1 .TH "LTTNG" "1" "February 9, 2012" "" ""
4 lttng \(em LTTng 2.0 tracer control command line tool
10 lttng [OPTIONS] <COMMAND>
15 The LTTng project aims at providing highly efficient tracing tools for Linux.
16 It's tracers help tracking down performance issues and debugging problems
17 involving multiple concurrent processes and threads. Tracing across multiple
18 systems is also possible.
20 The \fBlttng\fP command line tool from the lttng-tools package is used to control
21 both kernel and user-space tracing. Every interactions with the tracer should
22 be done by this tool or by the liblttng-ctl provided with the lttng-tools
25 LTTng uses a session daemon (lttng-sessiond(8)), acting as a tracing registry,
26 which permits you to interact with multiple tracers (kernel and user-space)
27 inside the same container, a tracing session. Traces can be gathered from the
28 kernel and/or instrumented applications (lttng-ust(3)). Aggregating and reading
29 those traces is done using the babeltrace(1) text viewer.
31 In order to trace the kernel, the session daemon needs to be running as root.
32 LTTng provides the use of a \fBtracing group\fP (default: tracing). Whomever is
33 in that group can interact with the root session daemon and thus trace the
34 kernel. Session daemons can co-exist meaning that you can have a session daemon
35 running as Alice that can be used to trace her applications along side with a
36 root daemon or even a Bob daemon. We highly recommend to start the session
37 daemon at boot time for stable and long term tracing.
39 Every user-space applications instrumented with lttng-ust(3), will
40 automatically register to the session daemon. This feature gives you the
41 ability to list available traceable applications and tracepoints on a per user
42 basis. (See \fBlist\fP command).
46 This program follow the usual GNU command line syntax with long options starting with
47 two dashes. Below is a summary of the available options.
52 Show summary of possible options and commands.
54 .BR "\-v, \-\-verbose"
56 Three levels of verbosity are available which are triggered by putting additional v to
57 the option (\-vv or \-vvv)
60 Suppress all messages (even errors).
62 .BR "\-g, \-\-group NAME"
63 Set unix tracing group name. (default: tracing)
65 .BR "\-n, \-\-no-sessiond"
66 Don't automatically spawn a session daemon.
68 .BR "\-\-sessiond\-path"
69 Set session daemon full binary path.
71 .BR "\-\-list\-options"
72 Simple listing of lttng options.
74 .BR "\-\-list\-commands"
75 Simple listing of lttng commands.
81 Add context to event(s) and/or channel(s).
83 A context is basically extra information appended to a channel or event. For
84 instance, you could ask the tracer to add the PID information within the
85 "sched_switch" kernel event. You can also add performance monitoring unit
86 counters (perf PMU) using the perf kernel API).
88 For example, this command will add the context information 'prio' and two perf
89 counters (hardware branch misses and cache misses), to all events in the trace
92 # lttng add-context \-k \-t prio \-t perf:branch-misses \-t perf:cache-misses
94 Please take a look at the help (\-h/\-\-help) for a detailed list of available
97 If no channel and no event is given (\-c/\-e), the context is added to all
98 channels (which applies automatically to all events in that channel). Otherwise
99 the context will be added only to the channel (\-c) and/or event (\-e) indicated.
101 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
109 Show summary of possible options and commands.
110 \-s, \-\-session NAME
111 Apply on session name.
112 \-c, \-\-channel NAME
113 Apply on channel name.
117 Apply for the kernel tracer
119 Apply for the user-space tracer
121 Context type. You can repeat this option on the command line. Please
122 use "lttng add-context \-h" to list all available types.
127 .IP "\fBcalibrate\fP"
129 Quantify LTTng overhead
131 The LTTng calibrate command can be used to find out the combined average
132 overhead of the LTTng tracer and the instrumentation mechanisms used. This
133 overhead can be calibrated in terms of time or using any of the PMU performance
134 counter available on the system.
136 For now, the only calibration implemented is that of the kernel function
137 instrumentation (kretprobes).
139 * Calibrate kernel function instrumentation
141 Let's use an example to show this calibration. We use an i7 processor with 4
142 general-purpose PMU registers. This information is available by issuing dmesg,
143 looking for "generic registers".
