lttng-track - Man Page

Allow specific processes to record LTTng events

Synopsis

Allow specific processes to record Linux kernel events:

lttng [GENERAL OPTIONS] track --kernel [--session=SESSION]
      (--pid=PID[,PID]... | --vpid=VPID[,VPID]... |
       --uid=UID[,UID]... | --vuid=VUSER[,VUSER]... |
       --gid=GID[,GID]... | --vgid=VGROUP[,VGROUP]...)...
lttng [GENERAL OPTIONS] track --kernel [--session=SESSION]
      --all (--pid | --vpid | --uid | --vuid | --gid | --vgid)...

Allow specific processes to record user space events:

lttng [GENERAL OPTIONS] track --userspace [--session=SESSION]
      (--vpid=VPID[,VPID]... | --vuid=VUSER[,VUSER]... |
       --vgid=VGROUP[,VGROUP]...)...
lttng [GENERAL OPTIONS] track --userspace [--session=SESSION]
      --all (--vpid | --vgid | --vuid)...

Description

The lttng track command allows one or more processes to record LTTng events based on their attributes within:

With the --session=SESSION option

The recording session named SESSION.

Without the --session option

The current recording session (see lttng-concepts(7) to learn more about the current recording session).

See lttng-concepts(7) to learn more about recording sessions and recording event rules.

The track command adds values to inclusion sets of process attributes. The available inclusion sets are, for a given recording session:

With the --kernel option

  • Process ID (PID).
  • Virtual process ID (VPID).

    This is the PID as seen by the application.

  • Unix user ID (UID).
  • Virtual Unix user ID (VUID).

    This is the UID as seen by the application.

  • Unix group ID (GID).
  • Virtual Unix group ID (VGID).

    This is the GID as seen by the application.

With the --userspace option

  • VPID
  • VUID
  • VGID

When an event E satisfies all the other explicit and implicit conditions of an event rule ER, ER matches E if the attributes of the process for which LTTng creates E are all part of the inclusion sets of the recording session and domain of ER.

By default, on recording session creation (see lttng-create(1)), all processes are allowed to record events. In other words, all the inclusion sets of the recording session contain all the possible process attribute values.

If a given inclusion set IS contains all the possible values (--all option), then using the track command to add one or more values V to IS:

  1. Removes all the values from IS.

    This effectively makes IS empty.

  2. Adds V to IS.

Example: with the PID inclusion set, you can record all the system calls of a given process:

$ lttng enable-event --kernel --all --syscall
$ lttng track --kernel --pid=2345
$ lttng start

See the “Examples” section below for usage examples.

Remove values from an inclusion set with the lttng-untrack(1) command.

Inclusion set example

This example operates on the Linux kernel process ID (PID) inclusion set of the current recording session to show how an inclusion set works.

Assume the maximum system PID is 7 for this example.

  1. Initial inclusion set:

    [0] [1] [2] [3] [4] [5] [6] [7]
  2. Command:

    $ lttng track --kernel --pid=3,6,7

    Inclusion set is now:

    [ ] [ ] [ ] [3] [ ] [ ] [6] [7]
  3. Command:

    $ lttng untrack --kernel --pid=7

    Inclusion set is now:

    [ ] [ ] [ ] [3] [ ] [ ] [6] [ ]
  4. Command:

    $ lttng track --kernel --pid=1,5

    Inclusion set is now:

    [ ] [1] [ ] [3] [ ] [5] [6] [ ]

Remove values from an inclusion set with the lttng-untrack(1) command.

Options

See lttng(1) for GENERAL OPTIONS.

Tracing domain

One of:

-k,  --kernel

Add values to one or more Linux kernel inclusion sets.

-u,  --userspace

Add values to one or more user space inclusion sets.

Recording target

-s SESSION, --session=SESSION

Add values to one or more inclusion sets of the recording session named SESSION instead of the current recording session.

Inclusion set selection

-p [PID[,PID]...], --pid[=PID[,PID]...]

For each PID argument, add PID to the process ID inclusion set of the selected recording session and domain.

PID is the process ID attribute of a process as seen from the root PID namespace (see pid_namespaces(7)).

Only available with --kernel option.

--vpid[=VPID[,VPID]...]

For each VPID argument, add VPID to the virtual process ID inclusion set of the selected recording session and domain.

VPID is the virtual process ID attribute of a process as seen from the PID namespace of the process (see pid_namespaces(7)).

--uid[=USER[,USER]...]

For each USER argument, add USER to the user ID inclusion set of the selected recording session and domain.

