lttng-track(1)
==============
:revdate: 14 March 2017


NAME
----
lttng-track - Add one or more entries to an LTTng resource tracker


SYNOPSIS
--------
[verse]
*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *track* (option:--kernel | option:--userspace)
      [option:--session='SESSION'] (option:--pid='PID'[,'PID']... | option:--all option:--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 man:lttng-enable-event(1)).

Tracker entries can be removed from the whitelist with
man: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:

[role="term"]
----
# 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:

[role="term"]
----
$ lttng track --userspace --pid=3,6,7
----

Whitelist:

-------------------------------
[ ] [ ] [ ] [3] [ ] [ ] [6] [7]
-------------------------------

Command:

[role="term"]
----
$ lttng untrack --userspace --pid=7
----

Whitelist:

-------------------------------
[ ] [ ] [ ] [3] [ ] [ ] [6] [ ]
-------------------------------

Command:

[role="term"]
----
$ 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 man:lttng-untrack(1) for more details about removing
entries.


include::common-cmd-options-head.txt[]


Domain
~~~~~~
One of:

option:-k, option:--kernel::
    Track resources in the Linux kernel domain.

option:-u, option:--userspace::
    Track resources in the user space domain.


Target
~~~~~~
option:-s 'SESSION', option:--session='SESSION'::
    Track resources in the tracing session named 'SESSION' instead of
    the current tracing session.


Tracking
~~~~~~~~
option:-a, option:--all::
    Used in conjunction with an empty option:--pid option: track _all_
    process IDs (add all entries to the whitelist).

option:-p ['PID'[,'PID']...], option:--pid[='PID'[,'PID']...]::
    Track process IDs 'PID' (add them to the current whitelist).
+
The 'PID' argument must be omitted when also using the option:--all
option.


include::common-cmd-help-options.txt[]


include::common-cmd-footer.txt[]


SEE ALSO
--------
man:lttng-untrack(1),
man:lttng(1)
