2.7: update OE/Yocto version
[lttng-docs.git] / 2.7 / lttng-docs-2.7.txt
1 The LTTng Documentation
2 =======================
3 Philippe Proulx <pproulx@efficios.com>
4 v2.7, 25 October 2016
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 You can skip this section if you’re familiar with software tracing and
26 with the 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 You can skip this section if you already properly installed LTTng on
33 your target 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 You can 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 You can skip this section if you do not 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 links and 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 {revision}?
76
77 * **Tracing control**:
78 ** Dynamic filter support for <<event,event rules>> in the Linux kernel
79 <<domain,tracing domain>>. For example:
80 +
81 --
82 [role="term"]
83 ----
84 lttng enable-event --kernel irq_handler_entry --filter='irq == 28'
85 ----
86 --
87
88 ** Wildcard support in the instrumentation point name of an event rule
89 in the Linux kernel tracing domain. For example:
90 +
91 --
92 [role="term"]
93 ----
94 lttng enable-event --kernel 'sched_*'
95 ----
96 --
97
98 ** New `lttng track` and `lttng untrack` commands to make
99 <<pid-tracking,PID tracking>> super-fast for both the Linux kernel
100 and the user space tracing domains.
101 +
102 When LTTng _tracks_ one or more PIDs, only the processes having those PIDs
103 can emit events for a given tracing session.
104
105 ** New `--shm-path` option of the `lttng create` command to specify the
106 path where LTTng creates the shared memory holding the ring buffers.
107 +
108 This feature is useful when used with persistent memory file systems to
109 extract the latest recorded trace data in the event of a crash requiring
110 a reboot.
111 +
112 The new man:lttng-crash(1) command-line utility can extract trace data
113 from such a file (see <<persistent-memory-file-systems,Record trace data
114 on persistent memory file systems>>).
115
116 * **User space tracing**:
117 ** New <<python-application,LTTng-UST Python agent>> which makes it easy
118 to trace existing Python applications that are using the standard
119 https://docs.python.org/3/howto/logging.html[`logging` package].
120 +
121 This agent is compatible with both the Python 2 and Python 3 languages.
122
123 ** New <<tracelog,`tracelog()`>> facility to ease the migration from
124 logging to tracing.
125 +
126 `tracelog()` is similar to <<tracef,`tracef()`>>,
127 but it accepts an additional log level parameter.
128
129 ** Plugin support in LTTng-UST to provide a custom clock source and to
130 retrieve the current CPU number.
131 +
132 This feature exists for very advanced use cases.
133 +
134 See the
135 https://github.com/lttng/lttng-ust/tree/stable-{revision}/doc/examples/clock-override[clock-override]
136 and
137 https://github.com/lttng/lttng-ust/tree/stable-{revision}/doc/examples/getcpu-override[getcpu-override]
138 examples for more details.
139
140 Moreover, LTTng{nbsp}{revision} boasts great stability, benifiting from
141 piles of bug fixes and more-than-welcome internal refactorings.
142
143 To learn more about the new features of LTTng{nbsp}{revision}, see
144 https://lttng.org/blog/2015/10/14/lttng-2.7-released/[the release announcement].
145
146
147 [[nuts-and-bolts]]
148 == Nuts and bolts
149
150 What is LTTng? As its name suggests, the _Linux Trace Toolkit: next
151 generation_ is a modern toolkit for tracing Linux systems and
152 applications. So your first question might be:
153 **what is tracing?**
154
155
156 [[what-is-tracing]]
157 === What is tracing?
158
159 As the history of software engineering progressed and led to what
160 we now take for granted--complex, numerous and
161 interdependent software applications running in parallel on
162 sophisticated operating systems like Linux--the authors of such
163 components, software developers, began feeling a natural
164 urge to have tools that would ensure the robustness and good performance
165 of their masterpieces.
166
167 One major achievement in this field is, inarguably, the
168 https://www.gnu.org/software/gdb/[GNU debugger (GDB)],
169 an essential tool for developers to find and fix bugs. But even the best
170 debugger won't help make your software run faster, and nowadays, faster
171 software means either more work done by the same hardware, or cheaper
172 hardware for the same work.
173
174 A _profiler_ is often the tool of choice to identify performance
175 bottlenecks. Profiling is suitable to identify _where_ performance is
176 lost in a given software. The profiler outputs a profile, a statistical
177 summary of observed events, which you may use to discover which
178 functions took the most time to execute. However, a profiler won't
179 report _why_ some identified functions are the bottleneck. Bottlenecks
180 might only occur when specific conditions are met, conditions that are
181 sometimes impossible to capture by a statistical profiler, or impossible
182 to reproduce with an application altered by the overhead of an
183 event-based profiler. For a thorough investigation of software
184 performance issues, a history of execution is essential, with the
185 recorded values of variables and context fields you choose, and
186 with as little influence as possible on the instrumented software. This
187 is where tracing comes in handy.
188
189 _Tracing_ is a technique used to understand what goes on in a running
190 software system. The software used for tracing is called a _tracer_,
191 which is conceptually similar to a tape recorder. When recording,
192 specific instrumentation points placed in the software source code
193 generate events that are saved on a giant tape: a _trace_ file. You
194 can trace user applications and the operating system at the same time,
195 opening the possibility of resolving a wide range of problems that would
196 otherwise be extremely challenging.
197
198 Tracing is often compared to _logging_. However, tracers and loggers are
199 two different tools, serving two different purposes. Tracers are
200 designed to record much lower-level events that occur much more
201 frequently than log messages, often in the range of thousands per
202 second, with very little execution overhead. Logging is more appropriate
203 for a very high-level analysis of less frequent events: user accesses,
204 exceptional conditions (errors and warnings, for example), database
205 transactions, instant messaging communications, and such. Simply put,
206 logging is one of the many use cases that can be satisfied with tracing.
207
208 The list of recorded events inside a trace file can be read manually
209 like a log file for the maximum level of detail, but it is generally
210 much more interesting to perform application-specific analyses to
211 produce reduced statistics and graphs that are useful to resolve a
212 given problem. Trace viewers and analyzers are specialized tools
213 designed to do this.
214
215 In the end, this is what LTTng is: a powerful, open source set of
216 tools to trace the Linux kernel and user applications at the same time.
217 LTTng is composed of several components actively maintained and
218 developed by its link:/community/#where[community].
219
220
221 [[lttng-alternatives]]
222 === Alternatives to noch:{LTTng}
223
224 Excluding proprietary solutions, a few competing software tracers
225 exist for Linux:
226
227 * https://github.com/dtrace4linux/linux[dtrace4linux] is a port of
228 Sun Microsystems's DTrace to Linux. The cmd:dtrace tool interprets
229 user scripts and is responsible for loading code into the
230 Linux kernel for further execution and collecting the outputted data.
231 * https://en.wikipedia.org/wiki/Berkeley_Packet_Filter[eBPF] is a
232 subsystem in the Linux kernel in which a virtual machine can execute
233 programs passed from the user space to the kernel. You can attach
234 such programs to tracepoints and KProbes thanks to a system call, and
235 they can output data to the user space when executed thanks to
236 different mechanisms (pipe, VM register values, and eBPF maps, to name
237 a few).
238 * https://www.kernel.org/doc/Documentation/trace/ftrace.txt[ftrace]
239 is the de facto function tracer of the Linux kernel. Its user
240 interface is a set of special files in sysfs.
241 * https://perf.wiki.kernel.org/[perf] is
242 a performance analyzing tool for Linux which supports hardware
243 performance counters, tracepoints, as well as other counters and
244 types of probes. perf's controlling utility is the cmd:perf command
245 line/curses tool.
246 * http://linux.die.net/man/1/strace[strace]
247 is a command-line utility which records system calls made by a
248 user process, as well as signal deliveries and changes of process
249 state. strace makes use of https://en.wikipedia.org/wiki/Ptrace[ptrace]
250 to fulfill its function.
251 * http://www.sysdig.org/[sysdig], like SystemTap, uses scripts to
252 analyze Linux kernel events. You write scripts, or _chisels_ in
253 sysdig's jargon, in Lua and sysdig executes them while the system is
254 being traced or afterwards. sysdig's interface is the cmd:sysdig
255 command-line tool as well as the curses-based cmd:csysdig tool.
256 * https://sourceware.org/systemtap/[SystemTap] is a Linux kernel and
257 user space tracer which uses custom user scripts to produce plain text
258 traces. SystemTap converts the scripts to the C language, and then
259 compiles them as Linux kernel modules which are loaded to produce
260 trace data. SystemTap's primary user interface is the cmd:stap
261 command-line tool.
262
263 The main distinctive features of LTTng is that it produces correlated
264 kernel and user space traces, as well as doing so with the lowest
265 overhead amongst other solutions. It produces trace files in the
266 http://diamon.org/ctf[CTF] format, a file format optimized
267 for the production and analyses of multi-gigabyte data.
268
269 LTTng is the result of more than 10 years of active open source
270 development by a community of passionate developers.
271 LTTng{nbsp}{revision} is currently available on major desktop and server
272 Linux distributions.
273
274 The main interface for tracing control is a single command-line tool
275 named cmd:lttng. The latter can create several tracing sessions, enable
276 and disable events on the fly, filter events efficiently with custom
277 user expressions, start and stop tracing, and much more. LTTng can
278 record the traces on the file system or send them over the network, and
279 keep them totally or partially. You can view the traces once tracing
280 becomes inactive or in real-time.
281
282 <<installing-lttng,Install LTTng now>> and
283 <<getting-started,start tracing>>!
284
285
286 [[installing-lttng]]
287 == Installation
288
289 **LTTng** is a set of software <<plumbing,components>> which interact to
290 <<instrumenting,instrument>> the Linux kernel and user applications, and
291 to <<controlling-tracing,control tracing>> (start and stop
292 tracing, enable and disable event rules, and the rest). Those
293 components are bundled into the following packages:
294
295 * **LTTng-tools**: Libraries and command-line interface to
296 control tracing.
297 * **LTTng-modules**: Linux kernel modules to instrument and
298 trace the kernel.
299 * **LTTng-UST**: Libraries and Java/Python packages to instrument and
300 trace user applications.
301
302 Most distributions mark the LTTng-modules and LTTng-UST packages as
303 optional when installing LTTng-tools (which is always required). In the
304 following sections, we always provide the steps to install all three,
305 but note that:
306
307 * You only need to install LTTng-modules if you intend to trace the
308 Linux kernel.
309 * You only need to install LTTng-UST if you intend to trace user
310 applications.
311
312 [role="growable"]
313 .Availability of LTTng{nbsp}{revision} for major Linux distributions.
314 |====
315 |Distribution |Available in releases |Alternatives
316
317 |Ubuntu
318 |<<ubuntu,Ubuntu{nbsp}16.04 _Xenial Xerus_>>
319 |LTTng{nbsp}2.8 for Ubuntu{nbsp}16.10 _Yakkety Yak_.
320
321 LTTng{nbsp}{revision} for Ubuntu{nbsp}12.04 _Precise Pangolin_,
322 Ubuntu{nbsp}14.04 _Trusty Tahr_, and Ubuntu{nbsp}16.04 _Xenial Xerus_:
323 <<ubuntu-ppa,use the LTTng Stable{nbsp}{revision} PPA>>.
324
325 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
326 other Ubuntu releases.
327
328 |Fedora
329 |_Not available_
330 |LTTng{nbsp}{revision} for Fedora{nbsp}25 and Fedora{nbsp}26 (not
331 released yet).
332
333 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
334 other Fedora releases.
335
336 |Debian
337 |_Not available_
338 |LTTng{nbsp}2.8 for Debian "stretch" (testing).
339
340 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
341 other Debian releases.
342
343 |openSUSE
344 |<<opensuse,openSUSE Leap{nbsp}42.1>>
345 |<<building-from-source,Build LTTng{nbsp}{revision} from source>> for
346 other openSUSE releases.
347
348 |Arch Linux
349 |_Not available_
350 |<<building-from-source,Build LTTng{nbsp}{revision} from source>>.
351
352 |Alpine Linux
353 |_Not available_
354 |LTTng{nbsp}2.8 for Alpine Linux "edge".
355
356 LTTng{nbsp}2.8 for Alpine Linux{nbsp}3.5 (not released yet).
357
358 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
359 other Alpine Linux releases.
360
361 |RHEL and SLES
362 |See http://packages.efficios.com/[EfficiOS Enterprise Packages].
363 |
364
365 |Buildroot
366 |<<"buildroot","Buildroot{nbsp}2016.02, Buildroot{nbsp}2016.05,
367 and Buildroot{nbsp}2016.08">>
368 |LTTng{nbsp}2.8 for Buildroot{nbsp}2016.11 (not released yet).
369
370 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
371 other Buildroot releases.
372
373 |OpenEmbedded and Yocto
374 |<<oe-yocto,Yocto Project{nbsp}2.1 _Krogoth_>> (`openembedded-core` layer)
375 |LTTng{nbsp}2.8 for Yocto Project{nbsp}2.2 _Morty_.
376
377 <<building-from-source,Build LTTng{nbsp}{revision} from source>> for
378 other Yocto releases.
379 |====
380
381
382 [[ubuntu]]
383 === [[ubuntu-official-repositories]]Ubuntu
384
385 LTTng{nbsp}{revision} is available on Ubuntu 16.04 _Xenial Xerus_. For
386 previous releases of Ubuntu, <<ubuntu-ppa,use the LTTng
387 Stable{nbsp}{revision} PPA>>.
388
389 To install LTTng{nbsp}{revision} on Ubuntu{nbsp}16.04 _Xenial Xerus_:
390
391 . Install the main LTTng{nbsp}{revision} packages:
392 +
393 --
394 [role="term"]
395 ----
396 sudo apt-get install lttng-tools
397 sudo apt-get install lttng-modules-dkms
398 sudo apt-get install liblttng-ust-dev
399 ----
400 --
401
402 . **If you need to instrument and trace
403 <<java-application,Java applications>>**, install the LTTng-UST
404 Java agent:
405 +
406 --
407 [role="term"]
408 ----
409 sudo apt-get install liblttng-ust-agent-java
410 ----
411 --
412
413 . **If you need to instrument and trace
414 <<python-application,Python applications>>**, install the
415 LTTng-UST Python agent:
416 +
417 --
418 [role="term"]
419 ----
420 sudo apt-get install python3-lttngust
421 ----
422 --
423
424
425 [[ubuntu-ppa]]
426 ==== noch:{LTTng} Stable {revision} PPA
427
428 The
429 https://launchpad.net/~lttng/+archive/ubuntu/stable-{revision}[LTTng Stable{nbsp}{revision} PPA]
430 offers the latest stable LTTng{nbsp}{revision} packages for:
431
432 * Ubuntu{nbsp}12.04 _Precise Pangolin_
433 * Ubuntu{nbsp}14.04 _Trusty Tahr_
434 * Ubuntu{nbsp}16.04 _Xenial Xerus_
435
436 To install LTTng{nbsp}{revision} from the LTTng Stable{nbsp}{revision}
437 PPA:
438
439 . Add the LTTng Stable{nbsp}{revision} PPA repository and update the
440 list of packages:
441 +
442 --
443 [role="term"]
444 ----
445 sudo apt-add-repository ppa:lttng/stable-2.7
446 sudo apt-get update
447 ----
448 --
449
450 . Install the main LTTng{nbsp}{revision} packages:
451 +
452 --
453 [role="term"]
454 ----
455 sudo apt-get install lttng-tools
456 sudo apt-get install lttng-modules-dkms
457 sudo apt-get install liblttng-ust-dev
458 ----
459 --
460
461 . **If you need to instrument and trace
462 <<java-application,Java applications>>**, install the LTTng-UST
463 Java agent:
464 +
465 --
466 [role="term"]
467 ----
468 sudo apt-get install liblttng-ust-agent-java
469 ----
470 --
471
472 . **If you need to instrument and trace
473 <<python-application,Python applications>>**, install the
474 LTTng-UST Python agent:
475 +
476 --
477 [role="term"]
478 ----
479 sudo apt-get install python3-lttngust
480 ----
481 --
482
483
484 [[opensuse]]
485 === noch:{openSUSE}/RPM
486
487 To install LTTng{nbsp}{revision} on openSUSE Leap{nbsp}42.1:
488
489 * Install the main LTTng{nbsp}{revision} packages:
490 +
491 --
492 [role="term"]
493 ----
494 sudo zypper install lttng-tools
495 sudo zypper install lttng-modules
496 sudo zypper install lttng-ust-devel
497 ----
498 --
499
500 [IMPORTANT]
501 .Java and Python application instrumentation and tracing
502 ====
503 If you need to instrument and trace <<java-application,Java
504 applications>> on openSUSE, you need to build and install
505 LTTng-UST{nbsp}{revision} <<building-from-source,from source>> and pass
506 the `--enable-java-agent-jul`, `--enable-java-agent-log4j`, or
507 `--enable-java-agent-all` options to the `configure` script, depending
508 on which Java logging framework you use.
509
510 If you need to instrument and trace <<python-application,Python
511 applications>> on openSUSE, you need to build and install
512 LTTng-UST{nbsp}{revision} from source and pass the
513 `--enable-python-agent` option to the `configure` script.
514 ====
515
516
517 [[buildroot]]
518 === Buildroot
519
520 To install LTTng{nbsp}{revision} on Buildroot{nbsp}2016.02,
521 Buildroot{nbsp}2016.05, or Buildroot{nbsp}2016.08:
522
523 . Launch the Buildroot configuration tool:
524 +
525 --
526 [role="term"]
527 ----
528 make menuconfig
529 ----
530 --
531
532 . In **Kernel**, check **Linux kernel**.
533 . In **Toolchain**, check **Enable WCHAR support**.
534 . In **Target packages**{nbsp}&#8594; **Debugging, profiling and benchmark**,
535 check **lttng-modules** and **lttng-tools**.
536 . In **Target packages**{nbsp}&#8594; **Libraries**{nbsp}&#8594;
537 **Other**, check **lttng-libust**.
538
539
540 [[oe-yocto]]
541 === OpenEmbedded and Yocto
542
543 LTTng{nbsp}{revision} recipes are available in the
544 http://layers.openembedded.org/layerindex/branch/master/layer/openembedded-core/[`openembedded-core`]
545 layer for Yocto Project{nbsp}2.1 _Krogoth_ under the following names:
546
547 * `lttng-tools`
548 * `lttng-modules`
549 * `lttng-ust`
550
551 With BitBake, the simplest way to include LTTng recipes in your target
552 image is to add them to `IMAGE_INSTALL_append` in path:{conf/local.conf}:
553
554 ----
555 IMAGE_INSTALL_append = " lttng-tools lttng-modules lttng-ust"
556 ----
557
558 If you use Hob:
559
560 . Select a machine and an image recipe.
561 . Click **Edit image recipe**.
562 . Under the **All recipes** tab, search for **lttng**.
563 . Check the desired LTTng recipes.
564
565 [IMPORTANT]
566 .Java and Python application instrumentation and tracing
567 ====
568 If you need to instrument and trace <<java-application,Java
569 applications>> on openSUSE, you need to build and install
570 LTTng-UST{nbsp}{revision} <<building-from-source,from source>> and pass
571 the `--enable-java-agent-jul`, `--enable-java-agent-log4j`, or
572 `--enable-java-agent-all` options to the `configure` script, depending
573 on which Java logging framework you use.
574
575 If you need to instrument and trace <<python-application,Python
576 applications>> on openSUSE, you need to build and install
577 LTTng-UST{nbsp}{revision} from source and pass the
578 `--enable-python-agent` option to the `configure` script.
579 ====
580
581
582 [[enterprise-distributions]]
583 === RHEL, SUSE, and other enterprise distributions
584
585 To install LTTng on enterprise Linux distributions, such as Red Hat
586 Enterprise Linux (RHEL) and SUSE Linux Enterprise Server (SUSE), please
587 see http://packages.efficios.com/[EfficiOS Enterprise Packages].
588
589
590 [[building-from-source]]
591 === Build from source
592
593 To build and install LTTng{nbsp}{revision} from source:
594
595 . Using your distribution's package manager, or from source, install
596 the following dependencies of LTTng-tools and LTTng-UST:
597 +
598 --
599 * https://sourceforge.net/projects/libuuid/[libuuid]
600 * http://directory.fsf.org/wiki/Popt[popt]
601 * http://liburcu.org/[Userspace RCU]
602 * http://www.xmlsoft.org/[libxml2]
603 --
604
605 . Download, build, and install the latest LTTng-modules{nbsp}{revision}:
606 +
607 --
608 [role="term"]
609 ----
610 cd $(mktemp -d) &&
611 wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.7.tar.bz2 &&
612 tar -xf lttng-modules-latest-2.7.tar.bz2 &&
613 cd lttng-modules-2.7.* &&
614 make &&
615 sudo make modules_install &&
616 sudo depmod -a
617 ----
618 --
619
620 . Download, build, and install the latest LTTng-UST{nbsp}{revision}:
621 +
622 --
623 [role="term"]
624 ----
625 cd $(mktemp -d) &&
626 wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.7.tar.bz2 &&
627 tar -xf lttng-ust-latest-2.7.tar.bz2 &&
628 cd lttng-ust-2.7.* &&
629 ./configure &&
630 make &&
631 sudo make install &&
632 sudo ldconfig
633 ----
634 --
635 +
636 --
637 [IMPORTANT]
638 .Java and Python application tracing
639 ====
640 If you need to instrument and trace <<java-application,Java
641 applications>>, pass the `--enable-java-agent-jul`,
642 `--enable-java-agent-log4j`, or `--enable-java-agent-all` options to the
643 `configure` script, depending on which Java logging framework you use.
644
645 If you need to instrument and trace <<python-application,Python
646 applications>>, pass the `--enable-python-agent` option to the
647 `configure` script. You can set the `PYTHON` environment variable to the
648 path to the Python interpreter for which to install the LTTng-UST Python
649 agent package.
650 ====
651 --
652 +
653 --
654 [NOTE]
655 ====
656 By default, LTTng-UST libraries are installed to
657 dir:{/usr/local/lib}, which is the de facto directory in which to
658 keep self-compiled and third-party libraries.
659
660 When <<building-tracepoint-providers-and-user-application,linking an
661 instrumented user application with `liblttng-ust`>>:
662
663 * Append `/usr/local/lib` to the env:LD_LIBRARY_PATH environment
664 variable.
665 * Pass the `-L/usr/local/lib` and `-Wl,-rpath,/usr/local/lib` options to
666 man:gcc(1), man:g++(1), or man:clang(1).
667 ====
668 --
669
670 . Download, build, and install the latest LTTng-tools{nbsp}{revision}:
671 +
672 --
673 [role="term"]
674 ----
675 cd $(mktemp -d) &&
676 wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.7.tar.bz2 &&
677 tar -xf lttng-tools-latest-2.7.tar.bz2 &&
678 cd lttng-tools-2.7.* &&
679 ./configure &&
680 make &&
681 sudo make install &&
682 sudo ldconfig
683 ----
684 --
685
686 TIP: The https://github.com/eepp/vlttng[vlttng tool] can do all the
687 previous steps automatically for a given version of LTTng and confine
688 the installed files in a specific directory. This can be useful to test
689 LTTng without installing it on your system.
690
691
692 [[getting-started]]
693 == Quick start
694
695 This is a short guide to get started quickly with LTTng kernel and user
696 space tracing.
697
698 Before you follow this guide, make sure to <<installing-lttng,install>>
699 LTTng.
700
701 This tutorial walks you through the steps to:
702
703 . <<tracing-the-linux-kernel,Trace the Linux kernel>>.
704 . <<tracing-your-own-user-application,Trace a user application>> written
705 in C.
706 . <<viewing-and-analyzing-your-traces,View and analyze the
707 recorded events>>.
708
709
710 [[tracing-the-linux-kernel]]
711 === Trace the Linux kernel
712
713 The following command lines start with cmd:sudo because you need root
714 privileges to trace the Linux kernel. You can avoid using cmd:sudo if
715 your Unix user is a member of the <<lttng-sessiond,tracing group>>.
716
717 . Create a <<tracing-session,tracing session>>:
718 +
719 --
720 [role="term"]
721 ----
722 sudo lttng create my-kernel-session
723 ----
724 --
725
726 . List the available kernel tracepoints and system calls:
727 +
728 --
729 [role="term"]
730 ----
731 lttng list --kernel
732 ----
733 --
734
735 . Create an <<event,event rule>> which matches the desired event names,
736 for example `sched_switch` and `sched_process_fork`:
737 +
738 --
739 [role="term"]
740 ----
741 sudo lttng enable-event --kernel sched_switch,sched_process_fork
742 ----
743 --
744 +
745 You can also create an event rule which _matches_ all the Linux kernel
746 tracepoints (this will generate a lot of data when tracing):
747 +
748 --
749 [role="term"]
750 ----
751 sudo lttng enable-event --kernel --all
752 ----
753 --
754
755 . Start tracing:
756 +
757 --
758 [role="term"]
759 ----
760 sudo lttng start
761 ----
762 --
763
764 . Do some operation on your system for a few seconds. For example,
765 load a website, or list the files of a directory.
766 . Stop tracing and destroy the tracing session:
767 +
768 --
769 [role="term"]
770 ----
771 sudo lttng stop
772 sudo lttng destroy
773 ----
774 --
775 +
776 The `destroy` command does not destroy the trace data; it only destroys
777 the state of the tracing session.
778
779 By default, LTTng saves the traces in
780 +$LTTNG_HOME/lttng-traces/__name__-__date__-__time__+,
781 where +__name__+ is the tracing session name. Note that the
782 env:LTTNG_HOME environment variable defaults to `$HOME` if not set.
783
784 See <<viewing-and-analyzing-your-traces,View and analyze the
785 recorded events>> to view the recorded events.
786
787
788 [[tracing-your-own-user-application]]
789 === Trace a user application
790
791 This section steps you through a simple example to trace a
792 _Hello world_ program written in C.
793
794 To create the traceable user application:
795
796 . Create the tracepoint provider header file, which defines the
797 tracepoints and the events they can generate:
798 +
799 --
800 [source,c]
801 .path:{hello-tp.h}
802 ----
803 #undef TRACEPOINT_PROVIDER
804 #define TRACEPOINT_PROVIDER hello_world
805
806 #undef TRACEPOINT_INCLUDE
807 #define TRACEPOINT_INCLUDE "./hello-tp.h"
808
809 #if !defined(_HELLO_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
810 #define _HELLO_TP_H
811
812 #include <lttng/tracepoint.h>
813
814 TRACEPOINT_EVENT(
815 hello_world,
816 my_first_tracepoint,
817 TP_ARGS(
818 int, my_integer_arg,
819 char*, my_string_arg
820 ),
821 TP_FIELDS(
822 ctf_string(my_string_field, my_string_arg)
823 ctf_integer(int, my_integer_field, my_integer_arg)
824 )
825 )
826
827 #endif /* _HELLO_TP_H */
828
829 #include <lttng/tracepoint-event.h>
830 ----
831 --
832
833 . Create the tracepoint provider package source file:
834 +
835 --
836 [source,c]
837 .path:{hello-tp.c}
838 ----
839 #define TRACEPOINT_CREATE_PROBES
840 #define TRACEPOINT_DEFINE
841
842 #include "hello-tp.h"
843 ----
844 --
845
846 . Build the tracepoint provider package:
847 +
848 --
849 [role="term"]
850 ----
851 gcc -c -I. hello-tp.c
852 ----
853 --
854
855 . Create the _Hello World_ application source file:
856 +
857 --
858 [source,c]
859 .path:{hello.c}
860 ----
861 #include <stdio.h>
862 #include "hello-tp.h"
863
864 int main(int argc, char *argv[])
865 {
866 int x;
867
868 puts("Hello, World!\nPress Enter to continue...");
869
870 /*
871 * The following getchar() call is only placed here for the purpose
872 * of this demonstration, to pause the application in order for
873 * you to have time to list its tracepoints. It is not
874 * needed otherwise.
875 */
876 getchar();
877
878 /*
879 * A tracepoint() call.
880 *
881 * Arguments, as defined in hello-tp.h:
882 *
883 * 1. Tracepoint provider name (required)
884 * 2. Tracepoint name (required)
885 * 3. my_integer_arg (first user-defined argument)
886 * 4. my_string_arg (second user-defined argument)
887 *
888 * Notice the tracepoint provider and tracepoint names are
889 * NOT strings: they are in fact parts of variables that the
890 * macros in hello-tp.h create.