USER is either:

  • The real user ID (see getuid(3)) of a process as seen from the root user namespace (see user_namespaces(7)).
  • A user name.

    The connected LTTng session daemon (see lttng-sessiond(8)) performs the user name resolution on addition to the user ID inclusion set.

Only available with --kernel option.

--vuid[=VUSER[,VUSER]...]

For each VUSER argument, add VUSER to the virtual user ID inclusion set of the selected recording session and domain.

VUSER is either:

  • The real user ID (see getuid(3)) of a process as seen from the user namespace (see user_namespaces(7)).
  • A user name.

    The connected LTTng session daemon (see lttng-sessiond(8)) performs the user name resolution on addition to the virtual user ID inclusion set.

--gid[=GROUP[,GROUP]...]

For each GROUP argument, add GROUP to the group ID inclusion set of the selected recording session and domain.

GROUP is either:

  • The real group ID (see getgid(3)) of a process as seen from the root user namespace (see user_namespaces(7)).
  • A group name.

    The connected LTTng session daemon (see lttng-sessiond(8)) performs the group name resolution on addition to the group ID inclusion set.

Only available with --kernel option.

--vgid[=VGROUP[,VGROUP]...]

For each VGROUP argument, add VGROUP to the virtual group ID inclusion set of the selected recording session and domain.

VGROUP is either:

  • The real group ID (see getgid(3)) of a process as seen from the user namespace (see user_namespaces(7)).
  • A group name.

    The connected LTTng session daemon (see lttng-sessiond(8)) performs the group name resolution on addition to the virtual group ID inclusion set.

Inclusion set operation

-a,  --all

With one or more empty --pid, --vpid, --uid, --vuid, --gid, and --vgid options: add all the possible values to the selected inclusion sets.

Program information

-h,  --help

Show help.

This option attempts to launch /usr/bin/man to view this manual page. Override the manual pager path with the LTTNG_MAN_BIN_PATH environment variable.

--list-options

List available command options and quit.

Exit Status

0

Success

1

Command error

2

Undefined command

3

Fatal error

4

Command warning (something went wrong during the command)

Environment

LTTNG_ABORT_ON_ERROR

Set to 1 to abort the process after the first error is encountered.

LTTNG_HOME

Path to the LTTng home directory.

Defaults to $HOME.

Useful when the Unix user running the commands has a non-writable home directory.

LTTNG_MAN_BIN_PATH

Absolute path to the manual pager to use to read the LTTng command-line help (with lttng-help(1) or with the --help option) instead of /usr/bin/man.

LTTNG_SESSION_CONFIG_XSD_PATH

Path to the directory containing the session.xsd recording session configuration XML schema.

LTTNG_SESSIOND_PATH

Absolute path to the LTTng session daemon binary (see lttng-sessiond(8)) to spawn from the lttng-create(1) command.

The --sessiond-path general option overrides this environment variable.

Files

$LTTNG_HOME/.lttngrc

Unix user’s LTTng runtime configuration.

This is where LTTng stores the name of the Unix user’s current recording session between executions of lttng(1). lttng-create(1) and lttng-set-session(1) set the current recording session.

$LTTNG_HOME/lttng-traces

Default output directory of LTTng traces in local and snapshot modes.

Override this path with the --output option of the lttng-create(1) command.

$LTTNG_HOME/.lttng

Unix user’s LTTng runtime and configuration directory.

$LTTNG_HOME/.lttng/sessions

Default directory containing the Unix user’s saved recording session configurations (see lttng-save(1) and lttng-load(1)).

/usr/local/etc/lttng/sessions

Directory containing the system-wide saved recording session configurations (see lttng-save(1) and lttng-load(1)).

Note

$LTTNG_HOME defaults to the value of the HOME environment variable.

Examples

Example 1. Add the PIDs 1728 and 3775 to the Linux kernel process ID inclusion set of the current recording session.

See the --pid option.

$ lttng track --kernel --pid=1728,3775

Example 2. Add the ID of a specific user to the user space virtual user ID inclusion set of a specific recording session.

See the --vuid and --session options.

$ lttng track --userspace --session=my-session --vuid=http

Example 3. Add all the possible group IDs to the Linux kernel group ID inclusion set of the current recording session.

See the --all and --gid options.

$ lttng track --kernel --all --gid

Resources

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

lttng(1), lttng-untrack(1), lttng-concepts(7)

Referenced By

lttng(1), lttng-concepts(7), lttng-create(1), lttng-enable-event(1), lttng-untrack(1).

14 June 2021 LTTng 2.13.8 LTTng Manual