1 .TH "LTTNG" "1" "July 17, 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.
245 Simple listing of options
250 .IP "\fBenable-channel\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
252 Enable tracing channel
254 To enable event, you must first enable a channel which contains event(s).
256 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
266 Simple listing of options
268 Apply on session name
270 Apply to the kernel tracer
272 Apply to the user-space tracer
275 Discard event when subbuffers are full (default)
277 Flight recorder mode : overwrites events when subbuffers are full
279 Subbuffer size in bytes (default: 4096, kernel default: 262144)
281 Number of subbuffers (default: 4)
282 Needs to be a power of 2 for kernel and ust tracers
284 Switch subbuffer timer interval in usec (default: 0)
285 Needs to be a power of 2 for kernel and ust tracers
287 Read timer interval in usec (default: 200)
292 .IP "\fBenable-event\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
296 A tracing event is always assigned to a channel. If \fB\-c, \-\-channel\fP is
297 omitted, a default channel named '\fBchannel0\fP' is created and the event is
298 added to it. For the user-space tracer, using \fB\-a, \-\-all\fP is the same as
299 using the wildcard "*".
301 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
309 Show summary of possible options and commands.
311 Simple listing of options
313 Apply on session name
315 Apply on channel name
317 Enable all tracepoints and syscalls
319 Apply for the kernel tracer
321 Apply for the user-space tracer
324 Tracepoint event (default)
325 - userspace tracer supports wildcards at end of string. Don't forget to
326 quote to deal with bash expansion.
332 \-\-probe [addr | symbol | symbol+offset]
333 Dynamic probe. Addr and offset can be octal (0NNN...), decimal (NNN...)
334 or hexadecimal (0xNNN...)
335 \-\-function [addr | symbol | symbol+offset]
336 Dynamic function entry/return probe. Addr and offset can be octal
337 (0NNN...), decimal (NNN...) or hexadecimal (0xNNN...)
340 Enabling syscalls tracing (kernel tracer), you will not be able to disable them
341 with disable-event. This is a known limitation. You can disable the entire
342 channel to do the trick.
344 \-\-filter 'expression'
345 Set a filter on a newly enabled event.
346 Filter expression on event fields, event recording
347 depends on evaluation. Only specify on first activation
348 of a given event within a session. Filter only allowed
349 when enabling events within a session before tracing is
350 started. If the filter fails to link with the event
351 within the traced domain, the event will be discarded.
352 Currently, filter is only implemented for the user-space
356 'intfield > 500 && intfield < 503'
357 '(stringfield == "test" || intfield != 10) && intfield > 33'
358 'doublefield > 1.1 && intfield < 5.3'
360 Wildcards are allowed at the end of strings:
362 In string literals, the escape character is a '\\'.
363 Use '\\*' for the '*' character, and '\\\\' for the
368 .IP "\fBdisable-channel\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
370 Disable tracing channel
372 Disabling a channel makes all event(s) in that channel to stop tracing. You can
373 enable it back by calling \fBlttng enable-channel NAME\fP again.
375 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
383 Show summary of possible options and commands.
385 Simple listing of options
387 Apply on session name
389 Apply for the kernel tracer
391 Apply for the user-space tracer
394 .IP "\fBdisable-event\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
396 Disable tracing event
398 The event, once disabled, can be re-enabled by calling \fBlttng enable-event
401 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
409 Show summary of possible options and commands.
411 Simple listing of options
413 Apply on session name
415 Apply for the kernel tracer
417 Apply for the user-space tracer
420 .IP "\fBlist\fP [\-k|\-u] [SESSION [SESSION_OPTIONS]]"
422 List tracing session information.
424 With no arguments, it will list available tracing session(s).
426 With the session name, it will display the details of the session including
427 the trace file path, the associated channels and their state (activated
428 and deactivated), the activated events and more.