891 */
892 tracepoint(hello_world, my_first_tracepoint, 23, "hi there!");
893
894 for (x = 0; x < argc; ++x) {
895 tracepoint(hello_world, my_first_tracepoint, x, argv[x]);
896 }
897
898 puts("Quitting now!");
899 tracepoint(hello_world, my_first_tracepoint, x * x, "x^2");
900
901 return 0;
902 }
903 ----
904 --
905
906 . Build the application:
907 +
908 --
909 [role="term"]
910 ----
911 gcc -c hello.c
912 ----
913 --
914
915 . Link the application with the tracepoint provider package,
916 `liblttng-ust`, and `libdl`:
917 +
918 --
919 [role="term"]
920 ----
921 gcc -o hello hello.o hello-tp.o -llttng-ust -ldl
922 ----
923 --
924
925 Here's the whole build process:
926
927 [role="img-100"]
928 .User space tracing tutorial's build steps.
929 image::ust-flow.png[]
930
931 To trace the user application:
932
933 . Run the application with a few arguments:
934 +
935 --
936 [role="term"]
937 ----
938 ./hello world and beyond
939 ----
940 --
941 +
942 You see:
943 +
944 --
945 ----
946 Hello, World!
947 Press Enter to continue...
948 ----
949 --
950
951 . Start an LTTng <<lttng-sessiond,session daemon>>:
952 +
953 --
954 [role="term"]
955 ----
956 lttng-sessiond --daemonize
957 ----
958 --
959 +
960 Note that a session daemon might already be running, for example as
961 a service that the distribution's service manager started.
962
963 . List the available user space tracepoints:
964 +
965 --
966 [role="term"]
967 ----
968 lttng list --userspace
969 ----
970 --
971 +
972 You see the `hello_world:my_first_tracepoint` tracepoint listed
973 under the `./hello` process.
974
975 . Create a <<tracing-session,tracing session>>:
976 +
977 --
978 [role="term"]
979 ----
980 lttng create my-user-space-session
981 ----
982 --
983
984 . Create an <<event,event rule>> which matches the
985 `hello_world:my_first_tracepoint` event name:
986 +
987 --
988 [role="term"]
989 ----
990 lttng enable-event --userspace hello_world:my_first_tracepoint
991 ----
992 --
993
994 . Start tracing:
995 +
996 --
997 [role="term"]
998 ----
999 lttng start
1000 ----
1001 --
1002
1003 . Go back to the running `hello` application and press Enter. The
1004 program executes all `tracepoint()` instrumentation points and exits.
1005 . Stop tracing and destroy the tracing session:
1006 +
1007 --
1008 [role="term"]
1009 ----
1010 sudo lttng stop
1011 sudo lttng destroy
1012 ----
1013 --
1014 +
1015 The `destroy` command does not destroy the trace data; it only destroys
1016 the state of the tracing session.
1017
1018 By default, LTTng saves the traces in
1019 +$LTTNG_HOME/lttng-traces/__name__-__date__-__time__+,
1020 where +__name__+ is the tracing session name. Note that the
1021 env:LTTNG_HOME environment variable defaults to `$HOME` if not set.
1022
1023 See <<viewing-and-analyzing-your-traces,View and analyze the
1024 recorded events>> to view the recorded events.
1025
1026
1027 [[viewing-and-analyzing-your-traces]]
1028 === View and analyze the recorded events
1029
1030 Once you have completed the <<tracing-the-linux-kernel,Trace the Linux
1031 kernel>> and <<tracing-your-own-user-application,Trace a user
1032 application>> tutorials, you can inspect the recorded events.
1033
1034 Many tools are available to read LTTng traces:
1035
1036 * **cmd:babeltrace** is a command-line utility which converts trace
1037 formats; it supports the format that LTTng produces, CTF, as well as a
1038 basic text output which can be ++grep++ed. The cmd:babeltrace command
1039 is part of the http://diamon.org/babeltrace[Babeltrace] project.
1040 * Babeltrace also includes
1041 **https://www.python.org/[Python] bindings** so
1042 that you can easily open and read an LTTng trace with your own script,
1043 benefiting from the power of Python.
1044 * http://tracecompass.org/[**Trace Compass**]
1045 is a graphical user interface for viewing and analyzing any type of
1046 logs or traces, including LTTng's.
1047 * https://github.com/lttng/lttng-analyses[**LTTng analyses**] is a
1048 project which includes many high-level analyses of LTTng kernel
1049 traces, like scheduling statistics, interrupt frequency distribution,
1050 top CPU usage, and more.
1051
1052 NOTE: This section assumes that the traces recorded during the previous
1053 tutorials were saved to their default location, in the
1054 dir:{$LTTNG_HOME/lttng-traces} directory. Note that the env:LTTNG_HOME
1055 environment variable defaults to `$HOME` if not set.
1056
1057
1058 [[viewing-and-analyzing-your-traces-bt]]
1059 ==== Use the cmd:babeltrace command-line tool
1060
1061 The simplest way to list all the recorded events of a trace is to pass
1062 its path to cmd:babeltrace with no options:
1063
1064 [role="term"]
1065 ----
1066 babeltrace ~/lttng-traces/my-user-space-session*
1067 ----
1068
1069 cmd:babeltrace finds all traces recursively within the given path and
1070 prints all their events, merging them in chronological order.
1071
1072 You can pipe the output of cmd:babeltrace into a tool like man:grep(1) for
1073 further filtering:
1074
1075 [role="term"]
1076 ----
1077 babeltrace ~/lttng-traces/my-kernel-session* | grep sys_
1078 ----
1079
1080 You can pipe the output of cmd:babeltrace into a tool like man:wc(1) to
1081 count the recorded events:
1082
1083 [role="term"]
1084 ----
1085 babeltrace ~/lttng-traces/my-kernel-session* | grep sys_read | wc --lines
1086 ----
1087
1088
1089 [[viewing-and-analyzing-your-traces-bt-python]]
1090 ==== Use the Babeltrace Python bindings
1091
1092 The <<viewing-and-analyzing-your-traces-bt,text output of cmd:babeltrace>>
1093 is useful to isolate events by simple matching using man:grep(1) and
1094 similar utilities. However, more elaborate filters, such as keeping only
1095 event records with a field value falling within a specific range, are
1096 not trivial to write using a shell. Moreover, reductions and even the
1097 most basic computations involving multiple event records are virtually
1098 impossible to implement.
1099
1100 Fortunately, Babeltrace ships with Python 3 bindings which makes it easy
1101 to read the event records of an LTTng trace sequentially and compute the
1102 desired information.
1103
1104 The following script accepts an LTTng Linux kernel trace path as its
1105 first argument and prints the short names of the top 5 running processes
1106 on CPU 0 during the whole trace:
1107
1108 [source,python]
1109 .path:{top5proc.py}
1110 ----
1111 from collections import Counter
1112 import babeltrace
1113 import sys
1114
1115
1116 def top5proc():
1117 if len(sys.argv) != 2:
1118 msg = 'Usage: python3 {} TRACEPATH'.format(sys.argv[0])
1119 print(msg, file=sys.stderr)
1120 return False
1121
1122 # A trace collection contains one or more traces
1123 col = babeltrace.TraceCollection()
1124
1125 # Add the trace provided by the user (LTTng traces always have
1126 # the 'ctf' format)
1127 if col.add_trace(sys.argv[1], 'ctf') is None:
1128 raise RuntimeError('Cannot add trace')
1129
1130 # This counter dict contains execution times:
1131 #
1132 # task command name -> total execution time (ns)
1133 exec_times = Counter()
1134
1135 # This contains the last `sched_switch` timestamp
1136 last_ts = None
1137
1138 # Iterate on events
1139 for event in col.events:
1140 # Keep only `sched_switch` events
1141 if event.name != 'sched_switch':
1142 continue
1143
1144 # Keep only events which happened on CPU 0
1145 if event['cpu_id'] != 0:
1146 continue
1147
1148 # Event timestamp
1149 cur_ts = event.timestamp
1150
1151 if last_ts is None:
1152 # We start here
1153 last_ts = cur_ts
1154
1155 # Previous task command (short) name
1156 prev_comm = event['prev_comm']
1157
1158 # Initialize entry in our dict if not yet done
1159 if prev_comm not in exec_times:
1160 exec_times[prev_comm] = 0
1161
1162 # Compute previous command execution time
1163 diff = cur_ts - last_ts
1164
1165 # Update execution time of this command
1166 exec_times[prev_comm] += diff
1167
1168 # Update last timestamp
1169 last_ts = cur_ts
1170
1171 # Display top 5
1172 for name, ns in exec_times.most_common(5):
1173 s = ns / 1000000000
1174 print('{:20}{} s'.format(name, s))
1175
1176 return True
1177
1178
1179 if __name__ == '__main__':
1180 sys.exit(0 if top5proc() else 1)
1181 ----
1182
1183 Run this script:
1184
1185 [role="term"]
1186 ----
1187 python3 top5proc.py ~/lttng-traces/my-kernel-session*/kernel
1188 ----
1189
1190 Output example:
1191
1192 ----
1193 swapper/0 48.607245889 s
1194 chromium 7.192738188 s
1195 pavucontrol 0.709894415 s
1196 Compositor 0.660867933 s
1197 Xorg.bin 0.616753786 s
1198 ----
1199
1200 Note that `swapper/0` is the "idle" process of CPU 0 on Linux; since we
1201 weren't using the CPU that much when tracing, its first position in the
1202 list makes sense.
1203
1204
1205 [[core-concepts]]
1206 == [[understanding-lttng]]Core concepts
1207
1208 From a user's perspective, the LTTng system is built on a few concepts,
1209 or objects, on which the <<lttng-cli,cmd:lttng command-line tool>>
1210 operates by sending commands to the <<lttng-sessiond,session daemon>>.
1211 Understanding how those objects relate to eachother is key in mastering
1212 the toolkit.
1213
1214 The core concepts are:
1215
1216 * <<tracing-session,Tracing session>>
1217 * <<domain,Tracing domain>>
1218 * <<channel,Channel and ring buffer>>
1219 * <<"event","Instrumentation point, event rule, event, and event record">>
1220
1221
1222 [[tracing-session]]
1223 === Tracing session
1224
1225 A _tracing session_ is a stateful dialogue between you and
1226 a <<lttng-sessiond,session daemon>>. You can
1227 <<creating-destroying-tracing-sessions,create a new tracing
1228 session>> with the `lttng create` command.
1229
1230 Anything that you do when you control LTTng tracers happens within a
1231 tracing session. In particular, a tracing session:
1232
1233 * Has its own name.
1234 * Has its own set of trace files.
1235 * Has its own state of activity (started or stopped).
1236 * Has its own <<tracing-session-mode,mode>> (local, network streaming,
1237 snapshot, or live).
1238 * Has its own <<channel,channels>> which have their own
1239 <<event,event rules>>.
1240
1241 [role="img-100"]
1242 .A _tracing session_ contains <<channel,channels>> that are members of <<domain,tracing domains>> and contain <<event,event rules>>.
1243 image::concepts.png[]
1244
1245 Those attributes and objects are completely isolated between different
1246 tracing sessions.
1247
1248 A tracing session is analogous to a cash machine session:
1249 the operations you do on the banking system through the cash machine do
1250 not alter the data of other users of the same system. In the case of
1251 the cash machine, a session lasts as long as your bank card is inside.
1252 In the case of LTTng, a tracing session lasts from the `lttng create`
1253 command to the `lttng destroy` command.
1254
1255 [role="img-100"]
1256 .Each Unix user has its own set of tracing sessions.
1257 image::many-sessions.png[]
1258
1259
1260 [[tracing-session-mode]]
1261 ==== Tracing session mode
1262
1263 LTTng can send the generated trace data to different locations. The
1264 _tracing session mode_ dictates where to send it. The following modes
1265 are available in LTTng{nbsp}{revision}:
1266
1267 Local mode::
1268 LTTng writes the traces to the file system of the machine being traced
1269 (target system).
1270
1271 Network streaming mode::
1272 LTTng sends the traces over the network to a
1273 <<lttng-relayd,relay daemon>> running on a remote system.
1274
1275 Snapshot mode::
1276 LTTng does not write the traces by default. Instead, you can request
1277 LTTng to <<taking-a-snapshot,take a snapshot>>, that is, a copy of the
1278 current tracing buffers, and to write it to the target's file system
1279 or to send it over the network to a <<lttng-relayd,relay daemon>>
1280 running on a remote system.
1281
1282 Live mode::
1283 This mode is similar to the network streaming mode, but a live
1284 trace viewer can connect to the distant relay daemon to
1285 <<lttng-live,view event records as LTTng generates them>> by
1286 the tracers.
1287
1288
1289 [[domain]]
1290 === Tracing domain
1291
1292 A _tracing domain_ is a namespace for event sources. A tracing domain
1293 has its own properties and features.
1294
1295 There are currently five available tracing domains:
1296
1297 * Linux kernel
1298 * User space
1299 * `java.util.logging` (JUL)
1300 * log4j
1301 * Python
1302
1303 You must specify a tracing domain when using some commands to avoid
1304 ambiguity. For example, since all the domains support named tracepoints
1305 as event sources (instrumentation points that you manually insert in the
1306 source code), you need to specify a tracing domain when
1307 <<enabling-disabling-events,creating an event rule>> because all the
1308 tracing domains could have tracepoints with the same names.
1309
1310 Some features are reserved to specific tracing domains. Dynamic function
1311 entry and return instrumentation points, for example, are currently only
1312 supported in the Linux kernel tracing domain, but support for other
1313 tracing domains could be added in the future.
1314
1315 You can create <<channel,channels>> in the Linux kernel and user space
1316 tracing domains. The other tracing domains have a single default
1317 channel.
1318
1319
1320 [[channel]]
1321 === Channel and ring buffer
1322
1323 A _channel_ is an object which is responsible for a set of ring buffers.
1324 Each ring buffer is divided into multiple sub-buffers. When an LTTng
1325 tracer emits an event, it can record it to one or more
1326 sub-buffers. The attributes of a channel determine what to do when
1327 there's no space left for a new event record because all sub-buffers
1328 are full, where to send a full sub-buffer, and other behaviours.
1329
1330 A channel is always associated to a <<domain,tracing domain>>. The
1331 `java.util.logging` (JUL), log4j, and Python tracing domains each have
1332 a default channel which you cannot configure.
1333
1334 A channel also owns <<event,event rules>>. When an LTTng tracer emits
1335 an event, it records it to the sub-buffers of all
1336 the enabled channels with a satisfied event rule, as long as those
1337 channels are part of active <<tracing-session,tracing sessions>>.
1338
1339
1340 [[channel-buffering-schemes]]
1341 ==== Per-user vs. per-process buffering schemes
1342
1343 A channel has at least one ring buffer _per CPU_. LTTng always
1344 records an event to the ring buffer associated to the CPU on which it
1345 occurred.
1346
1347 Two _buffering schemes_ are available when you
1348 <<enabling-disabling-channels,create a channel>> in the
1349 user space <<domain,tracing domain>>:
1350
1351 Per-user buffering::
1352 Allocate one set of ring buffers--one per CPU--shared by all the
1353 instrumented processes of each Unix user.
1354 +
1355 --
1356 [role="img-100"]
1357 .Per-user buffering scheme.
1358 image::per-user-buffering.png[]
1359 --
1360
1361 Per-process buffering::
1362 Allocate one set of ring buffers--one per CPU--for each
1363 instrumented process.
1364 +
1365 --
1366 [role="img-100"]
1367 .Per-process buffering scheme.
1368 image::per-process-buffering.png[]
1369 --
1370 +
1371 The per-process buffering scheme tends to consume more memory than the
1372 per-user option because systems generally have more instrumented
1373 processes than Unix users running instrumented processes. However, the
1374 per-process buffering scheme ensures that one process having a high
1375 event throughput won't fill all the shared sub-buffers of the same
1376 user, only its own.
1377
1378 The Linux kernel tracing domain has only one available buffering scheme
1379 which is to allocate a single set of ring buffers for the whole system.
1380 This scheme is similar to the per-user option, but with a single, global
1381 user "running" the kernel.
1382
1383
1384 [[channel-overwrite-mode-vs-discard-mode]]
1385 ==== Overwrite vs. discard event loss modes
1386
1387 When an event occurs, LTTng records it to a specific sub-buffer (yellow
1388 arc in the following animation) of a specific channel's ring buffer.
1389 When there's no space left in a sub-buffer, the tracer marks it as
1390 consumable (red) and another, empty sub-buffer starts receiving the
1391 following event records. A <<lttng-consumerd,consumer daemon>>
1392 eventually consumes the marked sub-buffer (returns to white).
1393
1394 [NOTE]
1395 [role="docsvg-channel-subbuf-anim"]
1396 ====
1397 {note-no-anim}
1398 ====
1399
1400 In an ideal world, sub-buffers are consumed faster than they are filled,
1401 as is the case in the previous animation. In the real world,
1402 however, all sub-buffers can be full at some point, leaving no space to
1403 record the following events.
1404
1405 By design, LTTng is a _non-blocking_ tracer: when no empty sub-buffer is
1406 available, it is acceptable to lose event records when the alternative
1407 would be to cause substantial delays in the instrumented application's
1408 execution. LTTng privileges performance over integrity; it aims at
1409 perturbing the traced system as little as possible in order to make
1410 tracing of subtle race conditions and rare interrupt cascades possible.
1411
1412 When it comes to losing event records because no empty sub-buffer is
1413 available, the channel's _event loss mode_ determines what to do. The
1414 available event loss modes are:
1415
1416 Discard mode::
1417 Drop the newest event records until a the tracer
1418 releases a sub-buffer.
1419
1420 Overwrite mode::
1421 Clear the sub-buffer containing the oldest event records and start
1422 writing the newest event records there.
1423 +
1424 This mode is sometimes called _flight recorder mode_ because it's
1425 similar to a
1426 https://en.wikipedia.org/wiki/Flight_recorder[flight recorder]:
1427 always keep a fixed amount of the latest data.
1428
1429 Which mechanism you should choose depends on your context: prioritize
1430 the newest or the oldest event records in the ring buffer?
1431
1432 Beware that, in overwrite mode, the tracer abandons a whole sub-buffer
1433 as soon as a there's no space left for a new event record, whereas in
1434 discard mode, the tracer only discards the event record that doesn't
1435 fit.
1436
1437 In discard mode, LTTng increments a count of lost event records when
1438 an event record is lost and saves this count to the trace. In
1439 overwrite mode, LTTng keeps no information when it overwrites a
1440 sub-buffer before consuming it.
1441
1442 There are a few ways to decrease your probability of losing event
1443 records.
1444 <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>> shows
1445 how you can fine-une the sub-buffer count and size of a channel to
1446 virtually stop losing event records, though at the cost of greater
1447 memory usage.
1448
1449
1450 [[channel-subbuf-size-vs-subbuf-count]]
1451 ==== Sub-buffer count and size
1452
1453 When you <<enabling-disabling-channels,create a channel>>, you can
1454 set its number of sub-buffers and their size.
1455
1456 Note that there is noticeable CPU overhead introduced when
1457 switching sub-buffers (marking a full one as consumable and switching
1458 to an empty one for the following events to be recorded). Knowing this,
1459 the following list presents a few practical situations along with how
1460 to configure the sub-buffer count and size for them:
1461
1462 * **High event throughput**: In general, prefer bigger sub-buffers to
1463 lower the risk of losing event records.
1464 +
1465 Having bigger sub-buffers also ensures a lower sub-buffer switching
1466 frequency.
1467 +
1468 The number of sub-buffers is only meaningful if you create the channel
1469 in overwrite mode: in this case, if a sub-buffer overwrite happens, the
1470 other sub-buffers are left unaltered.
1471
1472 * **Low event throughput**: In general, prefer smaller sub-buffers
1473 since the risk of losing event records is low.
1474 +
1475 Because events occur less frequently, the sub-buffer switching frequency
1476 should remain low and thus the tracer's overhead should not be a
1477 problem.
1478
1479 * **Low memory system**: If your target system has a low memory
1480 limit, prefer fewer first, then smaller sub-buffers.
1481 +
1482 Even if the system is limited in memory, you want to keep the
1483 sub-buffers as big as possible to avoid a high sub-buffer switching
1484 frequency.
1485
1486 Note that LTTng uses http://diamon.org/ctf/[CTF] as its trace format,
1487 which means event data is very compact. For example, the average
1488 LTTng kernel event record weights about 32{nbsp}bytes. Thus, a
1489 sub-buffer size of 1{nbsp}MiB is considered big.
1490
1491 The previous situations highlight the major trade-off between a few big
1492 sub-buffers and more, smaller sub-buffers: sub-buffer switching
1493 frequency vs. how much data is lost in overwrite mode. Assuming a
1494 constant event throughput and using the overwrite mode, the two
1495 following configurations have the same ring buffer total size:
1496
1497 [NOTE]
1498 [role="docsvg-channel-subbuf-size-vs-count-anim"]
1499 ====
1500 {note-no-anim}
1501 ====
1502
1503 * **2 sub-buffers of 4{nbsp}MiB each**: Expect a very low sub-buffer
1504 switching frequency, but if a sub-buffer overwrite happens, half of
1505 the event records so far (4{nbsp}MiB) are definitely lost.
1506 * **8 sub-buffers of 1{nbsp}MiB each**: Expect 4{nbsp}times the tracer's
1507 overhead as the previous configuration, but if a sub-buffer
1508 overwrite happens, only the eighth of event records so far are
1509 definitely lost.
1510
1511 In discard mode, the sub-buffers count parameter is pointless: use two
1512 sub-buffers and set their size according to the requirements of your
1513 situation.
1514
1515
1516 [[channel-switch-timer]]
1517 ==== Switch timer period
1518
1519 The _switch timer period_ is an important configurable attribute of
1520 a channel to ensure periodic sub-buffer flushing.
1521
1522 When the _switch timer_ expires, a sub-buffer switch happens. You can
1523 set the switch timer period attribute when you
1524 <<enabling-disabling-channels,create a channel>> to ensure that event
1525 data is consumed and committed to trace files or to a distant relay
1526 daemon periodically in case of a low event throughput.
1527
1528 [NOTE]
1529 [role="docsvg-channel-switch-timer"]
1530 ====
1531 {note-no-anim}
1532 ====
1533
1534 This attribute is also convenient when you use big sub-buffers to cope
1535 with a sporadic high event throughput, even if the throughput is
1536 normally low.
1537
1538
1539 [[channel-read-timer]]
1540 ==== Read timer period
1541
1542 By default, the LTTng tracers use a notification mechanism to signal a
1543 full sub-buffer so that a consumer daemon can consume it. When such
1544 notifications must be avoided, for example in real-time applications,
1545 you can use the channel's _read timer_ instead. When the read timer
1546 fires, the <<lttng-consumerd,consumer daemon>> checks for full,
1547 consumable sub-buffers.
1548
1549
1550 [[tracefile-rotation]]
1551 ==== Trace file count and size
1552
1553 By default, trace files can grow as large as needed. You can set the
1554 maximum size of each trace file that a channel writes when you
1555 <<enabling-disabling-channels,create a channel>>. When the size of
1556 a trace file reaches the channel's fixed maximum size, LTTng creates
1557 another file to contain the next event records. LTTng appends a file
1558 count to each trace file name in this case.
1559
1560 If you set the trace file size attribute when you create a channel, the
1561 maximum number of trace files that LTTng creates is _unlimited_ by
1562 default. To limit them, you can also set a maximum number of trace
1563 files. When the number of trace files reaches the channel's fixed
1564 maximum count, the oldest trace file is overwritten. This mechanism is
1565 called _trace file rotation_.
1566
1567
1568 [[event]]
1569 === Instrumentation point, event rule, event, and event record
1570
1571 An _event rule_ is a set of conditions which must be **all** satisfied
1572 for LTTng to record an occuring event.
1573
1574 You set the conditions when you <<enabling-disabling-events,create
1575 an event rule>>.
1576
1577 You always attach an event rule to <<channel,channel>> when you create
1578 it.
1579
1580 When an event passes the conditions of an event rule, LTTng records it
1581 in one of the attached channel's sub-buffers.
1582
1583 The available conditions, as of LTTng{nbsp}{revision}, are:
1584
1585 * The event rule _is enabled_.
1586 * The instrumentation point's type _is{nbsp}T_.
1587 * The instrumentation point's name (sometimes called _event name_)
1588 _matches{nbsp}N_, but _is not{nbsp}E_.
1589 * The instrumentation point's log level _is as severe as{nbsp}L_, or
1590 _is exactly{nbsp}L_.
1591 * The fields of the event's payload _satisfy_ a filter
1592 expression{nbsp}__F__.
1593
1594 As you can see, all the conditions but the dynamic filter are related to
1595 the event rule's status or to the instrumentation point, not to the
1596 occurring events. This is why, without a filter, checking if an event
1597 passes an event rule is not a dynamic task: when you create or modify an
1598 event rule, all the tracers of its tracing domain enable or disable the
1599 instrumentation points themselves once. This is possible because the
1600 attributes of an instrumentation point (type, name, and log level) are
1601 defined statically. In other words, without a dynamic filter, the tracer
1602 _does not evaluate_ the arguments of an instrumentation point unless it
1603 matches an enabled event rule.
1604
1605 Note that, for LTTng to record an event, the <<channel,channel>> to
1606 which a matching event rule is attached must also be enabled, and the
1607 tracing session owning this channel must be active.
1608
1609 [role="img-100"]
1610 .Logical path from an instrumentation point to an event record.
1611 image::event-rule.png[]
1612
1613 .Event, event record, or event rule?
1614 ****
1615 With so many similar terms, it's easy to get confused.
1616
1617 An **event** is the consequence of the execution of an _instrumentation
1618 point_, like a tracepoint that you manually place in some source code,
1619 or a Linux kernel KProbe. An event is said to _occur_ at a specific
1620 time. Different actions can be taken upon the occurance of an event,
1621 like record the event's payload to a buffer.
1622
1623 An **event record** is the representation of an event in a sub-buffer. A
1624 tracer is responsible for capturing the payload of an event, current
1625 context variables, the event's ID, and the event's timestamp. LTTng
1626 can append this sub-buffer to a trace file.
1627
1628 An **event rule** is a set of conditions which must all be satisfied for
1629 LTTng to record an occuring event. Events still occur without
1630 satisfying event rules, but LTTng does not record them.
1631 ****
1632
1633
1634 [[plumbing]]
1635 == Components of noch:{LTTng}
1636
1637 The second _T_ in _LTTng_ stands for _toolkit_: it would be wrong
1638 to call LTTng a simple _tool_ since it is composed of multiple
1639 interacting components. This section describes those components,
1640 explains their respective roles, and shows how they connect together to
1641 form the LTTng ecosystem.
1642
1643 The following diagram shows how the most important components of LTTng
1644 interact with user applications, the Linux kernel, and you:
1645
1646 [role="img-100"]
1647 .Control and trace data paths between LTTng components.
1648 image::plumbing.png[]
1649
1650 The LTTng project incorporates:
1651
1652 * **LTTng-tools**: Libraries and command-line interface to
1653 control tracing sessions.
1654 ** <<lttng-sessiond,Session daemon>> (man:lttng-sessiond(8)).
1655 ** <<lttng-consumerd,Consumer daemon>> (man:lttng-consumerd(8)).
1656 ** <<lttng-relayd,Relay daemon>> (man:lttng-relayd(8)).
1657 ** <<liblttng-ctl-lttng,Tracing control library>> (`liblttng-ctl`).
1658 ** <<lttng-cli,Tracing control command-line tool>> (man:lttng(1)).
1659 * **LTTng-UST**: Libraries and Java/Python packages to trace user
1660 applications.
1661 ** <<lttng-ust,User space tracing library>> (`liblttng-ust`) and its
1662 headers to instrument and trace any native user application.
1663 ** <<prebuilt-ust-helpers,Preloadable user space tracing helpers>>:
1664 *** `liblttng-ust-libc-wrapper`
1665 *** `liblttng-ust-pthread-wrapper`
1666 *** `liblttng-ust-cyg-profile`
1667 *** `liblttng-ust-cyg-profile-fast`
1668 *** `liblttng-ust-dl`
1669 ** User space tracepoint provider source files generator command-line
1670 tool (man:lttng-gen-tp(1)).
