lttng - Man Page

Control LTTng tracing

Synopsis

lttng [--group=GROUP] [--mi=xml] [--no-sessiond | --sessiond-path=PATH]
      [--relayd-path=PATH] [--quiet | -verbose...]
      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).

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:

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

Note

The LTTng project recommends that you start the session daemon at boot time for stable and long-term tracing.

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.

Session daemon connection

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)).

Options

-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.

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.

--list-commands

List available commands and quit.

-V,  --version

Show version and quit.

Commands

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

Recording session

CommandDescription
lttng-create(1)Create a recording session.
lttng-destroy(1)Destroy recording sessions.
lttng-disable-rotation(1)Unset a recording session rotation schedule.
lttng-enable-rotation(1)Set a recording session rotation schedule.
lttng-load(1)Load recording session configurations.
lttng-regenerate(1)Regenerate specific recording session data.
lttng-rotate(1)Archive the current trace chunk of a recording session.
lttng-save(1)Save recording session configurations.
lttng-set-session(1)Set the current recording session.
lttng-snapshot(1)Take a recording session snapshot.
lttng-start(1)Start a recording session.
lttng-status(1)Show the status of the current recording session.
lttng-stop(1)Stop a recording session.

Channel

CommandDescription
lttng-add-context(1)Add context fields to be recorded.
lttng-disable-channel(1)Disable channels.
lttng-enable-channel(1)Create or enable a channel.

Recording event rule

CommandDescription
lttng-disable-event(1)Disable recording event rules.
lttng-enable-event(1)Create or enable recording event rules.

Information

CommandDescription
lttng-list(1)List recording sessions and instrumentation points.

Resource tracking

CommandDescription
lttng-track(1)Allow specific processes to record events.
lttng-untrack(1)Disallow specific processes to record events.

Trigger

CommandDescription
lttng-add-trigger(1)Add a trigger.
lttng-list-triggers(1)List triggers.
lttng-remove-trigger(1)Remove a trigger.

Miscellaneous

CommandDescription
lttng-help(1)Show the help of a command.
lttng-version(1)Show LTTng-tools version information.
lttng-view(1)Launch a trace reader.

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.

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

Referenced By

babeltrace(1), babeltrace2-filter.lttng-utils.debug-info(7), babeltrace-log(1), lttng-add-context(1), lttng-add-trigger(1), lttng-clear(1), lttng-concepts(7), 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-enable-rotation(1), lttng-event-rule(7), lttng-health-check(3), lttng-help(1), lttng-list(1), lttng-list-triggers(1), lttng-load(1), lttng-metadata(1), lttng-regenerate(1), lttng-relayd(8), lttng-remove-trigger(1), 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_ust_tracef(3), lttng_ust_tracelog(3), lttng-version(1), lttng-view(1).

14 June 2021 LTTng 2.13.0 LTTng Manual