'\" t
.\"     Title: lttng-start
.\"    Author: [FIXME: author] [see http://www.docbook.org/tdg5/en/html/author]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 7 April 2016
.\"    Manual: LTTng Manual
.\"    Source: LTTng 2.12.3
.\"  Language: English
.\"
.TH "LTTNG\-START" "1" "7 April 2016" "LTTng 2\&.12\&.3" "LTTng Manual"
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.SH "NAME"
lttng-start \- Start LTTng tracers
.SH "SYNOPSIS"
.sp
.nf
\fBlttng\fR [\fIGENERAL OPTIONS\fR] \fBstart\fR [\fISESSION\fR]
.fi
.SH "DESCRIPTION"
.sp
The \fBlttng start\fR command starts the various LTTng tracers for a given inactive tracing session\&.
.sp
Starting the LTTng tracers has the effect that all enabled event rules within enabled channels can make their target event sources \fIemit\fR 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 \fBlttng-create\fR(1) for different session modes\&.
.sp
A tracing session with running tracers is said to be \fIactive\fR\&. Active tracing sessions can return to the inactive state using the \fBlttng-stop\fR(1) command\&.
.sp
If \fISESSION\fR is omitted, the LTTng tracers are started for the current tracing session (see \fBlttng-create\fR(1) for more information about the current tracing session)\&. Otherwise, they are started for the existing tracing session named \fISESSION\fR\&. \fBlttng list\fR outputs all the existing tracing sessions (see \fBlttng-list\fR(1))\&.
.SH "OPTIONS"
.sp
General options are described in \fBlttng\fR(1)\&.
.SS "Program information"
.PP
\fB-h\fR, \fB--help\fR
.RS 4
Show command help\&.
.sp
This option, like
\fBlttng-help\fR(1), attempts to launch
\fB/usr/bin/man\fR
to view the command\(cqs man page\&. The path to the man pager can be overridden by the
\fBLTTNG_MAN_BIN_PATH\fR
environment variable\&.
.RE
.PP
\fB--list-options\fR
.RS 4
List available command options\&.
.RE
.SH "ENVIRONMENT VARIABLES"
.PP
\fBLTTNG_ABORT_ON_ERROR\fR
.RS 4
Set to 1 to abort the process after the first error is encountered\&.
.RE
.PP
\fBLTTNG_HOME\fR
.RS 4
Overrides the
\fB$HOME\fR
environment variable\&. Useful when the user running the commands has a non\-writable home directory\&.
.RE
.PP
\fBLTTNG_MAN_BIN_PATH\fR
.RS 4
Absolute path to the man pager to use for viewing help information about LTTng commands (using
\fBlttng-help\fR(1)
or
\fBlttng COMMAND --help\fR)\&.
.RE
.PP
\fBLTTNG_SESSION_CONFIG_XSD_PATH\fR
.RS 4
Path in which the
\fBsession.xsd\fR
session configuration XML schema may be found\&.
.RE
.PP
\fBLTTNG_SESSIOND_PATH\fR
.RS 4
Full session daemon binary path\&.
.sp
The
\fB--sessiond-path\fR
option has precedence over this environment variable\&.
.RE
.sp
Note that the \fBlttng-create\fR(1) command can spawn an LTTng session daemon automatically if none is running\&. See \fBlttng-sessiond\fR(8) for the environment variables influencing the execution of the session daemon\&.
.SH "FILES"
.PP
\fB$LTTNG_HOME/.lttngrc\fR
.RS 4
User LTTng runtime configuration\&.
.sp
This is where the per\-user current tracing session is stored between executions of
\fBlttng\fR(1)\&. The current tracing session can be set with
\fBlttng-set-session\fR(1)\&. See
\fBlttng-create\fR(1)
for more information about tracing sessions\&.
.RE
.PP
\fB$LTTNG_HOME/lttng-traces\fR
.RS 4
Default output directory of LTTng traces\&. This can be overridden with the
\fB--output\fR
option of the
\fBlttng-create\fR(1)
command\&.
.RE
.PP
\fB$LTTNG_HOME/.lttng\fR
.RS 4
User LTTng runtime and configuration directory\&.
.RE
.PP
\fB$LTTNG_HOME/.lttng/sessions\fR
.RS 4
Default location of saved user tracing sessions (see
\fBlttng-save\fR(1)
and
\fBlttng-load\fR(1))\&.
.RE
.PP
\fB/etc/lttng/sessions\fR
.RS 4
System\-wide location of saved tracing sessions (see
\fBlttng-save\fR(1)
and
\fBlttng-load\fR(1))\&.
.RE
.if n \{\
.sp
.\}
.RS 4
.it 1 an-trap
.nr an-no-space-flag 1
.nr an-break-flag 1
.br
.ps +1
\fBNote\fR
.ps -1
.br
.sp
\fB$LTTNG_HOME\fR defaults to \fB$HOME\fR when not explicitly set\&.
.sp .5v
.RE
.SH "EXIT STATUS"
.PP
\fB0\fR
.RS 4
Success
.RE
.PP
\fB1\fR
.RS 4
Command error
.RE
.PP
\fB2\fR
.RS 4
Undefined command
.RE
.PP
\fB3\fR
.RS 4
Fatal error
.RE
.PP
\fB4\fR
.RS 4
Command warning (something went wrong during the command)
.RE
.SH "BUGS"
.sp
If you encounter any issue or usability problem, please report it on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-tools>\&.
.SH "RESOURCES"
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
LTTng project website <https://lttng.org>
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
LTTng documentation <https://lttng.org/docs>
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Git repositories <http://git.lttng.org>
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
GitHub organization <http://github.com/lttng>
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Continuous integration <http://ci.lttng.org/>
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
Mailing list <http://lists.lttng.org>
for support and development:
\fBlttng-dev@lists.lttng.org\fR
.RE
.sp
.RS 4
.ie n \{\
\h'-04'\(bu\h'+03'\c
.\}
.el \{\
.sp -1
.IP \(bu 2.3
.\}
IRC channel <irc://irc.oftc.net/lttng>:
\fB#lttng\fR
on
\fBirc.oftc.net\fR
.RE
.SH "COPYRIGHTS"
.sp
This program is part of the LTTng\-tools project\&.
.sp
LTTng\-tools is distributed under the GNU General Public License version 2 <http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html>\&. See the \fBLICENSE\fR <https://github.com/lttng/lttng-tools/blob/master/LICENSE> file for details\&.
.SH "THANKS"
.sp
Special thanks to Michel Dagenais and the DORSAL laboratory <http://www.dorsal.polymtl.ca/> at \('Ecole Polytechnique de Montr\('eal for the LTTng journey\&.
.sp
Also thanks to the Ericsson teams working on tracing which helped us greatly with detailed bug reports and unusual test cases\&.
.SH "SEE ALSO"
.sp
\fBlttng-stop\fR(1), \fBlttng\fR(1)