1 .TH "LTTNG" "1" "December 3rd, 2012" "" ""
4 lttng \(em LTTng 2.x 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 allows 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 We introduce the notion of \fBtracing domains\fP which is essentially a type of
32 tracer (kernel or user space for now). In the future, we could see a third
33 tracer being for instance an hypervisor. For some commands, you'll need to
34 specify on which domain the command applies (-u or -k). For instance, enabling
35 a kernel event, you must specify the kernel domain to the command so we know
36 for which tracer this event is for.
38 In order to trace the kernel, the session daemon needs to be running as root.
39 LTTng provides the use of a \fBtracing group\fP (default: tracing). Whomever is
40 in that group can interact with the root session daemon and thus trace the
41 kernel. Session daemons can co-exist meaning that you can have a session daemon
42 running as Alice that can be used to trace her applications along side with a
43 root daemon or even a Bob daemon. We highly recommend to start the session
44 daemon at boot time for stable and long term tracing.
46 Every user-space applications instrumented with lttng-ust(3), will
47 automatically register to the session daemon. This feature gives you the
48 ability to list available traceable applications and tracepoints on a per user
49 basis. (See \fBlist\fP command).
53 This program follow the usual GNU command line syntax with long options starting with
54 two dashes. Below is a summary of the available options.
59 Show summary of possible options and commands.
61 .BR "\-v, \-\-verbose"
63 Three levels of verbosity are available which are triggered by putting additional v to
64 the option (\-vv or \-vvv)
67 Suppress all messages (even errors).
69 .BR "\-g, \-\-group NAME"
70 Set unix tracing group name. (default: tracing)
72 .BR "\-n, \-\-no-sessiond"
73 Don't automatically spawn a session daemon.
75 .BR "\-\-sessiond\-path PATH"
76 Set session daemon full binary path.
78 .BR "\-\-list\-options"
79 Simple listing of lttng options.
81 .BR "\-\-list\-commands"
82 Simple listing of lttng commands.
88 Add context to event(s) and/or channel(s).
90 A context is basically extra information appended to a channel. For instance,
91 you could ask the tracer to add the PID information for all events in a
92 channel. You can also add performance monitoring unit counters (perf PMU) using
95 For example, this command will add the context information 'prio' and two perf
96 counters (hardware branch misses and cache misses), to all events in the trace
99 # lttng add-context \-k \-t prio \-t perf:branch-misses \-t perf:cache-misses
101 Please take a look at the help (\-h/\-\-help) for a detailed list of available
104 If no channel is given (\-c), the context is added to all channels. Otherwise
105 the context will be added only to the given channel (\-c).
107 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
115 Show summary of possible options and commands.
116 \-s, \-\-session NAME
117 Apply on session name.
118 \-c, \-\-channel NAME
119 Apply on channel name.
121 Apply for the kernel tracer
123 Apply for the user-space tracer
125 Context type. You can repeat this option on the command line. Please
126 use "lttng add-context \-h" to list all available types.
131 .IP "\fBcalibrate\fP"
133 Quantify LTTng overhead
135 The LTTng calibrate command can be used to find out the combined average
136 overhead of the LTTng tracer and the instrumentation mechanisms used. This
137 overhead can be calibrated in terms of time or using any of the PMU performance
138 counter available on the system.
140 For now, the only calibration implemented is that of the kernel function
141 instrumentation (kretprobes).
143 * Calibrate kernel function instrumentation
145 Let's use an example to show this calibration. We use an i7 processor with 4
146 general-purpose PMU registers. This information is available by issuing dmesg,
147 looking for "generic registers".
149 This sequence of commands will gather a trace executing a kretprobe hooked on
150 an empty function, gathering PMU counters LLC (Last Level Cache) misses
151 information (see lttng add-context \-\-help to see the list of available PMU
154 # lttng create calibrate-function
155 # lttng enable-event calibrate \-\-kernel \-\-function lttng_calibrate_kretprobe
156 # lttng add-context \-\-kernel \-t perf:LLC-load-misses \-t perf:LLC-store-misses \\
157 \-t perf:LLC-prefetch-misses
159 # for a in $(seq 1 10); do \\
160 lttng calibrate \-\-kernel \-\-function;
163 # babeltrace $(ls \-1drt ~/lttng-traces/calibrate-function-* | tail \-n 1)
165 The output from babeltrace can be saved to a text file and opened in a
166 spreadsheet (e.g. oocalc) to focus on the per-PMU counter delta between
167 consecutive "calibrate_entry" and "calibrate_return" events. Note that these
168 counters are per-CPU, so scheduling events would need to be present to account
169 for migration between CPU. Therefore, for calibration purposes, only events
170 staying on the same CPU must be considered.
