of each trace file that this channel writes within |
| 6180 | a stream to +__SIZE__+ bytes instead of no maximum. |
| 6181 | |
| 6182 | See <<tracefile-rotation,Trace file count and size>>. |
| 6183 | |
| 6184 | |+--tracefile-count=__COUNT__+ |
| 6185 | |
| 6186 | | |
| 6187 | Limit the number of trace files that this channel creates to |
| 6188 | +__COUNT__+ channels instead of no limit. |
| 6189 | |
| 6190 | See <<tracefile-rotation,Trace file count and size>>. |
| 6191 | |
| 6192 | |+--switch-timer=__PERIODUS__+ |
| 6193 | |
| 6194 | | |
| 6195 | Set the <<channel-switch-timer,switch timer period>> |
| 6196 | to +__PERIODUS__+{nbsp}µs. |
| 6197 | |
| 6198 | |+--read-timer=__PERIODUS__+ |
| 6199 | |
| 6200 | | |
| 6201 | Set the <<channel-read-timer,read timer period>> |
| 6202 | to +__PERIODUS__+{nbsp}µs. |
| 6203 | |
| 6204 | |[[opt-blocking-timeout]]+--blocking-timeout=__TIMEOUTUS__+ |
| 6205 | |
| 6206 | | |
| 6207 | Set the timeout of user space applications which load LTTng-UST |
| 6208 | in blocking mode to +__TIMEOUTUS__+: |
| 6209 | |
| 6210 | 0 (default):: |
| 6211 | Never block (non-blocking mode). |
| 6212 | |
| 6213 | `inf`:: |
| 6214 | Block forever until space is available in a sub-buffer to record |
| 6215 | the event. |
| 6216 | |
| 6217 | __n__, a positive value:: |
| 6218 | Wait for at most __n__ µs when trying to write into a sub-buffer. |
| 6219 | |
| 6220 | Note that, for this option to have any effect on an instrumented |
| 6221 | user space application, you need to run the application with a set |
| 6222 | env:LTTNG_UST_ALLOW_BLOCKING environment variable. |
| 6223 | |
| 6224 | |+--output=__TYPE__+ (Linux kernel tracing domain only) |
| 6225 | |
| 6226 | | |
| 6227 | Set the output type of the channel to +__TYPE__+, either `mmap` or |
| 6228 | `splice`. |
| 6229 | |
| 6230 | |==== |
| 6231 | |
| 6232 | You can only create a channel in the Linux kernel and user space |
| 6233 | <<domain,tracing domains>>: other tracing domains have their own channel |
| 6234 | created on the fly when <<enabling-disabling-events,creating event |
| 6235 | rules>>. |
| 6236 | |
| 6237 | [IMPORTANT] |
| 6238 | ==== |
| 6239 | Because of a current LTTng limitation, you must create all channels |
| 6240 | _before_ you <<basic-tracing-session-control,start tracing>> in a given |
| 6241 | tracing session, that is, before the first time you run |
| 6242 | man:lttng-start(1). |
| 6243 | |
| 6244 | Since LTTng automatically creates a default channel when you use the |
| 6245 | man:lttng-enable-event(1) command with a specific tracing domain, you |
| 6246 | can't, for example, create a Linux kernel event rule, start tracing, |
| 6247 | and then create a user space event rule, because no user space channel |
| 6248 | exists yet and it's too late to create one. |
| 6249 | |
| 6250 | For this reason, make sure to configure your channels properly |
| 6251 | before starting the tracers for the first time! |
| 6252 | ==== |
| 6253 | |
| 6254 | The following examples show how to combine the previous |
| 6255 | command-line options to create simple to more complex channels. |
| 6256 | |
| 6257 | .Create a Linux kernel channel with default attributes. |
| 6258 | ==== |
| 6259 | [role="term"] |
| 6260 | ---- |
| 6261 | $ lttng enable-channel --kernel my-channel |
| 6262 | ---- |
| 6263 | ==== |
| 6264 | |
| 6265 | .Create a user space channel with four sub-buffers or 1{nbsp}MiB each, per CPU, per instrumented process. |
| 6266 | ==== |
| 6267 | [role="term"] |
| 6268 | ---- |
| 6269 | $ lttng enable-channel --userspace --num-subbuf=4 --subbuf-size=1M \ |
| 6270 | --buffers-pid my-channel |
| 6271 | ---- |
| 6272 | ==== |
| 6273 | |
| 6274 | .[[blocking-timeout-example]]Create a default user space channel with an infinite blocking timeout. |
| 6275 | ==== |
| 6276 | <<creating-destroying-tracing-sessions,Create a tracing-session>>, |
| 6277 | create the channel, <<enabling-disabling-events,create an event rule>>, |
| 6278 | and <<basic-tracing-session-control,start tracing>>: |
| 6279 | |
| 6280 | [role="term"] |
| 6281 | ---- |
| 6282 | $ lttng create |
| 6283 | $ lttng enable-channel --userspace --blocking-timeout=inf blocking-channel |
| 6284 | $ lttng enable-event --userspace --channel=blocking-channel --all |
| 6285 | $ lttng start |
| 6286 | ---- |
| 6287 | |
| 6288 | Run an application instrumented with LTTng-UST and allow it to block: |
| 6289 | |
| 6290 | [role="term"] |
| 6291 | ---- |
| 6292 | $ LTTNG_UST_ALLOW_BLOCKING=1 my-app |
| 6293 | ---- |
| 6294 | ==== |
| 6295 | |
| 6296 | .Create a Linux kernel channel which rotates eight trace files of 4{nbsp}MiB each for each stream |
| 6297 | ==== |
| 6298 | [role="term"] |
| 6299 | ---- |
| 6300 | $ lttng enable-channel --kernel --tracefile-count=8 \ |
| 6301 | --tracefile-size=4194304 my-channel |
| 6302 | ---- |
| 6303 | ==== |
| 6304 | |
| 6305 | .Create a user space channel in overwrite (or _flight recorder_) mode. |
| 6306 | ==== |
| 6307 | [role="term"] |
| 6308 | ---- |
| 6309 | $ lttng enable-channel --userspace --overwrite my-channel |
| 6310 | ---- |
| 6311 | ==== |
| 6312 | |
| 6313 | <<enabling-disabling-events,Create>> the same event rule in |
| 6314 | two different channels: |
| 6315 | |
| 6316 | [role="term"] |
| 6317 | ---- |
| 6318 | $ lttng enable-event --userspace --channel=my-channel app:tp |
| 6319 | $ lttng enable-event --userspace --channel=other-channel app:tp |
| 6320 | ---- |
| 6321 | |
| 6322 | If both channels are enabled, when a tracepoint named `app:tp` is |
| 6323 | reached, LTTng records two events, one for each channel. |
| 6324 | |
| 6325 | |
| 6326 | [[disable-channel]] |
| 6327 | === Disable a channel |
| 6328 | |
| 6329 | To disable a specific channel that you <<enabling-disabling-channels,created>> |
| 6330 | previously, use the man:lttng-disable-channel(1) command. |
| 6331 | |
| 6332 | .Disable a specific Linux kernel channel. |
| 6333 | ==== |
| 6334 | [role="term"] |
| 6335 | ---- |
| 6336 | $ lttng disable-channel --kernel my-channel |
| 6337 | ---- |
| 6338 | ==== |
| 6339 | |
| 6340 | The state of a channel precedes the individual states of event rules |
| 6341 | attached to it: event rules which belong to a disabled channel, even if |
| 6342 | they are enabled, are also considered disabled. |
| 6343 | |
| 6344 | |
| 6345 | [[adding-context]] |
| 6346 | === Add context fields to a channel |
| 6347 | |
| 6348 | Event record fields in trace files provide important information about |
| 6349 | events that occured previously, but sometimes some external context may |
| 6350 | help you solve a problem faster. |
| 6351 | |
| 6352 | Examples of context fields are: |
| 6353 | |
| 6354 | * The **process ID**, **thread ID**, **process name**, and |
| 6355 | **process priority** of the thread in which the event occurs. |
| 6356 | * The **hostname** of the system on which the event occurs. |
| 6357 | * The Linux kernel and user call stacks (since |
| 6358 | LTTng{nbsp}2.11). |
| 6359 | * The current values of many possible **performance counters** using |
| 6360 | perf, for example: |
| 6361 | ** CPU cycles, stalled cycles, idle cycles, and the other cycle types. |
| 6362 | ** Cache misses. |
| 6363 | ** Branch instructions, misses, and loads. |
| 6364 | ** CPU faults. |
| 6365 | * Any context defined at the application level (supported for the |
| 6366 | JUL and log4j <<domain,tracing domains>>). |
| 6367 | |
| 6368 | To get the full list of available context fields, see |
| 6369 | `lttng add-context --list`. Some context fields are reserved for a |
| 6370 | specific <<domain,tracing domain>> (Linux kernel or user space). |
| 6371 | |
| 6372 | You add context fields to <<channel,channels>>. All the events |
| 6373 | that a channel with added context fields records contain those fields. |
| 6374 | |
| 6375 | To add context fields to one or all the channels of a given tracing |
| 6376 | session: |
| 6377 | |
| 6378 | * Use the man:lttng-add-context(1) command. |
| 6379 | |
| 6380 | .Add context fields to all the channels of the current tracing session. |
| 6381 | ==== |
| 6382 | The following command line adds the virtual process identifier and |
| 6383 | the per-thread CPU cycles count fields to all the user space channels |
| 6384 | of the |
| 6385 | <<cur-tracing-session,current tracing session>>. |
| 6386 | |
| 6387 | [role="term"] |
| 6388 | ---- |
| 6389 | $ lttng add-context --userspace --type=vpid --type=perf:thread:cpu-cycles |
| 6390 | ---- |
| 6391 | ==== |
| 6392 | |
| 6393 | .Add performance counter context fields by raw ID |
| 6394 | ==== |
| 6395 | See man:lttng-add-context(1) for the exact format of the context field |
| 6396 | type, which is partly compatible with the format used in |
| 6397 | man:perf-record(1). |
| 6398 | |
| 6399 | [role="term"] |
| 6400 | ---- |
| 6401 | $ lttng add-context --userspace --type=perf:thread:raw:r0110:test |
| 6402 | $ lttng add-context --kernel --type=perf:cpu:raw:r0013c:x86unhalted |
| 6403 | ---- |
| 6404 | ==== |
| 6405 | |
| 6406 | .Add context fields to a specific channel. |
| 6407 | ==== |
| 6408 | The following command line adds the thread identifier and user call |
| 6409 | stack context fields to the Linux kernel channel named `my-channel` in |
| 6410 | the current tracing session. |
| 6411 | |
| 6412 | [role="term"] |
| 6413 | ---- |
| 6414 | $ lttng add-context --kernel --channel=my-channel \ |
| 6415 | --type=tid --type=callstack-user |
| 6416 | ---- |
| 6417 | ==== |
| 6418 | |
| 6419 | .Add an application-specific context field to a specific channel. |
| 6420 | ==== |
| 6421 | The following command line adds the `cur_msg_id` context field of the |
| 6422 | `retriever` context retriever for all the instrumented |
| 6423 | <<java-application,Java applications>> recording <<event,event records>> |
| 6424 | in the channel named `my-channel`: |
| 6425 | |
| 6426 | [role="term"] |
| 6427 | ---- |
