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.TH "LTTNG" "1" "July 17, 2012" "" ""

.SH "NAME"
lttng \(em LTTng 2.0 tracer control command line tool

.SH "SYNOPSIS"

.PP
.nf
lttng [OPTIONS] <COMMAND>
.fi
.SH "DESCRIPTION"

.PP
The LTTng project aims at providing highly efficient tracing tools for Linux.
It's tracers help tracking down performance issues and debugging problems
involving multiple concurrent processes and threads. Tracing across multiple
systems is also possible.

The \fBlttng\fP command line tool from the lttng-tools package is used to control
both kernel and user-space tracing. Every interactions with the tracer should
be done by this tool or by the liblttng-ctl provided with the lttng-tools
package.

LTTng uses a session daemon (lttng-sessiond(8)), acting as a tracing registry,
which permits you to interact with multiple tracers (kernel and user-space)
inside the same container, a tracing session. Traces can be gathered from the
kernel and/or instrumented applications (lttng-ust(3)). Aggregating and reading
those traces is done using the babeltrace(1) text viewer.

In order to trace the kernel, the session daemon needs to be running as root.
LTTng provides the use of a \fBtracing group\fP (default: tracing). Whomever is
in that group can interact with the root session daemon and thus trace the
kernel. Session daemons can co-exist meaning that you can have a session daemon
running as Alice that can be used to trace her applications along side with a
root daemon or even a Bob daemon. We highly recommend to start the session
daemon at boot time for stable and long term tracing.

Every user-space applications instrumented with lttng-ust(3), will
automatically register to the session daemon. This feature gives you the
ability to list available traceable applications and tracepoints on a per user
basis. (See \fBlist\fP command).
.SH "OPTIONS"

.PP
This program follow the usual GNU command line syntax with long options starting with
two dashes. Below is a summary of the available options.
.PP

.TP
.BR "\-h, \-\-help"
Show summary of possible options and commands.
.TP
.BR "\-v, \-\-verbose"
Increase verbosity.
Three levels of verbosity are available which are triggered by putting additional v to
the option (\-vv or \-vvv)
.TP
.BR "\-q, \-\-quiet"
Suppress all messages (even errors).
.TP
.BR "\-g, \-\-group NAME"
Set unix tracing group name. (default: tracing)
.TP
.BR "\-n, \-\-no-sessiond"
Don't automatically spawn a session daemon.
.TP
.BR "\-\-sessiond\-path"
Set session daemon full binary path.
.TP
.BR "\-\-list\-options"
Simple listing of lttng options.
.TP
.BR "\-\-list\-commands"
Simple listing of lttng commands.
.SH "COMMANDS"

.TP
\fBadd-context\fP
.nf
Add context to event(s) and/or channel(s).

A context is basically extra information appended to a channel or event. For
instance, you could ask the tracer to add the PID information within the
"sched_switch" kernel event. You can also add performance monitoring unit
counters (perf PMU) using the perf kernel API).

For example, this command will add the context information 'prio' and two perf
counters (hardware branch misses and cache misses), to all events in the trace
data output:

# lttng add-context \-k \-t prio \-t perf:branch-misses \-t perf:cache-misses

Please take a look at the help (\-h/\-\-help) for a detailed list of available
contexts.

If no channel and no event is given (\-c/\-e), the context is added to all
channels (which applies automatically to all events in that channel). Otherwise
the context will be added only to the channel (\-c) and/or event (\-e) indicated.

If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-s, \-\-session NAME
        Apply on session name.
\-c, \-\-channel NAME
        Apply on channel name.
\-e, \-\-event NAME
        Apply on event name.
\-k, \-\-kernel
        Apply for the kernel tracer
\-u, \-\-userspace
        Apply for the user-space tracer
\-t, \-\-type TYPE
        Context type. You can repeat this option on the command line. Please
        use "lttng add-context \-h" to list all available types.
.fi

.IP

.IP "\fBcalibrate\fP"
.nf
Quantify LTTng overhead

The LTTng calibrate command can be used to find out the combined average
overhead of the LTTng tracer and the instrumentation mechanisms used. This
overhead can be calibrated in terms of time or using any of the PMU performance
counter available on the system.

For now, the only calibration implemented is that of the kernel function
instrumentation (kretprobes).