172 The average result, for the i7, on 10 samples:
175 perf_LLC_load_misses: 5.0 0.577
176 perf_LLC_store_misses: 1.6 0.516
177 perf_LLC_prefetch_misses: 9.0 14.742
179 As we can notice, the load and store misses are relatively stable across runs
180 (their standard deviation is relatively low) compared to the prefetch misses.
181 We can conclude from this information that LLC load and store misses can be
182 accounted for quite precisely, but prefetches within a function seems to behave
183 too erratically (not much causality link between the code executed and the CPU
184 prefetch activity) to be accounted for.
191 Show summary of possible options and commands.
193 Apply for the kernel tracer
195 Apply for the user-space tracer
197 Dynamic function entry/return probe (default)
202 .IP "\fBcreate\fP [NAME] [OPTIONS]
204 Create tracing session.
206 A tracing session contains channel(s) which contains event(s). It is domain
207 agnostic meaning that you can enable channels and events for either the
208 user-space tracer and/or the kernel tracer. It acts like a container
209 aggregating multiple tracing sources.
211 On creation, a \fB.lttngrc\fP file is created in your $HOME directory
212 containing the current session name. If NAME is omitted, a session name is
213 automatically created having this form: 'auto-yyyymmdd-hhmmss'.
215 If no \fB\-o, \-\-output\fP is specified, the traces will be written in
223 Show summary of possible options and commands.
225 Simple listing of options
227 Specify output path for traces
229 Using these options, each API call can be controlled individually. For
230 instance, \-C does not enable the consumer automatically. You'll need the \-e
234 Set URL for the consumer output destination. It is persistent for the
235 session lifetime. Redo the command to change it. This will set both
236 data and control URL for network.
237 \-C, \-\-ctrl-url=URL
238 Set control path URL. (Must use -D also)
239 \-D, \-\-data-url=URL
240 Set data path URL. (Must use -C also)
244 proto://[HOST|IP][:PORT1[:PORT2]][/TRACE_PATH]
246 Supported protocols are (proto):
248 Local filesystem full path.
251 This will use the default network transport layer which is TCP for both
252 control (PORT1) and data port (PORT2). The default ports are
253 respectively 5342 and 5343. Note that net[6]:// is not yet supported.
256 Can only be used with -C and -D together
258 NOTE: IPv6 address MUST be enclosed in brackets '[]' (rfc2732)
262 # lttng create -U net://192.168.1.42
263 Uses TCP and default ports for the given destination.
265 # lttng create -U net6://[fe80::f66d:4ff:fe53:d220]
266 Uses TCP, default ports and IPv6.
268 # lttng create s1 -U net://myhost.com:3229
269 Create session s1 and set its consumer to myhost.com on port 3229 for control.
274 .IP "\fBdestroy\fP [OPTIONS] [NAME]"
276 Teardown tracing session
278 Free memory on the session daemon and tracer side. It's gone!
280 If NAME is omitted, the session name is taken from the .lttngrc file.
287 Show summary of possible options and commands.
291 Simple listing of options
296 .IP "\fBenable-channel\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
298 Enable tracing channel
300 To enable an event, you must enable both the event and the channel that
303 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
306 It is important to note that if a certain type of buffers is used, the session
307 will be set with that type and all other subsequent channel need to have the
317 Simple listing of options
318 \-s, \-\-session NAME
319 Apply on session name
321 Apply to the kernel tracer
323 Apply to the user-space tracer
326 Discard event when subbuffers are full (default)
328 Flight recorder mode : overwrites events when subbuffers are full
330 Subbuffer size in bytes {+k,+M,+G}
331 (default UST uid: 131072, UST pid: 4096, kernel: 262144, metadata: 4096)
332 Rounded up to the next power of 2.
334 Number of subbuffers. (default UST uid: 4, UST pid: 4, kernel: 4, metadata: 2)
335 Rounded up to the next power of 2.
336 \-\-switch-timer USEC
337 Switch subbuffer timer interval in µsec.
338 (default UST uid: 0, UST pid: 0, kernel: 0, metadata: 0)
340 Read timer interval in µsec.
341 (default UST uid: 0, UST pid: 0, kernel: 200000, metadata: 0)
343 Channel output type. Possible values: mmap, splice
344 (default UST uid: mmap, UST pid: mmap, kernel: splice, metadata: mmap)
346 Use per UID buffer (\-u only). Buffers are shared between applications
347 that have the same UID.