1671 ** <<lttng-ust-agents,LTTng-UST Java agent>> to instrument and trace
1672 Java applications using `java.util.logging` or
1673 Apache log4j 1.2 logging.
1674 ** <<lttng-ust-agents,LTTng-UST Python agent>> to instrument
1675 Python applications using the standard `logging` package.
1676 * **LTTng-modules**: <<lttng-modules,Linux kernel modules>> to trace
1677 the kernel.
1678 ** LTTng kernel tracer module.
1679 ** Tracing ring buffer kernel modules.
1680 ** Probe kernel modules.
1681 ** LTTng logger kernel module.
1682
1683
1684 [[lttng-cli]]
1685 === Tracing control command-line interface
1686
1687 [role="img-100"]
1688 .The tracing control command-line interface.
1689 image::plumbing-lttng-cli.png[]
1690
1691 The _man:lttng(1) command-line tool_ is the standard user interface to
1692 control LTTng <<tracing-session,tracing sessions>>. The cmd:lttng tool
1693 is part of LTTng-tools.
1694
1695 The cmd:lttng tool is linked with
1696 <<liblttng-ctl-lttng,`liblttng-ctl`>> to communicate with
1697 one or more <<lttng-sessiond,session daemons>> behind the scenes.
1698
1699 The cmd:lttng tool has a Git-like interface:
1700
1701 [role="term"]
1702 ----
1703 lttng <general options> <command> <command options>
1704 ----
1705
1706 The <<controlling-tracing,Tracing control>> section explores the
1707 available features of LTTng using the cmd:lttng tool.
1708
1709
1710 [[liblttng-ctl-lttng]]
1711 === Tracing control library
1712
1713 [role="img-100"]
1714 .The tracing control library.
1715 image::plumbing-liblttng-ctl.png[]
1716
1717 The _LTTng control library_, `liblttng-ctl`, is used to communicate
1718 with a <<lttng-sessiond,session daemon>> using a C API that hides the
1719 underlying protocol's details. `liblttng-ctl` is part of LTTng-tools.
1720
1721 The <<lttng-cli,cmd:lttng command-line tool>>
1722 is linked with `liblttng-ctl`.
1723
1724 You can use `liblttng-ctl` in C or $$C++$$ source code by including its
1725 "master" header:
1726
1727 [source,c]
1728 ----
1729 #include <lttng/lttng.h>
1730 ----
1731
1732 Some objects are referenced by name (C string), such as tracing
1733 sessions, but most of them require to create a handle first using
1734 `lttng_create_handle()`.
1735
1736 The best available developer documentation for `liblttng-ctl` is, as of
1737 LTTng{nbsp}{revision}, its installed header files. Every function and
1738 structure is thoroughly documented.
1739
1740
1741 [[lttng-ust]]
1742 === User space tracing library
1743
1744 [role="img-100"]
1745 .The user space tracing library.
1746 image::plumbing-liblttng-ust.png[]
1747
1748 The _user space tracing library_, `liblttng-ust` (see man:lttng-ust(3)),
1749 is the LTTng user space tracer. It receives commands from a
1750 <<lttng-sessiond,session daemon>>, for example to
1751 enable and disable specific instrumentation points, and writes event
1752 records to ring buffers shared with a
1753 <<lttng-consumerd,consumer daemon>>.
1754 `liblttng-ust` is part of LTTng-UST.
1755
1756 Public C header files are installed beside `liblttng-ust` to
1757 instrument any <<c-application,C or $$C++$$ application>>.
1758
1759 <<lttng-ust-agents,LTTng-UST agents>>, which are regular Java and Python
1760 packages, use their own library providing tracepoints which is
1761 linked with `liblttng-ust`.
1762
1763 An application or library does not have to initialize `liblttng-ust`
1764 manually: its constructor does the necessary tasks to properly register
1765 to a session daemon. The initialization phase also enables the
1766 instrumentation points matching the <<event,event rules>> that you
1767 already created.
1768
1769
1770 [[lttng-ust-agents]]
1771 === User space tracing agents
1772
1773 [role="img-100"]
1774 .The user space tracing agents.
1775 image::plumbing-lttng-ust-agents.png[]
1776
1777 The _LTTng-UST Java and Python agents_ are regular Java and Python
1778 packages which add LTTng tracing capabilities to the
1779 native logging frameworks. The LTTng-UST agents are part of LTTng-UST.
1780
1781 In the case of Java, the
1782 https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[`java.util.logging`
1783 core logging facilities] and
1784 https://logging.apache.org/log4j/1.2/[Apache log4j 1.2] are supported.
1785 Note that Apache Log4{nbsp}2 is not supported.
1786
1787 In the case of Python, the standard
1788 https://docs.python.org/3/library/logging.html[`logging`] package
1789 is supported. Both Python 2 and Python 3 modules can import the
1790 LTTng-UST Python agent package.
1791
1792 The applications using the LTTng-UST agents are in the
1793 `java.util.logging` (JUL),
1794 log4j, and Python <<domain,tracing domains>>.
1795
1796 Both agents use the same mechanism to trace the log statements. When an
1797 agent is initialized, it creates a log handler that attaches to the root
1798 logger. The agent also registers to a <<lttng-sessiond,session daemon>>.
1799 When the application executes a log statement, it is passed to the
1800 agent's log handler by the root logger. The agent's log handler calls a
1801 native function in a tracepoint provider package shared library linked
1802 with <<lttng-ust,`liblttng-ust`>>, passing the formatted log message and
1803 other fields, like its logger name and its log level. This native
1804 function contains a user space instrumentation point, hence tracing the
1805 log statement.
1806
1807 The log level condition of an
1808 <<event,event rule>> is considered when tracing
1809 a Java or a Python application, and it's compatible with the standard
1810 JUL, log4j, and Python log levels.
1811
1812
1813 [[lttng-modules]]
1814 === LTTng kernel modules
1815
1816 [role="img-100"]
1817 .The LTTng kernel modules.
1818 image::plumbing-lttng-modules.png[]
1819
1820 The _LTTng kernel modules_ are a set of Linux kernel modules
1821 which implement the kernel tracer of the LTTng project. The LTTng
1822 kernel modules are part of LTTng-modules.
1823
1824 The LTTng kernel modules include:
1825
1826 * A set of _probe_ modules.
1827 +
1828 Each module attaches to a specific subsystem
1829 of the Linux kernel using its tracepoint instrument points. There are
1830 also modules to attach to the entry and return points of the Linux
1831 system call functions.
1832
1833 * _Ring buffer_ modules.
1834 +
1835 A ring buffer implementation is provided as kernel modules. The LTTng
1836 kernel tracer writes to the ring buffer; a
1837 <<lttng-consumerd,consumer daemon>> reads from the ring buffer.
1838
1839 * The _LTTng kernel tracer_ module.
1840 * The _LTTng logger_ module.
1841 +
1842 The LTTng logger module implements the special path:{/proc/lttng-logger}
1843 file so that any executable can generate LTTng events by opening and
1844 writing to this file.
1845 +
1846 See <<proc-lttng-logger-abi,LTTng logger>>.
1847
1848 Generally, you do not have to load the LTTng kernel modules manually
1849 (using man:modprobe(8), for example): a root <<lttng-sessiond,session
1850 daemon>> loads the necessary modules when starting. If you have extra
1851 probe modules, you can specify to load them to the session daemon on
1852 the command line.
1853
1854 The LTTng kernel modules are installed in
1855 +/usr/lib/modules/__release__/extra+ by default, where +__release__+ is
1856 the kernel release (see `uname --kernel-release`).
1857
1858
1859 [[lttng-sessiond]]
1860 === Session daemon
1861
1862 [role="img-100"]
1863 .The session daemon.
1864 image::plumbing-sessiond.png[]
1865
1866 The _session daemon_, man:lttng-sessiond(8), is a daemon responsible for
1867 managing tracing sessions and for controlling the various components of
1868 LTTng. The session daemon is part of LTTng-tools.
1869
1870 The session daemon sends control requests to and receives control
1871 responses from:
1872
1873 * The <<lttng-ust,user space tracing library>>.
1874 +
1875 Any instance of the user space tracing library first registers to
1876 a session daemon. Then, the session daemon can send requests to
1877 this instance, such as:
1878 +
1879 --
1880 ** Get the list of tracepoints.
1881 ** Share an <<event,event rule>> so that the user space tracing library
1882 can enable or disable tracepoints. Amongst the possible conditions
1883 of an event rule is a filter expression which `liblttng-ust` evalutes
1884 when an event occurs.
1885 ** Share <<channel,channel>> attributes and ring buffer locations.
1886 --
1887 +
1888 The session daemon and the user space tracing library use a Unix
1889 domain socket for their communication.
1890
1891 * The <<lttng-ust-agents,user space tracing agents>>.
1892 +
1893 Any instance of a user space tracing agent first registers to
1894 a session daemon. Then, the session daemon can send requests to
1895 this instance, such as:
1896 +
1897 --
1898 ** Get the list of loggers.
1899 ** Enable or disable a specific logger.
1900 --
1901 +
1902 The session daemon and the user space tracing agent use a TCP connection
1903 for their communication.
1904
1905 * The <<lttng-modules,LTTng kernel tracer>>.
1906 * The <<lttng-consumerd,consumer daemon>>.
1907 +
1908 The session daemon sends requests to the consumer daemon to instruct
1909 it where to send the trace data streams, amongst other information.
1910
1911 * The <<lttng-relayd,relay daemon>>.
1912
1913 The session daemon receives commands from the
1914 <<liblttng-ctl-lttng,tracing control library>>.
1915
1916 The root session daemon loads the appropriate
1917 <<lttng-modules,LTTng kernel modules>> on startup. It also spawns
1918 a <<lttng-consumerd,consumer daemon>> as soon as you create
1919 an <<event,event rule>>.
1920
1921 The session daemon does not send and receive trace data: this is the
1922 role of the <<lttng-consumerd,consumer daemon>> and
1923 <<lttng-relayd,relay daemon>>. It does, however, generate the
1924 http://diamon.org/ctf/[CTF] metadata stream.
1925
1926 Each Unix user can have its own session daemon instance. The
1927 tracing sessions managed by different session daemons are completely
1928 independent.
1929
1930 The root user's session daemon is the only one which is
1931 allowed to control the LTTng kernel tracer, and its spawned consumer
1932 daemon is the only one which is allowed to consume trace data from the
1933 LTTng kernel tracer. Note, however, that any Unix user which is a member
1934 of the <<tracing-group,tracing group>> is allowed
1935 to create <<channel,channels>> in the
1936 Linux kernel <<domain,tracing domain>>, and thus to trace the Linux
1937 kernel.
1938
1939 The <<lttng-cli,cmd:lttng command-line tool>> automatically starts a
1940 session daemon when using its `create` command if none is currently
1941 running. You can also start the session daemon manually.
1942
1943
1944 [[lttng-consumerd]]
1945 === Consumer daemon
1946
1947 [role="img-100"]
1948 .The consumer daemon.
1949 image::plumbing-consumerd.png[]
1950
1951 The _consumer daemon_, man:lttng-consumerd(8), is a daemon which shares
1952 ring buffers with user applications or with the LTTng kernel modules to
1953 collect trace data and send it to some location (on disk or to a
1954 <<lttng-relayd,relay daemon>> over the network). The consumer daemon
1955 is part of LTTng-tools.
1956
1957 You do not start a consumer daemon manually: a consumer daemon is always
1958 spawned by a <<lttng-sessiond,session daemon>> as soon as you create an
1959 <<event,event rule>>, that is, before you start tracing. When you kill
1960 its owner session daemon, the consumer daemon also exits because it is
1961 the session daemon's child process. Command-line options of
1962 man:lttng-sessiond(8) target the consumer daemon process.
1963
1964 There are up to two running consumer daemons per Unix user, whereas only
1965 one session daemon can run per user. This is because each process can be
1966 either 32-bit or 64-bit: if the target system runs a mixture of 32-bit
1967 and 64-bit processes, it is more efficient to have separate
1968 corresponding 32-bit and 64-bit consumer daemons. The root user is an
1969 exception: it can have up to _three_ running consumer daemons: 32-bit
1970 and 64-bit instances for its user applications, and one more
1971 reserved for collecting kernel trace data.
1972
1973
1974 [[lttng-relayd]]
1975 === Relay daemon
1976
1977 [role="img-100"]
1978 .The relay daemon.
1979 image::plumbing-relayd.png[]
1980
1981 The _relay daemon_, man:lttng-relayd(8), is a daemon acting as a bridge
1982 between remote session and consumer daemons, local trace files, and a
1983 remote live trace viewer. The relay daemon is part of LTTng-tools.
1984
1985 The main purpose of the relay daemon is to implement a receiver of
1986 <<sending-trace-data-over-the-network,trace data over the network>>.
1987 This is useful when the target system does not have much file system
1988 space to record trace files locally.
1989
1990 The relay daemon is also a server to which a
1991 <<lttng-live,live trace viewer>> can
1992 connect. The live trace viewer sends requests to the relay daemon to
1993 receive trace data as the target system emits events. The
1994 communication protocol is named _LTTng live_; it is used over TCP
1995 connections.
1996
1997 Note that you can start the relay daemon on the target system directly.
1998 This is the setup of choice when the use case is to view events as
1999 the target system emits them without the need of a remote system.
2000
2001
2002 [[instrumenting]]
2003 == [[using-lttng]]Instrumentation
2004
2005 There are many examples of tracing and monitoring in our everyday life:
2006
2007 * You have access to real-time and historical weather reports and
2008 forecasts thanks to weather stations installed around the country.
2009 * You know your heart is safe thanks to an electrocardiogram.
2010 * You make sure not to drive your car too fast and to have enough fuel
2011 to reach your destination thanks to gauges visible on your dashboard.
2012
2013 All the previous examples have something in common: they rely on
2014 **instruments**. Without the electrodes attached to the surface of your
2015 body's skin, cardiac monitoring is futile.
2016
2017 LTTng, as a tracer, is no different from those real life examples. If
2018 you're about to trace a software system or, in other words, record its
2019 history of execution, you better have **instrumentation points** in the
2020 subject you're tracing, that is, the actual software.
2021
2022 Various ways were developed to instrument a piece of software for LTTng
2023 tracing. The most straightforward one is to manually place
2024 instrumentation points, called _tracepoints_, in the software's source
2025 code. It is also possible to add instrumentation points dynamically in
2026 the Linux kernel <<domain,tracing domain>>.
2027
2028 If you're only interested in tracing the Linux kernel, your
2029 instrumentation needs are probably already covered by LTTng's built-in
2030 <<lttng-modules,Linux kernel tracepoints>>. You may also wish to trace a
2031 user application which is already instrumented for LTTng tracing.
2032 In such cases, you can skip this whole section and read the topics of
2033 the <<controlling-tracing,Tracing control>> section.
2034
2035 Many methods are available to instrument a piece of software for LTTng
2036 tracing. They are:
2037
2038 * <<c-application,User space instrumentation for C and $$C++$$
2039 applications>>.
2040 * <<prebuilt-ust-helpers,Prebuilt user space tracing helpers>>.
2041 * <<java-application,User space Java agent>>.
2042 * <<python-application,User space Python agent>>.
2043 * <<proc-lttng-logger-abi,LTTng logger>>.
2044 * <<instrumenting-linux-kernel,LTTng kernel tracepoints>>.
2045
2046
2047 [[c-application]]
2048 === [[cxx-application]]User space instrumentation for C and $$C++$$ applications
2049
2050 The procedure to instrument a C or $$C++$$ user application with
2051 the <<lttng-ust,LTTng user space tracing library>>, `liblttng-ust`, is:
2052
2053 . <<tracepoint-provider,Create the source files of a tracepoint provider
2054 package>>.
2055 . <<probing-the-application-source-code,Add tracepoints to
2056 the application's source code>>.
2057 . <<building-tracepoint-providers-and-user-application,Build and link
2058 a tracepoint provider package and the user application>>.
2059
2060 If you need quick, man:printf(3)-like instrumentation, you can skip
2061 those steps and use <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>>
2062 instead.
2063
2064 IMPORTANT: You need to <<installing-lttng,install>> LTTng-UST to
2065 instrument a user application with `liblttng-ust`.
2066
2067
2068 [[tracepoint-provider]]
2069 ==== Create the source files of a tracepoint provider package
2070
2071 A _tracepoint provider_ is a set of compiled functions which provide
2072 **tracepoints** to an application, the type of instrumentation point
2073 supported by LTTng-UST. Those functions can emit events with
2074 user-defined fields and serialize those events as event records to one
2075 or more LTTng-UST <<channel,channel>> sub-buffers. The `tracepoint()`
2076 macro, which you <<probing-the-application-source-code,insert in a user
2077 application's source code>>, calls those functions.
2078
2079 A _tracepoint provider package_ is an object file (`.o`) or a shared
2080 library (`.so`) which contains one or more tracepoint providers.
2081 Its source files are:
2082
2083 * One or more <<tpp-header,tracepoint provider header>> (`.h`).
2084 * A <<tpp-source,tracepoint provider package source>> (`.c`).
2085
2086 A tracepoint provider package is dynamically linked with `liblttng-ust`,
2087 the LTTng user space tracer, at run time.
2088
2089 [role="img-100"]
2090 .User application linked with `liblttng-ust` and containing a tracepoint provider.
2091 image::ust-app.png[]
2092
2093 NOTE: If you need quick, man:printf(3)-like instrumentation, you can
2094 skip creating and using a tracepoint provider and use
2095 <<tracef,`tracef()`>> or <<tracelog,`tracelog()`>> instead.
2096
2097
2098 [[tpp-header]]
2099 ===== Create a tracepoint provider header file template
2100
2101 A _tracepoint provider header file_ contains the tracepoint
2102 definitions of a tracepoint provider.
2103
2104 To create a tracepoint provider header file:
2105
2106 . Start from this template:
2107 +
2108 --
2109 [source,c]
2110 .Tracepoint provider header file template (`.h` file extension).
2111 ----
2112 #undef TRACEPOINT_PROVIDER
2113 #define TRACEPOINT_PROVIDER provider_name
2114
2115 #undef TRACEPOINT_INCLUDE
2116 #define TRACEPOINT_INCLUDE "./tp.h"
2117
2118 #if !defined(_TP_H) || defined(TRACEPOINT_HEADER_MULTI_READ)
2119 #define _TP_H
2120
2121 #include <lttng/tracepoint.h>
2122
2123 /*
2124 * Use TRACEPOINT_EVENT(), TRACEPOINT_EVENT_CLASS(),
2125 * TRACEPOINT_EVENT_INSTANCE(), and TRACEPOINT_LOGLEVEL() here.
2126 */
2127
2128 #endif /* _TP_H */
2129
2130 #include <lttng/tracepoint-event.h>
2131 ----
2132 --
2133
2134 . Replace:
2135 +
2136 * `provider_name` with the name of your tracepoint provider.
2137 * `"tp.h"` with the name of your tracepoint provider header file.
2138
2139 . Below the `#include <lttng/tracepoint.h>` line, put your
2140 <<defining-tracepoints,tracepoint definitions>>.
2141
2142 Your tracepoint provider name must be unique amongst all the possible
2143 tracepoint provider names used on the same target system. We
2144 suggest to include the name of your project or company in the name,
2145 for example, `org_lttng_my_project_tpp`.
2146
2147 TIP: [[lttng-gen-tp]]You can use the man:lttng-gen-tp(1) tool to create
2148 this boilerplate for you. When using cmd:lttng-gen-tp, all you need to
2149 write are the <<defining-tracepoints,tracepoint definitions>>.
2150
2151
2152 [[defining-tracepoints]]
2153 ===== Create a tracepoint definition
2154
2155 A _tracepoint definition_ defines, for a given tracepoint:
2156
2157 * Its **input arguments**. They are the macro parameters that the
2158 `tracepoint()` macro accepts for this particular tracepoint
2159 in the user application's source code.
2160 * Its **output event fields**. They are the sources of event fields
2161 that form the payload of any event that the execution of the
2162 `tracepoint()` macro emits for this particular tracepoint.
2163
2164 You can create a tracepoint definition by using the
2165 `TRACEPOINT_EVENT()` macro below the `#include <lttng/tracepoint.h>`
2166 line in the
2167 <<tpp-header,tracepoint provider header file template>>.
2168
2169 The syntax of the `TRACEPOINT_EVENT()` macro is:
2170
2171 [source,c]
2172 .`TRACEPOINT_EVENT()` macro syntax.
2173 ----
2174 TRACEPOINT_EVENT(
2175 /* Tracepoint provider name */
2176 provider_name,
2177
2178 /* Tracepoint name */
2179 tracepoint_name,
2180
2181 /* Input arguments */
2182 TP_ARGS(
2183 arguments
2184 ),
2185
2186 /* Output event fields */
2187 TP_FIELDS(
2188 fields
2189 )
2190 )
2191 ----
2192
2193 Replace:
2194
2195 * `provider_name` with your tracepoint provider name.
2196 * `tracepoint_name` with your tracepoint name.
2197 * `arguments` with the <<tpp-def-input-args,input arguments>>.
2198 * `fields` with the <<tpp-def-output-fields,output event field>>
2199 definitions.
2200
2201 This tracepoint emits events named `provider_name:tracepoint_name`.
2202
2203 [IMPORTANT]
2204 .Event name's length limitation
2205 ====
2206 The concatenation of the tracepoint provider name and the
2207 tracepoint name must not exceed **254 characters**. If it does, the
2208 instrumented application compiles and runs, but LTTng throws multiple
2209 warnings and you could experience serious issues.
2210 ====
2211
2212 [[tpp-def-input-args]]The syntax of the `TP_ARGS()` macro is:
2213
2214 [source,c]
2215 .`TP_ARGS()` macro syntax.
2216 ----
2217 TP_ARGS(
2218 type, arg_name
2219 )
2220 ----
2221
2222 Replace:
2223
2224 * `type` with the C type of the argument.
2225 * `arg_name` with the argument name.
2226
2227 You can repeat `type` and `arg_name` up to 10 times to have
2228 more than one argument.
2229
2230 .`TP_ARGS()` usage with three arguments.
2231 ====
2232 [source,c]
2233 ----
2234 TP_ARGS(
2235 int, count,
2236 float, ratio,
2237 const char*, query
2238 )
2239 ----
2240 ====
2241
2242 The `TP_ARGS()` and `TP_ARGS(void)` forms are valid to create a
2243 tracepoint definition with no input arguments.
2244
2245 [[tpp-def-output-fields]]The `TP_FIELDS()` macro contains a list of
2246 `ctf_*()` macros. Each `ctf_*()` macro defines one event field.
2247 See <<liblttng-ust-tp-fields,Tracepoint fields macros>> for a
2248 complete description of the available `ctf_*()` macros.
2249 A `ctf_*()` macro specifies the type, size, and byte order of
2250 one event field.
2251
2252 Each `ctf_*()` macro takes an _argument expression_ parameter. This is a
2253 C expression that the tracer evalutes at the `tracepoint()` macro site
2254 in the application's source code. This expression provides a field's
2255 source of data. The argument expression can include input argument names
2256 listed in the `TP_ARGS()` macro.
2257
2258 Each `ctf_*()` macro also takes a _field name_ parameter. Field names
2259 must be unique within a given tracepoint definition.
2260
2261 Here's a complete tracepoint definition example:
2262
2263 .Tracepoint definition.
2264 ====
2265 The following tracepoint definition defines a tracepoint which takes
2266 three input arguments and has four output event fields.
2267
2268 [source,c]
2269 ----
2270 #include "my-custom-structure.h"
2271
2272 TRACEPOINT_EVENT(
2273 my_provider,
2274 my_tracepoint,
2275 TP_ARGS(
2276 const struct my_custom_structure*, my_custom_structure,
2277 float, ratio,
2278 const char*, query
2279 ),
2280 TP_FIELDS(
2281 ctf_string(query_field, query)
2282 ctf_float(double, ratio_field, ratio)
2283 ctf_integer(int, recv_size, my_custom_structure->recv_size)
2284 ctf_integer(int, send_size, my_custom_structure->send_size)
2285 )
2286 )
2287 ----
2288
2289 You can refer to this tracepoint definition with the `tracepoint()`
2290 macro in your application's source code like this:
2291
2292 [source,c]
2293 ----
2294 tracepoint(my_provider, my_tracepoint,
2295 my_structure, some_ratio, the_query);
2296 ----
2297 ====
2298
2299 NOTE: The LTTng tracer only evaluates tracepoint arguments at run time
2300 if they satisfy an enabled <<event,event rule>>.
2301
2302
2303 [[using-tracepoint-classes]]
2304 ===== Use a tracepoint class
2305
2306 A _tracepoint class_ is a class of tracepoints which share the same
2307 output event field definitions. A _tracepoint instance_ is one
2308 instance of such a defined tracepoint class, with its own tracepoint
2309 name.
2310
2311 The <<defining-tracepoints,`TRACEPOINT_EVENT()` macro>> is actually a
2312 shorthand which defines both a tracepoint class and a tracepoint
2313 instance at the same time.
2314
2315 When you build a tracepoint provider package, the C or $$C++$$ compiler
2316 creates one serialization function for each **tracepoint class**. A
2317 serialization function is responsible for serializing the event fields
2318 of a tracepoint to a sub-buffer when tracing.
2319
2320 For various performance reasons, when your situation requires multiple
2321 tracepoint definitions with different names, but with the same event
2322 fields, we recommend that you manually create a tracepoint class
2323 and instantiate as many tracepoint instances as needed. One positive
2324 effect of such a design, amongst other advantages, is that all
2325 tracepoint instances of the same tracepoint class reuse the same
2326 serialization function, thus reducing
2327 https://en.wikipedia.org/wiki/Cache_pollution[cache pollution].
2328
2329 .Use a tracepoint class and tracepoint instances.
2330 ====
2331 Consider the following three tracepoint definitions:
2332
2333 [source,c]
2334 ----
2335 TRACEPOINT_EVENT(
2336 my_app,
2337 get_account,
2338 TP_ARGS(
2339 int, userid,
2340 size_t, len
2341 ),
2342 TP_FIELDS(
2343 ctf_integer(int, userid, userid)
2344 ctf_integer(size_t, len, len)
2345 )
2346 )
2347
2348 TRACEPOINT_EVENT(
2349 my_app,
2350 get_settings,
2351 TP_ARGS(
2352 int, userid,
2353 size_t, len
2354 ),
2355 TP_FIELDS(
2356 ctf_integer(int, userid, userid)
2357 ctf_integer(size_t, len, len)
2358 )
2359 )
2360
2361 TRACEPOINT_EVENT(
2362 my_app,
2363 get_transaction,
2364 TP_ARGS(
2365 int, userid,
2366 size_t, len
2367 ),
2368 TP_FIELDS(
2369 ctf_integer(int, userid, userid)
2370 ctf_integer(size_t, len, len)
2371 )
2372 )
2373 ----
2374
2375 In this case, we create three tracepoint classes, with one implicit
2376 tracepoint instance for each of them: `get_account`, `get_settings`, and
2377 `get_transaction`. However, they all share the same event field names
2378 and types. Hence three identical, yet independent serialization
2379 functions are created when you build the tracepoint provider package.
2380
2381 A better design choice is to define a single tracepoint class and three
2382 tracepoint instances:
2383
2384 [source,c]
2385 ----
2386 /* The tracepoint class */
2387 TRACEPOINT_EVENT_CLASS(
2388 /* Tracepoint provider name */
2389 my_app,
2390
2391 /* Tracepoint class name */
2392 my_class,
2393
2394 /* Input arguments */
2395 TP_ARGS(
2396 int, userid,
2397 size_t, len
2398 ),
2399
2400 /* Output event fields */
2401 TP_FIELDS(
2402 ctf_integer(int, userid, userid)
2403 ctf_integer(size_t, len, len)
2404 )
2405 )
2406
2407 /* The tracepoint instances */
2408 TRACEPOINT_EVENT_INSTANCE(
2409 /* Tracepoint provider name */
2410 my_app,
2411
2412 /* Tracepoint class name */
2413 my_class,
2414
2415 /* Tracepoint name */
2416 get_account,
2417
2418 /* Input arguments */
2419 TP_ARGS(
2420 int, userid,
2421 size_t, len
2422 )
2423 )
2424 TRACEPOINT_EVENT_INSTANCE(
2425 my_app,
2426 my_class,
2427 get_settings,
2428 TP_ARGS(
2429 int, userid,
2430 size_t, len
2431 )
2432 )
2433 TRACEPOINT_EVENT_INSTANCE(
2434 my_app,
2435 my_class,
2436 get_transaction,
2437 TP_ARGS(
2438 int, userid,
2439 size_t, len
2440 )
2441 )
2442 ----
2443 ====
2444
2445
2446 [[assigning-log-levels]]
2447 ===== Assign a log level to a tracepoint definition
2448
2449 You can assign an optional _log level_ to a
2450 <<defining-tracepoints,tracepoint definition>>.