* Calibrate kernel function instrumentation

Let's use an example to show this calibration. We use an i7 processor with 4
general-purpose PMU registers. This information is available by issuing dmesg,
looking for "generic registers".

This sequence of commands will gather a trace executing a kretprobe hooked on
an empty function, gathering PMU counters LLC (Last Level Cache) misses
information (see lttng add-context \-\-help to see the list of available PMU
counters).

# lttng create calibrate-function
# lttng enable-event calibrate \-\-kernel \-\-function lttng_calibrate_kretprobe
# lttng add-context \-\-kernel \-t perf:LLC-load-misses \-t perf:LLC-store-misses \\
                  \-t perf:LLC-prefetch-misses
# lttng start
# for a in $(seq 1 10); do \\
        lttng calibrate \-\-kernel \-\-function;
  done
# lttng destroy
# babeltrace $(ls \-1drt ~/lttng-traces/calibrate-function-* | tail \-n 1)

The output from babeltrace can be saved to a text file and opened in a
spreadsheet (e.g. oocalc) to focus on the per-PMU counter delta between
consecutive "calibrate_entry" and "calibrate_return" events. Note that these
counters are per-CPU, so scheduling events would need to be present to account
for migration between CPU. Therefore, for calibration purposes, only events
staying on the same CPU must be considered.

The average result, for the i7, on 10 samples:

                          Average     Std.Dev.
perf_LLC_load_misses:       5.0       0.577
perf_LLC_store_misses:      1.6       0.516
perf_LLC_prefetch_misses:   9.0      14.742

As we can notice, the load and store misses are relatively stable across runs
(their standard deviation is relatively low) compared to the prefetch misses.
We can conclude from this information that LLC load and store misses can be
accounted for quite precisely, but prefetches within a function seems to behave
too erratically (not much causality link between the code executed and the CPU
prefetch activity) to be accounted for.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-k, \-\-kernel
        Apply for the kernel tracer
\-u, \-\-userspace
        Apply for the user-space tracer
\-\-function
        Dynamic function entry/return probe (default)
.fi

.IP

.IP "\fBcreate\fP [OPTIONS] [NAME]
.nf
Create tracing session.

A tracing session contains channel(s) which contains event(s). It is domain
agnostic meaning that you can enable channels and events for either the
user-space tracer and/or the kernel tracer. It acts like a container
aggregating multiple tracing sources.

On creation, a \fB.lttngrc\fP file is created in your $HOME directory
containing the current session name. If NAME is omitted, a session name is
automatically created having this form: 'auto-yyyymmdd-hhmmss'.

If no \fB\-o, \-\-output\fP is specified, the traces will be written in
$HOME/lttng-traces.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
\-o, \-\-output PATH
        Specify output path for traces
.fi

.IP

.IP "\fBdestroy\fP [OPTIONS] [NAME]"
.nf
Teardown tracing session

Free memory on the session daemon and tracer side. It's gone!

If NAME is omitted, the session name is taken from the .lttngrc file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-a, \-\-all
        Destroy all sessions
\-\-list-options
        Simple listing of options
.fi

.IP

.IP "\fBenable-channel\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
.nf
Enable tracing channel

To enable event, you must first enable a channel which contains event(s).

If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show this help
\-\-list-options
        Simple listing of options
\-s, \-\-session
        Apply on session name
\-k, \-\-kernel
        Apply to the kernel tracer
\-u, \-\-userspace
        Apply to the user-space tracer

\-\-discard
        Discard event when subbuffers are full (default)
\-\-overwrite
        Flight recorder mode : overwrites events when subbuffers are full
\-\-subbuf-size
        Subbuffer size in bytes (default: 4096, kernel default: 262144)
\-\-num-subbuf
        Number of subbuffers (default: 4)
        Needs to be a power of 2 for kernel and ust tracers
\-\-switch-timer
        Switch subbuffer timer interval in usec (default: 0)
        Needs to be a power of 2 for kernel and ust tracers
\-\-read-timer
        Read timer interval in usec (default: 200)
.fi

.IP

.IP "\fBenable-event\fP NAME[,NAME2,...] [-k|-u] [OPTIONS]"
.nf
Enable tracing event

A tracing event is always assigned to a channel. If \fB\-c, \-\-channel\fP is
omitted, a default channel named '\fBchannel0\fP' is created and the event is
added to it. For the user-space tracer, using \fB\-a, \-\-all\fP is the same as
using the wildcard "*".

