The lttng snapshot command manages the snapshot outputs and takes
A snapshot is a dump of the current sub-buffers of all the channels
of a given tracing session. When a snapshot is taken, the memory dump
is sent to the registered snapshot outputs.
The tracing session should be created in snapshot mode to make sure
taking snapshots is allowed. This is done at tracing session creation
time using the lttng-create(1) command.
Note that, when a snapshot is taken, the sub-buffers are not cleared.
This means that different recorded snapshots may contain the same
Snapshot outputs are the destinations of snapshot files when a
snapshot is taken using the record action.
As of this version, only one snapshot output is allowed.
A snapshot output can be added using the add-output action. The
output destination URL is set using either the URL positional
argument, or both the --ctrl-url and --data-url options. See
lttng-create(1) to learn more about the URL format.
A name can be assigned to an output when adding it using the --name
option. This name is part of the names of the snapshot files written
to this output.
By default, the snapshot files can be as big as the sum of the sizes
of all the sub-buffers or all the channels of the selected tracing
session. The maximum total size of all the snapshot files can be
configured using the --max-size option.
Snapshot outputs can be listed using the list-output action.
Snapshot outputs can be removed using the del-output action. The
configured name can be used when removing an output, or an ID as
listed by the list-output action.
Taking a snapshot
Taking a snapshot of the current tracing session is as easy as:
lttng snapshot record
This writes the snapshot files to the configured output. It is
possible to use a custom, unregistered output at record time using
the same options supported by the add-output action.
Before taking a snapshot on a system with a high event
throughput, it is recommended to first run lttng stop (see
lttng-stop(1)). Otherwise, the snapshot could contain "holes",
the result of the tracers overwriting unconsumed trace packets
during the record operation. After the snapshot is recorded, the
tracers can be started again with lttng start (see
General options are described in lttng(1).
Target-s SESSION, --session=SESSION
Take a snapshot of the sub-buffers of the channels contained in
the tracing session named SESSION instead of the current tracing
Snapshot output-C URL, --ctrl-url=URL
Set control path URL to URL (must use --data-url option also).
-D URL, --data-url=URL
Set data path URL to URL (must use --ctrl-url option also).
-m SIZE, --max-size=SIZE
Limit the total size of all the snapshot files written when
recording a snapshot to SIZE bytes. The k (kiB), M (MiB), and G
(GiB) suffixes are supported.
-n NAME, --name=NAME
Assign the name NAME to the snapshot output.
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 available command options.
Set to 1 to abort the process after the first error is
Overrides the $HOME environment variable. Useful when the user
running the commands has a non-writable home directory.
Absolute path to the man pager to use for viewing help
information about LTTng commands (using lttng-help(1) or lttngCOMMAND --help).
Path in which the session.xsd session configuration XML schema
may be found.
Full session daemon binary path.
The --sessiond-path option has precedence over this environment
Note that the lttng-create(1) command can spawn an LTTng session
daemon automatically if none is running. See lttng-sessiond(8) for
the environment variables influencing the execution of the session
User LTTng runtime configuration.
This is where the per-user current tracing session is stored
between executions of lttng(1). The current tracing session can
be set with lttng-set-session(1). See lttng-create(1) for more
information about tracing sessions.
Default output directory of LTTng traces. This can be overridden
with the --output option of the lttng-create(1) command.
User LTTng runtime and configuration directory.
Default location of saved user tracing sessions (see
lttng-save(1) and lttng-load(1)).
System-wide location of saved tracing sessions (see lttng-save(1)
Note$LTTNG_HOME defaults to $HOME when not explicitly set.
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-tools was originally written by Mathieu Desnoyers, Julien
Desfossez, and David Goulet. More people have since contributed to
LTTng-tools is currently maintained by Jérémie Galarneau
This page is part of the LTTng-Tools ( LTTng tools) project.
Information about the project can be found at ⟨http://lttng.org/⟩.
It is not known how to report bugs for this man page; if you know,
please send a mail to firstname.lastname@example.org. This page was obtained
from the project's upstream Git repository
⟨git://git.lttng.org/lttng-tools.git⟩ on 2017-03-13. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
LTTng 2.10.0-pre 03/13/2017 LTTNG-SNAPSHOT(1)