2451
2452 Assigning different levels of severity to tracepoint definitions can
2453 be useful: when you <<enabling-disabling-events,create an event rule>>,
2454 you can target tracepoints having a log level as severe as a specific
2455 value.
2456
2457 The concept of LTTng-UST log levels is similar to the levels found
2458 in typical logging frameworks:
2459
2460 * In a logging framework, the log level is given by the function
2461 or method name you use at the log statement site: `debug()`,
2462 `info()`, `warn()`, `error()`, and so on.
2463 * In LTTng-UST, you statically assign the log level to a tracepoint
2464 definition; any `tracepoint()` macro invocation which refers to
2465 this definition has this log level.
2466
2467 You can assign a log level to a tracepoint definition with the
2468 `TRACEPOINT_LOGLEVEL()` macro. You must use this macro _after_ the
2469 <<defining-tracepoints,`TRACEPOINT_EVENT()`>> or
2470 <<using-tracepoint-classes,`TRACEPOINT_INSTANCE()`>> macro for a given
2471 tracepoint.
2472
2473 The syntax of the `TRACEPOINT_LOGLEVEL()` macro is:
2474
2475 [source,c]
2476 .`TRACEPOINT_LOGLEVEL()` macro syntax.
2477 ----
2478 TRACEPOINT_LOGLEVEL(provider_name, tracepoint_name, log_level)
2479 ----
2480
2481 Replace:
2482
2483 * `provider_name` with the tracepoint provider name.
2484 * `tracepoint_name` with the tracepoint name.
2485 * `log_level` with the log level to assign to the tracepoint
2486 definition named `tracepoint_name` in the `provider_name`
2487 tracepoint provider.
2488 +
2489 See <<liblttng-ust-tracepoint-loglevel,Tracepoint log levels>> for
2490 a list of available log level names.
2491
2492 .Assign the `TRACE_DEBUG_UNIT` log level to a tracepoint definition.
2493 ====
2494 [source,c]
2495 ----
2496 /* Tracepoint definition */
2497 TRACEPOINT_EVENT(
2498 my_app,
2499 get_transaction,
2500 TP_ARGS(
2501 int, userid,
2502 size_t, len
2503 ),
2504 TP_FIELDS(
2505 ctf_integer(int, userid, userid)
2506 ctf_integer(size_t, len, len)
2507 )
2508 )
2509
2510 /* Log level assignment */
2511 TRACEPOINT_LOGLEVEL(my_app, get_transaction, TRACE_DEBUG_UNIT)
2512 ----
2513 ====
2514
2515
2516 [[tpp-source]]
2517 ===== Create a tracepoint provider package source file
2518
2519 A _tracepoint provider package source file_ is a C source file which
2520 includes a <<tpp-header,tracepoint provider header file>> to expand its
2521 macros into event serialization and other functions.
2522
2523 You can always use the following tracepoint provider package source
2524 file template:
2525
2526 [source,c]
2527 .Tracepoint provider package source file template.
2528 ----
2529 #define TRACEPOINT_CREATE_PROBES
2530
2531 #include "tp.h"
2532 ----
2533
2534 Replace `tp.h` with the name of your <<tpp-header,tracepoint provider
2535 header file>> name. You may also include more than one tracepoint
2536 provider header file here to create a tracepoint provider package
2537 holding more than one tracepoint providers.
2538
2539
2540 [[probing-the-application-source-code]]
2541 ==== Add tracepoints to an application's source code
2542
2543 Once you <<tpp-header,create a tracepoint provider header file>>, you
2544 can use the `tracepoint()` macro in your application's
2545 source code to insert the tracepoints that this header
2546 <<defining-tracepoints,defined>> defines.
2547
2548 The `tracepoint()` macro takes at least two parameters: the tracepoint
2549 provider name and the tracepoint name. The corresponding tracepoint
2550 definition defines the other parameters.
2551
2552 .`tracepoint()` usage.
2553 ====
2554 The following <<defining-tracepoints,tracepoint definition>> defines a
2555 tracepoint which takes two input arguments and has two output event
2556 fields.
2557
2558 [source,c]
2559 .Tracepoint provider header file.
2560 ----
2561 #include "my-custom-structure.h"
2562
2563 TRACEPOINT_EVENT(
2564 my_provider,
2565 my_tracepoint,
2566 TP_ARGS(
2567 int, argc,
2568 const char*, cmd_name
2569 ),
2570 TP_FIELDS(
2571 ctf_string(cmd_name, cmd_name)
2572 ctf_integer(int, number_of_args, argc)
2573 )
2574 )
2575 ----
2576
2577 You can refer to this tracepoint definition with the `tracepoint()`
2578 macro in your application's source code like this:
2579
2580 [source,c]
2581 .Application's source file.
2582 ----
2583 #include "tp.h"
2584
2585 int main(int argc, char* argv[])
2586 {
2587 tracepoint(my_provider, my_tracepoint, argc, argv[0]);
2588
2589 return 0;
2590 }
2591 ----
2592
2593 Note how the application's source code includes
2594 the tracepoint provider header file containing the tracepoint
2595 definitions to use, path:{tp.h}.
2596 ====
2597
2598 .`tracepoint()` usage with a complex tracepoint definition.
2599 ====
2600 Consider this complex tracepoint definition, where multiple event
2601 fields refer to the same input arguments in their argument expression
2602 parameter:
2603
2604 [source,c]
2605 .Tracepoint provider header file.
2606 ----
2607 /* For `struct stat` */
2608 #include <sys/types.h>
2609 #include <sys/stat.h>
2610 #include <unistd.h>
2611
2612 TRACEPOINT_EVENT(
2613 my_provider,
2614 my_tracepoint,
2615 TP_ARGS(
2616 int, my_int_arg,
2617 char*, my_str_arg,
2618 struct stat*, st
2619 ),
2620 TP_FIELDS(
2621 ctf_integer(int, my_constant_field, 23 + 17)
2622 ctf_integer(int, my_int_arg_field, my_int_arg)
2623 ctf_integer(int, my_int_arg_field2, my_int_arg * my_int_arg)
2624 ctf_integer(int, sum4_field, my_str_arg[0] + my_str_arg[1] +
2625 my_str_arg[2] + my_str_arg[3])
2626 ctf_string(my_str_arg_field, my_str_arg)
2627 ctf_integer_hex(off_t, size_field, st->st_size)
2628 ctf_float(double, size_dbl_field, (double) st->st_size)
2629 ctf_sequence_text(char, half_my_str_arg_field, my_str_arg,
2630 size_t, strlen(my_str_arg) / 2)
2631 )
2632 )
2633 ----
2634
2635 You can refer to this tracepoint definition with the `tracepoint()`
2636 macro in your application's source code like this:
2637
2638 [source,c]
2639 .Application's source file.
2640 ----
2641 #define TRACEPOINT_DEFINE
2642 #include "tp.h"
2643
2644 int main(void)
2645 {
2646 struct stat s;
2647
2648 stat("/etc/fstab", &s);
2649 tracepoint(my_provider, my_tracepoint, 23, "Hello, World!", &s);
2650
2651 return 0;
2652 }
2653 ----
2654
2655 If you look at the event record that LTTng writes when tracing this
2656 program, assuming the file size of path:{/etc/fstab} is 301{nbsp}bytes,
2657 it should look like this:
2658
2659 .Event record fields
2660 |====
2661 |Field's name |Field's value
2662 |`my_constant_field` |40
2663 |`my_int_arg_field` |23
2664 |`my_int_arg_field2` |529
2665 |`sum4_field` |389
2666 |`my_str_arg_field` |`Hello, World!`
2667 |`size_field` |0x12d
2668 |`size_dbl_field` |301.0
2669 |`half_my_str_arg_field` |`Hello,`
2670 |====
2671 ====
2672
2673 Sometimes, the arguments you pass to `tracepoint()` are expensive to
2674 compute--they use the call stack, for example. To avoid this
2675 computation when the tracepoint is disabled, you can use the
2676 `tracepoint_enabled()` and `do_tracepoint()` macros.
2677
2678 The syntax of the `tracepoint_enabled()` and `do_tracepoint()` macros
2679 is:
2680
2681 [source,c]
2682 .`tracepoint_enabled()` and `do_tracepoint()` macros syntax.
2683 ----
2684 tracepoint_enabled(provider_name, tracepoint_name)
2685 do_tracepoint(provider_name, tracepoint_name, ...)
2686 ----
2687
2688 Replace:
2689
2690 * `provider_name` with the tracepoint provider name.
2691 * `tracepoint_name` with the tracepoint name.
2692
2693 `tracepoint_enabled()` returns a non-zero value if the tracepoint named
2694 `tracepoint_name` from the provider named `provider_name` is enabled
2695 **at run time**.
2696
2697 `do_tracepoint()` is like `tracepoint()`, except that it doesn't check
2698 if the tracepoint is enabled. Using `tracepoint()` with
2699 `tracepoint_enabled()` is dangerous since `tracepoint()` also contains
2700 the `tracepoint_enabled()` check, thus a race condition is
2701 possible in this situation:
2702
2703 [source,c]
2704 .Possible race condition when using `tracepoint_enabled()` with `tracepoint()`.
2705 ----
2706 if (tracepoint_enabled(my_provider, my_tracepoint)) {
2707 stuff = prepare_stuff();
2708 }
2709
2710 tracepoint(my_provider, my_tracepoint, stuff);
2711 ----
2712
2713 If the tracepoint is enabled after the condition, then `stuff` is not
2714 prepared: the emitted event will either contain wrong data, or the whole
2715 application could crash (segmentation fault, for example).
2716
2717 NOTE: Neither `tracepoint_enabled()` nor `do_tracepoint()` have an
2718 `STAP_PROBEV()` call. If you need it, you must emit
2719 this call yourself.
2720
2721
2722 [[building-tracepoint-providers-and-user-application]]
2723 ==== Build and link a tracepoint provider package and an application
2724
2725 Once you have one or more <<tpp-header,tracepoint provider header
2726 files>> and a <<tpp-source,tracepoint provider package source file>>,
2727 you can create the tracepoint provider package by compiling its source
2728 file. From here, multiple build and run scenarios are possible. The
2729 following table shows common application and library configurations
2730 along with the required command lines to achieve them.
2731
2732 In the following diagrams, we use the following file names:
2733
2734 `app`::
2735 Executable application.
2736
2737 `app.o`::
2738 Application's object file.
2739
2740 `tpp.o`::
2741 Tracepoint provider package object file.
2742
2743 `tpp.a`::
2744 Tracepoint provider package archive file.
2745
2746 `libtpp.so`::
2747 Tracepoint provider package shared object file.
2748
2749 `emon.o`::
2750 User library object file.
2751
2752 `libemon.so`::
2753 User library shared object file.
2754
2755 The red star indicates that this object file is instrumented
2756 (contains code which uses the `tracepoint()` macro). The spring
2757 symbol between the application and a library means the application is
2758 linked with the library at build time.
2759
2760 We assume that path:{.} is part of the env:LD_LIBRARY_PATH environment
2761 variable in the following instructions.
2762
2763 [role="growable ust-scenarios",cols="asciidoc,asciidoc"]
2764 .Common tracepoint provider package scenarios.
2765 |====
2766 |Scenario |Instructions
2767
2768 |
2769 The instrumented application is statically linked with
2770 the tracepoint provider package object.
2771
2772 image::ust-sit+app-linked-with-tp-o+app-instrumented.png[]
2773
2774 |
2775 include::../common/ust-sit-step-tp-o.txt[]
2776
2777 To build the instrumented application:
2778
2779 . In path:{app.c}, before including path:{tpp.h}, add the following line:
2780 +
2781 --
2782 [source,c]
2783 ----
2784 #define TRACEPOINT_DEFINE
2785 ----
2786 --
2787
2788 . Compile the application source file:
2789 +
2790 --
2791 [role="term"]
2792 ----
2793 gcc -c app.c
2794 ----
2795 --
2796
2797 . Build the application:
2798 +
2799 --
2800 [role="term"]
2801 ----
2802 gcc -o app app.o tpp.o -llttng-ust -ldl
2803 ----
2804 --
2805
2806 To run the instrumented application:
2807
2808 * Start the application:
2809 +
2810 --
2811 [role="term"]
2812 ----
2813 ./app
2814 ----
2815 --
2816
2817 |
2818 The instrumented application is statically linked with the
2819 tracepoint provider package archive file.
2820
2821 image::ust-sit+app-linked-with-tp-a+app-instrumented.png[]
2822
2823 |
2824 To create the tracepoint provider package archive file:
2825
2826 . Compile the <<tpp-source,tracepoint provider package source file>>:
2827 +
2828 --
2829 [role="term"]
2830 ----
2831 gcc -I. -c tpp.c
2832 ----
2833 --
2834
2835 . Create the tracepoint provider package archive file:
2836 +
2837 --
2838 [role="term"]
2839 ----
2840 ar rcs tpp.a tpp.o
2841 ----
2842 --
2843
2844 To build the instrumented application:
2845
2846 . In path:{app.c}, before including path:{tpp.h}, add the following line:
2847 +
2848 --
2849 [source,c]
2850 ----
2851 #define TRACEPOINT_DEFINE
2852 ----
2853 --
2854
2855 . Compile the application source file:
2856 +
2857 --
2858 [role="term"]
2859 ----
2860 gcc -c app.c
2861 ----
2862 --
2863
2864 . Build the application:
2865 +
2866 --
2867 [role="term"]
2868 ----
2869 gcc -o app app.o tpp.a -llttng-ust -ldl
2870 ----
2871 --
2872
2873 To run the instrumented application:
2874
2875 * Start the application:
2876 +
2877 --
2878 [role="term"]
2879 ----
2880 ./app
2881 ----
2882 --
2883
2884 |
2885 The instrumented application is linked with the tracepoint provider
2886 package shared object.
2887
2888 image::ust-sit+app-linked-with-tp-so+app-instrumented.png[]
2889
2890 |
2891 include::../common/ust-sit-step-tp-so.txt[]
2892
2893 To build the instrumented application:
2894
2895 . In path:{app.c}, before including path:{tpp.h}, add the following line:
2896 +
2897 --
2898 [source,c]
2899 ----
2900 #define TRACEPOINT_DEFINE
2901 ----
2902 --
2903
2904 . Compile the application source file:
2905 +
2906 --
2907 [role="term"]
2908 ----
2909 gcc -c app.c
2910 ----
2911 --
2912
2913 . Build the application:
2914 +
2915 --
2916 [role="term"]
2917 ----
2918 gcc -o app app.o -ldl -L. -ltpp
2919 ----
2920 --
2921
2922 To run the instrumented application:
2923
2924 * Start the application:
2925 +
2926 --
2927 [role="term"]
2928 ----
2929 ./app
2930 ----
2931 --
2932
2933 |
2934 The tracepoint provider package shared object is preloaded before the
2935 instrumented application starts.
2936
2937 image::ust-sit+tp-so-preloaded+app-instrumented.png[]
2938
2939 |
2940 include::../common/ust-sit-step-tp-so.txt[]
2941
2942 To build the instrumented application:
2943
2944 . In path:{app.c}, before including path:{tpp.h}, add the
2945 following lines:
2946 +
2947 --
2948 [source,c]
2949 ----
2950 #define TRACEPOINT_DEFINE
2951 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
2952 ----
2953 --
2954
2955 . Compile the application source file:
2956 +
2957 --
2958 [role="term"]
2959 ----
2960 gcc -c app.c
2961 ----
2962 --
2963
2964 . Build the application:
2965 +
2966 --
2967 [role="term"]
2968 ----
2969 gcc -o app app.o -ldl
2970 ----
2971 --
2972
2973 To run the instrumented application with tracing support:
2974
2975 * Preload the tracepoint provider package shared object and
2976 start the application:
2977 +
2978 --
2979 [role="term"]
2980 ----
2981 LD_PRELOAD=./libtpp.so ./app
2982 ----
2983 --
2984
2985 To run the instrumented application without tracing support:
2986
2987 * Start the application:
2988 +
2989 --
2990 [role="term"]
2991 ----
2992 ./app
2993 ----
2994 --
2995
2996 |
2997 The instrumented application dynamically loads the tracepoint provider
2998 package shared object.
2999
3000 See the <<dlclose-warning,warning about `dlclose()`>>.
3001
3002 image::ust-sit+app-dlopens-tp-so+app-instrumented.png[]
3003
3004 |
3005 include::../common/ust-sit-step-tp-so.txt[]
3006
3007 To build the instrumented application:
3008
3009 . In path:{app.c}, before including path:{tpp.h}, add the
3010 following lines:
3011 +
3012 --
3013 [source,c]
3014 ----
3015 #define TRACEPOINT_DEFINE
3016 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
3017 ----
3018 --
3019
3020 . Compile the application source file:
3021 +
3022 --
3023 [role="term"]
3024 ----
3025 gcc -c app.c
3026 ----
3027 --
3028
3029 . Build the application:
3030 +
3031 --
3032 [role="term"]
3033 ----
3034 gcc -o app app.o -ldl
3035 ----
3036 --
3037
3038 To run the instrumented application:
3039
3040 * Start the application:
3041 +
3042 --
3043 [role="term"]
3044 ----
3045 ./app
3046 ----
3047 --
3048
3049 |
3050 The application is linked with the instrumented user library.
3051
3052 The instrumented user library is statically linked with the tracepoint
3053 provider package object file.
3054
3055 image::ust-sit+app-linked-with-lib+lib-linked-with-tp-o+lib-instrumented.png[]
3056
3057 |
3058 include::../common/ust-sit-step-tp-o-fpic.txt[]
3059
3060 To build the instrumented user library:
3061
3062 . In path:{emon.c}, before including path:{tpp.h}, add the
3063 following line:
3064 +
3065 --
3066 [source,c]
3067 ----
3068 #define TRACEPOINT_DEFINE
3069 ----
3070 --
3071
3072 . Compile the user library source file:
3073 +
3074 --
3075 [role="term"]
3076 ----
3077 gcc -I. -fpic -c emon.c
3078 ----
3079 --
3080
3081 . Build the user library shared object:
3082 +
3083 --
3084 [role="term"]
3085 ----
3086 gcc -shared -o libemon.so emon.o tpp.o -llttng-ust -ldl
3087 ----
3088 --
3089
3090 To build the application:
3091
3092 . Compile the application source file:
3093 +
3094 --
3095 [role="term"]
3096 ----
3097 gcc -c app.c
3098 ----
3099 --
3100
3101 . Build the application:
3102 +
3103 --
3104 [role="term"]
3105 ----
3106 gcc -o app app.o -L. -lemon
3107 ----
3108 --
3109
3110 To run the application:
3111
3112 * Start the application:
3113 +
3114 --
3115 [role="term"]
3116 ----
3117 ./app
3118 ----
3119 --
3120
3121 |
3122 The application is linked with the instrumented user library.
3123
3124 The instrumented user library is linked with the tracepoint provider
3125 package shared object.
3126
3127 image::ust-sit+app-linked-with-lib+lib-linked-with-tp-so+lib-instrumented.png[]
3128
3129 |
3130 include::../common/ust-sit-step-tp-so.txt[]
3131
3132 To build the instrumented user library:
3133
3134 . In path:{emon.c}, before including path:{tpp.h}, add the
3135 following line:
3136 +
3137 --
3138 [source,c]
3139 ----
3140 #define TRACEPOINT_DEFINE
3141 ----
3142 --
3143
3144 . Compile the user library source file:
3145 +
3146 --
3147 [role="term"]
3148 ----
3149 gcc -I. -fpic -c emon.c
3150 ----
3151 --
3152
3153 . Build the user library shared object:
3154 +
3155 --
3156 [role="term"]
3157 ----
3158 gcc -shared -o libemon.so emon.o -ldl -L. -ltpp
3159 ----
3160 --
3161
3162 To build the application:
3163
3164 . Compile the application source file:
3165 +
3166 --
3167 [role="term"]
3168 ----
3169 gcc -c app.c
3170 ----
3171 --
3172
3173 . Build the application:
3174 +
3175 --
3176 [role="term"]
3177 ----
3178 gcc -o app app.o -L. -lemon
3179 ----
3180 --
3181
3182 To run the application:
3183
3184 * Start the application:
3185 +
3186 --
3187 [role="term"]
3188 ----
3189 ./app
3190 ----
3191 --
3192
3193 |
3194 The tracepoint provider package shared object is preloaded before the
3195 application starts.
3196
3197 The application is linked with the instrumented user library.
3198
3199 image::ust-sit+tp-so-preloaded+app-linked-with-lib+lib-instrumented.png[]
3200
3201 |
3202 include::../common/ust-sit-step-tp-so.txt[]
3203
3204 To build the instrumented user library:
3205
3206 . In path:{emon.c}, before including path:{tpp.h}, add the
3207 following line:
3208 +
3209 --
3210 [source,c]
3211 ----
3212 #define TRACEPOINT_DEFINE
3213 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
3214 ----
3215 --
3216
3217 . Compile the user library source file:
3218 +
3219 --
3220 [role="term"]
3221 ----
3222 gcc -I. -fpic -c emon.c
3223 ----
3224 --
3225
3226 . Build the user library shared object:
3227 +
3228 --
3229 [role="term"]
3230 ----
3231 gcc -shared -o libemon.so emon.o -ldl
3232 ----
3233 --
3234
3235 To build the application:
3236
3237 . Compile the application source file:
3238 +
3239 --
3240 [role="term"]
3241 ----
3242 gcc -c app.c
3243 ----
3244 --
3245
3246 . Build the application:
3247 +
3248 --
3249 [role="term"]
3250 ----
3251 gcc -o app app.o -L. -lemon
3252 ----
3253 --
3254
3255 To run the application with tracing support:
3256
3257 * Preload the tracepoint provider package shared object and
3258 start the application:
3259 +
3260 --
3261 [role="term"]
3262 ----
3263 LD_PRELOAD=./libtpp.so ./app
3264 ----
3265 --
3266
3267 To run the application without tracing support:
3268
3269 * Start the application:
3270 +
3271 --
3272 [role="term"]
3273 ----
3274 ./app
3275 ----
3276 --
3277
3278 |
3279 The application is linked with the instrumented user library.
3280
3281 The instrumented user library dynamically loads the tracepoint provider
3282 package shared object.
3283
3284 See the <<dlclose-warning,warning about `dlclose()`>>.
3285
3286 image::ust-sit+app-linked-with-lib+lib-dlopens-tp-so+lib-instrumented.png[]
3287
3288 |
3289 include::../common/ust-sit-step-tp-so.txt[]
3290
3291 To build the instrumented user library:
3292
3293 . In path:{emon.c}, before including path:{tpp.h}, add the
3294 following line:
3295 +
3296 --
3297 [source,c]
3298 ----
3299 #define TRACEPOINT_DEFINE
3300 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
3301 ----
3302 --
3303
3304 . Compile the user library source file:
3305 +
3306 --
3307 [role="term"]
3308 ----
3309 gcc -I. -fpic -c emon.c
3310 ----
3311 --
3312
3313 . Build the user library shared object:
3314 +
3315 --
3316 [role="term"]
3317 ----
3318 gcc -shared -o libemon.so emon.o -ldl
3319 ----
3320 --
3321
3322 To build the application:
3323
3324 . Compile the application source file:
3325 +
3326 --
3327 [role="term"]
3328 ----
3329 gcc -c app.c
3330 ----
3331 --
3332
3333 . Build the application:
3334 +
3335 --
3336 [role="term"]
3337 ----
3338 gcc -o app app.o -L. -lemon
3339 ----
3340 --
3341
3342 To run the application:
3343
3344 * Start the application:
3345 +
3346 --
3347 [role="term"]
3348 ----
3349 ./app
3350 ----
3351 --
3352
3353 |
3354 The application dynamically loads the instrumented user library.
3355
3356 The instrumented user library is linked with the tracepoint provider
3357 package shared object.
3358
3359 See the <<dlclose-warning,warning about `dlclose()`>>.
3360
3361 image::ust-sit+app-dlopens-lib+lib-linked-with-tp-so+lib-instrumented.png[]
3362
3363 |
3364 include::../common/ust-sit-step-tp-so.txt[]
3365
3366 To build the instrumented user library:
3367
3368 . In path:{emon.c}, before including path:{tpp.h}, add the
3369 following line:
3370 +
3371 --
3372 [source,c]
3373 ----
3374 #define TRACEPOINT_DEFINE
3375 ----
3376 --
3377
3378 . Compile the user library source file:
3379 +
3380 --
3381 [role="term"]
3382 ----
3383 gcc -I. -fpic -c emon.c
3384 ----
3385 --
3386
3387 . Build the user library shared object:
3388 +
3389 --
3390 [role="term"]
3391 ----
3392 gcc -shared -o libemon.so emon.o -ldl -L. -ltpp
3393 ----
3394 --
3395
3396 To build the application:
3397
3398 . Compile the application source file:
3399 +
3400 --
3401 [role="term"]
3402 ----
3403 gcc -c app.c
3404 ----
3405 --
3406
3407 . Build the application:
3408 +
3409 --
3410 [role="term"]
3411 ----
3412 gcc -o app app.o -ldl -L. -lemon
3413 ----
3414 --
3415
3416 To run the application:
3417
3418 * Start the application:
3419 +
3420 --
3421 [role="term"]
3422 ----
3423 ./app
3424 ----
3425 --
3426
3427 |
3428 The application dynamically loads the instrumented user library.
3429
3430 The instrumented user library dynamically loads the tracepoint provider
3431 package shared object.
3432
3433 See the <<dlclose-warning,warning about `dlclose()`>>.
3434
3435 image::ust-sit+app-dlopens-lib+lib-dlopens-tp-so+lib-instrumented.png[]
3436
3437 |
3438 include::../common/ust-sit-step-tp-so.txt[]
3439
3440 To build the instrumented user library:
3441
3442 . In path:{emon.c}, before including path:{tpp.h}, add the
3443 following line:
3444 +
3445 --
3446 [source,c]
3447 ----
3448 #define TRACEPOINT_DEFINE
3449 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
3450 ----
3451 --
3452
3453 . Compile the user library source file:
3454 +
3455 --
3456 [role="term"]
3457 ----
3458 gcc -I. -fpic -c emon.c
3459 ----
3460 --
3461
3462 . Build the user library shared object:
3463 +
3464 --
3465 [role="term"]
3466 ----
3467 gcc -shared -o libemon.so emon.o -ldl
3468 ----
3469 --
3470
3471 To build the application:
3472
3473 . Compile the application source file:
3474 +
3475 --
3476 [role="term"]
3477 ----
3478 gcc -c app.c
3479 ----
3480 --
3481
3482 . Build the application:
3483 +
3484 --
3485 [role="term"]
3486 ----
3487 gcc -o app app.o -ldl -L. -lemon
3488 ----
3489 --
3490
3491 To run the application:
3492
3493 * Start the application:
3494 +
3495 --
3496 [role="term"]
3497 ----
3498 ./app
3499 ----
3500 --
3501
3502 |
3503 The tracepoint provider package shared object is preloaded before the
3504 application starts.