| 6428 | $ lttng add-context --kernel --channel=my-channel \ |
| 6429 | --type='$app:retriever:cur_msg_id' |
| 6430 | ---- |
| 6431 | |
| 6432 | IMPORTANT: Make sure to always quote the `$` character when you |
| 6433 | use man:lttng-add-context(1) from a shell. |
| 6434 | ==== |
| 6435 | |
| 6436 | NOTE: You can't remove context fields from a channel once you add it. |
| 6437 | |
| 6438 | |
| 6439 | [role="since-2.7"] |
| 6440 | [[pid-tracking]] |
| 6441 | === Track process attributes |
| 6442 | |
| 6443 | It's often useful to only allow processes with specific attributes to |
| 6444 | emit events. For example, you may wish to record all the system calls |
| 6445 | which a given process makes (à la |
| 6446 | http://linux.die.net/man/1/strace[strace]). |
| 6447 | |
| 6448 | The man:lttng-track(1) and man:lttng-untrack(1) commands serve this |
| 6449 | purpose. Both commands operate on _inclusion sets_ of process attribute |
| 6450 | values. The available process attribute types are: |
| 6451 | |
| 6452 | Linux kernel <<domain,tracing domain>> only:: |
| 6453 | + |
| 6454 | * Process ID (PID). |
| 6455 | |
| 6456 | * Virtual process ID (VPID). |
| 6457 | + |
| 6458 | This is the PID as seen by the application. |
| 6459 | |
| 6460 | * Unix user ID (UID) (since LTTng{nbsp}2.12). |
| 6461 | |
| 6462 | * Virtual Unix user ID (VUID) (since LTTng{nbsp}2.12). |
| 6463 | + |
| 6464 | This is the UID as seen by the application. |
| 6465 | |
| 6466 | * Unix group ID (GID) (since LTTng{nbsp}2.12). |
| 6467 | |
| 6468 | * Virtual Unix group ID (VGID) (since LTTng{nbsp}2.12). |
| 6469 | + |
| 6470 | This is the GID as seen by the application. |
| 6471 | |
| 6472 | |
| 6473 | User space tracing domain:: |
| 6474 | + |
| 6475 | * VPID. |
| 6476 | * VUID (since LTTng{nbsp}2.12). |
| 6477 | * VGID (since LTTng{nbsp}2.12). |
| 6478 | |
| 6479 | Each tracing domain has one inclusion set per process attribute type: |
| 6480 | the Linux kernel tracing domain has six while the user space tracing |
| 6481 | domain has three. |
| 6482 | |
| 6483 | For a given event which passes an enabled <<event,event rule>> to be |
| 6484 | recorded, _all_ the attributes of its executing process must be part of |
| 6485 | the inclusion sets of the tracing domain of the event rule. |
| 6486 | |
| 6487 | Add entries to an inclusion set with the man:lttng-track(1) command and |
| 6488 | remove entries with the man:lttng-untrack(1) command. A process |
| 6489 | attribute is _tracked_ when it's part of an inclusion set and |
| 6490 | _untracked_ otherwise. |
| 6491 | |
| 6492 | [NOTE] |
| 6493 | ==== |
| 6494 | The process attribute values are _numeric_. |
| 6495 | |
| 6496 | Should a process with a given tracked process ID, for example, exit, and |
| 6497 | then a new process be given this ID, then the latter would also be |
| 6498 | allowed to emit events. |
| 6499 | |
| 6500 | With the `lttng track` command, you can add Unix user and group _names_ |
| 6501 | to the user and group inclusion sets: the <<lttng-sessiond,session |
| 6502 | daemon>> finds the corresponding UID, VUID, GID, or VGID once on |
| 6503 | _addition_ to the inclusion set. This means that if you rename the user |
| 6504 | or group after you run `lttng track`, its user/group ID remains tracked. |
| 6505 | ==== |
| 6506 | |
| 6507 | .Track and untrack virtual process IDs. |
| 6508 | ==== |
| 6509 | For the sake of the following example, assume the target system has |
| 6510 | 16{nbsp}possible VPIDs. |
| 6511 | |
| 6512 | When you |
| 6513 | <<creating-destroying-tracing-sessions,create a tracing session>>, |
| 6514 | the user space VPID inclusion set contains _all_ the possible VPIDs: |
| 6515 | |
| 6516 | [role="img-100"] |
| 6517 | .All VPIDs are tracked. |
| 6518 | image::track-all.png[] |
| 6519 | |
| 6520 | When the inclusion set is full and you use the man:lttng-track(1) |
| 6521 | command to specify some VPIDs to track, LTTng first clears the inclusion |
| 6522 | set, and then it adds the specific VPIDs to track. After: |
| 6523 | |
| 6524 | [role="term"] |
| 6525 | ---- |
| 6526 | $ lttng track --userspace --vpid=3,4,7,10,13 |
| 6527 | ---- |
| 6528 | |
| 6529 | the VPID inclusion set is: |
| 6530 | |
| 6531 | [role="img-100"] |
| 6532 | .VPIDs 3, 4, 7, 10, and 13 are tracked. |
| 6533 | image::track-3-4-7-10-13.png[] |
| 6534 | |
| 6535 | Add more VPIDs to the inclusion set afterwards: |
| 6536 | |
| 6537 | [role="term"] |
| 6538 | ---- |
| 6539 | $ lttng track --userspace --vpid=1,15,16 |
| 6540 | ---- |
| 6541 | |
| 6542 | The result is: |
| 6543 | |
| 6544 | [role="img-100"] |
| 6545 | .VPIDs 1, 15, and 16 are added to the inclusion set. |
| 6546 | image::track-1-3-4-7-10-13-15-16.png[] |
| 6547 | |
| 6548 | The man:lttng-untrack(1) command removes entries from process attribute |
| 6549 | inclusion sets. Given the previous example, the following command: |
| 6550 | |
| 6551 | [role="term"] |
| 6552 | ---- |
| 6553 | $ lttng untrack --userspace --vpid=3,7,10,13 |
| 6554 | ---- |
| 6555 | |
| 6556 | leads to this VPID inclusion set: |
| 6557 | |
| 6558 | [role="img-100"] |
| 6559 | .VPIDs 3, 7, 10, and 13 are removed from the inclusion set. |
| 6560 | image::track-1-4-15-16.png[] |
| 6561 | |
| 6562 | LTTng can track all the possible VPIDs again using the |
| 6563 | opt:lttng-track(1):--all option: |
| 6564 | |
| 6565 | [role="term"] |
| 6566 | ---- |
| 6567 | $ lttng track --userspace --vpid --all |
| 6568 | ---- |
| 6569 | |
| 6570 | The result is, again: |
| 6571 | |
| 6572 | [role="img-100"] |
| 6573 | .All VPIDs are tracked. |
| 6574 | image::track-all.png[] |
| 6575 | ==== |
| 6576 | |
| 6577 | .Track only specific process attributes. |
| 6578 | ==== |
| 6579 | A typical use case with process attribute tracking is to start with an |
| 6580 | empty inclusion set, then <<basic-tracing-session-control,start the |
| 6581 | tracers>>, and then add entries manually while the tracers are active. |
| 6582 | |
| 6583 | Use the opt:lttng-untrack(1):--all option of the |
| 6584 | man:lttng-untrack(1) command to clear the inclusion set after you |
| 6585 | <<creating-destroying-tracing-sessions,create a tracing session>>, for |
| 6586 | example (with UIDs): |
| 6587 | |
| 6588 | [role="term"] |
| 6589 | ---- |
| 6590 | $ lttng untrack --kernel --uid --all |
| 6591 | ---- |
| 6592 | |
| 6593 | gives: |
| 6594 | |
| 6595 | [role="img-100"] |
| 6596 | .No UIDs are tracked. |
| 6597 | image::untrack-all.png[] |
| 6598 | |
| 6599 | If you trace with this inclusion set configuration, the LTTng kernel |
| 6600 | tracer records no events within the <<cur-tracing-session,current |
| 6601 | tracing session>> because it doesn't track any UID. Use the |
| 6602 | man:lttng-track(1) command as usual to track specific UIDs when you need |
| 6603 | to, for example: |
| 6604 | |
| 6605 | [role="term"] |
| 6606 | ---- |
| 6607 | $ lttng track --kernel --uid=http,11 |
| 6608 | ---- |
| 6609 | |
| 6610 | Result: |
| 6611 | |
| 6612 | [role="img-100"] |
| 6613 | .UIDs 6 (`http`) and 11 are tracked. |
| 6614 | image::track-6-11.png[] |
| 6615 | ==== |
| 6616 | |
| 6617 | |
| 6618 | [role="since-2.5"] |
| 6619 | [[saving-loading-tracing-session]] |
| 6620 | === Save and load tracing session configurations |
| 6621 | |
| 6622 | Configuring a <<tracing-session,tracing session>> can be long. Some of |
| 6623 | the tasks involved are: |
| 6624 | |
| 6625 | * <<enabling-disabling-channels,Create channels>> with |
| 6626 | specific attributes. |
| 6627 | * <<adding-context,Add context fields>> to specific channels. |
| 6628 | * <<enabling-disabling-events,Create event rules>> with specific log |
| 6629 | level and filter conditions. |
| 6630 | |
| 6631 | If you use LTTng to solve real world problems, chances are you have to |
| 6632 | record events using the same tracing session setup over and over, |
| 6633 | modifying a few variables each time in your instrumented program |
| 6634 | or environment. To avoid constant tracing session reconfiguration, |
| 6635 | the man:lttng(1) command-line tool can save and load tracing session |
| 6636 | configurations to/from XML files. |
| 6637 | |
| 6638 | To save a given tracing session configuration: |
| 6639 | |
| 6640 | * Use the man:lttng-save(1) command: |
| 6641 | + |
| 6642 | -- |
| 6643 | [role="term"] |
| 6644 | ---- |
| 6645 | $ lttng save my-session |
| 6646 | ---- |
| 6647 | -- |
| 6648 | + |
| 6649 | Replace `my-session` with the name of the tracing session to save. |
| 6650 | |
| 6651 | LTTng saves tracing session configurations to |
| 6652 | dir:{$LTTNG_HOME/.lttng/sessions} by default. Note that the |
| 6653 | env:LTTNG_HOME environment variable defaults to `$HOME` if not set. Use |
| 6654 | the opt:lttng-save(1):--output-path option to change this destination |
| 6655 | directory. |
| 6656 | |
| 6657 | LTTng saves all configuration parameters, for example: |
| 6658 | |
| 6659 | * The tracing session name. |
| 6660 | * The trace data output path. |
| 6661 | * The channels with their state and all their attributes. |
| 6662 | * The context fields you added to channels. |
| 6663 | * The event rules with their state, log level and filter conditions. |
| 6664 | |
| 6665 | To load a tracing session: |
| 6666 | |
| 6667 | * Use the man:lttng-load(1) command: |
| 6668 | + |
| 6669 | -- |
| 6670 | [role="term"] |
| 6671 | ---- |
| 6672 | $ lttng load my-session |
| 6673 | ---- |
| 6674 | -- |
| 6675 | + |
| 6676 | Replace `my-session` with the name of the tracing session to load. |
| 6677 | |
| 6678 | When LTTng loads a configuration, it restores your saved tracing session |
| 6679 | as if you just configured it manually. |
| 6680 | |
| 6681 | See man:lttng-load(1) for the complete list of command-line options. You |
| 6682 | can also save and load many sessions at a time, and decide in which |
| 6683 | directory to output the XML files. |
| 6684 | |
| 6685 | |
| 6686 | [[sending-trace-data-over-the-network]] |
