lttng-rotate

Synopsis

lttng [GENERAL OPTIONS] rotate [--no-wait] [SESSION]

Description

The lttng rotate command archives the current trace chunk of the current tracing session, or of the tracing session named SESSION if provided, to the file system. This action is called a tracing session rotation.

Once a trace chunk is archived, LTTng does not manage it anymore: you can read it, modify it, move it, or remove it.

An archived trace chunk is a collection of metadata and data stream files which form a self-contained trace.

The current trace chunk of a given tracing session includes:

• The stream files already written to the file system, and which are not part of a previously archived trace chunk, since the most recent event amongst:

  • The first time the tracing session was started with lttng-start(1).
  • The last rotation, either an immediate one with lttng rotate, or an automatic one from a rotation schedule previously set with lttng-enable-rotation(1).
• The content of all the non-flushed sub-buffers of the tracing session’s channels.

You can use lttng rotate either at any time when the tracing session is active (see lttng-start(1)), or a single time once the tracing session becomes inactive (see lttng-stop(1)).

By default, the lttng rotate command ensures that the rotation is done before printing the archived trace chunk’s path and returning to the prompt. The printed path is absolute when the tracing session was created in normal mode and relative to the relay daemon’s output directory (see the --output option in lttng-relayd(8)) when it was created in network streaming mode (see lttng-create(1)).

With the --no-wait option, the command finishes immediately, hence a rotation might not be completed when the command is done. In this case, there is no easy way to know when the current trace chunk is archived, and the command does not print the archived trace chunk’s path.

Because a rotation causes the tracing session’s current sub-buffers to be flushed, archived trace chunks are never redundant, that is, they do not overlap over time like snapshots can (see lttng-snapshot(1)). Also, a rotation does not directly cause discarded event records or packets.

See Limitations for important limitations regarding this command.

BEGIN-END-ID

Options

General options are described in lttng(1).

-n, --no-wait

Do not ensure that the rotation is done before returning to the prompt.

Limitations

The lttng rotate command only works when:

• The tracing session is created in normal mode or in network streaming mode (see lttng-create(1)).
• No channel was created with a configured trace file count or size limit (see the --tracefile-size and --tracefile-count options in lttng-enable-channel(1)).
• No immediate rotation (lttng rotate) is currently happening.

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-enable-rotation(1), lttng-disable-rotation(1), lttng(1)

Referenced By

lttng-regenerate(1).