3505
3506 The application dynamically loads the instrumented user library.
3507
3508 image::ust-sit+tp-so-preloaded+app-dlopens-lib+lib-instrumented.png[]
3509
3510 |
3511 include::../common/ust-sit-step-tp-so.txt[]
3512
3513 To build the instrumented user library:
3514
3515 . In path:{emon.c}, before including path:{tpp.h}, add the
3516 following line:
3517 +
3518 --
3519 [source,c]
3520 ----
3521 #define TRACEPOINT_DEFINE
3522 #define TRACEPOINT_PROBE_DYNAMIC_LINKAGE
3523 ----
3524 --
3525
3526 . Compile the user library source file:
3527 +
3528 --
3529 [role="term"]
3530 ----
3531 gcc -I. -fpic -c emon.c
3532 ----
3533 --
3534
3535 . Build the user library shared object:
3536 +
3537 --
3538 [role="term"]
3539 ----
3540 gcc -shared -o libemon.so emon.o -ldl
3541 ----
3542 --
3543
3544 To build the application:
3545
3546 . Compile the application source file:
3547 +
3548 --
3549 [role="term"]
3550 ----
3551 gcc -c app.c
3552 ----
3553 --
3554
3555 . Build the application:
3556 +
3557 --
3558 [role="term"]
3559 ----
3560 gcc -o app app.o -L. -lemon
3561 ----
3562 --
3563
3564 To run the application with tracing support:
3565
3566 * Preload the tracepoint provider package shared object and
3567 start the application:
3568 +
3569 --
3570 [role="term"]
3571 ----
3572 LD_PRELOAD=./libtpp.so ./app
3573 ----
3574 --
3575
3576 To run the application without tracing support:
3577
3578 * Start the application:
3579 +
3580 --
3581 [role="term"]
3582 ----
3583 ./app
3584 ----
3585 --
3586
3587 |
3588 The application is statically linked with the tracepoint provider
3589 package object file.
3590
3591 The application is linked with the instrumented user library.
3592
3593 image::ust-sit+app-linked-with-tp-o+app-linked-with-lib+lib-instrumented.png[]
3594
3595 |
3596 include::../common/ust-sit-step-tp-o.txt[]
3597
3598 To build the instrumented user library:
3599
3600 . In path:{emon.c}, before including path:{tpp.h}, add the
3601 following line:
3602 +
3603 --
3604 [source,c]
3605 ----
3606 #define TRACEPOINT_DEFINE
3607 ----
3608 --
3609
3610 . Compile the user library source file:
3611 +
3612 --
3613 [role="term"]
3614 ----
3615 gcc -I. -fpic -c emon.c
3616 ----
3617 --
3618
3619 . Build the user library shared object:
3620 +
3621 --
3622 [role="term"]
3623 ----
3624 gcc -shared -o libemon.so emon.o
3625 ----
3626 --
3627
3628 To build the application:
3629
3630 . Compile the application source file:
3631 +
3632 --
3633 [role="term"]
3634 ----
3635 gcc -c app.c
3636 ----
3637 --
3638
3639 . Build the application:
3640 +
3641 --
3642 [role="term"]
3643 ----
3644 gcc -o app app.o tpp.o -llttng-ust -ldl -L. -lemon
3645 ----
3646 --
3647
3648 To run the instrumented application:
3649
3650 * Start the application:
3651 +
3652 --
3653 [role="term"]
3654 ----
3655 ./app
3656 ----
3657 --
3658
3659 |
3660 The application is statically linked with the tracepoint provider
3661 package object file.
3662
3663 The application dynamically loads the instrumented user library.
3664
3665 image::ust-sit+app-linked-with-tp-o+app-dlopens-lib+lib-instrumented.png[]
3666
3667 |
3668 include::../common/ust-sit-step-tp-o.txt[]
3669
3670 To build the application:
3671
3672 . In path:{app.c}, before including path:{tpp.h}, add the following line:
3673 +
3674 --
3675 [source,c]
3676 ----
3677 #define TRACEPOINT_DEFINE
3678 ----
3679 --
3680
3681 . Compile the application source file:
3682 +
3683 --
3684 [role="term"]
3685 ----
3686 gcc -c app.c
3687 ----
3688 --
3689
3690 . Build the application:
3691 +
3692 --
3693 [role="term"]
3694 ----
3695 gcc -Wl,--export-dynamic -o app app.o tpp.o \
3696 -llttng-ust -ldl
3697 ----
3698 --
3699 +
3700 The `--export-dynamic` option passed to the linker is necessary for the
3701 dynamically loaded library to ``see'' the tracepoint symbols defined in
3702 the application.
3703
3704 To build the instrumented user library:
3705
3706 . Compile the user library source file:
3707 +
3708 --
3709 [role="term"]
3710 ----
3711 gcc -I. -fpic -c emon.c
3712 ----
3713 --
3714
3715 . Build the user library shared object:
3716 +
3717 --
3718 [role="term"]
3719 ----
3720 gcc -shared -o libemon.so emon.o
3721 ----
3722 --
3723
3724 To run the application:
3725
3726 * Start the application:
3727 +
3728 --
3729 [role="term"]
3730 ----
3731 ./app
3732 ----
3733 --
3734 |====
3735
3736 [[dlclose-warning]]
3737 [IMPORTANT]
3738 .Do not use man:dlclose(3) on a tracepoint provider package
3739 ====
3740 Never use man:dlclose(3) on any shared object which:
3741
3742 * Is linked with, statically or dynamically, a tracepoint provider
3743 package.
3744 * Calls man:dlopen(3) itself to dynamically open a tracepoint provider
3745 package shared object.
3746
3747 This is currently considered **unsafe** due to a lack of reference
3748 counting from LTTng-UST to the shared object.
3749
3750 A known workaround (available since glibc 2.2) is to use the
3751 `RTLD_NODELETE` flag when calling man:dlopen(3) initially. This has the
3752 effect of not unloading the loaded shared object, even if man:dlclose(3)
3753 is called.
3754
3755 You can also preload the tracepoint provider package shared object with
3756 the env:LD_PRELOAD environment variable to overcome this limitation.
3757 ====
3758
3759
3760 [[using-lttng-ust-with-daemons]]
3761 ===== Use noch:{LTTng-UST} with daemons
3762
3763 If your instrumented application calls man:fork(2), man:clone(2),
3764 or BSD's man:rfork(2), without a following man:exec(3)-family
3765 system call, you must preload the path:{liblttng-ust-fork.so} shared
3766 object when starting the application.
3767
3768 [role="term"]
3769 ----
3770 LD_PRELOAD=liblttng-ust-fork.so ./my-app
3771 ----
3772
3773 If your tracepoint provider package is
3774 a shared library which you also preload, you must put both
3775 shared objects in env:LD_PRELOAD:
3776
3777 [role="term"]
3778 ----
3779 LD_PRELOAD=liblttng-ust-fork.so:/path/to/tp.so ./my-app
3780 ----
3781
3782
3783 [[lttng-ust-pkg-config]]
3784 ===== Use noch:{pkg-config}
3785
3786 On some distributions, LTTng-UST ships with a
3787 https://www.freedesktop.org/wiki/Software/pkg-config/[pkg-config]
3788 metadata file. If this is your case, then you can use cmd:pkg-config to
3789 build an application on the command line:
3790
3791 [role="term"]
3792 ----
3793 gcc -o my-app my-app.o tp.o $(pkg-config --cflags --libs lttng-ust)
3794 ----
3795
3796
3797 [[instrumenting-32-bit-app-on-64-bit-system]]
3798 ===== [[advanced-instrumenting-techniques]]Build a 32-bit instrumented application for a 64-bit target system
3799
3800 In order to trace a 32-bit application running on a 64-bit system,
3801 LTTng must use a dedicated 32-bit
3802 <<lttng-consumerd,consumer daemon>>.
3803
3804 The following steps show how to build and install a 32-bit consumer
3805 daemon, which is _not_ part of the default 64-bit LTTng build, how to
3806 build and install the 32-bit LTTng-UST libraries, and how to build and
3807 link an instrumented 32-bit application in that context.
3808
3809 To build a 32-bit instrumented application for a 64-bit target system,
3810 assuming you have a fresh target system with no installed Userspace RCU
3811 or LTTng packages:
3812
3813 . Download, build, and install a 32-bit version of Userspace RCU:
3814 +
3815 --
3816 [role="term"]
3817 ----
3818 cd $(mktemp -d) &&
3819 wget http://lttng.org/files/urcu/userspace-rcu-latest-0.9.tar.bz2 &&
3820 tar -xf userspace-rcu-latest-0.9.tar.bz2 &&
3821 cd userspace-rcu-0.9.* &&
3822 ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 &&
3823 make &&
3824 sudo make install &&
3825 sudo ldconfig
3826 ----
3827 --
3828
3829 . Using your distribution's package manager, or from source, install
3830 the following 32-bit versions of the following dependencies of
3831 LTTng-tools and LTTng-UST:
3832 +
3833 --
3834 * https://sourceforge.net/projects/libuuid/[libuuid]
3835 * http://directory.fsf.org/wiki/Popt[popt]
3836 * http://www.xmlsoft.org/[libxml2]
3837 --
3838
3839 . Download, build, and install a 32-bit version of the latest
3840 LTTng-UST{nbsp}{revision}:
3841 +
3842 --
3843 [role="term"]
3844 ----
3845 cd $(mktemp -d) &&
3846 wget http://lttng.org/files/lttng-ust/lttng-ust-latest-2.7.tar.bz2 &&
3847 tar -xf lttng-ust-latest-2.7.tar.bz2 &&
3848 cd lttng-ust-2.7.* &&
3849 ./configure --libdir=/usr/local/lib32 \
3850 CFLAGS=-m32 CXXFLAGS=-m32 \
3851 LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' &&
3852 make &&
3853 sudo make install &&
3854 sudo ldconfig
3855 ----
3856 --
3857 +
3858 [NOTE]
3859 ====
3860 Depending on your distribution,
3861 32-bit libraries could be installed at a different location than
3862 `/usr/lib32`. For example, Debian is known to install
3863 some 32-bit libraries in `/usr/lib/i386-linux-gnu`.
3864
3865 In this case, make sure to set `LDFLAGS` to all the
3866 relevant 32-bit library paths, for example:
3867
3868 [role="term"]
3869 ----
3870 LDFLAGS='-L/usr/lib/i386-linux-gnu -L/usr/lib32'
3871 ----
3872 ====
3873
3874 . Download the latest LTTng-tools{nbsp}{revision}, build, and install
3875 the 32-bit consumer daemon:
3876 +
3877 --
3878 [role="term"]
3879 ----
3880 cd $(mktemp -d) &&
3881 wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.7.tar.bz2 &&
3882 tar -xf lttng-tools-latest-2.7.tar.bz2 &&
3883 cd lttng-tools-2.7.* &&
3884 ./configure --libdir=/usr/local/lib32 CFLAGS=-m32 CXXFLAGS=-m32 \
3885 LDFLAGS='-L/usr/local/lib32 -L/usr/lib32' &&
3886 make &&
3887 cd src/bin/lttng-consumerd &&
3888 sudo make install &&
3889 sudo ldconfig
3890 ----
3891 --
3892
3893 . From your distribution or from source,
3894 <<installing-lttng,install>> the 64-bit versions of
3895 LTTng-UST and Userspace RCU.
3896 . Download, build, and install the 64-bit version of the
3897 latest LTTng-tools{nbsp}{revision}:
3898 +
3899 --
3900 [role="term"]
3901 ----
3902 cd $(mktemp -d) &&
3903 wget http://lttng.org/files/lttng-tools/lttng-tools-latest-2.7.tar.bz2 &&
3904 tar -xf lttng-tools-latest-2.7.tar.bz2 &&
3905 cd lttng-tools-2.7.* &&
3906 ./configure --with-consumerd32-libdir=/usr/local/lib32 \
3907 --with-consumerd32-bin=/usr/local/lib32/lttng/libexec/lttng-consumerd &&
3908 make &&
3909 sudo make install &&
3910 sudo ldconfig
3911 ----
3912 --
3913
3914 . Pass the following options to man:gcc(1), man:g++(1), or man:clang(1)
3915 when linking your 32-bit application:
3916 +
3917 ----
3918 -m32 -L/usr/lib32 -L/usr/local/lib32 \
3919 -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32
3920 ----
3921 +
3922 For example, let's rebuild the quick start example in
3923 <<tracing-your-own-user-application,Trace a user application>> as an
3924 instrumented 32-bit application:
3925 +
3926 --
3927 [role="term"]
3928 ----
3929 gcc -m32 -c -I. hello-tp.c
3930 gcc -m32 -c hello.c
3931 gcc -m32 -o hello hello.o hello-tp.o \
3932 -L/usr/lib32 -L/usr/local/lib32 \
3933 -Wl,-rpath,/usr/lib32,-rpath,/usr/local/lib32 \
3934 -llttng-ust -ldl
3935 ----
3936 --
3937
3938 No special action is required to execute the 32-bit application and
3939 to trace it: use the command-line man:lttng(1) tool as usual.
3940
3941
3942 [role="since-2.5"]
3943 [[tracef]]
3944 ==== Use `tracef()`
3945
3946 `tracef()` is a small LTTng-UST API designed for quick,
3947 man:printf(3)-like instrumentation without the burden of
3948 <<tracepoint-provider,creating>> and
3949 <<building-tracepoint-providers-and-user-application,building>>
3950 a tracepoint provider package.
3951
3952 To use `tracef()` in your application:
3953
3954 . In the C or C++ source files where you need to use `tracef()`,
3955 include `<lttng/tracef.h>`:
3956 +
3957 --
3958 [source,c]
3959 ----
3960 #include <lttng/tracef.h>
3961 ----
3962 --
3963
3964 . In the application's source code, use `tracef()` like you would use
3965 man:printf(3):
3966 +
3967 --
3968 [source,c]
3969 ----
3970 /* ... */
3971
3972 tracef("my message: %d (%s)", my_integer, my_string);
3973
3974 /* ... */
3975 ----
3976 --
3977
3978 . Link your application with `liblttng-ust`:
3979 +
3980 --
3981 [role="term"]
3982 ----
3983 gcc -o app app.c -llttng-ust
3984 ----
3985 --
3986
3987 To trace the events that `tracef()` calls emit:
3988
3989 * <<enabling-disabling-events,Create an event rule>> which matches the
3990 `lttng_ust_tracef:*` event name:
3991 +
3992 --
3993 [role="term"]
3994 ----
3995 lttng enable-event --userspace 'lttng_ust_tracef:*'
3996 ----
3997 --
3998
3999 [IMPORTANT]
4000 .Limitations of `tracef()`
4001 ====
4002 The `tracef()` utility function was developed to make user space tracing
4003 super simple, albeit with notable disadvantages compared to
4004 <<defining-tracepoints,user-defined tracepoints>>:
4005
4006 * All the emitted events have the same tracepoint provider and
4007 tracepoint names, respectively `lttng_ust_tracef` and `event`.
4008 * There is no static type checking.
4009 * The only event record field you actually get, named `msg`, is a string
4010 potentially containing the values you passed to `tracef()`
4011 using your own format string. This also means that you cannot filter
4012 events with a custom expression at run time because there are no
4013 isolated fields.
4014 * Since `tracef()` uses the C standard library's man:vasprintf(3)
4015 function behind the scenes to format the strings at run time, its
4016 expected performance is lower than with user-defined tracepoints,
4017 which do not require a conversion to a string.
4018
4019 Taking this into consideration, `tracef()` is useful for some quick
4020 prototyping and debugging, but you should not consider it for any
4021 permanent and serious applicative instrumentation.
4022 ====
4023
4024
4025 [role="since-2.7"]
4026 [[tracelog]]
4027 ==== Use `tracelog()`
4028
4029 The `tracelog()` API is very similar to <<tracef,`tracef()`>>, with
4030 the difference that it accepts an additional log level parameter.
4031
4032 The goal of `tracelog()` is to ease the migration from logging to
4033 tracing.
4034
4035 To use `tracelog()` in your application:
4036
4037 . In the C or C++ source files where you need to use `tracelog()`,
4038 include `<lttng/tracelog.h>`:
4039 +
4040 --
4041 [source,c]
4042 ----
4043 #include <lttng/tracelog.h>
4044 ----
4045 --
4046
4047 . In the application's source code, use `tracelog()` like you would use
4048 man:printf(3), except for the first parameter which is the log
4049 level:
4050 +
4051 --
4052 [source,c]
4053 ----
4054 /* ... */
4055
4056 tracelog(TRACE_WARNING, "my message: %d (%s)",
4057 my_integer, my_string);
4058
4059 /* ... */
4060 ----
4061 --
4062 +
4063 See <<liblttng-ust-tracepoint-loglevel,Tracepoint log levels>> for
4064 a list of available log level names.
4065
4066 . Link your application with `liblttng-ust`:
4067 +
4068 --
4069 [role="term"]
4070 ----
4071 gcc -o app app.c -llttng-ust
4072 ----
4073 --
4074
4075 To trace the events that `tracelog()` calls emit with a log level
4076 _as severe as_ a specific log level:
4077
4078 * <<enabling-disabling-events,Create an event rule>> which matches the
4079 `lttng_ust_tracelog:*` event name and a minimum level
4080 of severity:
4081 +
4082 --
4083 [role="term"]
4084 ----
4085 lttng enable-event --userspace 'lttng_ust_tracelog:*'
4086 --loglevel=TRACE_WARNING
4087 ----
4088 --
4089
4090 To trace the events that `tracelog()` calls emit with a
4091 _specific log level_:
4092
4093 * Create an event rule which matches the `lttng_ust_tracelog:*`
4094 event name and a specific log level:
4095 +
4096 --
4097 [role="term"]
4098 ----
4099 lttng enable-event --userspace 'lttng_ust_tracelog:*'
4100 --loglevel-only=TRACE_INFO
4101 ----
4102 --
4103
4104
4105 [[prebuilt-ust-helpers]]
4106 === Prebuilt user space tracing helpers
4107
4108 The LTTng-UST package provides a few helpers in the form or preloadable
4109 shared objects which automatically instrument system functions and
4110 calls.
4111
4112 The helper shared objects are normally found in dir:{/usr/lib}. If you
4113 built LTTng-UST <<building-from-source,from source>>, they are probably
4114 located in dir:{/usr/local/lib}.
4115
4116 The installed user space tracing helpers in LTTng-UST{nbsp}{revision}
4117 are:
4118
4119 path:{liblttng-ust-libc-wrapper.so}::
4120 path:{liblttng-ust-pthread-wrapper.so}::
4121 <<liblttng-ust-libc-pthread-wrapper,C{nbsp}standard library
4122 memory and POSIX threads function tracing>>.
4123
4124 path:{liblttng-ust-cyg-profile.so}::
4125 path:{liblttng-ust-cyg-profile-fast.so}::
4126 <<liblttng-ust-cyg-profile,Function entry and exit tracing>>.
4127
4128 path:{liblttng-ust-dl.so}::
4129 <<liblttng-ust-dl,Dynamic linker tracing>>.
4130
4131 To use a user space tracing helper with any user application:
4132
4133 * Preload the helper shared object when you start the application:
4134 +
4135 --
4136 [role="term"]
4137 ----
4138 LD_PRELOAD=liblttng-ust-libc-wrapper.so my-app
4139 ----
4140 --
4141 +
4142 You can preload more than one helper:
4143 +
4144 --
4145 [role="term"]
4146 ----
4147 LD_PRELOAD=liblttng-ust-libc-wrapper.so:liblttng-ust-dl.so my-app
4148 ----
4149 --
4150
4151
4152 [role="since-2.3"]
4153 [[liblttng-ust-libc-pthread-wrapper]]
4154 ==== Instrument C standard library memory and POSIX threads functions
4155
4156 The path:{liblttng-ust-libc-wrapper.so} and
4157 path:{liblttng-ust-pthread-wrapper.so} helpers
4158 add instrumentation to some C standard library and POSIX
4159 threads functions.
4160
4161 [role="growable"]
4162 .Functions instrumented by preloading path:{liblttng-ust-libc-wrapper.so}.
4163 |====
4164 |TP provider name |TP name |Instrumented function
4165
4166 .6+|`lttng_ust_libc` |`malloc` |man:malloc(3)
4167 |`calloc` |man:calloc(3)
4168 |`realloc` |man:realloc(3)
4169 |`free` |man:free(3)
4170 |`memalign` |man:memalign(3)
4171 |`posix_memalign` |man:posix_memalign(3)
4172 |====
4173
4174 [role="growable"]
4175 .Functions instrumented by preloading path:{liblttng-ust-pthread-wrapper.so}.
4176 |====
4177 |TP provider name |TP name |Instrumented function
4178
4179 .4+|`lttng_ust_pthread` |`pthread_mutex_lock_req` |man:pthread_mutex_lock(3p) (request time)
4180 |`pthread_mutex_lock_acq` |man:pthread_mutex_lock(3p) (acquire time)
4181 |`pthread_mutex_trylock` |man:pthread_mutex_trylock(3p)
4182 |`pthread_mutex_unlock` |man:pthread_mutex_unlock(3p)
4183 |====
4184
4185 When you preload the shared object, it replaces the functions listed
4186 in the previous tables by wrappers which contain tracepoints and call
4187 the replaced functions.
4188
4189
4190 [[liblttng-ust-cyg-profile]]
4191 ==== Instrument function entry and exit
4192
4193 The path:{liblttng-ust-cyg-profile*.so} helpers can add instrumentation
4194 to the entry and exit points of functions.
4195
4196 man:gcc(1) and man:clang(1) have an option named
4197 https://gcc.gnu.org/onlinedocs/gcc/Code-Gen-Options.html[`-finstrument-functions`]
4198 which generates instrumentation calls for entry and exit to functions.
4199 The LTTng-UST function tracing helpers,
4200 path:{liblttng-ust-cyg-profile.so} and
4201 path:{liblttng-ust-cyg-profile-fast.so}, take advantage of this feature
4202 to add tracepoints to the two generated functions (which contain
4203 `cyg_profile` in their names, hence the helper's name).
4204
4205 To use the LTTng-UST function tracing helper, the source files to
4206 instrument must be built using the `-finstrument-functions` compiler
4207 flag.
4208
4209 There are two versions of the LTTng-UST function tracing helper:
4210
4211 * **path:{liblttng-ust-cyg-profile-fast.so}** is a lightweight variant
4212 that you should only use when it can be _guaranteed_ that the
4213 complete event stream is recorded without any lost event record.
4214 Any kind of duplicate information is left out.
4215 +
4216 This version contains the following tracepoints:
4217 +
4218 --
4219 [role="growable"]
4220 .Points instrumented by preloading path:{liblttng-ust-cyg-profile-fast.so}.
4221 |====
4222 |TP provider name |TP name |Instrumented points
4223
4224 .2+|`lttng_ust_cyg_profile_fast`
4225
4226 |`func_entry`
4227 a|Function entry.
4228
4229 `addr`::
4230 Address of called function.
4231
4232 |`func_exit`
4233 |Function exit.
4234 |====
4235 --
4236 +
4237 Assuming no event record is lost, having only the function addresses on
4238 entry is enough to create a call graph, since an event record always
4239 contains the ID of the CPU that generated it.
4240 +
4241 You can use a tool like
4242 https://sourceware.org/binutils/docs/binutils/addr2line.html[cmd:addr2line]
4243 to convert function addresses back to source file names and
4244 line numbers.
4245
4246 * **path:{liblttng-ust-cyg-profile.so}** is a more robust variant
4247 which also works in use cases where event records might get discarded or
4248 not recorded from application startup.
4249 In these cases, the trace analyzer needs more information to be
4250 able to reconstruct the program flow.
4251 +
4252 This version contains the following tracepoints:
4253 +
4254 --
4255 [role="growable"]
4256 .Points instrumented by preloading path:{liblttng-ust-cyg-profile.so}.
4257 |====
4258 |TP provider name |TP name |Instrumented point
4259
4260 .2+|`lttng_ust_cyg_profile`
4261
4262 |`func_entry`
4263 a|Function entry.
4264
4265 `addr`::
4266 Address of called function.
4267
4268 `call_site`::
4269 Call site address.
4270
4271 |`func_exit`
4272 a|Function exit.
4273
4274 `addr`::
4275 Address of called function.
4276
4277 `call_site`::
4278 Call site address.
4279 |====
4280 --
4281
4282 TIP: It's sometimes a good idea to limit the number of source files that
4283 you compile with the `-finstrument-functions` option to prevent LTTng
4284 from writing an excessive amount of trace data at run time. When using
4285 man:gcc(1), you can use the
4286 `-finstrument-functions-exclude-function-list` option to avoid
4287 instrument entries and exits of specific function names.
4288
4289 All the tracepoints that this helper contains have the
4290 <<liblttng-ust-tracepoint-loglevel,log level>> `TRACE_DEBUG_FUNCTION`.
4291
4292
4293 [role="since-2.4"]
4294 [[liblttng-ust-dl]]
4295 ==== Instrument the dynamic linker
4296
4297 The path:{liblttng-ust-dl.so} helper adds instrumentation to the
4298 man:dlopen(3) and man:dlclose(3) function calls.
4299
4300 [role="growable"]
4301 .Functions instrumented by preloading path:{liblttng-ust-dl.so}.
4302 |====
4303 |TP provider name |TP name |Instrumented function
4304
4305 .2+|`lttng_ust_dl`
4306
4307 |`dlopen`
4308 a|man:dlopen(3)
4309
4310 `baddr`::
4311 Memory base address (where the dynamic linker placed the shared
4312 object).
4313
4314 `sopath`::
4315 File system path to the loaded shared object.
4316
4317 `size`::
4318 File size of the the loaded shared object.
4319
4320 `mtime`::
4321 Last modification time (seconds since Epoch time) of the loaded shared
4322 object.
4323
4324 |`dlclose`
4325 a|man:dlclose(3)
4326
4327 `baddr`::
4328 Memory base address (where the dynamic linker placed the shared
4329 object).
4330 |====
4331
4332
4333 [role="since-2.4"]
4334 [[java-application]]
4335 === User space Java agent
4336
4337 You can instrument a Java application which uses one of the following
4338 logging frameworks:
4339
4340 * The https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[**`java.util.logging`**]
4341 (JUL) core logging facilities.
4342 * http://logging.apache.org/log4j/1.2/[**Apache log4j 1.2**], since
4343 LTTng 2.6. Note that Apache Log4j{nbsp}2 is not supported.
4344
4345 Each log statement emits an LTTng event once the
4346 application initializes the <<lttng-ust-agents,LTTng-UST Java agent>>
4347 package.
4348
4349 [role="img-100"]
4350 .LTTng-UST Java agent imported by a Java application.
4351 image::java-app.png[]
4352
4353 NOTE: We use http://openjdk.java.net/[OpenJDK] 7 for development and
4354 https://ci.lttng.org/[continuous integration], thus this version is
4355 directly supported. However, the LTTng-UST Java agent is also
4356 tested with OpenJDK 6.
4357
4358 To use the LTTng-UST Java agent:
4359
4360 . In the Java application's source code, import the LTTng-UST Java
4361 agent:
4362 +
4363 --
4364 [source,java]
4365 ----
4366 import org.lttng.ust.agent.LTTngAgent;
4367 ----
4368 --
4369
4370 . As soon as possible after the entry point of the application,
4371 initialize the LTTng-UST Java agent:
4372 +
4373 --
4374 [source,java]
4375 ----
4376 LTTngAgent lttngAgent = LTTngAgent.getLTTngAgent();
4377 ----
4378 --
4379 +
4380 Any log statement that the application executes before this
4381 initialization does not emit an LTTng event.
4382
4383 . Use `java.util.logging` and/or log4j log statements and configuration
4384 as usual. Since the LTTng-UST Java agent adds a handler to the _root_
4385 loggers, you can trace any log statement from any logger.
4386
4387 . Before exiting the application, dispose the LTTng-UST Java agent:
4388 +
4389 --
4390 [source,java]
4391 ----
4392 lttngAgent.dispose();
4393 ----
4394 --
4395 +
4396 This is not strictly necessary, but it is recommended for a clean
4397 disposal of the agent's resources.
4398 +
4399 Any log statement that the application executes after this disposal does
4400 not emit an LTTng event.
4401
4402 . Include the LTTng-UST Java agent's JAR file, path:{liblttng-ust-agent.jar},
4403 in the
4404 https://docs.oracle.com/javase/tutorial/essential/environment/paths.html[class path]
4405 when building the Java application.
4406 +
4407 path:{liblttng-ust-agent.jar} is typically located in
4408 dir:{/usr/share/java}.