145 This sequence of commands will gather a trace executing a kretprobe hooked on
146 an empty function, gathering PMU counters LLC (Last Level Cache) misses
147 information (see lttng add-context \-\-help to see the list of available PMU
150 # lttng create calibrate-function
151 # lttng enable-event calibrate \-\-kernel \-\-function lttng_calibrate_kretprobe
152 # lttng add-context \-\-kernel \-t perf:LLC-load-misses \-t perf:LLC-store-misses \\
153 \-t perf:LLC-prefetch-misses
155 # for a in $(seq 1 10); do \\
156 lttng calibrate \-\-kernel \-\-function;
159 # babeltrace $(ls \-1drt ~/lttng-traces/calibrate-function-* | tail \-n 1)
161 The output from babeltrace can be saved to a text file and opened in a
162 spreadsheet (e.g. oocalc) to focus on the per-PMU counter delta between
163 consecutive "calibrate_entry" and "calibrate_return" events. Note that these
164 counters are per-CPU, so scheduling events would need to be present to account
165 for migration between CPU. Therefore, for calibration purposes, only events
166 staying on the same CPU must be considered.
168 The average result, for the i7, on 10 samples:
171 perf_LLC_load_misses: 5.0 0.577
172 perf_LLC_store_misses: 1.6 0.516
173 perf_LLC_prefetch_misses: 9.0 14.742
175 As we can notice, the load and store misses are relatively stable across runs
176 (their standard deviation is relatively low) compared to the prefetch misses.
177 We can conclude from this information that LLC load and store misses can be
178 accounted for quite precisely, but prefetches within a function seems to behave
179 too erratically (not much causality link between the code executed and the CPU
180 prefetch activity) to be accounted for.
187 Show summary of possible options and commands.
189 Apply for the kernel tracer
191 Apply for the user-space tracer
193 Dynamic function entry/return probe (default)
198 .IP "\fBcreate\fP [OPTIONS] [NAME]
200 Create tracing session.
202 A tracing session contains channel(s) which contains event(s). It is domain
203 agnostic meaning that you can enable channels and events for either the
204 user-space tracer and/or the kernel tracer. It acts like a container
205 aggregating multiple tracing sources.
207 On creation, a \fB.lttngrc\fP file is created in your $HOME directory
208 containing the current session name. If NAME is omitted, a session name is
209 automatically created having this form: 'auto-yyyymmdd-hhmmss'.
211 If no \fB\-o, \-\-output\fP is specified, the traces will be written in
219 Show summary of possible options and commands.
221 Simple listing of options
223 Specify output path for traces
228 .IP "\fBdestroy\fP [OPTIONS] [NAME]"
230 Teardown tracing session
232 Free memory on the session daemon and tracer side. It's gone!
234 If NAME is omitted, the session name is taken from the .lttngrc file.
241 Show summary of possible options and commands.
243 Simple listing of options
248 .IP "\fBenable-channel\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
250 Enable tracing channel
252 To enable event, you must first enable a channel which contains event(s).
254 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
264 Simple listing of options
266 Apply on session name
268 Apply to the kernel tracer
270 Apply to the user-space tracer
273 Discard event when subbuffers are full (default)
275 Flight recorder mode : overwrites events when subbuffers are full
277 Subbuffer size in bytes (default: 4096, kernel default: 262144)
279 Number of subbuffers (default: 4)
280 Needs to be a power of 2 for kernel and ust tracers
282 Switch subbuffer timer interval in usec (default: 0)
283 Needs to be a power of 2 for kernel and ust tracers
285 Read timer interval in usec (default: 200)
290 .IP "\fBenable-event\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
294 A tracing event is always assigned to a channel. If \fB\-c, \-\-channel\fP is
295 omitted, a default channel named '\fBchannel0\fP' is created and the event is
296 added to it. For the user-space tracer, using \fB\-a, \-\-all\fP is the same as
297 using the wildcard "*".
299 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
307 Show summary of possible options and commands.
309 Simple listing of options
311 Apply on session name
313 Apply on channel name
315 Enable all tracepoints and syscalls
317 Apply for the kernel tracer
319 Apply for the user-space tracer
322 Tracepoint event (default)
323 - userspace tracer supports wildcards at end of string. Don't forget to
324 quote to deal with bash expansion.
330 \-\-probe [addr | symbol | symbol+offset]
331 Dynamic probe. Addr and offset can be octal (0NNN...), decimal (NNN...)
332 or hexadecimal (0xNNN...)
333 \-\-function [addr | symbol | symbol+offset]
334 Dynamic function entry/return probe. Addr and offset can be octal
335 (0NNN...), decimal (NNN...) or hexadecimal (0xNNN...)
338 Enabling syscalls tracing (kernel tracer), you will not be able to disable them
339 with disable-event. This is a known limitation. You can disable the entire
340 channel to do the trick.
343 .IP "\fBdisable-channel\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
345 Disable tracing channel
347 Disabling a channel makes all event(s) in that channel to stop tracing. You can
348 enable it back by calling \fBlttng enable-channel NAME\fP again.