430 With \-k alone, it will list all available kernel events (except the system
432 With \-u alone, it will list all available user-space events from registered
433 applications. Here is an example of 'lttng list \-u':
435 PID: 7448 - Name: /tmp/lttng-ust/tests/hello/.libs/lt-hello
436 ust_tests_hello:tptest_sighandler (type: tracepoint)
437 ust_tests_hello:tptest (type: tracepoint)
439 You can now enable any event listed by using the name :
440 \fBust_tests_hello:tptest\fP.
447 Show summary of possible options and commands.
449 Simple listing of options
453 Select user-space domain.
456 \-c, \-\-channel NAME
457 List details of a channel
459 List available domain(s)
462 .IP "\fBset-session\fP NAME"
464 Set current session name
466 Will change the session name in the .lttngrc file.
473 Show summary of possible options and commands.
475 Simple listing of options
480 .IP "\fBstart\fP [OPTIONS] [NAME]"
484 It will start tracing for all tracers for a specific tracing session.
486 If NAME is omitted, the session name is taken from the .lttngrc file.
493 Show summary of possible options and commands.
495 Simple listing of options
500 .IP "\fBstop\fP [OPTIONS] [NAME]"
504 It will stop tracing for all tracers for a specific tracing session.
506 If NAME is omitted, the session name is taken from the .lttngrc file.
513 Show summary of possible options and commands.
515 Simple listing of options
522 Show version information
529 Show summary of possible options and commands.
531 Simple listing of options
536 .IP "\fBview\fP [SESSION_NAME] [OPTIONS]"
538 View traces of a tracing session
540 By default, the babeltrace viewer will be used for text viewing.
542 If SESSION_NAME is omitted, the session name is taken from the .lttngrc file.
552 Simple listing of options
553 \-t, \-\-trace-path PATH
554 Trace directory path for the viewer
556 Specify viewer and/or options to use
557 This will completely override the default viewers so
558 please make sure to specify the full command. The trace
559 directory path of the session will be appended at the end
581 No session found by the name given
584 Error in session creation
587 Error in application(s) listing
590 Session name already exists
593 Kernel tracer unavailable
599 Kernel channel exists
602 Kernel channel creation failed
605 Kernel channel not found
608 Kernel channel disable failed
611 Kernel channel enable failed
614 Kernel context failed
617 Kernel enable event failed
620 Kernel disable event failed
623 Kernel listing events failed
626 UST channel disable failed
629 UST channel enable failed
632 UST adding context failed
635 UST event enable failed
638 UST event disable failed
659 Tracing the kernel requires a root lttng-sessiond daemon and "tracing" group
663 Tracing already started
666 Tracing already stopped
669 No UST consumer detected
672 No Kernel consumer detected
675 Event already enabled with different loglevel
677 .SH "ENVIRONMENT VARIABLES"
680 Note that all command line options override environment variables.
684 .IP "LTTNG_SESSIOND_PATH"
685 Allows one to specify the full session daemon binary path to lttng command line
686 tool. You can also use \-\-sessiond-path option having the same effect.
690 babeltrace(1), lttng-ust(3), lttng-sessiond(8)
695 No show stopper bugs are known yet in this version.
697 If you encounter any issues or usability problem, please report it on our
698 mailing list <lttng-dev@lists.lttng.org> to help improve this project.
702 lttng is distributed under the GNU General Public License version 2. See the file
705 A Web site is available at http://lttng.org for more information on the LTTng
708 You can also find our git tree at http://git.lttng.org.
710 Mailing lists for support and development: <lttng-dev@lists.lttng.org>.
712 You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
717 Thanks to Yannick Brosseau without whom this project would never have been so
718 lean and mean! Also thanks to the Ericsson teams working on tracing which
719 helped us greatly with detailed bug reports and unusual test cases.
721 Thanks to our beloved packager Alexandre Montplaisir-Goncalves (Ubuntu and PPA
722 maintainer) and Jon Bernard for our Debian packages.
724 Special thanks to Michel Dagenais and the DORSAL laboratory at Polytechnique de
725 Montreal for the LTTng journey.
730 lttng-tools was originally written by Mathieu Desnoyers, Julien Desfossez and
731 David Goulet. More people have since contributed to it. It is currently
732 maintained by David Goulet <dgoulet@efficios.com>.