# lttng-start

## NAME



           lttng-start - Start LTTng tracers
    


## SYNOPSIS



           **lttng**[_GENERAL OPTIONS_] **start**[_SESSION_]
    


## DESCRIPTION



           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)).
    


## OPTIONS



           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-options**
               List available command options.
    


## ENVIRONMENT VARIABLES



           **LTTNG_ABORT_ON_ERROR**
               Set to 1 to abort the process after the first error is
               encountered.
    
           **LTTNG_HOME**
               Overrides the **$HOME** environment variable. Useful when the user
               running the commands has a non-writable home directory.
    
           **LTTNG_MAN_BIN_PATH**
               Absolute path to the man pager to use for viewing help
               information about LTTng commands (using lttng-help(1) or **lttng**
               **COMMAND --help**).
    
           **LTTNG_SESSION_CONFIG_XSD_PATH**
               Path in which the **session.xsd** session configuration XML schema
               may be found.
    
           **LTTNG_SESSIOND_PATH**
               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.
    


## FILES



           **$LTTNG_HOME/.lttngrc**
               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.
    
           **$LTTNG_HOME/lttng-traces**
               Default output directory of LTTng traces. This can be
               overridden with the **--output** option of the lttng-create(1)
               command.
    
           **$LTTNG_HOME/.lttng**
               User LTTng runtime and configuration directory.
    
           **$LTTNG_HOME/.lttng/sessions**
               Default location of saved user tracing sessions (see
               lttng-save(1) and lttng-load(1)).
    
           **/usr/local/etc/lttng/sessions**
               System-wide location of saved tracing sessions (see
               lttng-save(1) and lttng-load(1)).
    
               **Note**
    
               **$LTTNG_HOME** defaults to **$HOME** when not explicitly set.
    


## EXIT STATUS



           **0**
               Success
    
           **1**
               Command error
    
           **2**
               Undefined command
    
           **3**
               Fatal error
    
           **4**
               Command warning (something went wrong during the command)
    


## BUGS



           If you encounter any issue or usability problem, please report it
           on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-
           tools>.
    


## RESOURCES



           •   LTTng project website <https://lttng.org>
    
           •   LTTng documentation <https://lttng.org/docs>
    
           •   Git repositories <http://git.lttng.org>
    
           •   GitHub organization <http://github.com/lttng>
    
           •   Continuous integration <http://ci.lttng.org/>
    
           •   Mailing list <http://lists.lttng.org> for support and
               development: **lttng-dev@lists.lttng.org**
    
           •   IRC channel <irc://irc.oftc.net/lttng>: **#lttng** on **irc.oftc.net**
    


## THANKS



           Special thanks to Michel Dagenais and the DORSAL laboratory
           <http://www.dorsal.polymtl.ca/> 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.
    


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