lttng-rotate — Archive a tracing session's current trace chunk
lttng [GENERAL OPTIONS] rotate [--no-wait] [SESSION]
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.
Trace chunk archive naming
A trace chunk archive is a subdirectory of a tracing session’s output directory (see the --output option in lttng-create(1) and lttng-relayd(8)) which contains, through tracing domain and possibly UID/PID subdirectories, metadata and data stream files.
A trace chunk archive is, at the same time:
- A self-contained LTTng trace.
- A member of a set of trace chunk archives which form the complete trace of a tracing session.
In other words, an LTTng trace reader can read both the tracing session output directory (all the trace chunk archives), or a single trace chunk archive.
When a tracing session rotation occurs, the created trace chunk archive is named:
Date and time of the beginning of the trace chunk archive with the ISO 8601-compatible YYYYmmddTHHMMSS±HHMM form, where YYYYmmdd is the date and HHMMSS±HHMM is the time with the time zone offset from UTC.
Date and time of the end of the trace chunk archive with the ISO 8601-compatible YYYYmmddTHHMMSS±HHMM form, where YYYYmmdd is the date and HHMMSS±HHMM is the time with the time zone offset from UTC.
Unique numeric identifier of the trace chunk within its tracing session.
Trace chunk archive name example: 20171119T152407-0500-20171119T151422-0500-3
General options are described in lttng(1).
- -n, --no-wait
Do not ensure that the rotation is done before returning to the prompt.
- -h, --help
Show command help.
This option, like lttng-help(1), attempts to launch /usr/bin/man to view the command’s man page. The path to the man pager can be overridden by the LTTNG_MAN_BIN_PATH environment variable.
List available command options.
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.
Set to 1 to abort the process after the first error is encountered.
Overrides the $HOME environment variable. Useful when the user running the commands has a non-writable home directory.
Absolute path to the man pager to use for viewing help information about LTTng commands (using lttng-help(1) or lttng COMMAND --help).
Path in which the session.xsd session configuration XML schema may be found.
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.
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.
Default output directory of LTTng traces. This can be overridden with the --output option of the lttng-create(1) command.
User LTTng runtime and configuration directory.
Default location of saved user tracing sessions (see lttng-save(1) and lttng-load(1)).
System-wide location of saved tracing sessions (see lttng-save(1) and lttng-load(1)).
$LTTNG_HOME defaults to $HOME when not explicitly set.
Command warning (something went wrong during the command)
If you encounter any issue or usability problem, please report it on the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-tools>.
- 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: email@example.com
- IRC channel <irc://irc.oftc.net/lttng>: #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 <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.
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.
lttng-enable-rotation(1), lttng-disable-rotation(1), lttng(1)