lttng-track — Add one or more entries to an LTTng resource tracker
Synopsis
lttng [GENERAL OPTIONS] track (--kernel | --userspace)
[--session=SESSION] (--pid=PID[,PID]... | --all --pid)Description
The lttng track commands adds one or more entries to a resource tracker.
A resource tracker is a whitelist of resources. Tracked resources are allowed to emit events, provided those events are targeted by enabled event rules (see lttng-enable-event(1)).
Tracker entries can be removed from the whitelist with lttng-untrack(1).
As of this version, the only available tracker is the PID tracker. The process ID (PID) tracker follows one or more process IDs; only the processes with a tracked PID are allowed to emit events. By default, all possible PIDs on the system are tracked: any process may emit enabled events (equivalent of lttng track --pid --all for all domains).
With the PID tracker, it is possible, for example, to record all system calls called by a given process:
# lttng enable-event --kernel --all --syscall # lttng track --kernel --pid=2345 # lttng start
If all the PIDs are tracked (i.e. lttng track --pid --all, which is the default state of all domains when creating a tracing session), then using the track command with one or more specific PIDs has the effect of first removing all the PIDs from the whitelist, then adding the specified PIDs.
Example
Assume the maximum system PID is 7 for this example.
Initial whitelist:
[0] [1] [2] [3] [4] [5] [6] [7]
Command:
$ lttng track --userspace --pid=3,6,7
Whitelist:
[ ] [ ] [ ] [3] [ ] [ ] [6] [7]
Command:
$ lttng untrack --userspace --pid=7
Whitelist:
[ ] [ ] [ ] [3] [ ] [ ] [6] [ ]
Command:
$ lttng track --userspace --pid=1,5
Whitelist:
[ ] [1] [ ] [3] [ ] [5] [6] [ ]
It should be noted that the PID tracker tracks the numeric process IDs. Should a process with a given ID exit and another process be given this ID, then the latter would also be allowed to emit events.
See the lttng-untrack(1) for more details about removing entries.
Options
General options are described in lttng(1).
Domain
One of:
- -k, --kernel
Track resources in the Linux kernel domain.
- -u, --userspace
Track resources in the user space domain.
Target
- -s SESSION, --session=SESSION
Track resources in the tracing session named SESSION instead of the current tracing session.
Tracking
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
Copyrights
This program is part of the LTTng-tools project.
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 LICENSE <https://github.com/lttng/lttng-tools/blob/master/LICENSE> file for details.
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.
See Also
Referenced By
lttng(1), lttng-enable-event(1), lttng-untrack(1).