| 6687 | === Send trace data over the network |
| 6688 | |
| 6689 | LTTng can send the recorded trace data to a remote system over the |
| 6690 | network instead of writing it to the local file system. |
| 6691 | |
| 6692 | To send the trace data over the network: |
| 6693 | |
| 6694 | . On the _remote_ system (which can also be the target system), |
| 6695 | start an LTTng <<lttng-relayd,relay daemon>> (man:lttng-relayd(8)): |
| 6696 | + |
| 6697 | -- |
| 6698 | [role="term"] |
| 6699 | ---- |
| 6700 | $ lttng-relayd |
| 6701 | ---- |
| 6702 | -- |
| 6703 | |
| 6704 | . On the _target_ system, create a tracing session configured to |
| 6705 | send trace data over the network: |
| 6706 | + |
| 6707 | -- |
| 6708 | [role="term"] |
| 6709 | ---- |
| 6710 | $ lttng create my-session --set-url=net://remote-system |
| 6711 | ---- |
| 6712 | -- |
| 6713 | + |
| 6714 | Replace `remote-system` by the host name or IP address of the |
| 6715 | remote system. See man:lttng-create(1) for the exact URL format. |
| 6716 | |
| 6717 | . On the target system, use the man:lttng(1) command-line tool as usual. |
| 6718 | When tracing is active, the consumer daemon of the target sends |
| 6719 | sub-buffers to the relay daemon running on the remote system instead |
| 6720 | of flushing them to the local file system. The relay daemon writes the |
| 6721 | received packets to the local file system. |
| 6722 | |
| 6723 | The relay daemon writes trace files to |
| 6724 | +$LTTNG_HOME/lttng-traces/__hostname__/__session__+ by default, where |
| 6725 | +__hostname__+ is the host name of the target system and +__session__+ |
| 6726 | is the tracing session name. Note that the env:LTTNG_HOME environment |
| 6727 | variable defaults to `$HOME` if not set. Use the |
| 6728 | opt:lttng-relayd(8):--output option of man:lttng-relayd(8) to write |
| 6729 | trace files to another base directory. |
| 6730 | |
| 6731 | |
| 6732 | [role="since-2.4"] |
| 6733 | [[lttng-live]] |
| 6734 | === View events as LTTng emits them (noch:{LTTng} live) |
| 6735 | |
| 6736 | LTTng live is a network protocol implemented by the <<lttng-relayd,relay |
| 6737 | daemon>> (man:lttng-relayd(8)) to allow compatible trace viewers to |
| 6738 | display events as LTTng emits them on the target system while tracing is |
| 6739 | active. |
| 6740 | |
| 6741 | The relay daemon creates a _tee_: it forwards the trace data to both |
| 6742 | the local file system and to connected live viewers: |
| 6743 | |
| 6744 | [role="img-90"] |
| 6745 | .The relay daemon creates a _tee_, forwarding the trace data to both trace files and a connected live viewer. |
| 6746 | image::live.png[] |
| 6747 | |
| 6748 | To use LTTng live: |
| 6749 | |
| 6750 | . On the _target system_, create a <<tracing-session,tracing session>> |
| 6751 | in _live mode_: |
| 6752 | + |
| 6753 | -- |
| 6754 | [role="term"] |
| 6755 | ---- |
| 6756 | $ lttng create my-session --live |
| 6757 | ---- |
| 6758 | -- |
| 6759 | + |
| 6760 | This spawns a local relay daemon. |
| 6761 | |
| 6762 | . Start the live viewer and configure it to connect to the relay |
| 6763 | daemon. For example, with |
| 6764 | https://babeltrace.org/docs/v2.0/man1/babeltrace2.1/[cmd:babeltrace2]: |
| 6765 | + |
| 6766 | -- |
| 6767 | [role="term"] |
| 6768 | ---- |
| 6769 | $ babeltrace2 net://localhost/host/hostname/my-session |
| 6770 | ---- |
| 6771 | -- |
| 6772 | + |
| 6773 | Replace: |
| 6774 | + |
| 6775 | -- |
| 6776 | * `hostname` with the host name of the target system. |
| 6777 | * `my-session` with the name of the tracing session to view. |
| 6778 | -- |
| 6779 | |
| 6780 | . Configure the tracing session as usual with the man:lttng(1) |
| 6781 | command-line tool, and <<basic-tracing-session-control,start tracing>>. |
| 6782 | |
| 6783 | List the available live tracing sessions with Babeltrace{nbsp}2: |
| 6784 | |
| 6785 | [role="term"] |
| 6786 | ---- |
| 6787 | $ babeltrace2 net://localhost |
| 6788 | ---- |
| 6789 | |
| 6790 | You can start the relay daemon on another system. In this case, you need |
| 6791 | to specify the URL of the relay daemon when you create the tracing |
| 6792 | session with the opt:lttng-create(1):--set-url option. You also need to |
| 6793 | replace `localhost` in the procedure above with the host name of the |
| 6794 | system on which the relay daemon is running. |
| 6795 | |
| 6796 | See man:lttng-create(1) and man:lttng-relayd(8) for the complete list of |
| 6797 | command-line options. |
| 6798 | |
| 6799 | |
| 6800 | [role="since-2.3"] |
| 6801 | [[taking-a-snapshot]] |
| 6802 | === Take a snapshot of the current sub-buffers of a tracing session |
| 6803 | |
| 6804 | The normal behavior of LTTng is to append full sub-buffers to growing |
| 6805 | trace data files. This is ideal to keep a full history of the events |
| 6806 | that occurred on the target system, but it can |
| 6807 | represent too much data in some situations. For example, you may wish |
| 6808 | to trace your application continuously until some critical situation |
| 6809 | happens, in which case you only need the latest few recorded |
| 6810 | events to perform the desired analysis, not multi-gigabyte trace files. |
| 6811 | |
| 6812 | With the man:lttng-snapshot(1) command, you can take a snapshot of the |
| 6813 | current sub-buffers of a given <<tracing-session,tracing session>>. |
| 6814 | LTTng can write the snapshot to the local file system or send it over |
| 6815 | the network. |
| 6816 | |
| 6817 | [role="img-100"] |
| 6818 | .A snapshot is a copy of the current sub-buffers, which aren't cleared after the operation. |
| 6819 | image::snapshot.png[] |
| 6820 | |
| 6821 | If you wish to create unmanaged, self-contained, non-overlapping |
| 6822 | trace chunk archives instead of a simple copy of the current |
| 6823 | sub-buffers, see the <<session-rotation,tracing session rotation>> |
| 6824 | feature (available since LTTng{nbsp}2.11). |
| 6825 | |
| 6826 | To take a snapshot: |
| 6827 | |
| 6828 | . Create a tracing session in _snapshot mode_: |
| 6829 | + |
| 6830 | -- |
| 6831 | [role="term"] |
| 6832 | ---- |
| 6833 | $ lttng create my-session --snapshot |
| 6834 | ---- |
| 6835 | -- |
| 6836 | + |
| 6837 | The <<channel-overwrite-mode-vs-discard-mode,event record loss mode>> of |
| 6838 | <<channel,channels>> created in this mode is automatically set to |
| 6839 | _overwrite_ (flight recorder mode). |
| 6840 | |
| 6841 | . Configure the tracing session as usual with the man:lttng(1) |
| 6842 | command-line tool, and <<basic-tracing-session-control,start tracing>>. |
| 6843 | |
| 6844 | . **Optional**: When you need to take a snapshot, |
| 6845 | <<basic-tracing-session-control,stop tracing>>. |
| 6846 | + |
| 6847 | You can take a snapshot when the tracers are active, but if you stop |
| 6848 | them first, you're sure that the data in the sub-buffers doesn't |
| 6849 | change before you actually take the snapshot. |
| 6850 | |
| 6851 | . Take a snapshot: |
| 6852 | + |
| 6853 | -- |
| 6854 | [role="term"] |
| 6855 | ---- |
| 6856 | $ lttng snapshot record --name=my-first-snapshot |
| 6857 | ---- |
| 6858 | -- |
| 6859 | + |
| 6860 | LTTng writes the current sub-buffers of all the channels of the |
| 6861 | <<cur-tracing-session,current tracing session>> to |
| 6862 | trace files on the local file system. Those trace files have |
| 6863 | `my-first-snapshot` in their name. |
| 6864 | |
| 6865 | There is no difference between the format of a normal trace file and the |
| 6866 | format of a snapshot: viewers of LTTng traces also support LTTng |
| 6867 | snapshots. |
| 6868 | |
| 6869 | By default, LTTng writes snapshot files to the path shown by |
| 6870 | `lttng snapshot list-output`. You can change this path or decide to send |
| 6871 | snapshots over the network using either: |
| 6872 | |
| 6873 | . An output path or URL that you specify when you |
| 6874 | <<creating-destroying-tracing-sessions,create the tracing session>>. |
| 6875 | . A snapshot output path or URL that you add using |
| 6876 | `lttng snapshot add-output`. |
| 6877 | . An output path or URL that you provide directly to the |
| 6878 | `lttng snapshot record` command. |
| 6879 | |
| 6880 | Method{nbsp}3 overrides method{nbsp}2, which overrides method 1. When |
| 6881 | you specify a URL, a relay daemon must listen on a remote system (see |
| 6882 | <<sending-trace-data-over-the-network,Send trace data over the |
| 6883 | network>>). |
| 6884 | |
| 6885 | |
| 6886 | [role="since-2.11"] |
| 6887 | [[session-rotation]] |
| 6888 | === Archive the current trace chunk (rotate a tracing session) |
| 6889 | |
| 6890 | The <<taking-a-snapshot,snapshot user guide>> shows how to dump the |
| 6891 | current sub-buffers of a tracing session to the file system or send them |
| 6892 | over the network. When you take a snapshot, LTTng doesn't clear the ring |
| 6893 | buffers of the tracing session: if you take another snapshot immediately |
| 6894 | after, both snapshots could contain overlapping trace data. |
| 6895 | |
| 6896 | Inspired by https://en.wikipedia.org/wiki/Log_rotation[log rotation], |
| 6897 | _tracing session rotation_ is a feature which appends the content of the |
| 6898 | ring buffers to what's already on the file system or sent over the |
| 6899 | network since the creation of the tracing session or since the last |
| 6900 | rotation, and then clears those ring buffers to avoid trace data |
| 6901 | overlaps. |
| 6902 | |
| 6903 | What LTTng is about to write when performing a tracing session rotation |
| 6904 | is called the _current trace chunk_. When this current trace chunk is |
| 6905 | written to the file system or sent over the network, it becomes a _trace |
| 6906 | chunk archive_. Therefore, a tracing session rotation _archives_ the |
| 6907 | current trace chunk. |
| 6908 | |
| 6909 | [role="img-100"] |
| 6910 | .A tracing session rotation operation _archives_ the current trace chunk. |
