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 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.
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
General options are described in lttng(1).
-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.
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 immediate rotation (lttng rotate) is currently happening.
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.
$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.
$LTTNG_HOME/.lttng/sessions
Default location of saved user tracing sessions (see lttng-save(1) and lttng-load(1)).
/etc/lttng/sessions
System-wide location of saved tracing sessions (see lttng-save(1) and lttng-load(1)).
Note:$LTTNG_HOME defaults to $HOME when not explicitly set.
Success
Command error
Undefined command
Fatal error
Command warning (something went wrong during the command)
If you encounter any issue or usability problem, please report it on the LTTng bug tracker.
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.