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The LTTng project aims at providing highly efficient tracing tools for
Linux. It's tracers help tracking down performance issues and debug-
ging problems involving multiple concurrent processes and threads.
Tracing across multiple systems is also possible.
The session daemon, acting as a tracing registry, allow you to interact
with multiple tracers (kernel and user-space) inside the same con-
tainer, a tracing session. Trace can be gathered from the kernel and/or
instrumented applications (lttng-ust(3)). Aggregating those traces is
done using a viewer, like 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 tracing group (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.
The session daemon is in charge of managing trace data consumers by
spawning them when the time has come. The user don't need to manage the
This program follow the usual GNU command line syntax with long options
starting with two dashes. Below is a summary of the available options.
Show summary of possible options and commands
There is three debugging level which will print on stderr. Maxi-
mum verbosity is -vvv.
Verbose mode for consumer. Activate DBG() macro.
Start as a daemon
Specify the tracing group name. (default: tracing)
No kernel tracer support
Specify path for the client unix socket
-a, --apps-sock PATH
Specify path for apps unix socket
Specify path for the kernel consumer error socket
Specify path for the kernel consumer command socket
Specify path for the 32-bit UST consumer error socket
Specify path for the 64-bit UST consumer error socket
Specify path for the 32-bit UST consumer command socket
Specify path for the 64-bit UST consumer command socket
Specify path for the 32-bit UST consumer daemon binary
Specify path for the 32-bit UST consumer daemon libraries
Specify path for the 64-bit UST consumer daemon binary
Specify path for the 64-bit UST consumer daemon libraries
Note that all command line options will override environment variables.
Specify the 32-bit consumer binary path. --consumerd32-path
override this variable.
Specify the 64-bit consumer binary path. --consumerd64-path
babeltrace(1), lttng-ust(3), lttng(1)
For unprivileged user running lttng-sessiond, the maximum number of
file descriptors per process is usually 1024. This limits the number of
traceable applications since for each instrumented application there is
two file descriptors per-CPU and one more socktet for bidirectional
For the root user, the limit is bumped to 65535. Future version will
deal with this limitation.
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 <firstname.lastname@example.org> to help improve this
lttng-sessiond is distributed under the GNU General Public License ver-
sion 2. See the file COPYING for details.
A Web site is available at http://lttng.org for more information on the
You can also find our git tree at http://git.lttng.org.
Mailing lists for support and development: <email@example.com>.
You can find us on IRC server irc.oftc.net (OFTC) in #lttng.
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
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 Poly-
technique de Montreal for the LTTng journey.