| 6911 | image::rotation.png[] |
| 6912 | |
| 6913 | A trace chunk archive is a self-contained LTTng trace which LTTng |
| 6914 | doesn't manage anymore: you can read it, modify it, move it, or remove |
| 6915 | it. |
| 6916 | |
| 6917 | There are two methods to perform a tracing session rotation: immediately |
| 6918 | or with a rotation schedule. |
| 6919 | |
| 6920 | To perform an immediate tracing session rotation: |
| 6921 | |
| 6922 | . <<creating-destroying-tracing-sessions,Create a tracing session>> |
| 6923 | in _normal mode_ or _network streaming mode_ |
| 6924 | (only those two creation modes support tracing session rotation): |
| 6925 | + |
| 6926 | -- |
| 6927 | [role="term"] |
| 6928 | ---- |
| 6929 | $ lttng create my-session |
| 6930 | ---- |
| 6931 | -- |
| 6932 | |
| 6933 | . <<enabling-disabling-events,Create one or more event rules>> |
| 6934 | and <<basic-tracing-session-control,start tracing>>: |
| 6935 | + |
| 6936 | -- |
| 6937 | [role="term"] |
| 6938 | ---- |
| 6939 | $ lttng enable-event --kernel sched_'*' |
| 6940 | $ lttng start |
| 6941 | ---- |
| 6942 | -- |
| 6943 | |
| 6944 | . When needed, immediately rotate the |
| 6945 | <<cur-tracing-session,current tracing session>>: |
| 6946 | + |
| 6947 | -- |
| 6948 | [role="term"] |
| 6949 | ---- |
| 6950 | $ lttng rotate |
| 6951 | ---- |
| 6952 | -- |
| 6953 | + |
| 6954 | The cmd:lttng-rotate command prints the path to the created trace |
| 6955 | chunk archive. See man:lttng-rotate(1) to learn about the format |
| 6956 | of trace chunk archive directory names. |
| 6957 | + |
| 6958 | Perform other immediate rotations while the tracing session is |
| 6959 | active. It is guaranteed that all the trace chunk archives don't |
| 6960 | contain overlapping trace data. You can also perform an immediate |
| 6961 | rotation once you have <<basic-tracing-session-control,stopped>> the |
| 6962 | tracing session. |
| 6963 | |
| 6964 | . When you're done tracing, |
| 6965 | <<creating-destroying-tracing-sessions,destroy the current tracing |
| 6966 | session>>: |
| 6967 | + |
| 6968 | -- |
| 6969 | [role="term"] |
| 6970 | ---- |
| 6971 | $ lttng destroy |
| 6972 | ---- |
| 6973 | -- |
| 6974 | + |
| 6975 | The tracing session destruction operation creates one last trace |
| 6976 | chunk archive from the current trace chunk. |
| 6977 | |
| 6978 | A tracing session rotation schedule is a planned rotation which LTTng |
| 6979 | performs automatically based on one of the following conditions: |
| 6980 | |
| 6981 | * A timer with a configured period times out. |
| 6982 | |
| 6983 | * The total size of the flushed part of the current trace chunk |
| 6984 | becomes greater than or equal to a configured value. |
| 6985 | |
| 6986 | To schedule a tracing session rotation, set a _rotation schedule_: |
| 6987 | |
| 6988 | . <<creating-destroying-tracing-sessions,Create a tracing session>> |
| 6989 | in _normal mode_ or _network streaming mode_ |
| 6990 | (only those two creation modes support tracing session rotation): |
| 6991 | + |
| 6992 | -- |
| 6993 | [role="term"] |
| 6994 | ---- |
| 6995 | $ lttng create my-session |
| 6996 | ---- |
| 6997 | -- |
| 6998 | |
| 6999 | . <<enabling-disabling-events,Create one or more event rules>>: |
| 7000 | + |
| 7001 | -- |
| 7002 | [role="term"] |
| 7003 | ---- |
| 7004 | $ lttng enable-event --kernel sched_'*' |
| 7005 | ---- |
| 7006 | -- |
| 7007 | |
| 7008 | . Set a tracing session rotation schedule: |
| 7009 | + |
| 7010 | -- |
| 7011 | [role="term"] |
| 7012 | ---- |
| 7013 | $ lttng enable-rotation --timer=10s |
| 7014 | ---- |
| 7015 | -- |
| 7016 | + |
| 7017 | In this example, we set a rotation schedule so that LTTng performs a |
| 7018 | tracing session rotation every ten seconds. |
| 7019 | + |
| 7020 | See man:lttng-enable-rotation(1) to learn more about other ways to set a |
| 7021 | rotation schedule. |
| 7022 | |
| 7023 | . <<basic-tracing-session-control,Start tracing>>: |
| 7024 | + |
| 7025 | -- |
| 7026 | [role="term"] |
| 7027 | ---- |
| 7028 | $ lttng start |
| 7029 | ---- |
| 7030 | -- |
| 7031 | + |
| 7032 | LTTng performs tracing session rotations automatically while the tracing |
| 7033 | session is active thanks to the rotation schedule. |
| 7034 | |
| 7035 | . When you're done tracing, |
| 7036 | <<creating-destroying-tracing-sessions,destroy the current tracing |
| 7037 | session>>: |
| 7038 | + |
| 7039 | -- |
| 7040 | [role="term"] |
| 7041 | ---- |
| 7042 | $ lttng destroy |
| 7043 | ---- |
| 7044 | -- |
| 7045 | + |
| 7046 | The tracing session destruction operation creates one last trace chunk |
| 7047 | archive from the current trace chunk. |
| 7048 | |
| 7049 | Use man:lttng-disable-rotation(1) to unset a tracing session |
| 7050 | rotation schedule. |
| 7051 | |
| 7052 | NOTE: man:lttng-rotate(1) and man:lttng-enable-rotation(1) list |
| 7053 | limitations regarding those two commands. |
| 7054 | |
| 7055 | |
| 7056 | [role="since-2.6"] |
| 7057 | [[mi]] |
| 7058 | === Use the machine interface |
| 7059 | |
| 7060 | With any command of the man:lttng(1) command-line tool, set the |
| 7061 | opt:lttng(1):--mi option to `xml` (before the command name) to get an |
| 7062 | XML machine interface output, for example: |
| 7063 | |
| 7064 | [role="term"] |
| 7065 | ---- |
| 7066 | $ lttng --mi=xml enable-event --kernel --syscall open |
| 7067 | ---- |
| 7068 | |
| 7069 | A schema definition (XSD) is |
| 7070 | https://github.com/lttng/lttng-tools/blob/stable-{revision}/src/common/src/common/mi-lttng-4.0.xsd[available] |
| 7071 | to ease the integration with external tools as much as possible. |
| 7072 | |
| 7073 | |
| 7074 | [role="since-2.8"] |
| 7075 | [[metadata-regenerate]] |
| 7076 | === Regenerate the metadata of an LTTng trace |
| 7077 | |
| 7078 | An LTTng trace, which is a http://diamon.org/ctf[CTF] trace, has both |
| 7079 | data stream files and a metadata file. This metadata file contains, |
| 7080 | amongst other things, information about the offset of the clock sources |
| 7081 | used to timestamp <<event,event records>> when tracing. |
| 7082 | |
| 7083 | If, once a <<tracing-session,tracing session>> is |
| 7084 | <<basic-tracing-session-control,started>>, a major |
| 7085 | https://en.wikipedia.org/wiki/Network_Time_Protocol[NTP] correction |
| 7086 | happens, the clock offset of the trace also needs to be updated. Use |
| 7087 | the `metadata` item of the man:lttng-regenerate(1) command to do so. |
| 7088 | |
| 7089 | The main use case of this command is to allow a system to boot with |
| 7090 | an incorrect wall time and trace it with LTTng before its wall time |
| 7091 | is corrected. Once the system is known to be in a state where its |
| 7092 | wall time is correct, it can run `lttng regenerate metadata`. |
| 7093 | |
| 7094 | To regenerate the metadata of an LTTng trace: |
| 7095 | |
| 7096 | * Use the `metadata` item of the man:lttng-regenerate(1) command: |
| 7097 | + |
| 7098 | -- |
| 7099 | [role="term"] |
| 7100 | ---- |
| 7101 | $ lttng regenerate metadata |
| 7102 | ---- |
| 7103 | -- |
| 7104 | |
| 7105 | [IMPORTANT] |
| 7106 | ==== |
| 7107 | `lttng regenerate metadata` has the following limitations: |
| 7108 | |
| 7109 | * Tracing session <<creating-destroying-tracing-sessions,created>> |
| 7110 | in non-live mode. |
| 7111 | * User space <<channel,channels>>, if any, are using |
| 7112 | <<channel-buffering-schemes,per-user buffering>>. |
| 7113 | ==== |
| 7114 | |
| 7115 | |
| 7116 | [role="since-2.9"] |
| 7117 | [[regenerate-statedump]] |
| 7118 | === Regenerate the state dump of a tracing session |
| 7119 | |
| 7120 | The LTTng kernel and user space tracers generate state dump |
| 7121 | <<event,event records>> when the application starts or when you |
| 7122 | <<basic-tracing-session-control,start a tracing session>>. An analysis |
| 7123 | can use the state dump event records to set an initial state before it |
| 7124 | builds the rest of the state from the following event records. |
| 7125 | http://tracecompass.org/[Trace Compass] is a notable example of an |
| 7126 | application which uses the state dump of an LTTng trace. |
| 7127 | |
| 7128 | When you <<taking-a-snapshot,take a snapshot>>, it's possible that the |
| 7129 | state dump event records aren't included in the snapshot because they |
| 7130 | were recorded to a sub-buffer that has been consumed or overwritten |
| 7131 | already. |
| 7132 | |
| 7133 | Use the `lttng regenerate statedump` command to emit the state |
| 7134 | dump event records again. |
| 7135 | |
| 7136 | To regenerate the state dump of the current tracing session, provided |
| 7137 | create it in snapshot mode, before you take a snapshot: |
| 7138 | |
| 7139 | . Use the `statedump` item of the man:lttng-regenerate(1) command: |
| 7140 | + |
| 7141 | -- |
| 7142 | [role="term"] |
| 7143 | ---- |
| 7144 | $ lttng regenerate statedump |
| 7145 | ---- |
| 7146 | -- |
| 7147 | |
| 7148 | . <<basic-tracing-session-control,Stop the tracing session>>: |
| 7149 | + |
| 7150 | -- |
| 7151 | [role="term"] |
| 7152 | ---- |
| 7153 | $ lttng stop |
| 7154 | ---- |
| 7155 | -- |
| 7156 | |
| 7157 | . <<taking-a-snapshot,Take a snapshot>>: |
| 7158 | + |
| 7159 | -- |
| 7160 | [role="term"] |
| 7161 | ---- |
| 7162 | $ lttng snapshot record --name=my-snapshot |
| 7163 | ---- |
| 7164 | -- |
| 7165 | |
| 7166 | Depending on the event throughput, you should run steps 1 and 2 |
| 7167 | as closely as possible. |
| 7168 | |
| 7169 | NOTE: To record the state dump events, you need to |
| 7170 | <<enabling-disabling-events,create event rules>> which enable them. |
| 7171 | LTTng-UST state dump tracepoints start with `lttng_ust_statedump:`. |
| 7172 | LTTng-modules state dump tracepoints start with `lttng_statedump_`. |
| 7173 | |
| 7174 | |
| 7175 | [role="since-2.7"] |
| 7176 | [[persistent-memory-file-systems]] |