If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
\-s, \-\-session
        Apply on session name
\-c, \-\-channel
        Apply on channel name
\-a, \-\-all
        Enable all tracepoints and syscalls
\-k, \-\-kernel
        Apply for the kernel tracer
\-u, \-\-userspace
        Apply for the user-space tracer

\-\-tracepoint
        Tracepoint event (default)
        - userspace tracer supports wildcards at end of string. Don't forget to
        quote to deal with bash expansion.
        e.g.:
        "*"
        "app_component:na*"
\-\-loglevel
        Tracepoint loglevel
\-\-probe [addr | symbol | symbol+offset]
        Dynamic probe. Addr and offset can be octal (0NNN...), decimal (NNN...)
        or hexadecimal (0xNNN...)
\-\-function [addr | symbol | symbol+offset]
        Dynamic function entry/return probe. Addr and offset can be octal
        (0NNN...), decimal (NNN...) or hexadecimal (0xNNN...)
\-\-syscall
        System call event
        Enabling syscalls tracing (kernel tracer), you will not be able to disable them
        with disable-event. This is a known limitation. You can disable the entire
        channel to do the trick.

\-\-filter 'expression'
	Set a filter on a newly enabled event.
	Filter expression on event fields, event recording
	depends on evaluation. Only specify on first activation
	of a given event within a session. Filter only allowed
	when enabling events within a session before tracing is
	started. If the filter fails to link with the event
	within the traced domain, the event will be discarded.
	Currently, filter is only implemented for the user-space 
	tracer.
	Expression examples:

	'intfield > 500 && intfield < 503'
	'(stringfield == "test" || intfield != 10) && intfield > 33'
	'doublefield > 1.1 && intfield < 5.3'

	Wildcards are allowed at the end of strings:
	'seqfield1 == "te*"'
	In string literals, the escape character is a '\\'.
	Use '\\*' for the '*' character, and '\\\\' for the
	'\\' character.

.fi

.IP "\fBdisable-channel\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
.nf
Disable tracing channel

Disabling a channel makes all event(s) in that channel to stop tracing. You can
enable it back by calling \fBlttng enable-channel NAME\fP again.

If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
\-s, \-\-session
        Apply on session name
\-k, \-\-kernel
        Apply for the kernel tracer
\-u, \-\-userspace
        Apply for the user-space tracer
.fi

.IP "\fBdisable-event\fP NAME[,NAME2,...] [\-k|\-u] [OPTIONS]"
.nf
Disable tracing event

The event, once disabled, can be re-enabled by calling \fBlttng enable-event
NAME\fP again.

If \fB\-s, \-\-session\fP is omitted, the session name is taken from the .lttngrc
file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
\-s, \-\-session
        Apply on session name
\-k, \-\-kernel
        Apply for the kernel tracer
\-u, \-\-userspace
        Apply for the user-space tracer
.fi

.IP "\fBlist\fP [\-k|\-u] [SESSION [SESSION_OPTIONS]]"
.nf
List tracing session information.

With no arguments, it will list available tracing session(s).

With the session name, it will display the details of the session including
the trace file path, the associated channels and their state (activated
and deactivated), the activated events and more.

With \-k alone, it will list all available kernel events (except the system
calls events).
With \-u alone, it will list all available user-space events from registered
applications. Here is an example of 'lttng list \-u':

PID: 7448 - Name: /tmp/lttng-ust/tests/hello/.libs/lt-hello
      ust_tests_hello:tptest_sighandler (type: tracepoint)
      ust_tests_hello:tptest (type: tracepoint)

You can now enable any event listed by using the name :
\fBust_tests_hello:tptest\fP.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
\-k, \-\-kernel
        Select kernel domain
\-u, \-\-userspace
        Select user-space domain.

Session options:
\-c, \-\-channel NAME
        List details of a channel
\-d, \-\-domain
        List available domain(s)
.fi

.IP "\fBset-session\fP NAME"
.nf
Set current session name

Will change the session name in the .lttngrc file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
.fi

.IP

.IP "\fBstart\fP [OPTIONS] [NAME]"
.nf
Start tracing

It will start tracing for all tracers for a specific tracing session.

