lttng-start — Start LTTng tracers




The lttng start command starts the various LTTng tracers for a given inactive tracing session.

Starting the LTTng tracers has the effect that all enabled event rules within enabled channels can make their target event sources emit trace events. Whether they are recorded to the local file system, sent over the network, or not recorded at all depends on the specific configuration of the tracing session in which tracing is started. See lttng-create(1) for different session modes.

A tracing session with running tracers is said to be active. Active tracing sessions can return to the inactive state using the lttng-stop(1) command.

If SESSION is omitted, the LTTng tracers are started for the current tracing session (see lttng-create(1) for more information about the current tracing session). Otherwise, they are started for the existing tracing session named SESSION. lttng list outputs all the existing tracing sessions (see lttng-list(1)).


General options are described in lttng(1).

Program information

-h, --help

Show command help.

This option, like lttng-help(1), attempts to launch /usr/bin/man to view the command’s man page. The path to the man pager can be overridden by the LTTNG_MAN_BIN_PATH environment variable.


List available command options.

Environment Variables


Set to 1 to abort the process after the first error is encountered.


Overrides the $HOME environment variable. Useful when the user running the commands has a non-writable home directory.


Absolute path to the man pager to use for viewing help information about LTTng commands (using lttng-help(1) or lttng COMMAND --help).


Path in which the session.xsd session configuration XML schema may be found.


Full session daemon binary path.

The --sessiond-path option has precedence over this environment variable.

Note that the lttng-create(1) command can spawn an LTTng session daemon automatically if none is running. See lttng-sessiond(8) for the environment variables influencing the execution of the session daemon.



User LTTng runtime configuration.

This is where the per-user current tracing session is stored between executions of lttng(1). The current tracing session can be set with lttng-set-session(1). See lttng-create(1) for more information about tracing sessions.


Default output directory of LTTng traces. This can be overridden with the --output option of the lttng-create(1) command.


User LTTng runtime and configuration directory.


Default location of saved user tracing sessions (see lttng-save(1) and lttng-load(1)).


System-wide location of saved tracing sessions (see lttng-save(1) and lttng-load(1)).


$LTTNG_HOME defaults to $HOME when not explicitly set.

Exit Status




Command error


Undefined command


Fatal error


Command warning (something went wrong during the command)


If you encounter any issue or usability problem, please report it on the LTTng bug tracker <>.



This program is part of the LTTng-tools project.

LTTng-tools is distributed under the GNU General Public License version 2 <>. See the LICENSE <> file for details.


Special thanks to Michel Dagenais and the DORSAL laboratory <> at École Polytechnique de Montréal for the LTTng journey.

Also thanks to the Ericsson teams working on tracing which helped us greatly with detailed bug reports and unusual test cases.

See Also

lttng-stop(1), lttng(1)

Referenced By

lttng(1), lttng-add-context(1), lttng-disable-event(1), lttng-enable-event(1), lttng-rotate(1), lttng-snapshot(1), lttng-stop(1).

10/17/2019 LTTng 2.11.0 LTTng Manual