| 7177 | === Record trace data on persistent memory file systems |
| 7178 | |
| 7179 | https://en.wikipedia.org/wiki/Non-volatile_random-access_memory[Non-volatile random-access memory] |
| 7180 | (NVRAM) is random-access memory that retains its information when power |
| 7181 | is turned off (non-volatile). Systems with such memory can store data |
| 7182 | structures in RAM and retrieve them after a reboot, without flushing |
| 7183 | to typical _storage_. |
| 7184 | |
| 7185 | Linux supports NVRAM file systems thanks to either |
| 7186 | https://www.kernel.org/doc/Documentation/filesystems/dax.txt[DAX]{nbsp}+{nbsp}http://lkml.iu.edu/hypermail/linux/kernel/1504.1/03463.html[pmem] |
| 7187 | (requires Linux{nbsp}4.1+) or http://pramfs.sourceforge.net/[PRAMFS] (requires Linux{nbsp}<{nbsp}4). |
| 7188 | |
| 7189 | This section doesn't describe how to operate such file systems; |
| 7190 | we assume that you have a working persistent memory file system. |
| 7191 | |
| 7192 | When you create a <<tracing-session,tracing session>>, you can specify |
| 7193 | the path of the shared memory holding the sub-buffers. If you specify a |
| 7194 | location on an NVRAM file system, then you can retrieve the latest |
| 7195 | recorded trace data when the system reboots after a crash. |
| 7196 | |
| 7197 | To record trace data on a persistent memory file system and retrieve the |
| 7198 | trace data after a system crash: |
| 7199 | |
| 7200 | . Create a tracing session with a sub-buffer shared memory path located |
| 7201 | on an NVRAM file system: |
| 7202 | + |
| 7203 | -- |
| 7204 | [role="term"] |
| 7205 | ---- |
| 7206 | $ lttng create my-session --shm-path=/path/to/shm |
| 7207 | ---- |
| 7208 | -- |
| 7209 | |
| 7210 | . Configure the tracing session as usual with the man:lttng(1) |
| 7211 | command-line tool, and <<basic-tracing-session-control,start tracing>>. |
| 7212 | |
| 7213 | . After a system crash, use the man:lttng-crash(1) command-line tool to |
| 7214 | view the trace data recorded on the NVRAM file system: |
| 7215 | + |
| 7216 | -- |
| 7217 | [role="term"] |
| 7218 | ---- |
| 7219 | $ lttng-crash /path/to/shm |
| 7220 | ---- |
| 7221 | -- |
| 7222 | |
| 7223 | The binary layout of the ring buffer files isn't exactly the same as |
| 7224 | the trace files layout. This is why you need to use man:lttng-crash(1) |
| 7225 | instead of your preferred trace viewer directly. |
| 7226 | |
| 7227 | To convert the ring buffer files to LTTng trace files: |
| 7228 | |
| 7229 | * Use the opt:lttng-crash(1):--extract option of man:lttng-crash(1): |
| 7230 | + |
| 7231 | -- |
| 7232 | [role="term"] |
| 7233 | ---- |
| 7234 | $ lttng-crash --extract=/path/to/trace /path/to/shm |
| 7235 | ---- |
| 7236 | -- |
| 7237 | |
| 7238 | |
| 7239 | [role="since-2.10"] |
| 7240 | [[notif-trigger-api]] |
| 7241 | === Get notified when the buffer usage of a channel is too high or too low |
| 7242 | |
| 7243 | With the $$C/C++$$ notification and trigger API of LTTng, your user |
| 7244 | application can get notified when the buffer usage of one or more |
| 7245 | <<channel,channels>> becomes too low or too high. Use this API |
| 7246 | and enable or disable <<event,event rules>> during tracing to avoid |
| 7247 | <<channel-overwrite-mode-vs-discard-mode,discarded event records>>. |
| 7248 | |
| 7249 | .Have a user application get notified when the buffer usage of an LTTng channel is too high. |
| 7250 | ==== |
| 7251 | In this example, we create and build an application which gets notified |
| 7252 | when the buffer usage of a specific LTTng channel is higher than |
| 7253 | 75{nbsp}%. We only print that it is the case in the example, but we |
| 7254 | could as well use the API of <<liblttng-ctl-lttng,`liblttng-ctl`>> to |
| 7255 | disable event rules when this happens. |
| 7256 | |
| 7257 | . Create the C{nbsp}source file of application: |
| 7258 | + |
| 7259 | -- |
| 7260 | [source,c] |
| 7261 | .path:{notif-app.c} |
| 7262 | ---- |
| 7263 | #include <stdio.h> |
| 7264 | #include <assert.h> |
| 7265 | #include <lttng/domain.h> |
| 7266 | #include <lttng/action/action.h> |
| 7267 | #include <lttng/action/notify.h> |
| 7268 | #include <lttng/condition/condition.h> |
| 7269 | #include <lttng/condition/buffer-usage.h> |
| 7270 | #include <lttng/condition/evaluation.h> |
| 7271 | #include <lttng/notification/channel.h> |
| 7272 | #include <lttng/notification/notification.h> |
| 7273 | #include <lttng/trigger/trigger.h> |
| 7274 | #include <lttng/endpoint.h> |
| 7275 | |
| 7276 | int main(int argc, char *argv[]) |
| 7277 | { |
| 7278 | int exit_status = 0; |
| 7279 | struct lttng_notification_channel *notification_channel; |
| 7280 | struct lttng_condition *condition; |
| 7281 | struct lttng_action *action; |
| 7282 | struct lttng_trigger *trigger; |
| 7283 | const char *tracing_session_name; |
| 7284 | const char *channel_name; |
| 7285 | |
| 7286 | assert(argc >= 3); |
| 7287 | tracing_session_name = argv[1]; |
| 7288 | channel_name = argv[2]; |
| 7289 | |
| 7290 | /* |
| 7291 | * Create a notification channel. A notification channel |
| 7292 | * connects the user application to the LTTng session daemon. |
| 7293 | * This notification channel can be used to listen to various |
| 7294 | * types of notifications. |
| 7295 | */ |
| 7296 | notification_channel = lttng_notification_channel_create( |
| 7297 | lttng_session_daemon_notification_endpoint); |
| 7298 | |
| 7299 | /* |
| 7300 | * Create a "high buffer usage" condition. In this case, the |
| 7301 | * condition is reached when the buffer usage is greater than or |
| 7302 | * equal to 75 %. We create the condition for a specific tracing |
| 7303 | * session name, channel name, and for the user space tracing |
| 7304 | * domain. |
| 7305 | * |
| 7306 | * The "low buffer usage" condition type also exists. |
| 7307 | */ |
| 7308 | condition = lttng_condition_buffer_usage_high_create(); |
| 7309 | lttng_condition_buffer_usage_set_threshold_ratio(condition, .75); |
| 7310 | lttng_condition_buffer_usage_set_session_name( |
| 7311 | condition, tracing_session_name); |
| 7312 | lttng_condition_buffer_usage_set_channel_name(condition, |
| 7313 | channel_name); |
| 7314 | lttng_condition_buffer_usage_set_domain_type(condition, |
| 7315 | LTTNG_DOMAIN_UST); |
| 7316 | |
| 7317 | /* |
| 7318 | * Create an action (get a notification) to take when the |
| 7319 | * condition created above is reached. |
| 7320 | */ |
| 7321 | action = lttng_action_notify_create(); |
| 7322 | |
| 7323 | /* |
| 7324 | * Create a trigger. A trigger associates a condition to an |
| 7325 | * action: the action is executed when the condition is reached. |
| 7326 | */ |
| 7327 | trigger = lttng_trigger_create(condition, action); |
| 7328 | |
| 7329 | /* Register the trigger to LTTng. */ |
| 7330 | lttng_register_trigger(trigger); |
| 7331 | |
| 7332 | /* |
| 7333 | * Now that we have registered a trigger, a notification will be |
| 7334 | * emitted everytime its condition is met. To receive this |
| 7335 | * notification, we must subscribe to notifications that match |
| 7336 | * the same condition. |
| 7337 | */ |
| 7338 | lttng_notification_channel_subscribe(notification_channel, |
| 7339 | condition); |
| 7340 | |
| 7341 | /* |
| 7342 | * Notification loop. Put this in a dedicated thread to avoid |
| 7343 | * blocking the main thread. |
| 7344 | */ |
| 7345 | for (;;) { |
| 7346 | struct lttng_notification *notification; |
| 7347 | enum lttng_notification_channel_status status; |
| 7348 | const struct lttng_evaluation *notification_evaluation; |
| 7349 | const struct lttng_condition *notification_condition; |
| 7350 | double buffer_usage; |
| 7351 | |
| 7352 | /* Receive the next notification. */ |
| 7353 | status = lttng_notification_channel_get_next_notification( |
| 7354 | notification_channel, ¬ification); |
| 7355 | |
| 7356 | switch (status) { |
| 7357 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_OK: |
| 7358 | break; |
| 7359 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_NOTIFICATIONS_DROPPED: |
| 7360 | /* |
| 7361 | * The session daemon can drop notifications if a monitoring |
| 7362 | * application isn't consuming the notifications fast |
| 7363 | * enough. |
| 7364 | */ |
| 7365 | continue; |
| 7366 | case LTTNG_NOTIFICATION_CHANNEL_STATUS_CLOSED: |
| 7367 | /* |
| 7368 | * The notification channel has been closed by the |
| 7369 | * session daemon. This is typically caused by a session |
| 7370 | * daemon shutting down. |
| 7371 | */ |
| 7372 | goto end; |
| 7373 | default: |
| 7374 | /* Unhandled conditions or errors. */ |
| 7375 | exit_status = 1; |
| 7376 | goto end; |
| 7377 | } |
| 7378 | |
| 7379 | /* |
| 7380 | * A notification provides, amongst other things: |
| 7381 | * |
| 7382 | * * The condition that caused this notification to be |
| 7383 | * emitted. |
| 7384 | * * The condition evaluation, which provides more |
| 7385 | * specific information on the evaluation of the |
| 7386 | * condition. |
| 7387 | * |
| 7388 | * The condition evaluation provides the buffer usage |
| 7389 | * value at the moment the condition was reached. |
| 7390 | */ |
| 7391 | notification_condition = lttng_notification_get_condition( |
| 7392 | notification); |
| 7393 | notification_evaluation = lttng_notification_get_evaluation( |
| 7394 | notification); |
| 7395 | |
| 7396 | /* We're subscribed to only one condition. */ |
| 7397 | assert(lttng_condition_get_type(notification_condition) == |
| 7398 | LTTNG_CONDITION_TYPE_BUFFER_USAGE_HIGH); |
| 7399 | |
| 7400 | /* |
| 7401 | * Get the exact sampled buffer usage from the |
| 7402 | * condition evaluation. |
| 7403 | */ |
| 7404 | lttng_evaluation_buffer_usage_get_usage_ratio( |
| 7405 | notification_evaluation, &buffer_usage); |
| 7406 | |
| 7407 | /* |
| 7408 | * At this point, instead of printing a message, we |
| 7409 | * could do something to reduce the buffer usage of the channel, |