4409 +
4410 IMPORTANT: The LTTng-UST Java agent must be
4411 <<installing-lttng,installed>> for the logging framework your
4412 application uses.
4413
4414 .[[jul]]Use the LTTng-UST Java agent with `java.util.logging`.
4415 ====
4416 [source,java]
4417 .path:{Test.java}
4418 ----
4419 import java.util.logging.Logger;
4420 import org.lttng.ust.agent.LTTngAgent;
4421
4422 public class Test
4423 {
4424 private static final int answer = 42;
4425
4426 public static void main(String[] argv) throws Exception
4427 {
4428 // Create a logger
4429 Logger logger = Logger.getLogger("jello");
4430
4431 // Call this as soon as possible (before logging)
4432 LTTngAgent lttngAgent = LTTngAgent.getLTTngAgent();
4433
4434 // Log at will!
4435 logger.info("some info");
4436 logger.warning("some warning");
4437 Thread.sleep(500);
4438 logger.finer("finer information; the answer is " + answer);
4439 Thread.sleep(123);
4440 logger.severe("error!");
4441
4442 // Not mandatory, but cleaner
4443 lttngAgent.dispose();
4444 }
4445 }
4446 ----
4447
4448 You can build this example like this:
4449
4450 [role="term"]
4451 ----
4452 javac -cp /usr/share/java/liblttng-ust-agent.jar Test.java
4453 ----
4454
4455 You can run the compiled class like this:
4456
4457 [role="term"]
4458 ----
4459 java -cp /usr/share/java/liblttng-ust-agent.jar:. Test
4460 ----
4461 ====
4462
4463 .[[log4j]]Use the LTTng-UST Java agent with Apache log4j 1.2.
4464 ====
4465 [source,java]
4466 .path:{Test.java}
4467 ----
4468 import org.apache.log4j.Logger;
4469 import org.apache.log4j.BasicConfigurator;
4470 import org.lttng.ust.agent.LTTngAgent;
4471
4472 public class Test
4473 {
4474 private static final int answer = 42;
4475
4476 public static void main(String[] argv) throws Exception
4477 {
4478 // Create and configure a logger
4479 Logger logger = Logger.getLogger(Test.class);
4480 BasicConfigurator.configure();
4481
4482 // Call this as soon as possible (before logging)
4483 LTTngAgent lttngAgent = LTTngAgent.getLTTngAgent();
4484
4485 // Log at will!
4486 logger.info("some info");
4487 logger.warn("some warning");
4488 Thread.sleep(500);
4489 logger.debug("debug information; the answer is " + answer);
4490 Thread.sleep(123);
4491 logger.error("error!");
4492 logger.fatal("fatal error!");
4493
4494 // Not mandatory, but cleaner
4495 lttngAgent.dispose();
4496 }
4497 }
4498 ----
4499
4500 You can build this example like this:
4501
4502 [role="term"]
4503 ----
4504 javac -cp /usr/share/java/liblttng-ust-agent.jar:$LOG4JCP Test.java
4505 ----
4506
4507 where `$LOG4JCP` is the path to log4j's JAR file.
4508
4509 You can run the compiled class like this:
4510
4511 [role="term"]
4512 ----
4513 java -cp /usr/share/java/liblttng-ust-agent.jar:$LOG4JCP:. Test
4514 ----
4515 ====
4516
4517 When you <<enabling-disabling-events,create an event rule>>, use the
4518 `--jul` (`java.util.logging`) or `--log4j` (log4j) option to target
4519 the desired Java
4520 <<domain,tracing domain>>. You can also use the `--loglevel` or
4521 `--loglevel-only` option to target a range of JUL/log4j log levels or a
4522 specific JUL/log4j log level.
4523
4524
4525 [role="since-2.7"]
4526 [[python-application]]
4527 === User space Python agent
4528
4529 You can instrument a Python 2 or Python 3 application which uses the
4530 standard https://docs.python.org/3/library/logging.html[`logging`]
4531 package.
4532
4533 Each log statement emits an LTTng event once the
4534 application module imports the
4535 <<lttng-ust-agents,LTTng-UST Python agent>> package.
4536
4537 [role="img-100"]
4538 .A Python application importing the LTTng-UST Python agent.
4539 image::python-app.png[]
4540
4541 To use the LTTng-UST Python agent:
4542
4543 . In the Python application's source code, import the LTTng-UST Python
4544 agent:
4545 +
4546 --
4547 [source,python]
4548 ----
4549 import lttngust
4550 ----
4551 --
4552 +
4553 The LTTng-UST Python agent automatically adds its logging handler to the
4554 root logger at import time.
4555 +
4556 Any log statement that the application executes before this import does
4557 not emit an LTTng event.
4558 +
4559 IMPORTANT: The LTTng-UST Python agent must be
4560 <<installing-lttng,installed>>.
4561
4562 . Use log statements and logging configuration as usual.
4563 Since the LTTng-UST Python agent adds a handler to the _root_
4564 logger, you can trace any log statement from any logger.
4565
4566 .Use the LTTng-UST Python agent.
4567 ====
4568 [source,python]
4569 ----
4570 import lttngust
4571 import logging
4572 import time
4573
4574
4575 def example():
4576 logging.basicConfig()
4577 logger = logging.getLogger('my-logger')
4578
4579 while True:
4580 logger.debug('debug message')
4581 logger.info('info message')
4582 logger.warn('warn message')
4583 logger.error('error message')
4584 logger.critical('critical message')
4585 time.sleep(1)
4586
4587
4588 if __name__ == '__main__':
4589 example()
4590 ----
4591
4592 NOTE: `logging.basicConfig()`, which adds to the root logger a basic
4593 logging handler which prints to the standard error stream, is not
4594 strictly required for LTTng-UST tracing to work, but in versions of
4595 Python preceding 3.2, you could see a warning message which indicates
4596 that no handler exists for the logger `my-logger`.
4597 ====
4598
4599 When you <<enabling-disabling-events,create an event rule>>, use the
4600 `--python` option to target the Python
4601 <<domain,tracing domain>>. You can also use
4602 the `--loglevel` or `--loglevel-only` option to target a range of
4603 Python log levels or a specific Python log level.
4604
4605 When an application imports the LTTng-UST Python agent, the agent tries
4606 to register to a <<lttng-sessiond,session daemon>>. Note that you must
4607 start the session daemon _before_ you start the Python application.
4608 If a session daemon is found, the agent tries to register to it
4609 during 5{nbsp}seconds, after which the application continues without
4610 LTTng tracing support. You can override this timeout value with the
4611 env:LTTNG_UST_PYTHON_REGISTER_TIMEOUT environment variable
4612 (milliseconds).
4613
4614 If the session daemon stops while a Python application with an imported
4615 LTTng-UST Python agent runs, the agent retries to connect and to
4616 register to a session daemon every 3{nbsp}seconds. You can override this
4617 delay with the env:LTTNG_UST_PYTHON_REGISTER_RETRY_DELAY environment
4618 variable.
4619
4620
4621 [role="since-2.5"]
4622 [[proc-lttng-logger-abi]]
4623 === LTTng logger
4624
4625 The `lttng-tracer` Linux kernel module, part of
4626 <<lttng-modules,LTTng-modules>>, creates the special LTTng logger file
4627 path:{/proc/lttng-logger} when it's loaded. Any application can write
4628 text data to this file to emit an LTTng event.
4629
4630 [role="img-100"]
4631 .An application writes to the LTTng logger file to emit an LTTng event.
4632 image::lttng-logger.png[]
4633
4634 The LTTng logger is the quickest method--not the most efficient,
4635 however--to add instrumentation to an application. It is designed
4636 mostly to instrument shell scripts:
4637
4638 [role="term"]
4639 ----
4640 echo "Some message, some $variable" > /proc/lttng-logger
4641 ----
4642
4643 Any event that the LTTng logger emits is named `lttng_logger` and
4644 belongs to the Linux kernel <<domain,tracing domain>>. However, unlike
4645 other instrumentation points in the kernel tracing domain, **any Unix
4646 user** can <<enabling-disabling-events,create an event rule>> which
4647 matches its event name, not only the root user or users in the tracing
4648 group.
4649
4650 To use the LTTng logger:
4651
4652 * From any application, write text data to the path:{/proc/lttng-logger}
4653 file.
4654
4655 The `msg` field of `lttng_logger` event records contains the
4656 recorded message.
4657
4658 NOTE: The maximum message length of an LTTng logger event is
4659 1024{nbsp}bytes. Writing more than this makes the LTTng logger emit more
4660 than one event to contain the remaining data.
4661
4662 You should not use the LTTng logger to trace a user application which
4663 can be instrumented in a more efficient way, namely:
4664
4665 * <<c-application,C and $$C++$$ applications>>.
4666 * <<java-application,Java applications>>.
4667 * <<python-application,Python applications>>.
4668
4669
4670 [[instrumenting-linux-kernel]]
4671 === LTTng kernel tracepoints
4672
4673 NOTE: This section shows how to _add_ instrumentation points to the
4674 Linux kernel. The kernel's subsystems are already thoroughly
4675 instrumented at strategic places for LTTng when you
4676 <<installing-lttng,install>> the <<lttng-modules,LTTng-modules>>
4677 package.
4678
4679 ////
4680 There are two methods to instrument the Linux kernel:
4681
4682 . <<linux-add-lttng-layer,Add an LTTng layer>> over an existing ftrace
4683 tracepoint which uses the `TRACE_EVENT()` API.
4684 +
4685 Choose this if you want to instrumentation a Linux kernel tree with an
4686 instrumentation point compatible with ftrace, perf, and SystemTap.
4687
4688 . Use an <<linux-lttng-tracepoint-event,LTTng-only approach>> to
4689 instrument an out-of-tree kernel module.
4690 +
4691 Choose this if you don't need ftrace, perf, or SystemTap support.
4692 ////
4693
4694
4695 [[linux-add-lttng-layer]]
4696 ==== [[instrumenting-linux-kernel-itself]][[mainline-trace-event]][[lttng-adaptation-layer]]Add an LTTng layer to an existing ftrace tracepoint
4697
4698 This section shows how to add an LTTng layer to existing ftrace
4699 instrumentation using the `TRACE_EVENT()` API.
4700
4701 This section does not document the `TRACE_EVENT()` macro. You can
4702 read the following articles to learn more about this API:
4703
4704 * http://lwn.net/Articles/379903/[Using the TRACE_EVENT() macro (Part 1)]
4705 * http://lwn.net/Articles/381064/[Using the TRACE_EVENT() macro (Part 2)]
4706 * http://lwn.net/Articles/383362/[Using the TRACE_EVENT() macro (Part 3)]
4707
4708 The following procedure assumes that your ftrace tracepoints are
4709 correctly defined in their own header and that they are created in
4710 one source file using the `CREATE_TRACE_POINTS` definition.
4711
4712 To add an LTTng layer over an existing ftrace tracepoint:
4713
4714 . Make sure the following kernel configuration options are
4715 enabled:
4716 +
4717 --
4718 * `CONFIG_MODULES`
4719 * `CONFIG_KALLSYMS`
4720 * `CONFIG_HIGH_RES_TIMERS`
4721 * `CONFIG_TRACEPOINTS`
4722 --
4723
4724 . Build the Linux source tree with your custom ftrace tracepoints.
4725 . Boot the resulting Linux image on your target system.
4726 +
4727 Confirm that the tracepoints exist by looking for their names in the
4728 dir:{/sys/kernel/debug/tracing/events/subsys} directory, where `subsys`
4729 is your subsystem's name.
4730
4731 . Get a copy of the latest LTTng-modules{nbsp}{revision}:
4732 +
4733 --
4734 [role="term"]
4735 ----
4736 cd $(mktemp -d) &&
4737 wget http://lttng.org/files/lttng-modules/lttng-modules-latest-2.8.tar.bz2 &&
4738 tar -xf lttng-modules-latest-2.8.tar.bz2 &&
4739 cd lttng-modules-2.8.*
4740 ----
4741 --
4742
4743 . In dir:{instrumentation/events/lttng-module}, relative to the root
4744 of the LTTng-modules source tree, create a header file named
4745 +__subsys__.h+ for your custom subsystem +__subsys__+ and write your
4746 LTTng-modules tracepoint definitions using the LTTng-modules
4747 macros in it.
4748 +
4749 Start with this template:
4750 +
4751 --
4752 [source,c]
4753 .path:{instrumentation/events/lttng-module/my_subsys.h}
4754 ----
4755 #undef TRACE_SYSTEM
4756 #define TRACE_SYSTEM my_subsys
4757
4758 #if !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ)
4759 #define _LTTNG_MY_SUBSYS_H
4760
4761 #include "../../../probes/lttng-tracepoint-event.h"
4762 #include <linux/tracepoint.h>
4763
4764 LTTNG_TRACEPOINT_EVENT(
4765 /*
4766 * Format is identical to TRACE_EVENT()'s version for the three
4767 * following macro parameters:
4768 */
4769 my_subsys_my_event,
4770 TP_PROTO(int my_int, const char *my_string),
4771 TP_ARGS(my_int, my_string),
4772
4773 /* LTTng-modules specific macros */
4774 TP_FIELDS(
4775 ctf_integer(int, my_int_field, my_int)
4776 ctf_string(my_bar_field, my_bar)
4777 )
4778 )
4779
4780 #endif /* !defined(_LTTNG_MY_SUBSYS_H) || defined(TRACE_HEADER_MULTI_READ) */
4781
4782 #include "../../../probes/define_trace.h"
4783 ----
4784 --
4785 +
4786 The entries in the `TP_FIELDS()` section are the list of fields for the
4787 LTTng tracepoint. This is similar to the `TP_STRUCT__entry()` part of
4788 ftrace's `TRACE_EVENT()` macro.
4789 +
4790 See <<lttng-modules-tp-fields,Tracepoint fields macros>> for a
4791 complete description of the available `ctf_*()` macros.
4792
4793 . Create the LTTng-modules probe's kernel module C source file,
4794 +probes/lttng-probe-__subsys__.c+, where +__subsys__+ is your
4795 subsystem name:
4796 +
4797 --
4798 [source,c]
4799 .path:{probes/lttng-probe-my-subsys.c}
4800 ----
4801 #include <linux/module.h>
4802 #include "../lttng-tracer.h"
4803
4804 /*
4805 * Build-time verification of mismatch between mainline
4806 * TRACE_EVENT() arguments and the LTTng-modules adaptation
4807 * layer LTTNG_TRACEPOINT_EVENT() arguments.
4808 */
4809 #include <trace/events/my_subsys.h>
4810
4811 /* Create LTTng tracepoint probes */
4812 #define LTTNG_PACKAGE_BUILD
4813 #define CREATE_TRACE_POINTS
4814 #define TRACE_INCLUDE_PATH ../instrumentation/events/lttng-module
4815
4816 #include "../instrumentation/events/lttng-module/my_subsys.h"
4817
4818 MODULE_LICENSE("GPL and additional rights");
4819 MODULE_AUTHOR("Your name <your-email>");
4820 MODULE_DESCRIPTION("LTTng my_subsys probes");
4821 MODULE_VERSION(__stringify(LTTNG_MODULES_MAJOR_VERSION) "."
4822 __stringify(LTTNG_MODULES_MINOR_VERSION) "."
4823 __stringify(LTTNG_MODULES_PATCHLEVEL_VERSION)
4824 LTTNG_MODULES_EXTRAVERSION);
4825 ----
4826 --
4827
4828 . Edit path:{probes/Makefile} and add your new kernel module object
4829 next to the existing ones:
4830 +
4831 --
4832 [source,make]
4833 .path:{probes/Makefile}
4834 ----
4835 # ...
4836
4837 obj-m += lttng-probe-module.o
4838 obj-m += lttng-probe-power.o
4839
4840 obj-m += lttng-probe-my-subsys.o
4841
4842 # ...
4843 ----
4844 --
4845
4846 . Build and install the LTTng kernel modules:
4847 +
4848 --
4849 [role="term"]
4850 ----
4851 make KERNELDIR=/path/to/linux
4852 sudo make modules_install
4853 ----
4854 --
4855 +
4856 Replace `/path/to/linux` with the path to the Linux source tree where
4857 you defined and used tracepoints with ftrace's `TRACE_EVENT()` macro.
4858
4859 Note that you can also use the
4860 <<lttng-tracepoint-event-code,`LTTNG_TRACEPOINT_EVENT_CODE()` macro>>
4861 instead of `LTTNG_TRACEPOINT_EVENT()` to use custom local variables and
4862 C code that need to be executed before the event fields are recorded.
4863
4864 The best way to learn how to use the previous LTTng-modules macros is to
4865 inspect the existing LTTng-modules tracepoint definitions in the
4866 dir:{instrumentation/events/lttng-module} header files. Compare them
4867 with the Linux kernel mainline versions in the
4868 dir:{include/trace/events} directory of the Linux source tree.
4869
4870
4871 [role="since-2.7"]
4872 [[lttng-tracepoint-event-code]]
4873 ===== Use custom C code to access the data for tracepoint fields
4874
4875 Although we recommended to always use the
4876 <<lttng-adaptation-layer,`LTTNG_TRACEPOINT_EVENT()`>> macro to describe
4877 the arguments and fields of an LTTng-modules tracepoint when possible,
4878 sometimes you need a more complex process to access the data that the
4879 tracer records as event record fields. In other words, you need local
4880 variables and multiple C{nbsp}statements instead of simple
4881 argument-based expressions that you pass to the
4882 <<lttng-modules-tp-fields,`ctf_*()` macros of `TP_FIELDS()`>>.
4883
4884 You can use the `LTTNG_TRACEPOINT_EVENT_CODE()` macro instead of
4885 `LTTNG_TRACEPOINT_EVENT()` to declare custom local variables and define
4886 a block of C{nbsp}code to be executed before LTTng records the fields.
4887 The structure of this macro is:
4888
4889 [source,c]
4890 .`LTTNG_TRACEPOINT_EVENT_CODE()` macro syntax.
4891 ----
4892 LTTNG_TRACEPOINT_EVENT_CODE(
4893 /*
4894 * Format identical to the LTTNG_TRACEPOINT_EVENT()
4895 * version for the following three macro parameters:
4896 */
4897 my_subsys_my_event,
4898 TP_PROTO(int my_int, const char *my_string),
4899 TP_ARGS(my_int, my_string),
4900
4901 /* Declarations of custom local variables */
4902 TP_locvar(
4903 int a = 0;
4904 unsigned long b = 0;
4905 const char *name = "(undefined)";
4906 struct my_struct *my_struct;
4907 ),
4908
4909 /*
4910 * Custom code which uses both tracepoint arguments
4911 * (in TP_ARGS()) and local variables (in TP_locvar()).
4912 *
4913 * Local variables are actually members of a structure pointed
4914 * to by the special variable tp_locvar.
4915 */
4916 TP_code(
4917 if (my_int) {
4918 tp_locvar->a = my_int + 17;
4919 tp_locvar->my_struct = get_my_struct_at(tp_locvar->a);
4920 tp_locvar->b = my_struct_compute_b(tp_locvar->my_struct);
4921 tp_locvar->name = my_struct_get_name(tp_locvar->my_struct);
4922 put_my_struct(tp_locvar->my_struct);
4923
4924 if (tp_locvar->b) {
4925 tp_locvar->a = 1;
4926 }
4927 }
4928 ),
4929
4930 /*
4931 * Format identical to the LTTNG_TRACEPOINT_EVENT()
4932 * version for this, except that tp_locvar members can be
4933 * used in the argument expression parameters of
4934 * the ctf_*() macros.
4935 */
4936 TP_FIELDS(
4937 ctf_integer(unsigned long, my_struct_b, tp_locvar->b)
4938 ctf_integer(int, my_struct_a, tp_locvar->a)
4939 ctf_string(my_string_field, my_string)
4940 ctf_string(my_struct_name, tp_locvar->name)
4941 )
4942 )
4943 ----
4944
4945 IMPORTANT: The C code defined in `TP_code()` must not have any side
4946 effects when executed. In particular, the code must not allocate
4947 memory or get resources without deallocating this memory or putting
4948 those resources afterwards.
4949
4950
4951 [[instrumenting-linux-kernel-tracing]]
4952 ==== Load and unload a custom probe kernel module
4953
4954 You must load a <<lttng-adaptation-layer,created LTTng-modules probe
4955 kernel module>> in the kernel before it can emit LTTng events.
4956
4957 To load the default probe kernel modules and a custom probe kernel
4958 module:
4959
4960 * Use the `--extra-kmod-probes` option to give extra probe modules
4961 to load when starting a root <<lttng-sessiond,session daemon>>:
4962 +
4963 --
4964 .Load the `my_subsys`, `usb`, and the default probe modules.
4965 ====
4966 [role="term"]
4967 ----
4968 sudo lttng-sessiond --extra-kmod-probes=my_subsys,usb
4969 ----
4970 ====
4971 --
4972 +
4973 You only need to pass the subsystem name, not the whole kernel module
4974 name.
4975
4976 To load _only_ a given custom probe kernel module:
4977
4978 * Use the `--kmod-probes` option to give the probe modules
4979 to load when starting a root session daemon:
4980 +
4981 --
4982 .Load only the `my_subsys` and `usb` probe modules.
4983 ====
4984 [role="term"]
4985 ----
4986 sudo lttng-sessiond --kmod-probes=my_subsys,usb
4987 ----
4988 ====
4989 --
4990
4991 To confirm that a probe module is loaded:
4992
4993 * Use man:lsmod(8):
4994 +
4995 --
4996 [role="term"]
4997 ----
4998 lsmod | grep lttng_probe_usb
4999 ----
5000 --
5001
5002 To unload the loaded probe modules:
5003
5004 * Kill the session daemon with `SIGTERM`:
5005 +
5006 --
5007 [role="term"]
5008 ----
5009 sudo pkill lttng-sessiond
5010 ----
5011 --
5012 +
5013 You can also use man:modprobe(8)'s `--remove` option if the session
5014 daemon terminates abnormally.
5015
5016
5017 [[controlling-tracing]]
5018 == Tracing control
5019
5020 Once an application or a Linux kernel is
5021 <<instrumenting,instrumented>> for LTTng tracing,
5022 you can _trace_ it.
5023
5024 This section is divided in topics on how to use the various
5025 <<plumbing,components of LTTng>>, in particular the <<lttng-cli,cmd:lttng
5026 command-line tool>>, to _control_ the LTTng daemons and tracers.
5027
5028 Note that the <<online-lttng-manpages,Online LTTng man pages>> are
5029 more comprehensive than the guides of this section. Refer to them if
5030 your use case is not included in this section.
5031
5032
5033 [[start-sessiond]]
5034 === Start a session daemon
5035
5036 In some situations, you need to run a <<lttng-sessiond,session daemon>>
5037 _before_ you can use the cmd:lttng command-line tool.
5038
5039 You will see the following error when you run a command while no session
5040 daemon is running:
5041
5042 ----
5043 Error: No session daemon is available
5044 ----
5045
5046 The only command that automatically runs a session daemon is `create`,
5047 which you use to <<creating-destroying-tracing-sessions,create a tracing
5048 session>>. While this is most of the time the first operation that you
5049 do, sometimes it's not. Some examples are:
5050
5051 * <<list-instrumentation-points,List the available instrumentation points>>.
5052 * <<saving-loading-tracing-session,Load a tracing session configuration>>.
5053
5054 [[tracing-group]] Each Unix user must have its own running session
5055 daemon to trace user applications. The session daemon that the root user
5056 starts is the only one allowed to control the LTTng kernel tracer. Users
5057 that are part of the _tracing group_ can control the root session
5058 daemon. The default tracing group name is `tracing`; you can set it to
5059 something else with the `--group` option when you start the root session
5060 daemon.
5061
5062 To start a user session daemon:
5063
5064 * Run cmd:lttng-sessiond:
5065 +
5066 --
5067 [role="term"]
5068 ----
5069 lttng-sessiond --daemonize
5070 ----
5071 --
5072
5073 To start the root session daemon:
5074
5075 * Run cmd:lttng-sessiond as the root user:
5076 +
5077 --
5078 [role="term"]
5079 ----
5080 sudo lttng-sessiond --daemonize
5081 ----
5082 --
5083
5084 In both cases, remove the `--daemonize` option to start the session
5085 daemon in foreground.
5086
5087 To stop a session daemon, use cmd:kill on its process ID (standard
5088 `TERM` signal).
5089
5090 Note that some Linux distributions could manage the LTTng session daemon
5091 as a service. In this case, you should use the service manager to
5092 start, restart, and stop session daemons.
5093
5094
5095 [[creating-destroying-tracing-sessions]]
5096 === Create and destroy a tracing session
5097
5098 Almost all the LTTng control operations happen in the scope of
5099 a <<tracing-session,tracing session>>, which is the dialogue between the
5100 <<lttng-sessiond,session daemon>> and you.
5101
5102 To create a tracing session with a generated name:
5103
5104 * Use the `create` command:
5105 +
5106 --
5107 [role="term"]
5108 ----
5109 lttng create
5110 ----
5111 --
5112
5113 The created tracing session's name is `auto` followed by the
5114 creation date.
5115
5116 To create a tracing session with a specific name:
5117
5118 * Use the optional argument of the `create` command:
5119 +
5120 --
5121 [role="term"]
5122 ----
5123 lttng create my-session
5124 ----
5125 --
5126 +
5127 Replace `my-session` with the specific tracing session name.
5128
5129 LTTng appends the creation date to the created tracing session's name.
5130
5131 LTTng writes the traces of a tracing session in
5132 +$LTTNG_HOME/lttng-trace/__name__+ by default, where +__name__+ is the
5133 name of the tracing session. Note that the env:LTTNG_HOME environment
5134 variable defaults to `$HOME` if not set.
5135
5136 To output LTTng traces to a non-default location:
5137
5138 * Use the `--output` option of the `create` command:
5139 +
5140 --
5141 [role="term"]
5142 ----
5143 lttng create --output=/tmp/some-directory my-session
5144 ----
5145 --
5146
5147 You may create as many tracing sessions as you wish.
5148
5149 To list all the existing tracing sessions for your Unix user:
5150
5151 * Use the `list` command:
5152 +
5153 --
5154 [role="term"]
5155 ----
5156 lttng list
5157 ----
5158 --
5159
5160 When you create a tracing session, it is set as the _current tracing
5161 session_. The following man:lttng(1) commands operate on the current
5162 tracing session when you don't specify one:
5163
5164 [role="list-3-cols"]
5165 * `add-context`
5166 * `destroy`
5167 * `disable-channel`
5168 * `disable-event`
5169 * `enable-channel`
5170 * `enable-event`
5171 * `load`
5172 * `save`
5173 * `snapshot`
5174 * `start`
5175 * `stop`
5176 * `track`
5177 * `untrack`
5178 * `view`
5179
5180 To change the current tracing session:
5181
5182 * Use the `set-session` command:
5183 +
5184 --
5185 [role="term"]
5186 ----
5187 lttng set-session new-session
5188 ----
5189 --
5190 +
5191 Replace `new-session` by the name of the new current tracing session.
5192
5193 When you are done tracing in a given tracing session, you can destroy
5194 it. This operation frees the resources taken by the tracing session
5195 to destroy; it does not destroy the trace data that LTTng wrote for
5196 this tracing session.
5197
5198 To destroy the current tracing session:
5199
5200 * Use the `destroy` command:
5201 +
5202 --
5203 [role="term"]
5204 ----
5205 lttng destroy
5206 ----
5207 --
5208
5209
5210 [[list-instrumentation-points]]
5211 === List the available instrumentation points
5212
5213 The <<lttng-sessiond,session daemon>> can query the running instrumented
5214 user applications and the Linux kernel to get a list of available
5215 instrumentation points. For the Linux kernel <<domain,tracing domain>>,
5216 they are tracepoints and system calls. For the user space tracing
5217 domain, they are tracepoints. For the other tracing domains, they are
5218 logger names.
5219
5220 To list the available instrumentation points:
5221
5222 * Use the `list` command with the requested tracing domain's option
5223 amongst:
5224 +
5225 --
5226 * `--kernel`: Linux kernel tracepoints (your Unix user must be a root
5227 user, or it must be a member of the tracing group).
5228 * `--kernel --syscall`: Linux kernel system calls (your Unix user must
5229 be a root user, or it must be a member of the tracing group).
5230 * `--userspace`: user space tracepoints.
