LTTNG-ROTATE(1)

NAME
lttng-rotate - Archive a tracing session's current trace chunk

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 LTTng archives a trace chunk, it 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 LTTng 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:

    • At any time when the tracing session is active (see lttng-start(1)).

    • A single time once the tracing session becomes inactive (see lttng-stop(1)).

By default, the lttng rotate command ensures that LTTng finished performing the tracing session rotation before it prints the archived trace chunk’s path and exits. 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, so that LTTng might not have completed the rotation when the command exits. In this case, there is no easy way to know when the current trace chunk becomes archived, and the command does not print the archived trace chunk’s path.

Because when LTTng performs a tracing session rotation, it flushes the tracing session’s current sub-buffers, 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 the archives subdirectory within a tracing session’s output directory (see the --output option in lttng-create(1) and lttng-relayd(8)).

A trace chunk archive 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 LTTng performs a tracing session rotation, it names the resulting trace chunk archive as such, relative to the tracing session’s output directory:

    archives/BEGIN-END-ID

BEGIN
    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.

    Example: 20171119T152407-0500

END
    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.

    Example: 20180118T152407+0930

ID
    Unique numeric identifier of the trace chunk within its tracing session.

Trace chunk archive name example:

    archives/20171119T152407-0500-20171119T151422-0500-3

OPTIONS

General options are described in lttng(1).

-n, --no-wait
    Do not ensure that the rotation is done before returning to the prompt.

  Program information

-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-options
    List available command options.

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)).

    Note

    $LTTNG_HOME defaults to $HOME when not explicitly set.

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)