| 7410 | * like disable specific events. |
| 7411 | */ |
| 7412 | printf("Buffer usage is %f %% in tracing session \"%s\", " |
| 7413 | "user space channel \"%s\".\n", buffer_usage * 100, |
| 7414 | tracing_session_name, channel_name); |
| 7415 | lttng_notification_destroy(notification); |
| 7416 | } |
| 7417 | |
| 7418 | end: |
| 7419 | lttng_action_destroy(action); |
| 7420 | lttng_condition_destroy(condition); |
| 7421 | lttng_trigger_destroy(trigger); |
| 7422 | lttng_notification_channel_destroy(notification_channel); |
| 7423 | return exit_status; |
| 7424 | } |
| 7425 | ---- |
| 7426 | -- |
| 7427 | |
| 7428 | . Build the `notif-app` application, linking it to `liblttng-ctl`: |
| 7429 | + |
| 7430 | -- |
| 7431 | [role="term"] |
| 7432 | ---- |
| 7433 | $ gcc -o notif-app notif-app.c -llttng-ctl |
| 7434 | ---- |
| 7435 | -- |
| 7436 | |
| 7437 | . <<creating-destroying-tracing-sessions,Create a tracing session>>, |
| 7438 | <<enabling-disabling-events,create an event rule>> matching all the |
| 7439 | user space tracepoints, and |
| 7440 | <<basic-tracing-session-control,start tracing>>: |
| 7441 | + |
| 7442 | -- |
| 7443 | [role="term"] |
| 7444 | ---- |
| 7445 | $ lttng create my-session |
| 7446 | $ lttng enable-event --userspace --all |
| 7447 | $ lttng start |
| 7448 | ---- |
| 7449 | -- |
| 7450 | + |
| 7451 | If you create the channel manually with the man:lttng-enable-channel(1) |
| 7452 | command, control how frequently LTTng samples the current values of the |
| 7453 | channel properties to evaluate user conditions with the |
| 7454 | opt:lttng-enable-channel(1):--monitor-timer option. |
| 7455 | |
| 7456 | . Run the `notif-app` application. This program accepts the |
| 7457 | <<tracing-session,tracing session>> name and the user space channel |
| 7458 | name as its two first arguments. The channel which LTTng automatically |
| 7459 | creates with the man:lttng-enable-event(1) command above is named |
| 7460 | `channel0`: |
| 7461 | + |
| 7462 | -- |
| 7463 | [role="term"] |
| 7464 | ---- |
| 7465 | $ ./notif-app my-session channel0 |
| 7466 | ---- |
| 7467 | -- |
| 7468 | |
| 7469 | . In another terminal, run an application with a very high event |
| 7470 | throughput so that the 75{nbsp}% buffer usage condition is reached. |
| 7471 | + |
| 7472 | In the first terminal, the application should print lines like this: |
| 7473 | + |
| 7474 | ---- |
| 7475 | Buffer usage is 81.45197 % in tracing session "my-session", user space |
| 7476 | channel "channel0". |
| 7477 | ---- |
| 7478 | + |
| 7479 | If you don't see anything, try modifying the condition in |
| 7480 | path:{notif-app.c} to a lower value (0.1, for example), rebuilding it |
| 7481 | (step{nbsp}2) and running it again (step{nbsp}4). |
| 7482 | ==== |
| 7483 | |
| 7484 | |
| 7485 | [[reference]] |
| 7486 | == Reference |
| 7487 | |
| 7488 | [[lttng-modules-ref]] |
| 7489 | === noch:{LTTng-modules} |
| 7490 | |
| 7491 | |
| 7492 | [role="since-2.9"] |
| 7493 | [[lttng-tracepoint-enum]] |
| 7494 | ==== `LTTNG_TRACEPOINT_ENUM()` usage |
| 7495 | |
| 7496 | Use the `LTTNG_TRACEPOINT_ENUM()` macro to define an enumeration: |
| 7497 | |
| 7498 | [source,c] |
| 7499 | ---- |
| 7500 | LTTNG_TRACEPOINT_ENUM(name, TP_ENUM_VALUES(entries)) |
| 7501 | ---- |
| 7502 | |
| 7503 | Replace: |
| 7504 | |
| 7505 | * `name` with the name of the enumeration (C identifier, unique |
| 7506 | amongst all the defined enumerations). |
| 7507 | * `entries` with a list of enumeration entries. |
| 7508 | |
| 7509 | The available enumeration entry macros are: |
| 7510 | |
| 7511 | +ctf_enum_value(__name__, __value__)+:: |
| 7512 | Entry named +__name__+ mapped to the integral value +__value__+. |
| 7513 | |
| 7514 | +ctf_enum_range(__name__, __begin__, __end__)+:: |
| 7515 | Entry named +__name__+ mapped to the range of integral values between |
| 7516 | +__begin__+ (included) and +__end__+ (included). |
| 7517 | |
| 7518 | +ctf_enum_auto(__name__)+:: |
| 7519 | Entry named +__name__+ mapped to the integral value following the |
| 7520 | last mapping value. |
| 7521 | + |
| 7522 | The last value of a `ctf_enum_value()` entry is its +__value__+ |
| 7523 | parameter. |
| 7524 | + |
| 7525 | The last value of a `ctf_enum_range()` entry is its +__end__+ parameter. |
| 7526 | + |
| 7527 | If `ctf_enum_auto()` is the first entry in the list, its integral |
| 7528 | value is 0. |
| 7529 | |
| 7530 | Use the `ctf_enum()` <<lttng-modules-tp-fields,field definition macro>> |
| 7531 | to use a defined enumeration as a tracepoint field. |
| 7532 | |
| 7533 | .Define an enumeration with `LTTNG_TRACEPOINT_ENUM()`. |
| 7534 | ==== |
| 7535 | [source,c] |
| 7536 | ---- |
| 7537 | LTTNG_TRACEPOINT_ENUM( |
| 7538 | my_enum, |
| 7539 | TP_ENUM_VALUES( |
| 7540 | ctf_enum_auto("AUTO: EXPECT 0") |
| 7541 | ctf_enum_value("VALUE: 23", 23) |
| 7542 | ctf_enum_value("VALUE: 27", 27) |
| 7543 | ctf_enum_auto("AUTO: EXPECT 28") |
| 7544 | ctf_enum_range("RANGE: 101 TO 303", 101, 303) |
| 7545 | ctf_enum_auto("AUTO: EXPECT 304") |
| 7546 | ) |
| 7547 | ) |
| 7548 | ---- |
| 7549 | ==== |
| 7550 | |
| 7551 | |
| 7552 | [role="since-2.7"] |
| 7553 | [[lttng-modules-tp-fields]] |
| 7554 | ==== Tracepoint fields macros (for `TP_FIELDS()`) |
| 7555 | |
| 7556 | [[tp-fast-assign]][[tp-struct-entry]]The available macros to define |
| 7557 | tracepoint fields, which must be listed within `TP_FIELDS()` in |
| 7558 | `LTTNG_TRACEPOINT_EVENT()`, are: |
| 7559 | |
| 7560 | [role="func-desc growable",cols="asciidoc,asciidoc"] |
| 7561 | .Available macros to define LTTng-modules tracepoint fields |
| 7562 | |==== |
| 7563 | |Macro |Description and parameters |
| 7564 | |
| 7565 | | |
| 7566 | +ctf_integer(__t__, __n__, __e__)+ |
| 7567 | |
| 7568 | +ctf_integer_nowrite(__t__, __n__, __e__)+ |
| 7569 | |
| 7570 | +ctf_user_integer(__t__, __n__, __e__)+ |
| 7571 | |
| 7572 | +ctf_user_integer_nowrite(__t__, __n__, __e__)+ |
| 7573 | | |
| 7574 | Standard integer, displayed in base{nbsp}10. |
| 7575 | |
| 7576 | +__t__+:: |
| 7577 | Integer C type (`int`, `long`, `size_t`, ...). |
| 7578 | |
| 7579 | +__n__+:: |
| 7580 | Field name. |
| 7581 | |
| 7582 | +__e__+:: |
| 7583 | Argument expression. |
| 7584 | |
| 7585 | | |
| 7586 | +ctf_integer_hex(__t__, __n__, __e__)+ |
| 7587 | |
| 7588 | +ctf_user_integer_hex(__t__, __n__, __e__)+ |
| 7589 | | |
| 7590 | Standard integer, displayed in base{nbsp}16. |
| 7591 | |
| 7592 | +__t__+:: |
| 7593 | Integer C type. |
| 7594 | |
| 7595 | +__n__+:: |
| 7596 | Field name. |
| 7597 | |
| 7598 | +__e__+:: |
| 7599 | Argument expression. |
| 7600 | |
| 7601 | |+ctf_integer_oct(__t__, __n__, __e__)+ |
| 7602 | | |
| 7603 | Standard integer, displayed in base{nbsp}8. |
| 7604 | |
| 7605 | +__t__+:: |
| 7606 | Integer C type. |
| 7607 | |
| 7608 | +__n__+:: |
| 7609 | Field name. |
| 7610 | |
| 7611 | +__e__+:: |
| 7612 | Argument expression. |
| 7613 | |
| 7614 | | |
| 7615 | +ctf_integer_network(__t__, __n__, __e__)+ |
| 7616 | |
| 7617 | +ctf_user_integer_network(__t__, __n__, __e__)+ |
| 7618 | | |
| 7619 | Integer in network byte order (big-endian), displayed in base{nbsp}10. |
| 7620 | |
| 7621 | +__t__+:: |
| 7622 | Integer C type. |
| 7623 | |
| 7624 | +__n__+:: |
| 7625 | Field name. |
| 7626 | |
| 7627 | +__e__+:: |
| 7628 | Argument expression. |
| 7629 | |
| 7630 | | |
| 7631 | +ctf_integer_network_hex(__t__, __n__, __e__)+ |
| 7632 | |
| 7633 | +ctf_user_integer_network_hex(__t__, __n__, __e__)+ |
| 7634 | | |
| 7635 | Integer in network byte order, displayed in base{nbsp}16. |
| 7636 | |
| 7637 | +__t__+:: |
| 7638 | Integer C type. |
| 7639 | |
| 7640 | +__n__+:: |
| 7641 | Field name. |
| 7642 | |
| 7643 | +__e__+:: |
| 7644 | Argument expression. |
| 7645 | |
| 7646 | | |
| 7647 | +ctf_enum(__N__, __t__, __n__, __e__)+ |
| 7648 | |
| 7649 | +ctf_enum_nowrite(__N__, __t__, __n__, __e__)+ |
| 7650 | |
| 7651 | +ctf_user_enum(__N__, __t__, __n__, __e__)+ |
| 7652 | |
| 7653 | +ctf_user_enum_nowrite(__N__, __t__, __n__, __e__)+ |
| 7654 | | |
| 7655 | Enumeration. |
| 7656 | |
| 7657 | +__N__+:: |
| 7658 | Name of a <<lttng-tracepoint-enum,previously defined enumeration>>. |
| 7659 | |
| 7660 | +__t__+:: |
| 7661 | Integer C type (`int`, `long`, `size_t`, ...). |
| 7662 | |
| 7663 | +__n__+:: |
| 7664 | Field name. |
| 7665 | |
| 7666 | +__e__+:: |
| 7667 | Argument expression. |
| 7668 | |
| 7669 | | |
| 7670 | +ctf_string(__n__, __e__)+ |
| 7671 | |
| 7672 | +ctf_string_nowrite(__n__, __e__)+ |
| 7673 | |
| 7674 | +ctf_user_string(__n__, __e__)+ |
| 7675 | |
| 7676 | +ctf_user_string_nowrite(__n__, __e__)+ |
| 7677 | | |
| 7678 | Null-terminated string; undefined behavior if +__e__+ is `NULL`. |
| 7679 | |
| 7680 | +__n__+:: |
| 7681 | Field name. |
| 7682 | |
| 7683 | +__e__+:: |
| 7684 | Argument expression. |
| 7685 | |
| 7686 | | |
| 7687 | +ctf_array(__t__, __n__, __e__, __s__)+ |
| 7688 | |
| 7689 | +ctf_array_nowrite(__t__, __n__, __e__, __s__)+ |
| 7690 | |
| 7691 | +ctf_user_array(__t__, __n__, __e__, __s__)+ |
| 7692 | |
| 7693 | +ctf_user_array_nowrite(__t__, __n__, __e__, __s__)+ |
| 7694 | | |
| 7695 | Statically-sized array of integers. |
| 7696 | |
| 7697 | +__t__+:: |
| 7698 | Array element C type. |
| 7699 | |
| 7700 | +__n__+:: |
| 7701 | Field name. |
| 7702 | |
| 7703 | +__e__+:: |
| 7704 | Argument expression. |
| 7705 | |
| 7706 | +__s__+:: |
| 7707 | Number of elements. |
| 7708 | |
| 7709 | | |
| 7710 | +ctf_array_bitfield(__t__, __n__, __e__, __s__)+ |
| 7711 | |
| 7712 | +ctf_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ |
| 7713 | |
| 7714 | +ctf_user_array_bitfield(__t__, __n__, __e__, __s__)+ |
| 7715 | |
| 7716 | +ctf_user_array_bitfield_nowrite(__t__, __n__, __e__, __s__)+ |
| 7717 | | |
| 7718 | Statically-sized array of bits. |
| 7719 | |
| 7720 | The type of +__e__+ must be an integer type. +__s__+ is the number |
| 7721 | of elements of such type in +__e__+, not the number of bits. |
