lttng-track — Add one or more entries to an LTTng resource tracker
lttng track commands adds one or more entries to a
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
Assume the maximum system PID is 7 for this example.
       
lttng track --userspace --pid=3,6,7
[ ] [ ] [ ]  [ ] [ ]  
lttng untrack --userspace --pid=7
[ ] [ ] [ ]  [ ] [ ]  [ ]
lttng track --userspace --pid=1,5
[ ]  [ ]  [ ]   [ ]
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.
Set to 1 to abort the process after the first error is encountered.
$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.
--sessiond-path option has precedence over this
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
--output option of the lttng-create(1)
User LTTng runtime and configuration directory.
$LTTNG_HOME defaults to
$HOME when not explicitly set.
Command warning (something went wrong during the command)
If you encounter any issue or usability problem, please report it on the LTTng bug tracker.
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.