5231 * `--jul`: `java.util.logging` loggers.
5232 * `--log4j`: Apache log4j loggers.
5233 * `--python`: Python loggers.
5234 --
5235
5236 .List the available user space tracepoints.
5237 ====
5238 [role="term"]
5239 ----
5240 lttng list --userspace
5241 ----
5242 ====
5243
5244 .List the available Linux kernel system call tracepoints.
5245 ====
5246 [role="term"]
5247 ----
5248 lttng list --kernel --syscall
5249 ----
5250 ====
5251
5252
5253 [[enabling-disabling-events]]
5254 === Create and enable an event rule
5255
5256 Once you <<creating-destroying-tracing-sessions,create a tracing
5257 session>>, you can create <<event,event rules>> with the
5258 `enable-event` command.
5259
5260 You specify each condition with a command-line option. The available
5261 condition options are shown in the following table.
5262
5263 [role="growable",cols="asciidoc,asciidoc,default"]
5264 .Condition command-line options for the `enable-event` command.
5265 |====
5266 |Option |Description |Applicable tracing domains
5267
5268 |
5269 One of:
5270
5271 . `--syscall`
5272 . +--probe=__ADDR__+
5273 . +--function=__ADDR__+
5274
5275 |
5276 Instead of using the default _tracepoint_ instrumentation type, use:
5277
5278 . A Linux system call.
5279 . A Linux https://lwn.net/Articles/132196/[KProbe] (symbol or address).
5280 . The entry and return points of a Linux function (symbol or address).
5281
5282 |Linux kernel.
5283
5284 |First positional argument.
5285
5286 |
5287 Tracepoint or system call name. In the case of a Linux KProbe or
5288 function, this is a custom name given to the event rule. With the
5289 JUL, log4j, and Python domains, this is a logger name.
5290
5291 With a tracepoint, logger, or system call name, the last character
5292 can be `*` to match anything that remains.
5293
5294 |All.
5295
5296 |
5297 One of:
5298
5299 . +--loglevel=__LEVEL__+
5300 . +--loglevel-only=__LEVEL__+
5301
5302 |
5303 . Match only tracepoints or log statements with a logging level at
5304 least as severe as +__LEVEL__+.
5305 . Match only tracepoints or log statements with a logging level
5306 equal to +__LEVEL__+.
5307
5308 You can get the list of available logging level names with
5309 `lttng enable-event --help`.
5310
5311 |User space, JUL, log4j, and Python.
5312
5313 |+--exclude=__EXCLUSIONS__+
5314
5315 |
5316 When you use a `*` character at the end of the tracepoint or logger
5317 name (first positional argument), exclude the specific names in the
5318 comma-delimited list +__EXCLUSIONS__+.
5319
5320 |
5321 User space, JUL, log4j, and Python.
5322
5323 |+--filter=__EXPR__+
5324
5325 |
5326 Match only events which satisfy the expression +__EXPR__+.
5327
5328 +__EXPR__+ is a C-like logical expression where identifiers are event
5329 fields (preceded with `$ctx.` for context fields). Nested expressions
5330 with `(` and `)`, and all the logical and comparison operators of the C
5331 language are supported. The precedence rules of those operators are the
5332 same as in the C language.
5333
5334 When a comparison includes a non-existent event field, the whole filter
5335 expression evaluates to false.
5336
5337 C integer and floating point number constants are supported, as well as
5338 literal strings between double quotes (`"`). Literal strings can
5339 contain a wildcard character (`*`) at the end to match anything that
5340 remains. This wildcard can be escaped using `\*`.
5341
5342 Note that, although it is possible to use this option with the JUL,
5343 log4j, and Python tracing domains, the tracer evalutes the expression
5344 against the equivalent user space event.
5345
5346 |All.
5347
5348 |====
5349
5350 See man:lttng(1)
5351 for more details about those command-line options.
5352
5353 You attach an event rule to a <<channel,channel>> on creation. If you
5354 do not specify the channel with the `--channel` option, and if the event
5355 rule to create is the first in its <<domain,tracing domain>> for a given
5356 tracing session, then LTTng creates a _default channel_ for you. This
5357 default channel is reused in subsequent invocations of the
5358 `enable-event` command for the same tracing domain.
5359
5360 An event rule is always enabled at creation time.
5361
5362 The following examples show how you can combine the previous
5363 command-line options to create simple to more complex event rules.
5364
5365 .Create an event rule targetting a Linux kernel tracepoint (default channel).
5366 ====
5367 [role="term"]
5368 ----
5369 lttng enable-event --kernel sched_switch
5370 ----
5371 ====
5372
5373 .Create an event rule matching four Linux kernel system calls (default channel).
5374 ====
5375 [role="term"]
5376 ----
5377 lttng enable-event --kernel --syscall open,write,read,close
5378 ----
5379 ====
5380
5381 .Create an event rule matching a Linux kernel tracepoint with a filter expression (default channel).
5382 ====
5383 [role="term"]
5384 ----
5385 lttng enable-event --kernel sched_switch --filter='prev_comm == "bash"'
5386 ----
5387
5388 IMPORTANT: Make sure to always quote the filter string when you
5389 use man:lttng(1) from a shell.
5390 ====
5391
5392 .Create an event rule matching any user space tracepoint of a given tracepoint provider with a log level range (default channel).
5393 ====
5394 [role="term"]
5395 ----
5396 lttng enable-event --userspace my_app:'*' --loglevel=TRACE_INFO
5397 ----
5398
5399 IMPORTANT: Make sure to always quote the wildcard character when you
5400 use man:lttng(1) from a shell.
5401 ====
5402
5403 .Create an event rule matching multiple Python loggers with a wildcard and with exclusions (default channel).
5404 ====
5405 [role="term"]
5406 ----
5407 lttng enable-event --python my-app.'*' \
5408 --exclude='my-app.module,my-app.hello'
5409 ----
5410 ====
5411
5412 .Create an event rule matching any Apache log4j logger with a specific log level (default channel).
5413 ====
5414 [role="term"]
5415 ----
5416 lttng enable-event --log4j --all --loglevel-only=LOG4J_WARN
5417 ----
5418 ====
5419
5420 .Create an event rule attached to a specific channel matching a specific user space tracepoint provider and tracepoint.
5421 ====
5422 [role="term"]
5423 ----
5424 lttng enable-event --userspace my_app:my_tracepoint --channel=my-channel
5425 ----
5426 ====
5427
5428 The event rules of a given channel form a whitelist: as soon as an
5429 emitted event passes one of them, LTTng can record the event. For
5430 example, an event named `my_app:my_tracepoint` emitted from a user space
5431 tracepoint with a `TRACE_ERROR` log level passes both of the following
5432 rules:
5433
5434 [role="term"]
5435 ----
5436 lttng enable-event --userspace my_app:my_tracepoint
5437 lttng enable-event --userspace my_app:my_tracepoint \
5438 --loglevel=TRACE_INFO
5439 ----
5440
5441 The second event rule is redundant: the first one includes
5442 the second one.
5443
5444
5445 [[disable-event-rule]]
5446 === Disable an event rule
5447
5448 To disable an event rule that you <<enabling-disabling-events,created>>
5449 previously, use the `disable-event` command. This command disables _all_
5450 the event rules (of a given tracing domain and channel) which match an
5451 instrumentation point. The other conditions are not supported as of
5452 LTTng{nbsp}{revision}.
5453
5454 The LTTng tracer does not record an emitted event which passes
5455 a _disabled_ event rule.
5456
5457 .Disable an event rule matching a Python logger (default channel).
5458 ====
5459 [role="term"]
5460 ----
5461 lttng disable-event --python my-logger
5462 ----
5463 ====
5464
5465 .Disable an event rule matching all `java.util.logging` loggers (default channel).
5466 ====
5467 [role="term"]
5468 ----
5469 lttng disable-event --jul '*'
5470 ----
5471 ====
5472
5473 .Disable _all_ the event rules of the default channel.
5474 ====
5475 The `--all-events` option is not, like the `--all` option of
5476 `enable-event`, the equivalent of the event name `*` (wildcard): it
5477 disables _all_ the event rules of a given channel.
5478
5479 [role="term"]
5480 ----
5481 lttng disable-event --jul --all-events
5482 ----
5483 ====
5484
5485 NOTE: You cannot delete an event rule once you create it.
5486
5487
5488 [[status]]
5489 === Get the status of a tracing session
5490
5491 To get the status of a tracing session, that is, its channels, event
5492 rules, and their attributes:
5493
5494 * Use the `list` command with the tracing session's name:
5495 +
5496 --
5497 [role="term"]
5498 ----
5499 lttng list my-session
5500 ----
5501 --
5502 +
5503 Replace `my-session` with your tracing session's name.
5504
5505
5506 [[basic-tracing-session-control]]
5507 === Start and stop a tracing session
5508
5509 Once you <<creating-destroying-tracing-sessions,create a tracing
5510 session>> and
5511 <<enabling-disabling-events,create one or more event rules>>,
5512 you can start and stop the tracers for this tracing session.
5513
5514 To start tracing in the current tracing session:
5515
5516 * Use the `start` command:
5517 +
5518 --
5519 [role="term"]
5520 ----
5521 lttng start
5522 ----
5523 --
5524
5525 To stop tracing in the current tracing session:
5526
5527 * Use the `stop` command:
5528 +
5529 --
5530 [role="term"]
5531 ----
5532 lttng stop
5533 ----
5534 --
5535
5536 LTTng is very flexible: you can launch user applications before
5537 or after the you start the tracers. The tracers only record the events
5538 if they pass enabled event rules and if they occur while the tracers are
5539 started.
5540
5541
5542 [[enabling-disabling-channels]]
5543 === Create a channel
5544
5545 Once you create a tracing session, you can create a <<channel,channel>>
5546 with the `enable-channel` command.
5547
5548 Note that LTTng automatically creates a default channel when, for a
5549 given <<domain,tracing domain>>, no channels exist and you
5550 <<enabling-disabling-events,create>> the first event rule. This default
5551 channel is named `channel0` and its attributes are set to reasonable
5552 values. Therefore, you only need to create a channel when you need
5553 non-default attributes.
5554
5555 You specify each non-default channel attribute with a command-line
5556 option when you use the `enable-channel` command. The available
5557 command-line options are:
5558
5559 [role="growable",cols="asciidoc,asciidoc"]
5560 .Command-line options for the `enable-channel` command.
5561 |====
5562 |Option |Description
5563
5564 |`--overwrite`
5565
5566 |
5567 Use the _overwrite_
5568 <<channel-overwrite-mode-vs-discard-mode,event loss mode>> instead of
5569 the default _discard_ mode.
5570
5571 |`--buffers-pid` (user space tracing domain only)
5572
5573 |
5574 Use the per-process <<channel-buffering-schemes,buffering scheme>>
5575 instead of the default per-user buffering scheme.
5576
5577 |+--subbuf-size=__SIZE__+
5578
5579 |
5580 Allocate sub-buffers of +__SIZE__+ bytes (power of two), for each CPU,
5581 either for each Unix user (default), or for each instrumented process.
5582
5583 See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>.
5584
5585 |+--num-subbuf=__COUNT__+
5586
5587 |
5588 Allocate +__COUNT__+ sub-buffers (power of two), for each CPU, either
5589 for each Unix user (default), or for each instrumented process.
5590
5591 See <<channel-subbuf-size-vs-subbuf-count,Sub-buffer count and size>>.
5592
5593 |+--tracefile-size=__SIZE__+
5594
5595 |
5596 Set the maximum size of each trace file that this channel writes within
5597 a stream to +__SIZE__+ bytes instead of no maximum.
5598
5599 See <<tracefile-rotation,Trace file count and size>>.
5600
5601 |+--tracefile-count=__COUNT__+
5602
5603 |
5604 Limit the number of trace files that this channel creates to
5605 +__COUNT__+ channels instead of no limit.
5606
5607 See <<tracefile-rotation,Trace file count and size>>.
5608
5609 |+--switch-timer=__PERIODUS__+
5610
5611 |
5612 Set the <<channel-switch-timer,switch timer period>>
5613 to +__PERIODUS__+{nbsp}µs.
5614
5615 |+--read-timer=__PERIODUS__+
5616
5617 |
5618 Set the <<channel-read-timer,read timer period>>
5619 to +__PERIODUS__+{nbsp}µs.
5620
5621 |+--output=__TYPE__+ (Linux kernel tracing domain only)
5622
5623 |
5624 Set the channel's output type to +__TYPE__+, either `mmap` or `splice`.
5625
5626 |====
5627
5628 See man:lttng(1)
5629 for more details about those command-line options.
5630
5631 You can only create a channel in the Linux kernel and user space
5632 <<domain,tracing domains>>: other tracing domains have their own
5633 channel created on the fly when
5634 <<enabling-disabling-events,creating event rules>>.
5635
5636 [IMPORTANT]
5637 ====
5638 Because of a current LTTng limitation, you must create all channels
5639 _before_ you <<basic-tracing-session-control,start tracing>> in a given
5640 tracing session, that is, before the first time you run `lttng start`.
5641
5642 Since LTTng automatically creates a default channel when you use the
5643 `enable-event` command with a specific tracing domain, you cannot, for
5644 example, create a Linux kernel event rule, start tracing, and then
5645 create a user space event rule, because no user space channel exists yet
5646 and it's too late to create one.
5647
5648 For this reason, make sure to configure your channels properly
5649 before starting the tracers for the first time!
5650 ====
5651
5652 The following examples show how you can combine the previous
5653 command-line options to create simple to more complex channels.
5654
5655 .Create a Linux kernel channel with default attributes.
5656 ====
5657 [role="term"]
5658 ----
5659 lttng enable-channel --kernel my-channel
5660 ----
5661 ====
5662
5663 .Create a user space channel with 4 sub-buffers or 1{nbsp}MiB each, per CPU, per instrumented process.
5664 ====
5665 [role="term"]
5666 ----
5667 lttng enable-channel --userspace --num-subbuf=4 --subbuf-size=1M \
5668 --buffers-pid my-channel
5669 ----
5670 ====
5671
5672 .Create a Linux kernel channel which rotates 8 trace files of 4{nbsp}MiB each for each stream
5673 ====
5674 [role="term"]
5675 ----
5676 lttng enable-channel --kernel --tracefile-count=8 \
5677 --tracefile-size=4194304 my-channel
5678 ----
5679 ====
5680
5681 .Create a user space channel in overwrite (or _flight recorder_) mode.
5682 ====
5683 [role="term"]
5684 ----
5685 lttng enable-channel --userspace --overwrite my-channel
5686 ----
5687 ====
5688
5689 You can <<enabling-disabling-events,create>> the same event rule in
5690 two different channels:
5691
5692 [role="term"]
5693 ----
5694 lttng enable-event --userspace --channel=my-channel app:tp
5695 lttng enable-event --userspace --channel=other-channel app:tp
5696 ----
5697
5698 If both channels are enabled, when a tracepoint named `app:tp` is
5699 reached, LTTng records two events, one for each channel.
5700
5701
5702 [[disable-channel]]
5703 === Disable a channel
5704
5705 To disable a specific channel that you <<enabling-disabling-channels,created>>
5706 previously, use the `disable-channel` command.
5707
5708 .Disable a specific Linux kernel channel.
5709 ====
5710 [role="term"]
5711 ----
5712 lttng disable-channel --kernel my-channel
5713 ----
5714 ====
5715
5716 The state of a channel precedes the individual states of event rules
5717 attached to it: event rules which belong to a disabled channel, even if
5718 they are enabled, are also considered disabled.
5719
5720
5721 [[adding-context]]
5722 === Add context fields to a channel
5723
5724 Event record fields in trace files provide important information about
5725 events that occured previously, but sometimes some external context may
5726 help you solve a problem faster. Examples of context fields are:
5727
5728 * The **process ID**, **thread ID**, **process name**, and
5729 **process priority** of the thread in which the event occurs.
5730 * The **hostname** of the system on which the event occurs.
5731 * The current values of many possible **performance counters** using
5732 perf, for example:
5733 ** CPU cycles, stalled cycles, idle cycles, and the other cycle types.
5734 ** Cache misses.
5735 ** Branch instructions, misses, and loads.
5736 ** CPU faults.
5737
5738 To get the full list of available context fields, see
5739 `lttng add-context --help`. Some context fields are reserved for a
5740 specific <<domain,tracing domain>> (Linux kernel or user space).
5741
5742 You add context fields to <<channel,channels>>. All the events
5743 that a channel with added context fields records contain those fields.
5744
5745 To add context fields to one or all the channels of a given tracing
5746 session, use the `add-context` command.
5747
5748 .Add context fields to all the channels of the current tracing session.
5749 ====
5750 The following command line adds the virtual process identifier and
5751 the per-thread CPU cycles count fields to all the user space channels
5752 of the current tracing session.
5753
5754 [role="term"]
5755 ----
5756 lttng add-context --userspace --type=vpid --type=perf:thread:cpu-cycles
5757 ----
5758 ====
5759
5760 .Add a context field to a specific channel.
5761 ====
5762 The following command line adds the thread identifier context field
5763 to the Linux kernel channel named `my-channel` in the current
5764 tracing session.
5765
5766 [role="term"]
5767 ----
5768 lttng add-context --kernel --channel=my-channel --type=tid
5769 ----
5770 ====
5771
5772 NOTE: You cannot remove context fields from a channel once you add it.
5773
5774
5775 [role="since-2.7"]
5776 [[pid-tracking]]
5777 === Track process IDs
5778
5779 It's often useful to allow only specific process IDs (PIDs) to emit
5780 events. For example, you may wish to record all the system calls made by
5781 a given process (Ă  la http://linux.die.net/man/1/strace[strace]).
5782
5783 The `track` and `untrack` commands serve this purpose. Both commands
5784 operate on a whitelist of process IDs. You _add_ entries to this
5785 whitelist with the `track` command and remove entries with the `untrack`
5786 command. Any process which has one of the PIDs in the whitelist is
5787 allowed to emit LTTng events which pass an enabled <<event,event rule>>.
5788
5789 NOTE: The PID tracker tracks the _numeric process IDs_. Should a
5790 process with a given tracked ID exit and another process be given this
5791 ID, then the latter would also be allowed to emit events.
5792
5793 .Track and untrack process IDs.
5794 ====
5795 For the sake of the following example, assume the target system has 16
5796 possible PIDs.
5797
5798 When you
5799 <<creating-destroying-tracing-sessions,create a tracing session>>,
5800 the whitelist contains all the possible PIDs:
5801
5802 [role="img-100"]
5803 .All PIDs are tracked.
5804 image::track-all.png[]
5805
5806 When the whitelist is full and you use the `track` command to specify
5807 some PIDs to track, LTTng first clears the whitelist, then it tracks
5808 the specific PIDs. After:
5809
5810 [role="term"]
5811 ----
5812 lttng track --pid=3,4,7,10,13
5813 ----
5814
5815 the whitelist is:
5816
5817 [role="img-100"]
5818 .PIDs 3, 4, 7, 10, and 13 are tracked.
5819 image::track-3-4-7-10-13.png[]
5820
5821 You can add more PIDs to the whitelist afterwards:
5822
5823 [role="term"]
5824 ----
5825 lttng track --pid=1,15,16
5826 ----
5827
5828 The result is:
5829
5830 [role="img-100"]
5831 .PIDs 1, 15, and 16 are added to the whitelist.
5832 image::track-1-3-4-7-10-13-15-16.png[]
5833
5834 The `untrack` command removes entries from the PID tracker's whitelist.
5835 Given the previous example, the following command:
5836
5837 [role="term"]
5838 ----
5839 lttng untrack --pid=3,7,10,13
5840 ----
5841
5842 leads to this whitelist:
5843
5844 [role="img-100"]
5845 .PIDs 3, 7, 10, and 13 are removed from the whitelist.
5846 image::track-1-4-15-16.png[]
5847
5848 LTTng can track all possible PIDs again using the `--all` option:
5849
5850 [role="term"]
5851 ----
5852 lttng track --pid --all
5853 ----
5854
5855 The result is, again:
5856
5857 [role="img-100"]
5858 .All PIDs are tracked.
5859 image::track-all.png[]
5860 ====
5861
5862 .Track only specific PIDs
5863 ====
5864 A very typical use case with PID tracking is to start with an empty
5865 whitelist, then <<basic-tracing-session-control,start the tracers>>,
5866 and then add PIDs manually while tracers are active. You can accomplish
5867 this by using the `--all` option of the `untrack` command to clear the
5868 whitelist after you create a tracing session:
5869
5870 [role="term"]
5871 ----
5872 lttng untrack --pid --all
5873 ----
5874
5875 gives:
5876
5877 [role="img-100"]
5878 .No PIDs are tracked.
5879 image::untrack-all.png[]
5880
5881 If you trace with this whitelist configuration, the tracer records no
5882 events for this <<domain,tracing domain>> because no processes are
5883 tracked. You can use the `track` command as usual to track specific
5884 PIDs, for example:
5885
5886 [role="term"]
5887 ----
5888 lttng track --pid=6,11
5889 ----
5890
5891 Result:
5892
5893 [role="img-100"]
5894 .PIDs 6 and 11 are tracked.
5895 image::track-6-11.png[]
5896 ====
5897
5898
5899 [role="since-2.5"]
5900 [[saving-loading-tracing-session]]
5901 === Save and load tracing session configurations
5902
5903 Configuring a <<tracing-session,tracing session>> can be long. Some of
5904 the tasks involved are:
5905
5906 * <<enabling-disabling-channels,Create channels>> with
5907 specific attributes.
5908 * <<adding-context,Add context fields>> to specific channels.
5909 * <<enabling-disabling-events,Create event rules>> with specific log
5910 level and filter conditions.
5911
5912 If you use LTTng to solve real world problems, chances are you have to
5913 record events using the same tracing session setup over and over,
5914 modifying a few variables each time in your instrumented program
5915 or environment. To avoid constant tracing session reconfiguration,
5916 the cmd:lttng command-line tool can save and load tracing session
5917 configurations to/from XML files.
5918
5919 To save a given tracing session configuration:
5920
5921 * Use the `save` command:
5922 +
5923 --
5924 [role="term"]
5925 ----
5926 lttng save my-session
5927 ----
5928 --
5929 +
5930 Replace `my-session` with the name of the tracing session to save.
5931
5932 LTTng saves tracing session configurations to
5933 dir:{$LTTNG_HOME/.lttng/sessions} by default. Note that the
5934 env:LTTNG_HOME environment variable defaults to `$HOME` if not set. Use
5935 the `--output-path` option to change this destination directory.
5936
5937 LTTng saves all configuration parameters, for example:
5938
5939 * The tracing session name.
5940 * The trace data output path.
5941 * The channels with their state and all their attributes.
5942 * The context fields you added to channels.
5943 * The event rules with their state, log level and filter conditions.
5944
5945 To load a tracing session:
5946
5947 * Use the `load` command:
5948 +
5949 --
5950 [role="term"]
5951 ----
5952 lttng load my-session
5953 ----
5954 --
5955 +
5956 Replace `my-session` with the name of the tracing session to load.
5957
5958 When LTTng loads a configuration, it restores your saved tracing session
5959 as if you just configured it manually.
5960
5961 See man:lttng(1) for the complete list of command-line options. You
5962 can also save and load all many sessions at a time, and decide in which
5963 directory to output the XML files.
5964
5965
5966 [[sending-trace-data-over-the-network]]
5967 === Send trace data over the network
5968
5969 LTTng can send the recorded trace data to a remote system over the
5970 network instead of writing it to the local file system.
5971
5972 To send the trace data over the network:
5973
5974 . On the _remote_ system (which can also be the target system),
5975 start an LTTng <<lttng-relayd,relay daemon>>:
5976 +
5977 --
5978 [role="term"]
5979 ----
5980 lttng-relayd
5981 ----
5982 --
5983
5984 . On the _target_ system, create a tracing session configured to
5985 send trace data over the network:
5986 +
5987 --
5988 [role="term"]
5989 ----
5990 lttng create my-session --set-url=net://remote-system
5991 ----
5992 --
5993 +
5994 Replace `remote-system` by the host name or IP address of the
5995 remote system. See `lttng create --help` for the exact URL format.
5996
5997 . On the target system, use the cmd:lttng command-line tool as usual.
5998 When tracing is active, the target's consumer daemon sends sub-buffers
5999 to the relay daemon running on the remote system intead of flushing
6000 them to the local file system. The relay daemon writes the received
6001 packets to the local file system.
6002
6003 The relay daemon writes trace files to
6004 +$LTTNG_HOME/lttng-traces/__hostname__/__session__+ by default, where
6005 +__hostname__+ is the host name of the target system and +__session__+
6006 is the tracing session name. Note that the env:LTTNG_HOME environment
6007 variable defaults to `$HOME` if not set. Use the `--output` option of
6008 cmd:lttng-relayd to write trace files to another base directory.
6009
6010
6011 [role="since-2.4"]
6012 [[lttng-live]]
6013 === View events as LTTng emits them (noch:{LTTng} live)
6014
6015 LTTng live is a network protocol implemented by the
6016 <<lttng-relayd,relay daemon>> to allow compatible trace viewers to
6017 display events as LTTng emits them on the target system while tracing
6018 is active.
6019
6020 The relay daemon creates a _tee_: it forwards the trace data to both
6021 the local file system and to connected live viewers:
6022
6023 [role="img-90"]
6024 .The relay daemon creates a _tee_, forwarding the trace data to both trace files and a connected live viewer.
6025 image::live.png[]
6026
6027 To use LTTng live:
6028
6029 . On the _target system_, create a <<tracing-session,tracing session>>
6030 in _live mode_:
6031 +
6032 --
6033 [role="term"]
6034 ----
6035 lttng create --live my-session
6036 ----
6037 --
6038 +
6039 This spawns a local relay daemon.
6040
6041 . Start the live viewer and configure it to connect to the relay
6042 daemon. For example, with http://diamon.org/babeltrace[Babeltrace]:
6043 +
6044 --
6045 [role="term"]
6046 ----
6047 babeltrace --input-format=lttng-live net://localhost/host/hostname/my-session
6048 ----
6049 --
6050 +
6051 Replace:
6052 +
6053 --
6054 * `hostname` with the host name of the target system.
6055 * `my-session` with the name of the tracing session to view.
6056 --
6057
6058 . Configure the tracing session as usual with the cmd:lttng
6059 command-line tool, and <<basic-tracing-session-control,start tracing>>.
6060
6061 You can list the available live tracing sessions with Babeltrace:
6062
6063 [role="term"]
6064 ----
6065 babeltrace --input-format=lttng-live net://localhost
6066 ----
6067
6068 You can start the relay daemon on another system. In this case, you need
6069 to specify the relay daemon's URL when you create the tracing session
6070 with the `--set-url` option. You also need to replace `localhost`
6071 in the procedure above with the host name of the system on which the
6072 relay daemon is running.
6073
6074 See man:lttng(1) and man:lttng-relayd(8) for the complete list of
6075 command-line options.
6076
6077
6078 [role="since-2.3"]
6079 [[taking-a-snapshot]]
6080 === Take a snapshot of the current sub-buffers of a tracing session
6081
6082 The normal behavior of LTTng is to append full sub-buffers to growing
6083 trace data files. This is ideal to keep a full history of the events
6084 that occurred on the target system, but it can
6085 represent too much data in some situations. For example, you may wish
6086 to trace your application continuously until some critical situation
6087 happens, in which case you only need the latest few recorded
6088 events to perform the desired analysis, not multi-gigabyte trace files.
6089
6090 With the `snapshot` command, you can take a snapshot of the current
6091 sub-buffers of a given <<tracing-session,tracing session>>. LTTng can
6092 write the snapshot to the local file system or send it over the network.
6093
6094 To take a snapshot:
6095
6096 . Create a tracing session in _snapshot mode_:
6097 +
6098 --
6099 [role="term"]
6100 ----
6101 lttng create --snapshot my-session
6102 ----
6103 --
6104 +
6105 The <<channel-overwrite-mode-vs-discard-mode,event loss mode>> of
6106 <<channel,channels>> created in this mode is automatically set to
6107 _overwrite_ (flight recorder mode).
6108
6109 . Configure the tracing session as usual with the cmd:lttng
6110 command-line tool, and <<basic-tracing-session-control,start tracing>>.