349 Use per PID buffer (\-u only). Each application has its own buffers.
351 Use shared buffer for the whole system (\-k only)
352 \-C, \-\-tracefile-size SIZE
353 Maximum size of each tracefile within a stream (in bytes).
354 0 means unlimited. (default: 0)
355 \-W, \-\-tracefile-count COUNT
356 Used in conjunction with \-C option, this will limit the number
357 of files created to the specified count. 0 means unlimited. (default: 0)
361 $ lttng enable-channel -C 4096 -W 32 chan1
362 For each stream, the maximum size of a trace file will be 4096 bytes divided
363 over a \fBmaximum\fP of 32 different files. The file count is appended after
364 the stream number as seen in the following example. The last trace file is
365 smaller than 4096 since it was not completely filled.
367 ~/lttng-traces/[...]/chan1_0_0 (4096)
368 ~/lttng-traces/[...]/chan1_0_1 (4096)
369 ~/lttng-traces/[...]/chan1_0_2 (3245)
370 ~/lttng-traces/[...]/chan1_1_0 (4096)
373 $ lttng enable-channel -C 4096
374 This will create trace files of 4096 bytes and will create new ones as long as
375 there is data available.
380 .IP "\fBenable-event\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
384 A tracing event is always assigned to a channel. If \fB\-c, \-\-channel\fP is
385 omitted, a default channel named '\fBchannel0\fP' is created and the event is
386 added to it. For the user-space tracer, using \fB\-a, \-\-all\fP is the same as
387 using the wildcard "*".
389 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
397 Show summary of possible options and commands.
399 Simple listing of options
400 \-s, \-\-session NAME
401 Apply on session name
402 \-c, \-\-channel NAME
403 Apply on channel name
405 Enable all tracepoints and syscalls. This actually enable a single
408 Apply for the kernel tracer
410 Apply for the user-space tracer
413 Tracepoint event (default)
414 - userspace tracer supports wildcards at end of string. Don't forget to
415 quote to deal with bash expansion.
420 Tracepoint loglevel range from 0 to loglevel. Listed in the help (\-h).
421 \-\-loglevel-only NAME
422 Tracepoint loglevel (only this loglevel).
424 The loglevel or loglevel-only options should be combined with a
425 tracepoint name or tracepoint wildcard.
426 \-\-probe [addr | symbol | symbol+offset]
427 Dynamic probe. Addr and offset can be octal (0NNN...), decimal (NNN...)
428 or hexadecimal (0xNNN...)
429 \-\-function [addr | symbol | symbol+offset]
430 Dynamic function entry/return probe. Addr and offset can be octal
431 (0NNN...), decimal (NNN...) or hexadecimal (0xNNN...)
433 System call event. Enabling syscalls tracing (kernel tracer), you will
434 not be able to disable them with disable-event. This is a known
435 limitation. You can disable the entire channel to do the trick.
437 \-\-filter 'expression'
438 Set a filter on a newly enabled event. Filter expression on event
439 fields and context. Event recording depends on evaluation. Only
440 specify on first activation of a given event within a session.
441 Filter only allowed when enabling events within a session before
442 tracing is started. If the filter fails to link with the event
443 within the traced domain, the event will be discarded.
444 Currently, filter is only implemented for the user-space tracer.
448 'intfield > 500 && intfield < 503'
449 '(stringfield == "test" || intfield != 10) && intfield > 33'
450 'doublefield > 1.1 && intfield < 5.3'
452 Wildcards are allowed at the end of strings:
454 In string literals, the escape character is a '\\'. Use '\\*' for
455 the '*' character, and '\\\\' for the '\\' character. Wildcard
456 match any sequence of characters, including an empty sub-string
457 (match 0 or more characters).
459 Context information can be used for filtering. The examples
460 below show usage of context filtering on process name (with a
461 wildcard), process ID range, and unique thread ID for filtering.
462 The process and thread ID of running applications can be found
463 under columns "PID" and "LWP" of the "ps -eLf" command.
465 '$ctx.procname == "demo*"'
466 '$ctx.vpid >= 4433 && $ctx.vpid < 4455'
470 .IP "\fBdisable-channel\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
472 Disable tracing channel
474 Disabling a channel makes all event(s) in that channel to stop tracing. You can
475 enable it back by calling \fBlttng enable-channel NAME\fP again.
477 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
485 Show summary of possible options and commands.
487 Simple listing of options
488 \-s, \-\-session NAME
489 Apply on session name
491 Apply for the kernel tracer
493 Apply for the user-space tracer
496 .IP "\fBdisable-event\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
498 Disable tracing event
500 The event, once disabled, can be re-enabled by calling \fBlttng enable-event
503 If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
511 Show summary of possible options and commands.
513 Simple listing of options
514 \-s, \-\-session NAME
515 Apply on session name
517 Disable all events. This does NOT disable "*" but rather
518 every known events of the session.
