lttng

Synopsis

lttng [--group=GROUP] [--mi=TYPE] [--no-sessiond | --sessiond-path=PATH]
      [--quiet | -v | -vv | -vvv] COMMAND [COMMAND OPTIONS]

Description

The Linux Trace Toolkit: next generation <https://lttng.org/> is an open source software package used for correlated tracing of the Linux kernel, user applications, and user libraries.

LTTng consists of Linux kernel modules (for Linux kernel tracing) and dynamically loaded libraries (for user application and library tracing).

An LTTng session daemon, lttng-sessiond(8), receives commands from the command-line interface lttng to control the LTTng tracers. All interactions with the LTTng tracers happen through the lttng tool or through the liblttng-ctl library shipped with the LTTng-tools package.

A tracing domain is a tracer category. There are five available domains. For some commands, the domain needs to be specified with a command-line option. The domain options are:

-j, --jul

Apply command to the java.util.logging (JUL) domain.

-k, --kernel

Apply command to the Linux kernel domain.

-l, --log4j

Apply command to the Apache log4j 1.2 <https://logging.apache.org/log4j/1.2/> (Java) domain.

-p, --python

Apply command to the Python <https://www.python.org/> domain.

-u, --userspace

Apply command to the user space domain (application using liblttng-ust directly; see lttng-ust(3)).

The LTTng session daemon is a tracing registry which allows the user to interact with multiple tracers (kernel and user space) within the same container, a tracing session. Traces can be gathered from the Linux kernel and/or from instrumented applications (see lttng-ust(3)). You can aggregate and read the events of LTTng traces using babeltrace(1).

To trace the Linux kernel, the session daemon needs to be running as root. LTTng uses a tracing group to allow specific users to interact with the root session daemon. The default tracing group name is tracing. You can use the --group option to set the tracing group name to use.

Session daemons can coexist. You can have a session daemon running as user Alice that can be used to trace her applications alongside a root session daemon or a session daemon running as user Bob.

User applications instrumented with LTTng automatically register to the root session daemon and to user session daemons. This allows any session daemon to list the available traceable applications and event sources (see lttng-list(1)).

By default, the lttng-create(1) command automatically spawns a user session daemon if none is currently running. The --no-sessiond general option can be set to avoid this.

Options

-g GROUP, --group=GROUP

Use GROUP as Unix tracing group (default: tracing).

-m TYPE, --mi=TYPE

Print the command’s result using the machine interface type TYPE instead of a human-readable output.

Supported types: xml.

The machine interface (MI) mode converts the traditional pretty-printing to a machine output syntax. The MI mode provides a change-resistant way to access information generated by the lttng command-line program.

When using the MI mode, the data is printed to the standard output. Errors and warnings are printed on the standard error with the pretty-print default format.

If any error occurs during the execution of a command, the return value of the command will be different than 0. In this case, lttng does NOT guarantee the syntax and data validity of the generated MI output.

For the xml MI type, an XML schema definition (XSD) file used for validation is available: see the src/common/mi_lttng.xsd file in the LTTng-tools source tree.

-n, --no-sessiond

Do not automatically spawn a session daemon.

-q, --quiet

Suppress all messages, including warnings and errors.

--sessiond-path=PATH

Set the session daemon binary’s absolute path to PATH.

-v, --verbose

Increase verbosity.

Three levels of verbosity are available, which are triggered by appending additional v letters to the option (that is, -vv and -vvv).

Commands

The following commands also have their own --help option.

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)).

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

lttng-sessiond(8), lttng-relayd(8), lttng-crash(1), lttng-ust(3), babeltrace(1)

Referenced By

babeltrace(1), babeltrace-log(1), lttng-add-context(1), lttng-crash(1), lttng-create(1), lttng-destroy(1), lttng-disable-channel(1), lttng-disable-event(1), lttng-disable-rotation(1), lttng-enable-channel(1), lttng-enable-event(1), lttng-health-check(3), lttng-help(1), lttng-list(1), lttng-load(1), lttng-metadata(1), lttng-regenerate(1), lttng-relayd(8), lttng-rotate(1), lttng-save(1), lttng-sessiond(8), lttng-set-session(1), lttng-snapshot(1), lttng-start(1), lttng-status(1), lttng-stop(1), lttng-track(1), lttng-untrack(1), lttng-ust(3), lttng-ust-cyg-profile(3), lttng-ust-dl(3), lttng-version(1), lttng-view(1), tracef(3), tracelog(3).