6111
6112 . **Optional**: When you need to take a snapshot, stop tracing.
6113 +
6114 You can take a snapshot when the tracers are active, but if you stop
6115 them first, you are sure that the data in the sub-buffers does not
6116 change before you actually take the snapshot.
6117
6118 . Take a snapshot:
6119 +
6120 --
6121 [role="term"]
6122 ----
6123 lttng snapshot record --name=my-first-snapshot
6124 ----
6125 --
6126 +
6127 LTTng writes the current sub-buffers of all the current tracing
6128 session's channels to trace files on the local file system. Those trace
6129 files have `my-first-snapshot` in their name.
6130
6131 There is no difference between the format of a normal trace file and the
6132 format of a snapshot: viewers of LTTng traces also support LTTng
6133 snapshots.
6134
6135 By default, LTTng writes snapshot files to the path shown by
6136 `lttng snapshot list-output`. You can change this path or decide to send
6137 snapshots over the network using either:
6138
6139 . An output path or URL that you specify when you create the
6140 tracing session.
6141 . An snapshot output path or URL that you add using
6142 `lttng snapshot add-output`
6143 . An output path or URL that you provide directly to the
6144 `lttng snapshot record` command.
6145
6146 Method 3 overrides method 2, which overrides method 1. When you
6147 specify a URL, a relay daemon must listen on a remote system (see
6148 <<sending-trace-data-over-the-network,Send trace data over the network>>).
6149
6150
6151 [role="since-2.6"]
6152 [[mi]]
6153 === Use the machine interface
6154
6155 With any command of the cmd:lttng command-line tool, you can use the
6156 `--mi=xml` argument (before the command name) to get an XML machine
6157 interface output, for example:
6158
6159 [role="term"]
6160 ----
6161 lttng --mi=xml enable-event --kernel --syscall open
6162 ----
6163
6164 A schema definition (XSD) is
6165 https://github.com/lttng/lttng-tools/blob/stable-{revision}/src/common/mi_lttng.xsd[available]
6166 to ease the integration with external tools as much as possible.
6167
6168
6169 [role="since-2.7"]
6170 [[persistent-memory-file-systems]]
6171 === Record trace data on persistent memory file systems
6172
6173 https://en.wikipedia.org/wiki/Non-volatile_random-access_memory[Non-volatile random-access memory]
6174 (NVRAM) is random-access memory that retains its information when power
6175 is turned off (non-volatile). Systems with such memory can store data
6176 structures in RAM and retrieve them after a reboot, without flushing
6177 to typical _storage_.
6178
6179 Linux supports NVRAM file systems thanks to either
6180 http://pramfs.sourceforge.net/[PRAMFS] or
6181 https://www.kernel.org/doc/Documentation/filesystems/dax.txt[DAX]{nbsp}+{nbsp}http://lkml.iu.edu/hypermail/linux/kernel/1504.1/03463.html[pmem]
6182 (requires Linux 4.1+).
6183
6184 This section does not describe how to operate such file systems;
6185 we assume that you have a working persistent memory file system.
6186
6187 When you create a <<tracing-session,tracing session>>, you can specify
6188 the path of the shared memory holding the sub-buffers. If you specify a
6189 location on an NVRAM file system, then you can retrieve the latest
6190 recorded trace data when the system reboots after a crash.
6191
6192 To record trace data on a persistent memory file system and retrieve the
6193 trace data after a system crash:
6194
6195 . Create a tracing session with a sub-buffer shared memory path located
6196 on an NVRAM file system:
6197 +
6198 --
6199 [role="term"]
6200 ----
6201 lttng create --shm-path=/path/to/shm
6202 ----
6203 --
6204
6205 . Configure the tracing session as usual with the cmd:lttng
6206 command-line tool, and <<basic-tracing-session-control,start tracing>>.
6207
6208 . After a system crash, use the cmd:lttng-crash command-line tool to
6209 view the trace data recorded on the NVRAM file system:
6210 +
6211 --
6212 [role="term"]
6213 ----
6214 lttng-crash /path/to/shm
6215 ----
6216 --
6217
6218 The binary layout of the ring buffer files is not exactly the same as
6219 the trace files layout. This is why you need to use the cmd:lttng-crash
6220 utility instead of your preferred trace viewer directly.
6221
6222 To convert the ring buffer files to LTTng trace files:
6223
6224 * Use the `--extract` option of cmd:lttng-crash:
6225 +
6226 --
6227 [role="term"]
6228 ----
6229 lttng-crash --extract=/path/to/trace /path/to/shm
6230 ----
6231 --
6232
6233 See man:lttng-crash(1) for the complete list of command-line options.
6234
6235
6236 [[reference]]
6237 == Reference
6238
6239 This section presents various references for LTTng packages such as
6240 links to online manpages, tables that the rest of the text needs,
6241 descriptions of library functions, and more.
6242
6243
6244 [[online-lttng-manpages]]
6245 === Online noch:{LTTng} manpages
6246
6247 LTTng packages currently install the following link:/man[man pages],
6248 available online using the links below:
6249
6250 * **LTTng-tools**
6251 ** man:lttng(1)
6252 ** man:lttng-crash(1)
6253 ** man:lttng-sessiond(8)
6254 ** man:lttng-relayd(8)
6255 * **LTTng-UST**
6256 ** man:lttng-gen-tp(1)
6257 ** man:lttng-ust(3)
6258 ** man:lttng-ust-cyg-profile(3)
6259 ** man:lttng-ust-dl(3)
6260
6261
6262 [[lttng-ust-ref]]
6263 === noch:{LTTng-UST}
6264
6265 This section presents references of the LTTng-UST package.
6266
6267
6268 [[liblttng-ust]]
6269 ==== noch:{LTTng-UST} library (+liblttng&#8209;ust+)
6270
6271 The LTTng-UST library, or `liblttng-ust`, is the main shared object
6272 against which user applications are linked to make LTTng user space
6273 tracing possible.
6274
6275 The <<c-application,C application>> guide shows the complete
6276 process to instrument, build and run a C/$$C++$$ application using
6277 LTTng-UST, while this section contains a few important tables.
6278
6279
6280 [[liblttng-ust-tp-fields]]
6281 ===== Tracepoint fields macros (for `TP_FIELDS()`)
6282
6283 The available macros to define tracepoint fields, which you must use
6284 within `TP_FIELDS()` in `TRACEPOINT_EVENT()`, are:
6285
6286 [role="func-desc growable",cols="asciidoc,asciidoc"]
6287 .Available macros to define LTTng-UST tracepoint fields
6288 |====
6289 |Macro |Description and parameters
6290
6291 |
6292 +ctf_integer(__t__, __n__, __e__)+
6293
6294 +ctf_integer_nowrite(__t__, __n__, __e__)+
6295 |
6296 Standard integer, displayed in base 10.
6297
6298 +__t__+::
6299 Integer C type (`int`, `long`, `size_t`, ...).
6300
6301 +__n__+::
6302 Field name.
6303
6304 +__e__+::
6305 Argument expression.
6306
6307 |+ctf_integer_hex(__t__, __n__, __e__)+
6308 |
6309 Standard integer, displayed in base 16.
6310
6311 +__t__+::
6312 Integer C type.
6313
6314 +__n__+::
6315 Field name.
6316
6317 +__e__+::
6318 Argument expression.
6319
6320 |+ctf_integer_network(__t__, __n__, __e__)+
6321 |
6322 Integer in network byte order (big-endian), displayed in base 10.
6323
6324 +__t__+::
6325 Integer C type.
6326
6327 +__n__+::
6328 Field name.
6329
6330 +__e__+::
6331 Argument expression.
6332
6333 |+ctf_integer_network_hex(__t__, __n__, __e__)+
6334 |
6335 Integer in network byte order, displayed in base 16.
6336
6337 +__t__+::
6338 Integer C type.
6339
6340 +__n__+::
6341 Field name.
6342
6343 +__e__+::
6344 Argument expression.
6345
6346 |
6347 +ctf_float(__t__, __n__, __e__)+
6348
6349 +ctf_float_nowrite(__t__, __n__, __e__)+
6350 |
6351 Floating point number.
6352
6353 +__t__+::
6354 Floating point number C type (`float` or `double`).
6355
6356 +__n__+::
6357 Field name.
6358
6359 +__e__+::
6360 Argument expression.
6361
6362 |
6363 +ctf_string(__n__, __e__)+
6364
6365 +ctf_string_nowrite(__n__, __e__)+
6366 |
6367 Null-terminated string; undefined behavior if +__e__+ is `NULL`.
6368
6369 +__n__+::
6370 Field name.
6371
6372 +__e__+::
6373 Argument expression.
6374
6375 |
6376 +ctf_array(__t__, __n__, __e__, __s__)+
6377
6378 +ctf_array_nowrite(__t__, __n__, __e__, __s__)+
6379 |
6380 Statically-sized array of integers
6381
6382 +__t__+::
6383 Array element C type.
6384
6385 +__n__+::
6386 Field name.
6387
6388 +__e__+::
6389 Argument expression.
6390
6391 +__s__+::
6392 Number of elements.
6393
6394 |
6395 +ctf_array_text(__t__, __n__, __e__, __s__)+
6396
6397 +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+
6398 |
6399 Statically-sized array, printed as text.
6400
6401 The string does not need to be null-terminated.
6402
6403 +__t__+::
6404 Array element C type (always `char`).
6405
6406 +__n__+::
6407 Field name.
6408
6409 +__e__+::
6410 Argument expression.
6411
6412 +__s__+::
6413 Number of elements.
6414
6415 |
6416 +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+
6417
6418 +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+
6419 |
6420 Dynamically-sized array of integers.
6421
6422 The type of +__E__+ must be unsigned.
6423
6424 +__t__+::
6425 Array element C type.
6426
6427 +__n__+::
6428 Field name.
6429
6430 +__e__+::
6431 Argument expression.
6432
6433 +__T__+::
6434 Length expression C type.
6435
6436 +__E__+::
6437 Length expression.
6438
6439 |
6440 +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+
6441
6442 +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+
6443 |
6444 Dynamically-sized array, displayed as text.
6445
6446 The string does not need to be null-terminated.
6447
6448 The type of +__E__+ must be unsigned.
6449
6450 The behaviour is undefined if +__e__+ is `NULL`.
6451
6452 +__t__+::
6453 Sequence element C type (always `char`).
6454
6455 +__n__+::
6456 Field name.
6457
6458 +__e__+::
6459 Argument expression.
6460
6461 +__T__+::
6462 Length expression C type.
6463
6464 +__E__+::
6465 Length expression.
6466 |====
6467
6468 The `_nowrite` versions omit themselves from the session trace, but are
6469 otherwise identical. This means the tracer does not write the `_nowrite`
6470 fields to the trace. Their primary purpose is to make some of the event
6471 context available to the <<enabling-disabling-events,event filters>>
6472 without having to commit the data to sub-buffers.
6473
6474
6475 [[liblttng-ust-tracepoint-loglevel]]
6476 ===== Tracepoint log levels (for `TRACEPOINT_LOGLEVEL()`)
6477
6478 The following table shows the available log level values for the
6479 `TRACEPOINT_LOGLEVEL()` macro:
6480
6481 `TRACE_EMERG`::
6482 System is unusable.
6483
6484 `TRACE_ALERT`::
6485 Action must be taken immediately.
6486
6487 `TRACE_CRIT`::
6488 Critical conditions.
6489
6490 `TRACE_ERR`::
6491 Error conditions.
6492
6493 `TRACE_WARNING`::
6494 Warning conditions.
6495
6496 `TRACE_NOTICE`::
6497 Normal, but significant, condition.
6498
6499 `TRACE_INFO`::
6500 Informational message.
6501
6502 `TRACE_DEBUG_SYSTEM`::
6503 Debug information with system-level scope (set of programs).
6504
6505 `TRACE_DEBUG_PROGRAM`::
6506 Debug information with program-level scope (set of processes).
6507
6508 `TRACE_DEBUG_PROCESS`::
6509 Debug information with process-level scope (set of modules).
6510
6511 `TRACE_DEBUG_MODULE`::
6512 Debug information with module (executable/library) scope (set of units).
6513
6514 `TRACE_DEBUG_UNIT`::
6515 Debug information with compilation unit scope (set of functions).
6516
6517 `TRACE_DEBUG_FUNCTION`::
6518 Debug information with function-level scope.
6519
6520 `TRACE_DEBUG_LINE`::
6521 Debug information with line-level scope (TRACEPOINT_EVENT default).
6522
6523 `TRACE_DEBUG`::
6524 Debug-level message.
6525
6526 Log levels `TRACE_EMERG` through `TRACE_INFO` and `TRACE_DEBUG` match
6527 http://man7.org/linux/man-pages/man3/syslog.3.html[syslog]
6528 level semantics. Log levels `TRACE_DEBUG_SYSTEM` through `TRACE_DEBUG`
6529 offer more fine-grained selection of debug information.
6530
6531
6532 [[lttng-modules-ref]]
6533 === noch:{LTTng-modules}
6534
6535 This section presents references of the LTTng-modules package.
6536
6537
6538 [role="since-2.7"]
6539 [[lttng-modules-tp-fields]]
6540 ==== Tracepoint fields macros (for `TP_FIELDS()`)
6541
6542 [[tp-fast-assign]][[tp-struct-entry]]The available macros to define
6543 tracepoint fields, which must be listed within `TP_FIELDS()` in
6544 `LTTNG_TRACEPOINT_EVENT()`, are:
6545
6546 [role="func-desc growable",cols="asciidoc,asciidoc"]
6547 .Available macros to define LTTng-modules tracepoint fields
6548 |====
6549 |Macro |Description and parameters
6550
6551 |
6552 +ctf_integer(__t__, __n__, __e__)+
6553
6554 +ctf_integer_nowrite(__t__, __n__, __e__)+
6555
6556 +ctf_user_integer(__t__, __n__, __e__)+
6557
6558 +ctf_user_integer_nowrite(__t__, __n__, __e__)+
6559 |
6560 Standard integer, displayed in base 10.
6561
6562 +__t__+::
6563 Integer C type (`int`, `long`, `size_t`, ...).
6564
6565 +__n__+::
6566 Field name.
6567
6568 +__e__+::
6569 Argument expression.
6570
6571 |
6572 +ctf_integer_hex(__t__, __n__, __e__)+
6573
6574 +ctf_user_integer_hex(__t__, __n__, __e__)+
6575 |
6576 Standard integer, displayed in base 16.
6577
6578 +__t__+::
6579 Integer C type.
6580
6581 +__n__+::
6582 Field name.
6583
6584 +__e__+::
6585 Argument expression.
6586
6587 |+ctf_integer_oct(__t__, __n__, __e__)+
6588 |
6589 Standard integer, displayed in base 8.
6590
6591 +__t__+::
6592 Integer C type.
6593
6594 +__n__+::
6595 Field name.
6596
6597 +__e__+::
6598 Argument expression.
6599
6600 |
6601 +ctf_integer_network(__t__, __n__, __e__)+
6602
6603 +ctf_user_integer_network(__t__, __n__, __e__)+
6604 |
6605 Integer in network byte order (big-endian), displayed in base 10.
6606
6607 +__t__+::
6608 Integer C type.
6609
6610 +__n__+::
6611 Field name.
6612
6613 +__e__+::
6614 Argument expression.
6615
6616 |
6617 +ctf_integer_network_hex(__t__, __n__, __e__)+
6618
6619 +ctf_user_integer_network_hex(__t__, __n__, __e__)+
6620 |
6621 Integer in network byte order, displayed in base 16.
6622
6623 +__t__+::
6624 Integer C type.
6625
6626 +__n__+::
6627 Field name.
6628
6629 +__e__+::
6630 Argument expression.
6631
6632 |
6633 +ctf_string(__n__, __e__)+
6634
6635 +ctf_string_nowrite(__n__, __e__)+
6636
6637 +ctf_user_string(__n__, __e__)+
6638
6639 +ctf_user_string_nowrite(__n__, __e__)+
6640 |
6641 Null-terminated string; undefined behavior if +__e__+ is `NULL`.
6642
6643 +__n__+::
6644 Field name.
6645
6646 +__e__+::
6647 Argument expression.
6648
6649 |
6650 +ctf_array(__t__, __n__, __e__, __s__)+
6651
6652 +ctf_array_nowrite(__t__, __n__, __e__, __s__)+
6653
6654 +ctf_user_array(__t__, __n__, __e__, __s__)+
6655
6656 +ctf_user_array_nowrite(__t__, __n__, __e__, __s__)+
6657 |
6658 Statically-sized array of integers
6659
6660 +__t__+::
6661 Array element C type.
6662
6663 +__n__+::
6664 Field name.
6665
6666 +__e__+::
6667 Argument expression.
6668
6669 +__s__+::
6670 Number of elements.
6671
6672 |
6673 +ctf_array_text(__t__, __n__, __e__, __s__)+
6674
6675 +ctf_array_text_nowrite(__t__, __n__, __e__, __s__)+
6676
6677 +ctf_user_array_text(__t__, __n__, __e__, __s__)+
6678
6679 +ctf_user_array_text_nowrite(__t__, __n__, __e__, __s__)+
6680 |
6681 Statically-sized array, printed as text.
6682
6683 The string does not need to be null-terminated.
6684
6685 +__t__+::
6686 Array element C type (always `char`).
6687
6688 +__n__+::
6689 Field name.
6690
6691 +__e__+::
6692 Argument expression.
6693
6694 +__s__+::
6695 Number of elements.
6696
6697 |
6698 +ctf_sequence(__t__, __n__, __e__, __T__, __E__)+
6699
6700 +ctf_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+
6701
6702 +ctf_user_sequence(__t__, __n__, __e__, __T__, __E__)+
6703
6704 +ctf_user_sequence_nowrite(__t__, __n__, __e__, __T__, __E__)+
6705 |
6706 Dynamically-sized array of integers.
6707
6708 The type of +__E__+ must be unsigned.
6709
6710 +__t__+::
6711 Array element C type.
6712
6713 +__n__+::
6714 Field name.
6715
6716 +__e__+::
6717 Argument expression.
6718
6719 +__T__+::
6720 Length expression C type.
6721
6722 +__E__+::
6723 Length expression.
6724
6725 |+ctf_sequence_hex(__t__, __n__, __e__, __T__, __E__)+
6726 |
6727 Dynamically-sized array of integers, displayed in base 16.
6728
6729 The type of +__E__+ must be unsigned.
6730
6731 +__t__+::
6732 Array element C type.
6733
6734 +__n__+::
6735 Field name.
6736
6737 +__e__+::
6738 Argument expression.
6739
6740 +__T__+::
6741 Length expression C type.
6742
6743 +__E__+::
6744 Length expression.
6745
6746 |+ctf_sequence_network(__t__, __n__, __e__, __T__, __E__)+
6747 |
6748 Dynamically-sized array of integers in network byte order (big-endian),
6749 displayed in base 10.
6750
6751 The type of +__E__+ must be unsigned.
6752
6753 +__t__+::
6754 Array element C type.
6755
6756 +__n__+::
6757 Field name.
6758
6759 +__e__+::
6760 Argument expression.
6761
6762 +__T__+::
6763 Length expression C type.
6764
6765 +__E__+::
6766 Length expression.
6767
6768 |
6769 +ctf_sequence_text(__t__, __n__, __e__, __T__, __E__)+
6770
6771 +ctf_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+
6772
6773 +ctf_user_sequence_text(__t__, __n__, __e__, __T__, __E__)+
6774
6775 +ctf_user_sequence_text_nowrite(__t__, __n__, __e__, __T__, __E__)+
6776 |
6777 Dynamically-sized array, displayed as text.
6778
6779 The string does not need to be null-terminated.
6780
6781 The type of +__E__+ must be unsigned.
6782
6783 The behaviour is undefined if +__e__+ is `NULL`.
6784
6785 +__t__+::
6786 Sequence element C type (always `char`).
6787
6788 +__n__+::
6789 Field name.
6790
6791 +__e__+::
6792 Argument expression.
6793
6794 +__T__+::
6795 Length expression C type.
6796
6797 +__E__+::
6798 Length expression.
6799 |====
6800
6801 Use the `_user` versions when the argument expression, `e`, is
6802 a user space address. In the cases of `ctf_user_integer*()` and
6803 `ctf_user_float*()`, `&e` must be a user space address, thus `e` must
6804 be addressable.
6805
6806 The `_nowrite` versions omit themselves from the session trace, but are
6807 otherwise identical. This means the `_nowrite` fields won't be written
6808 in the recorded trace. Their primary purpose is to make some
6809 of the event context available to the
6810 <<enabling-disabling-events,event filters>> without having to
6811 commit the data to sub-buffers.
6812
6813
6814 [[glossary]]
6815 == Glossary
6816
6817 Terms related to LTTng and to tracing in general:
6818
6819 Babeltrace::
6820 The http://diamon.org/babeltrace[Babeltrace] project, which includes
6821 the cmd:babeltrace command, some libraries, and Python bindings.
6822
6823 <<channel-buffering-schemes,buffering scheme>>::
6824 A layout of sub-buffers applied to a given channel.
6825
6826 <<channel,channel>>::
6827 An entity which is responsible for a set of ring buffers.
6828 +
6829 <<event,Event rules>> are always attached to a specific channel.
6830
6831 clock::
6832 A reference of time for a tracer.
6833
6834 <<lttng-consumerd,consumer daemon>>::
6835 A process which is responsible for consuming the full sub-buffers
6836 and write them to a file system or send them over the network.
6837
6838 <<channel-overwrite-mode-vs-discard-mode,discard mode>>:: The event loss
6839 mode in which the tracer _discards_ new event records when there's no
6840 sub-buffer space left to store them.
6841
6842 event::
6843 The consequence of the execution of an instrumentation
6844 point, like a tracepoint that you manually place in some source code,
6845 or a Linux kernel KProbe.
6846 +
6847 An event is said to _occur_ at a specific time. Different actions can
6848 be taken upon the occurance of an event, like record the event's payload
6849 to a sub-buffer.
6850
6851 <<channel-overwrite-mode-vs-discard-mode,event loss mode>>::
6852 The mechanism by which event records of a given channel are lost
6853 (not recorded) when there is no sub-buffer space left to store them.
6854
6855 [[def-event-name]]event name::
6856 The name of an event, which is also the name of the event record.
6857 This is also called the _instrumentation point name_.
6858
6859 event record::
6860 A record, in a trace, of the payload of an event which occured.
6861
6862 <<event,event rule>>::
6863 Set of conditions which must be satisfied for one or more occuring
6864 events to be recorded.
6865
6866 `java.util.logging`::
6867 Java platform's
6868 https://docs.oracle.com/javase/7/docs/api/java/util/logging/package-summary.html[core logging facilities].
6869
6870 <<instrumenting,instrumentation>>::
6871 The use of LTTng probes to make a piece of software traceable.
6872
6873 instrumentation point::
6874 A point in the execution path of a piece of software that, when
6875 reached by this execution, can emit an event.
6876
6877 instrumentation point name::
6878 See _<<def-event-name,event name>>_.
6879
6880 log4j::
6881 A http://logging.apache.org/log4j/1.2/[logging library] for Java
6882 developed by the Apache Software Foundation.
6883
6884 log level::
6885 Level of severity of a log statement or user space
6886 instrumentation point.
6887
6888 LTTng::
6889 The _Linux Trace Toolkit: next generation_ project.
6890
6891 <<lttng-cli,cmd:lttng>>::
6892 A command-line tool provided by the LTTng-tools project which you
6893 can use to send and receive control messages to and from a
6894 session daemon.
6895
6896 LTTng analyses::
6897 The https://github.com/lttng/lttng-analyses[LTTng analyses] project,
6898 which is a set of analyzing programs that are used to obtain a
6899 higher level view of an LTTng trace.
6900
6901 cmd:lttng-consumerd::
6902 The name of the consumer daemon program.
6903
6904 cmd:lttng-crash::
6905 A utility provided by the LTTng-tools project which can convert
6906 ring buffer files (usually
6907 <<persistent-memory-file-systems,saved on a persistent memory file system>>)
6908 to trace files.
6909
6910 LTTng Documentation::
6911 This document.
6912
6913 <<lttng-live,LTTng live>>::
6914 A communication protocol between the relay daemon and live viewers
6915 which makes it possible to see events "live", as they are received by
6916 the relay daemon.
6917
6918 <<lttng-modules,LTTng-modules>>::
6919 The https://github.com/lttng/lttng-modules[LTTng-modules] project,
6920 which contains the Linux kernel modules to make the Linux kernel
6921 instrumentation points available for LTTng tracing.
6922
6923 cmd:lttng-relayd::
6924 The name of the relay daemon program.
6925
6926 cmd:lttng-sessiond::
6927 The name of the session daemon program.
6928
6929 LTTng-tools::
6930 The https://github.com/lttng/lttng-tools[LTTng-tools] project, which
6931 contains the various programs and libraries used to
6932 <<controlling-tracing,control tracing>>.
6933
6934 <<lttng-ust,LTTng-UST>>::
6935 The https://github.com/lttng/lttng-ust[LTTng-UST] project, which
6936 contains libraries to instrument user applications.
6937
6938 <<lttng-ust-agents,LTTng-UST Java agent>>::
6939 A Java package provided by the LTTng-UST project to allow the
6940 LTTng instrumentation of `java.util.logging` and Apache log4j 1.2
6941 logging statements.
6942
6943 <<lttng-ust-agents,LTTng-UST Python agent>>::
6944 A Python package provided by the LTTng-UST project to allow the
6945 LTTng instrumentation of Python logging statements.
6946
6947 <<channel-overwrite-mode-vs-discard-mode,overwrite mode>>::
6948 The event loss mode in which new event records overwrite older
6949 event records when there's no sub-buffer space left to store them.
6950
6951 <<channel-buffering-schemes,per-process buffering>>::
6952 A buffering scheme in which each instrumented process has its own
6953 sub-buffers for a given user space channel.
6954
6955 <<channel-buffering-schemes,per-user buffering>>::
6956 A buffering scheme in which all the processes of a Unix user share the
6957 same sub-buffer for a given user space channel.
6958
6959 <<lttng-relayd,relay daemon>>::
6960 A process which is responsible for receiving the trace data sent by
6961 a distant consumer daemon.
6962
6963 ring buffer::
6964 A set of sub-buffers.
6965
6966 <<lttng-sessiond,session daemon>>::
6967 A process which receives control commands from you and orchestrates
6968 the tracers and various LTTng daemons.
6969
6970 <<taking-a-snapshot,snapshot>>::
6971 A copy of the current data of all the sub-buffers of a given tracing
6972 session, saved as trace files.
6973
6974 sub-buffer::
6975 One part of an LTTng ring buffer which contains event records.
6976
6977 timestamp::
6978 The time information attached to an event when it is emitted.
6979
6980 trace (_noun_)::
6981 A set of files which are the concatenations of one or more
6982 flushed sub-buffers.
6983
6984 trace (_verb_)::
6985 The action of recording the events emitted by an application
6986 or by a system, or to initiate such recording by controlling
6987 a tracer.
6988
6989 Trace Compass::
6990 The http://tracecompass.org[Trace Compass] project and application.
6991
6992 tracepoint::
6993 An instrumentation point using the tracepoint mechanism of the Linux
6994 kernel or of LTTng-UST.
6995
6996 tracepoint definition::
6997 The definition of a single tracepoint.
6998
6999 tracepoint name::
7000 The name of a tracepoint.
7001
7002 tracepoint provider::
7003 A set of functions providing tracepoints to an instrumented user
7004 application.
7005 +
7006 Not to be confused with a _tracepoint provider package_: many tracepoint
7007 providers can exist within a tracepoint provider package.
7008
7009 tracepoint provider package::
7010 One or more tracepoint providers compiled as an object file or as
7011 a shared library.
7012
7013 tracer::
7014 A software which records emitted events.
7015
7016 <<domain,tracing domain>>::
7017 A namespace for event sources.
7018
7019 tracing group::
7020 The Unix group in which a Unix user can be to be allowed to trace the
7021 Linux kernel.
7022
7023 <<tracing-session,tracing session>>::
7024 A stateful dialogue between you and a <<lttng-sessiond,session
7025 daemon>>.
7026
7027 user application::
7028 An application running in user space, as opposed to a Linux kernel
7029 module, for example.
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