520 Apply for the kernel tracer
522 Apply for the user-space tracer
525 .IP "\fBlist\fP [\-k|\-u] [SESSION [SESSION_OPTIONS]]"
527 List tracing session information.
529 With no arguments, it will list available tracing session(s).
531 With the session name, it will display the details of the session including
532 the trace file path, the associated channels and their state (activated
533 and deactivated), the activated events and more.
535 With \-k alone, it will list all available kernel events (except the system
537 With \-u alone, it will list all available user-space events from registered
538 applications. Here is an example of 'lttng list \-u':
540 PID: 7448 - Name: /tmp/lttng-ust/tests/hello/.libs/lt-hello
541 ust_tests_hello:tptest_sighandler (type: tracepoint)
542 ust_tests_hello:tptest (type: tracepoint)
544 You can now enable any event listed by using the name :
545 \fBust_tests_hello:tptest\fP.
552 Show summary of possible options and commands.
554 Simple listing of options
558 Select user-space domain.
562 \-c, \-\-channel NAME
563 List details of a channel
565 List available domain(s)
568 .IP "\fBset-session\fP NAME"
570 Set current session name
572 Will change the session name in the .lttngrc file.
579 Show summary of possible options and commands.
581 Simple listing of options
586 .IP "\fBstart\fP [NAME] [OPTIONS]"
590 It will start tracing for all tracers for a specific tracing session.
592 If NAME is omitted, the session name is taken from the .lttngrc file.
599 Show summary of possible options and commands.
601 Simple listing of options
606 .IP "\fBstop\fP [NAME] [OPTIONS]"
610 It will stop tracing for all tracers for a specific tracing session. Before
611 returning, the command checks for data availability meaning that it will wait
612 until the trace is readable for the session. Use \-\-no-wait to avoid this
615 If NAME is omitted, the session name is taken from the .lttngrc file.
622 Show summary of possible options and commands.
624 Simple listing of options
626 Don't wait for data availability.
633 Show version information
640 Show summary of possible options and commands.
642 Simple listing of options
647 .IP "\fBview\fP [SESSION_NAME] [OPTIONS]"
649 View traces of a tracing session
651 By default, the babeltrace viewer will be used for text viewing.
653 If SESSION_NAME is omitted, the session name is taken from the .lttngrc file.
663 Simple listing of options
664 \-t, \-\-trace-path PATH
665 Trace directory path for the viewer
667 Specify viewer and/or options to use
668 This will completely override the default viewers so
669 please make sure to specify the full command. The trace
670 directory path of the session will be appended at the end
675 On success 0 is returned and a positive value on error. Value of 1 means a command
676 error, 2 an undefined command, 3 a fatal error and 4 a command warning meaning that
677 something went wrong during the command.
679 Any other value above 10, please refer to
680 .BR <lttng/lttng-error.h>
681 for a detailed list or use lttng_strerror() to get a human readable string of
685 .SH "ENVIRONMENT VARIABLES"
688 Note that all command line options override environment variables.
692 .IP "LTTNG_SESSIOND_PATH"
693 Allows one to specify the full session daemon binary path to lttng command line
694 tool. You can also use \-\-sessiond-path option having the same effect.
698 .BR lttng-sessiond(8),
700 .BR lttng-health-check(3)
703 If you encounter any issues or usability problem, please report it on our
704 mailing list <lttng-dev@lists.lttng.org> to help improve this project or
705 at https://bugs.lttng.org which is a bugtracker.
709 lttng is distributed under the GNU General Public License version 2. See the file
712 A Web site is available at http://lttng.org for more information on the LTTng
715 You can also find our git tree at http://git.lttng.org.
717 Mailing lists for support and development: <lttng-dev@lists.lttng.org>.
719 You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
724 Thanks to Yannick Brosseau without whom this project would never have been so
725 lean and mean! Also thanks to the Ericsson teams working on tracing which
726 helped us greatly with detailed bug reports and unusual test cases.
728 Thanks to our beloved packager Alexandre Montplaisir-Goncalves (Ubuntu and PPA
729 maintainer) and Jon Bernard for our Debian packages.
731 Special thanks to Michel Dagenais and the DORSAL laboratory at Polytechnique de
732 Montreal for the LTTng journey.
737 lttng-tools was originally written by Mathieu Desnoyers, Julien Desfossez and
738 David Goulet. More people have since contributed to it. It is currently
739 maintained by David Goulet <dgoulet@efficios.com>.