lttng(1) (v2.13)

lttng — Control LTTng tracing

lttng [--group=GROUP] [--mi=xml] [--no-sessiond | --sessiond-path=PATH]
      [--relayd-path=PATH] [--quiet | -verbose…]
      COMMAND [COMMAND OPTIONS]

The Linux Trace Toolkit: next generation 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).

The lttng command-line tool, as well as any user application linked with the LTTng control library (liblttng-ctl), sends commands to a listening LTTng session daemon (lttng-sessiond(8)). A session daemon:

• Manages recording sessions (see lttng-concepts(7) to learn more about recording sessions).

• Controls the various components (like tracers and consumer daemons) of LTTng.

• Sends asynchronous notifications to user applications.

By default, the lttng-create(1) command automatically spawns:

• A session daemon for your Unix user if none is currently running.

  Override the path of the session daemon binary to spawn with the --sessiond-path option.

  Avoid automatically spawning a session daemon with the --no-sessiond option.

• A relay daemon (see lttng-relayd(8)) if all the following statements are true:

  • You specify the --live option.

  • You don’t specify any of the --set-url, --ctrl-url, or --data-url options.

  • No relay daemon is currently listening for TCP connections on 127.0.0.1:5344 (default LTTng live reader connection address and port).

  Override the path of the relay daemon binary to spawn with the --relayd-path option.

See lttng-concepts(7) to learn more about the foundational concepts of LTTng.

The lttng tool offers a subcommand-based command-line interface. The “COMMANDS” section below lists the available commands.

For most of its commands, the lttng tool needs to connect to a listening LTTng session daemon (lttng-sessiond(8)) to control LTTng tracing.

Each Unix user may have its own independent running session daemon. However, the lttng tool must connect to the session daemon of the root user (the root session daemon) to control Linux kernel tracing.

How the lttng tool chooses which session daemon to connect to is as follows:

If your Unix user is root

Connect to the root session daemon.

If your Unix user is not root

If your Unix user is part of the Unix tracing group

Try to connect to the root session daemon.

If the root session daemon isn’t running, connect to the session daemon of your Unix user.

If your Unix user is not part of the tracing group

Connect to the session daemon of your Unix user.

The name of the Unix tracing group is one of:

With the --group=GROUP option of the root session daemon (lttng-sessiond(8))

GROUP

In that case, you must use the --group=GROUP option, with the same GROUP argument, of the lttng tool.

Without the --group option of the root session daemon

tracing

LTTng-instrumented user applications automatically register to both the root and user session daemons. This makes it possible for both session daemons to list the available instrumented applications and their instrumentation points (see lttng-list(1)).

-g GROUP, --group=GROUP

Set the name of the Unix tracing group to GROUP instead of tracing.

You must use this option to be able to connect to a root session daemon (lttng-sessiond(8)) which was started with its own --group=GROUP option.

-m xml, --mi=xml

Print the command’s result using a stable XML machine interface (MI) output instead of the default, unstable human-readable output.

With this mode, lttng prints the resulting XML document to the standard output, while it prints any error/warning to the standard error with an unstable, human-readable format.

If any error occurs during the execution of lttng, the command exits with a status different than 0, and lttng does not guarantee the syntax and data validity of its MI output.

An XML schema definition (XSD) file used for validation of the MI output 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 for your Unix user when running the lttng-create(1) command.

You may not use this option with the --sessiond-path option.

-q, --quiet

Suppress all messages, including warnings and errors.

You may not use this option with the --verbose option.

--sessiond-path=PATH

Set the absolute path of the session daemon binary to spawn from the lttng-create(1) command to PATH.

You may not use this option with the --no-sessiond option.

--relayd-path=PATH

Set the absolute path of the relay daemon binary to spawn from the lttng-create(1) command to PATH.

-v, --verbose

Increase verbosity.

Specify this option up to three times to get more levels of verbosity.

You may not use this option with the --quiet option.

-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.

--list-commands

List available commands and quit.

-V, --version

Show version and quit.

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

0

Success

1

Command error

2

Undefined command

3

Fatal error

4

Command warning (something went wrong during the command)

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.

$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)).

/etc/lttng/sessions

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

• LTTng project website

• LTTng documentation

• LTTng bug tracker

• Git repositories

• GitHub organization

• Continuous integration

• Mailing list for support and development: lttng-dev@lists.lttng.org

• IRC channel: #lttng on irc.oftc.net

This program is part of the LTTng-tools project.

LTTng-tools is distributed under the GNU General Public License version 2. See the LICENSE file for details.

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.

lttng-concepts(7) lttng-relayd(8), lttng-sessiond(8)