350 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
358 Show summary of possible options and commands.
360 Simple listing of options
362 Apply on session name
364 Apply for the kernel tracer
366 Apply for the user-space tracer
369 .IP "\fBdisable-event\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
371 Disable tracing event
373 The event, once disabled, can be re-enabled by calling \fBlttng enable-event
376 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
384 Show summary of possible options and commands.
386 Simple listing of options
388 Apply on session name
390 Apply for the kernel tracer
392 Apply for the user-space tracer
395 .IP "\fBlist\fP [\-k|\-u] [SESSION [SESSION_OPTIONS]]"
397 List tracing session information.
399 With no arguments, it will list available tracing session(s).
401 With the session name, it will display the details of the session including
402 the trace file path, the associated channels and their state (activated
403 and deactivated), the activated events and more.
405 With \-k alone, it will list all available kernel events (except the system
407 With \-u alone, it will list all available user-space events from registered
408 applications. Here is an example of 'lttng list \-u':
410 PID: 7448 - Name: /tmp/lttng-ust/tests/hello/.libs/lt-hello
411 ust_tests_hello:tptest_sighandler (type: tracepoint)
412 ust_tests_hello:tptest (type: tracepoint)
414 You can now enable any event listed by using the name :
415 \fBust_tests_hello:tptest\fP.
422 Show summary of possible options and commands.
424 Simple listing of options
428 Select user-space domain.
431 \-c, \-\-channel NAME
432 List details of a channel
434 List available domain(s)
437 .IP "\fBset-session\fP NAME"
439 Set current session name
441 Will change the session name in the .lttngrc file.
448 Show summary of possible options and commands.
450 Simple listing of options
455 .IP "\fBstart\fP [OPTIONS] [NAME]"
459 It will start tracing for all tracers for a specific tracing session.
461 If NAME is omitted, the session name is taken from the .lttngrc file.
468 Show summary of possible options and commands.
470 Simple listing of options
475 .IP "\fBstop\fP [OPTIONS] [NAME]"
479 It will stop tracing for all tracers for a specific tracing session.
481 If NAME is omitted, the session name is taken from the .lttngrc file.
488 Show summary of possible options and commands.
490 Simple listing of options
497 Show version information
504 Show summary of possible options and commands.
506 Simple listing of options
511 .IP "\fBview\fP [SESSION_NAME] [OPTIONS]"
513 View traces of a tracing session
515 By default, the babeltrace viewer will be used for text viewing.
517 If SESSION_NAME is omitted, the session name is taken from the .lttngrc file.
527 Simple listing of options
528 \-t, \-\-trace-path PATH
529 Trace directory path for the viewer
531 Specify viewer and/or options to use
532 This will completely override the default viewers so
533 please make sure to specify the full command. The trace
534 directory path of the session will be appended at the end
556 No session found by the name given
559 Error in session creation
562 Error in application(s) listing
565 Session name already exists
568 Kernel tracer unavailable
574 Kernel channel exists
577 Kernel channel creation failed
580 Kernel channel not found
583 Kernel channel disable failed
586 Kernel channel enable failed
589 Kernel context failed
592 Kernel enable event failed
595 Kernel disable event failed
598 Kernel listing events failed
601 UST channel disable failed
604 UST channel enable failed
607 UST adding context failed
610 UST event enable failed
613 UST event disable failed
634 Tracing the kernel requires a root lttng-sessiond daemon and "tracing" group
638 Tracing already started
641 Tracing already stopped
643 .SH "ENVIRONMENT VARIABLES"
646 Note that all command line options override environment variables.
650 .IP "LTTNG_SESSIOND_PATH"
651 Allows one to specify the full session daemon binary path to lttng command line
652 tool. You can also use \-\-sessiond-path option having the same effect.
656 babeltrace(1), lttng-ust(3), lttng-sessiond(8)
661 No show stopper bugs are known yet in this version.
663 If you encounter any issues or usability problem, please report it on our
664 mailing list <lttng-dev@lists.lttng.org> to help improve this project.
668 lttng is distributed under the GNU General Public License version 2. See the file
671 A Web site is available at http://lttng.org for more information on the LTTng
674 You can also find our git tree at http://git.lttng.org.
676 Mailing lists for support and development: <lttng-dev@lists.lttng.org>.
678 You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
683 Thanks to Yannick Brosseau without whom this project would never have been so
684 lean and mean! Also thanks to the Ericsson teams working on tracing which
685 helped us greatly with detailed bug reports and unusual test cases.
687 Thanks to our beloved packager Alexandre Montplaisir-Goncalves (Ubuntu and PPA
688 maintainer) and Jon Bernard for our Debian packages.
690 Special thanks to Michel Dagenais and the DORSAL laboratory at Polytechnique de
691 Montreal for the LTTng journey.
696 lttng-tools was originally written by Mathieu Desnoyers, Julien Desfossez and
697 David Goulet. More people have since contributed to it. It is currently
698 maintained by David Goulet <dgoulet@efficios.com>.