If NAME is omitted, the session name is taken from the .lttngrc file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
.fi

.IP

.IP "\fBstop\fP [OPTIONS] [NAME]"
.nf
Stop tracing

It will stop tracing for all tracers for a specific tracing session.

If NAME is omitted, the session name is taken from the .lttngrc file.
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
.fi

.IP

.IP "\fBversion\fP"
.nf
Show version information
.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show summary of possible options and commands.
\-\-list-options
        Simple listing of options
.fi

.IP

.IP "\fBview\fP [SESSION_NAME] [OPTIONS]"
.nf
View traces of a tracing session

By default, the babeltrace viewer will be used for text viewing.

If SESSION_NAME is omitted, the session name is taken from the .lttngrc file.

.fi

.B OPTIONS:

.nf
\-h, \-\-help
        Show this help
\-\-list-options
        Simple listing of options
\-t, \-\-trace-path PATH
        Trace directory path for the viewer
\-e, \-\-viewer CMD
        Specify viewer and/or options to use
        This will completely override the default viewers so
        please make sure to specify the full command. The trace
        directory path of the session will be appended at the end
        to the arguments
.fi

.SH "EXIT VALUES"

.IP "0"
Success

.IP "1"
Command error

.IP "2"
Undefined command

.IP "3"
Fatal error

.IP "4"
Command warning

.IP "16"
No session found by the name given

.IP "18"
Error in session creation

.IP "21"
Error in application(s) listing

.IP "28"
Session name already exists

.IP "33"
Kernel tracer unavailable

.IP "35"
Kernel event exists

.IP "37"
Kernel channel exists

.IP "38"
Kernel channel creation failed

.IP "39"
Kernel channel not found

.IP "40"
Kernel channel disable failed

.IP "41"
Kernel channel enable failed

.IP "42"
Kernel context failed

.IP "43"
Kernel enable event failed

.IP "44"
Kernel disable event failed

.IP "53"
Kernel listing events failed

.IP "60"
UST channel disable failed

.IP "61"
UST channel enable failed

.IP "62"
UST adding context failed

.IP "63"
UST event enable failed

.IP "64"
UST event disable failed

.IP "66"
UST start failed

.IP "67"
UST stop failed

.IP "75"
UST event exists

.IP "76"
UST event not found

.IP "77"
UST context exists

.IP "78"
UST invalid context

.IP "79"
Tracing the kernel requires a root lttng-sessiond daemon and "tracing" group
user membership.

.IP "80"
Tracing already started

.IP "81"
Tracing already stopped

.IP "98"
No UST consumer detected

.IP "99"
No Kernel consumer detected

.IP "100"
Event already enabled with different loglevel
.PP
.SH "ENVIRONMENT VARIABLES"

.PP
Note that all command line options override environment variables.
.PP

.PP
.IP "LTTNG_SESSIOND_PATH"
Allows one to specify the full session daemon binary path to lttng command line
tool. You can also use \-\-sessiond-path option having the same effect.
.SH "SEE ALSO"

.PP
babeltrace(1), lttng-ust(3), lttng-sessiond(8)
.PP
.SH "BUGS"

.PP
No show stopper bugs are known yet in this version.

If you encounter any issues or usability problem, please report it on our
mailing list <lttng-dev@lists.lttng.org> to help improve this project.
.SH "CREDITS"

.PP
lttng is distributed under the GNU General Public License version 2. See the file
COPYING for details.
.PP
A Web site is available at http://lttng.org for more information on the LTTng
project.
.PP
You can also find our git tree at http://git.lttng.org.
.PP
Mailing lists for support and development: <lttng-dev@lists.lttng.org>.
.PP
You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
.PP
.SH "THANKS"

.PP
Thanks to Yannick Brosseau without whom this project would never have been so
lean and mean! Also thanks to the Ericsson teams working on tracing which
helped us greatly with detailed bug reports and unusual test cases.

Thanks to our beloved packager Alexandre Montplaisir-Goncalves (Ubuntu and PPA
maintainer) and Jon Bernard for our Debian packages.

Special thanks to Michel Dagenais and the DORSAL laboratory at Polytechnique de
Montreal for the LTTng journey.
.PP
.SH "AUTHORS"

.PP
lttng-tools was originally written by Mathieu Desnoyers, Julien Desfossez and
David Goulet. More people have since contributed to it. It is currently
maintained by David Goulet <dgoulet@efficios.com>.
.PP