| 7722 | |
| 7723 | +__t__+:: |
| 7724 | Array element C type. |
| 7725 | |
| 7726 | +__n__+:: |
| 7727 | Field name. |
| 7728 | |
| 7729 | +__e__+:: |
| 7730 | Argument expression. |
| 7731 | |
| 7732 | +__s__+:: |
| 7733 | Number of elements. |
| 7734 | |
| 7735 | | |
| 7736 | +ctf_array_text(__t__, __n__, __e__, __s__)+ |
| 7737 | |
| 7738 | +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+ |
| 7739 | |
| 7740 | +ctf_user_array_text(__t__, __n__, __e__, __s__)+ |
| 7741 | |
| 7742 | +ctf_user_array_text_nowrite(__t__, __n__, __e__, __s__)+ |
| 7743 | | |
| 7744 | Statically-sized array, printed as text. |
| 7745 | |
| 7746 | The string doesn't need to be null-terminated. |
| 7747 | |
| 7748 | +__t__+:: |
| 7749 | Array element C type (always `char`). |
| 7750 | |
| 7751 | +__n__+:: |
| 7752 | Field name. |
| 7753 | |
| 7754 | +__e__+:: |
| 7755 | Argument expression. |
| 7756 | |
| 7757 | +__s__+:: |
| 7758 | Number of elements. |
| 7759 | |
| 7760 | | |
| 7761 | +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+ |
| 7762 | |
| 7763 | +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7764 | |
| 7765 | +ctf_user_sequence(__t__, __n__, __e__, __T__, __E__)+ |
| 7766 | |
| 7767 | +ctf_user_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7768 | | |
| 7769 | Dynamically-sized array of integers. |
| 7770 | |
| 7771 | The type of +__E__+ must be unsigned. |
| 7772 | |
| 7773 | +__t__+:: |
| 7774 | Array element C type. |
| 7775 | |
| 7776 | +__n__+:: |
| 7777 | Field name. |
| 7778 | |
| 7779 | +__e__+:: |
| 7780 | Argument expression. |
| 7781 | |
| 7782 | +__T__+:: |
| 7783 | Length expression C type. |
| 7784 | |
| 7785 | +__E__+:: |
| 7786 | Length expression. |
| 7787 | |
| 7788 | | |
| 7789 | +ctf_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ |
| 7790 | |
| 7791 | +ctf_user_sequence_hex(__t__, __n__, __e__, __T__, __E__)+ |
| 7792 | | |
| 7793 | Dynamically-sized array of integers, displayed in base{nbsp}16. |
| 7794 | |
| 7795 | The type of +__E__+ must be unsigned. |
| 7796 | |
| 7797 | +__t__+:: |
| 7798 | Array element C type. |
| 7799 | |
| 7800 | +__n__+:: |
| 7801 | Field name. |
| 7802 | |
| 7803 | +__e__+:: |
| 7804 | Argument expression. |
| 7805 | |
| 7806 | +__T__+:: |
| 7807 | Length expression C type. |
| 7808 | |
| 7809 | +__E__+:: |
| 7810 | Length expression. |
| 7811 | |
| 7812 | |+ctf_sequence_network(__t__, __n__, __e__, __T__, __E__)+ |
| 7813 | | |
| 7814 | Dynamically-sized array of integers in network byte order (big-endian), |
| 7815 | displayed in base{nbsp}10. |
| 7816 | |
| 7817 | The type of +__E__+ must be unsigned. |
| 7818 | |
| 7819 | +__t__+:: |
| 7820 | Array element C type. |
| 7821 | |
| 7822 | +__n__+:: |
| 7823 | Field name. |
| 7824 | |
| 7825 | +__e__+:: |
| 7826 | Argument expression. |
| 7827 | |
| 7828 | +__T__+:: |
| 7829 | Length expression C type. |
| 7830 | |
| 7831 | +__E__+:: |
| 7832 | Length expression. |
| 7833 | |
| 7834 | | |
| 7835 | +ctf_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ |
| 7836 | |
| 7837 | +ctf_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7838 | |
| 7839 | +ctf_user_sequence_bitfield(__t__, __n__, __e__, __T__, __E__)+ |
| 7840 | |
| 7841 | +ctf_user_sequence_bitfield_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7842 | | |
| 7843 | Dynamically-sized array of bits. |
| 7844 | |
| 7845 | The type of +__e__+ must be an integer type. +__s__+ is the number |
| 7846 | of elements of such type in +__e__+, not the number of bits. |
| 7847 | |
| 7848 | The type of +__E__+ must be unsigned. |
| 7849 | |
| 7850 | +__t__+:: |
| 7851 | Array element C type. |
| 7852 | |
| 7853 | +__n__+:: |
| 7854 | Field name. |
| 7855 | |
| 7856 | +__e__+:: |
| 7857 | Argument expression. |
| 7858 | |
| 7859 | +__T__+:: |
| 7860 | Length expression C type. |
| 7861 | |
| 7862 | +__E__+:: |
| 7863 | Length expression. |
| 7864 | |
| 7865 | | |
| 7866 | +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+ |
| 7867 | |
| 7868 | +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7869 | |
| 7870 | +ctf_user_sequence_text(__t__, __n__, __e__, __T__, __E__)+ |
| 7871 | |
| 7872 | +ctf_user_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+ |
| 7873 | | |
| 7874 | Dynamically-sized array, displayed as text. |
| 7875 | |
| 7876 | The string doesn't need to be null-terminated. |
| 7877 | |
| 7878 | The type of +__E__+ must be unsigned. |
| 7879 | |
| 7880 | The behaviour is undefined if +__e__+ is `NULL`. |
| 7881 | |
| 7882 | +__t__+:: |
| 7883 | Sequence element C type (always `char`). |
| 7884 | |
| 7885 | +__n__+:: |
| 7886 | Field name. |
| 7887 | |
| 7888 | +__e__+:: |
| 7889 | Argument expression. |
| 7890 | |
| 7891 | +__T__+:: |
| 7892 | Length expression C type. |
| 7893 | |
| 7894 | +__E__+:: |
| 7895 | Length expression. |
| 7896 | |==== |
| 7897 | |
| 7898 | Use the `_user` versions when the argument expression, `e`, is |
| 7899 | a user space address. In the cases of `ctf_user_integer*()` and |
| 7900 | `ctf_user_float*()`, `&e` must be a user space address, thus `e` must |
| 7901 | be addressable. |
| 7902 | |
| 7903 | The `_nowrite` versions omit themselves from the session trace, but are |
| 7904 | otherwise identical. This means the `_nowrite` fields won't be written |
| 7905 | in the recorded trace. Their primary purpose is to make some |
| 7906 | of the event context available to the |
| 7907 | <<enabling-disabling-events,event filters>> without having to |
| 7908 | commit the data to sub-buffers. |
| 7909 | |
| 7910 | |
| 7911 | [[glossary]] |
| 7912 | == Glossary |
| 7913 | |
| 7914 | Terms related to LTTng and to tracing in general: |
| 7915 | |
| 7916 | Babeltrace:: |
| 7917 | The http://diamon.org/babeltrace[Babeltrace] project, which includes: |
| 7918 | + |
| 7919 | * The |
| 7920 | https://babeltrace.org/docs/v2.0/man1/babeltrace2.1/[cmd:babeltrace2] |
| 7921 | command-line interface. |
| 7922 | * The libbabeltrace2 library which offers a |
| 7923 | https://babeltrace.org/docs/v2.0/libbabeltrace2/[C API]. |
| 7924 | * https://babeltrace.org/docs/v2.0/python/bt2/[Python{nbsp}3 bindings]. |
| 7925 | * Plugins. |
| 7926 | |
| 7927 | [[def-buffering-scheme]]<<channel-buffering-schemes,buffering scheme>>:: |
| 7928 | A layout of <<def-sub-buffer,sub-buffers>> applied to a given channel. |
| 7929 | |
| 7930 | [[def-channel]]<<channel,channel>>:: |
| 7931 | An entity which is responsible for a set of |
| 7932 | <<def-ring-buffer,ring buffers>>. |
| 7933 | + |
| 7934 | <<def-event-rule,Event rules>> are always attached to a specific |
| 7935 | channel. |
| 7936 | |
| 7937 | clock:: |
| 7938 | A source of time for a <<def-tracer,tracer>>. |
| 7939 | |
| 7940 | [[def-consumer-daemon]]<<lttng-consumerd,consumer daemon>>:: |
| 7941 | A process which is responsible for consuming the full |
| 7942 | <<def-sub-buffer,sub-buffers>> and write them to a file system or |
| 7943 | send them over the network. |
| 7944 | |
| 7945 | [[def-current-trace-chunk]]current trace chunk:: |
| 7946 | A <<def-trace-chunk,trace chunk>> which includes the current content |
| 7947 | of all the <<def-sub-buffer,sub-buffers>> of the |
| 7948 | <<def-tracing-session-rotation,tracing session>> and the stream files |
| 7949 | produced since the latest event amongst: |
| 7950 | + |
| 7951 | * The creation of the <<def-tracing-session,tracing session>>. |
| 7952 | * The last tracing session rotation, if any. |
| 7953 | |
| 7954 | <<channel-overwrite-mode-vs-discard-mode,discard mode>>:: |
| 7955 | The <<def-event-record-loss-mode,event record loss mode>> in which |
| 7956 | the <<def-tracer,tracer>> _discards_ new event records when there's no |
| 7957 | <<def-sub-buffer,sub-buffer>> space left to store them. |
| 7958 | |
| 7959 | [[def-event]]event:: |
| 7960 | The consequence of the execution of an |
| 7961 | <<def-instrumentation-point,instrumentation point>>, like a |
| 7962 | <<def-tracepoint,tracepoint>> that you manually place in some source |
| 7963 | code, or a Linux kernel kprobe. |
| 7964 | + |
| 7965 | An event is said to _occur_ at a specific time. <<def-lttng,LTTng>> can |
| 7966 | take various actions upon the occurrence of an event, like record its |
| 7967 | payload to a <<def-sub-buffer,sub-buffer>>. |
| 7968 | |
| 7969 | [[def-event-name]]event name:: |
| 7970 | The name of an <<def-event,event>>, which is also the name of the |
| 7971 | <<def-event-record,event record>>. |
| 7972 | + |
| 7973 | This is also called the _instrumentation point name_. |
| 7974 | |
| 7975 | [[def-event-record]]event record:: |
| 7976 | A record, in a <<def-trace,trace>>, of the payload of an |
| 7977 | <<def-event,event>> which occured. |
| 7978 | |
| 7979 | [[def-event-record-loss-mode]]<<channel-overwrite-mode-vs-discard-mode,event record loss mode>>:: |
| 7980 | The mechanism by which event records of a given |
| 7981 | <<def-channel,channel>> are lost (not recorded) when there is no |
| 7982 | <<def-sub-buffer,sub-buffer>> space left to store them. |
| 7983 | |
| 7984 | [[def-event-rule]]<<event,event rule>>:: |
| 7985 | Set of conditions which must be satisfied for one or more occuring |
| 7986 | <<def-event,events>> to be recorded. |
| 7987 | |
| 7988 | [[def-incl-set]]inclusion set:: |
| 7989 | In the <<pid-tracking,process attribute tracking>> context: a |
| 7990 | set of <<def-proc-attr,process attributes>> of a given type. |
| 7991 | |
| 7992 | <<instrumenting,instrumentation>>:: |
| 7993 | The use of <<def-lttng,LTTng>> probes to make a piece of software |
| 7994 | traceable. |
| 7995 | |
| 7996 | [[def-instrumentation-point]]instrumentation point:: |
| 7997 | A point in the execution path of a piece of software that, when |
| 7998 | reached by this execution, can emit an <<def-event,event>>. |
| 7999 | |
| 8000 | instrumentation point name:: |
| 8001 | See _<<def-event-name,event name>>_. |
| 8002 | |
| 8003 | `java.util.logging`:: |
| 8004 | The |
| 8005 | https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[core logging facilities] |
| 8006 | of the Java platform. |
| 8007 | |
| 8008 | log4j:: |
| 8009 | A http://logging.apache.org/log4j/1.2/[logging library] for Java |
| 8010 | developed by the Apache Software Foundation. |
| 8011 | |
| 8012 | log level:: |
| 8013 | Level of severity of a log statement or user space |
| 8014 | <<def-instrumentation-point,instrumentation point>>. |
| 8015 | |
| 8016 | [[def-lttng]]LTTng:: |
| 8017 | The _Linux Trace Toolkit: next generation_ project. |
| 8018 | |
| 8019 | <<lttng-cli,cmd:lttng>>:: |
| 8020 | A command-line tool provided by the <<def-lttng-tools,LTTng-tools>> |
| 8021 | project which you can use to send and receive control messages to and |
| 8022 | from a <<def-session-daemon,session daemon>>. |
| 8023 | |
| 8024 | LTTng analyses:: |
| 8025 | The https://github.com/lttng/lttng-analyses[LTTng analyses] project, |
| 8026 | which is a set of analyzing programs that you can use to obtain a |
| 8027 | higher level view of an <<def-lttng,LTTng>> <<def-trace,trace>>. |
| 8028 | |
| 8029 | cmd:lttng-consumerd:: |
| 8030 | The name of the <<def-consumer-daemon,consumer daemon>> program. |
| 8031 | |
| 8032 | cmd:lttng-crash:: |
| 8033 | A utility provided by the <<def-lttng-tools,LTTng-tools>> project |
| 8034 | which can convert <<def-ring-buffer,ring buffer>> files (usually |
| 8035 | <<persistent-memory-file-systems,saved on a persistent memory file |
| 8036 | system>>) to <<def-trace,trace>> files. |
| 8037 | + |
| 8038 | See man:lttng-crash(1). |
| 8039 | |
| 8040 | LTTng Documentation:: |
| 8041 | This document. |
| 8042 | |
| 8043 | <<lttng-live,LTTng live>>:: |
| 8044 | A communication protocol between the <<lttng-relayd,relay daemon>> and |
| 8045 | live viewers which makes it possible to see <<def-event-record,event |
| 8046 | records>> ``live'', as they are received by the |
| 8047 | <<def-relay-daemon,relay daemon>>. |
| 8048 | |
| 8049 | <<lttng-modules,LTTng-modules>>:: |
| 8050 | The https://github.com/lttng/lttng-modules[LTTng-modules] project, |
| 8051 | which contains the Linux kernel modules to make the Linux kernel |
| 8052 | <<def-instrumentation-point,instrumentation points>> available for |
| 8053 | <<def-lttng,LTTng>> tracing. |
| 8054 | |
| 8055 | cmd:lttng-relayd:: |
| 8056 | The name of the <<def-relay-daemon,relay daemon>> program. |
| 8057 | |
| 8058 | cmd:lttng-sessiond:: |
| 8059 | The name of the <<def-session-daemon,session daemon>> program. |
| 8060 | |
| 8061 | [[def-lttng-tools]]LTTng-tools:: |
| 8062 | The https://github.com/lttng/lttng-tools[LTTng-tools] project, which |
| 8063 | contains the various programs and libraries used to |
| 8064 | <<controlling-tracing,control tracing>>. |
| 8065 | |
| 8066 | [[def-lttng-ust]]<<lttng-ust,LTTng-UST>>:: |
| 8067 | The https://github.com/lttng/lttng-ust[LTTng-UST] project, which |
| 8068 | contains libraries to instrument |
| 8069 | <<def-user-application,user applications>>. |
| 8070 | |
| 8071 | <<lttng-ust-agents,LTTng-UST Java agent>>:: |
| 8072 | A Java package provided by the <<def-lttng-ust,LTTng-UST>> project to |
| 8073 | allow the LTTng instrumentation of `java.util.logging` and Apache |
| 8074 | log4j{nbsp}1.2 logging statements. |
| 8075 | |
| 8076 | <<lttng-ust-agents,LTTng-UST Python agent>>:: |
| 8077 | A Python package provided by the <<def-lttng-ust,LTTng-UST>> project |
| 8078 | to allow the <<def-lttng,LTTng>> instrumentation of Python logging |
| 8079 | statements. |
| 8080 | |
| 8081 | <<channel-overwrite-mode-vs-discard-mode,overwrite mode>>:: |
| 8082 | The <<def-event-record-loss-mode,event record loss mode>> in which new |
| 8083 | <<def-event-record,event records>> _overwrite_ older event records |
| 8084 | when there's no <<def-sub-buffer,sub-buffer>> space left to store |
| 8085 | them. |
| 8086 | |
| 8087 | <<channel-buffering-schemes,per-process buffering>>:: |
| 8088 | A <<def-buffering-scheme,buffering scheme>> in which each instrumented |
| 8089 | process has its own <<def-sub-buffer,sub-buffers>> for a given user |
| 8090 | space <<def-channel,channel>>. |
| 8091 | |
| 8092 | <<channel-buffering-schemes,per-user buffering>>:: |
| 8093 | A <<def-buffering-scheme,buffering scheme>> in which all the processes |
| 8094 | of a Unix user share the same <<def-sub-buffer,sub-buffers>> for a |
| 8095 | given user space <<def-channel,channel>>. |
| 8096 | |
| 8097 | [[def-proc-attr]]process attribute:: |
| 8098 | In the <<pid-tracking,process attribute tracking>> context: |
| 8099 | + |
| 8100 | * A process ID. |
| 8101 | * A virtual process ID. |
| 8102 | * A Unix user ID. |
| 8103 | * A virtual Unix user ID. |
| 8104 | * A Unix group ID. |
| 8105 | * A virtual Unix group ID. |
| 8106 | |
| 8107 | [[def-relay-daemon]]<<lttng-relayd,relay daemon>>:: |
| 8108 | A process which is responsible for receiving the <<def-trace,trace>> |
| 8109 | data which a distant <<def-consumer-daemon,consumer daemon>> sends. |
| 8110 | |
| 8111 | [[def-ring-buffer]]ring buffer:: |
| 8112 | A set of <<def-sub-buffer,sub-buffers>>. |
| 8113 | |
| 8114 | rotation:: |
| 8115 | See _<<def-tracing-session-rotation,tracing session rotation>>_. |
| 8116 | |
| 8117 | [[def-session-daemon]]<<lttng-sessiond,session daemon>>:: |
| 8118 | A process which receives control commands from you and orchestrates |
| 8119 | the <<def-tracer,tracers>> and various <<def-lttng,LTTng>> daemons. |
| 8120 | |
| 8121 | <<taking-a-snapshot,snapshot>>:: |
| 8122 | A copy of the current data of all the <<def-sub-buffer,sub-buffers>> |
| 8123 | of a given <<def-tracing-session,tracing session>>, saved as |
| 8124 | <<def-trace,trace>> files. |
| 8125 | |
| 8126 | [[def-sub-buffer]]sub-buffer:: |
| 8127 | One part of an <<def-lttng,LTTng>> <<def-ring-buffer,ring buffer>> |
| 8128 | which contains <<def-event-record,event records>>. |
| 8129 | |
| 8130 | timestamp:: |
| 8131 | The time information attached to an <<def-event,event>> when it is |
| 8132 | emitted. |
| 8133 | |
| 8134 | [[def-trace]]trace (_noun_):: |
| 8135 | A set of: |
| 8136 | + |
| 8137 | * One http://diamon.org/ctf/[CTF] metadata stream file. |
| 8138 | * One or more CTF data stream files which are the concatenations of one |
| 8139 | or more flushed <<def-sub-buffer,sub-buffers>>. |
| 8140 | |
| 8141 | [[def-trace-verb]]trace (_verb_):: |
| 8142 | The action of recording the <<def-event,events>> emitted by an |
| 8143 | application or by a system, or to initiate such recording by |
| 8144 | controlling a <<def-tracer,tracer>>. |
| 8145 | |
| 8146 | [[def-trace-chunk]]trace chunk:: |
| 8147 | A self-contained <<def-trace,trace>> which is part of a |
| 8148 | <<def-tracing-session,tracing session>>. Each |
| 8149 | <<def-tracing-session-rotation, tracing session rotation>> produces a |
| 8150 | <<def-trace-chunk-archive,trace chunk archive>>. |
| 8151 | |
| 8152 | [[def-trace-chunk-archive]]trace chunk archive:: |
| 8153 | The result of a <<def-tracing-session-rotation, tracing session rotation>>. |
| 8154 | + |
| 8155 | <<def-lttng,LTTng>> doesn't manage any trace chunk archive, even if its |
| 8156 | containing <<def-tracing-session,tracing session>> is still active: you |
| 8157 | are free to read it, modify it, move it, or remove it. |
| 8158 | |
| 8159 | Trace Compass:: |
| 8160 | The http://tracecompass.org[Trace Compass] project and application. |
| 8161 | |
| 8162 | [[def-tracepoint]]tracepoint:: |
| 8163 | An instrumentation point using the tracepoint mechanism of the Linux |
| 8164 | kernel or of <<def-lttng-ust,LTTng-UST>>. |
| 8165 | |
| 8166 | tracepoint definition:: |
| 8167 | The definition of a single <<def-tracepoint,tracepoint>>. |
| 8168 | |
| 8169 | tracepoint name:: |
| 8170 | The name of a <<def-tracepoint,tracepoint>>. |
| 8171 | |
| 8172 | [[def-tracepoint-provider]]tracepoint provider:: |
| 8173 | A set of functions providing <<def-tracepoint,tracepoints>> to an |
| 8174 | instrumented <<def-user-application,user application>>. |
| 8175 | + |
| 8176 | Not to be confused with a <<def-tracepoint-provider-package,tracepoint |
| 8177 | provider package>>: many tracepoint providers can exist within a |
| 8178 | tracepoint provider package. |
| 8179 | |
| 8180 | [[def-tracepoint-provider-package]]tracepoint provider package:: |
| 8181 | One or more <<def-tracepoint-provider,tracepoint providers>> compiled |
| 8182 | as an https://en.wikipedia.org/wiki/Object_file[object file] or as a |
| 8183 | link:https://en.wikipedia.org/wiki/Library_(computing)#Shared_libraries[shared |
| 8184 | library]. |
| 8185 | |
| 8186 | [[def-tracer]]tracer:: |
| 8187 | A software which records emitted <<def-event,events>>. |
| 8188 | |
| 8189 | <<domain,tracing domain>>:: |
| 8190 | A namespace for <<def-event,event>> sources. |
| 8191 | |
| 8192 | <<tracing-group,tracing group>>:: |
| 8193 | The Unix group in which a Unix user can be to be allowed to |
| 8194 | <<def-trace-verb,trace>> the Linux kernel. |
| 8195 | |
| 8196 | [[def-tracing-session]]<<tracing-session,tracing session>>:: |
| 8197 | A stateful dialogue between you and a <<lttng-sessiond,session daemon>>. |
| 8198 | |
| 8199 | [[def-tracing-session-rotation]]<<session-rotation,tracing session rotation>>:: |
| 8200 | The action of archiving the |
| 8201 | <<def-current-trace-chunk,current trace chunk>> of a |
| 8202 | <<def-tracing-session,tracing session>>. |
| 8203 | |
| 8204 | tracked <<def-proc-attr,process attribute>>:: |
| 8205 | A process attribute which is part of an <<def-incl-set,inclusion |
| 8206 | set>>. |
| 8207 | |
| 8208 | untracked process attribute:: |
| 8209 | A process attribute which isn't part of an <<def-incl-set,inclusion |
| 8210 | set>>. |
| 8211 | |
| 8212 | [[def-user-application]]user application:: |
| 8213 | An application running in user space, as opposed to a Linux kernel |
| 8214 | module, for example. |