lttng-create — Create an LTTng tracing session
Synopsis
Local mode:
lttng [GENERAL OPTIONS] create [SESSION] [--shm-path=PATH]
[--no-output | --output=PATH | --set-url=file://PATH]
Network streaming mode:
lttng [GENERAL OPTIONS] create [SESSION] [--shm-path=PATH]
(--set-url=URL | --ctrl-url=URL --data-url=URL)
Snapshot mode:
lttng [GENERAL OPTIONS] create [SESSION] --snapshot
[--shm-path=PATH] [--set-url=URL | --ctrl-url=URL --data-url=URL]
Live mode:
lttng [GENERAL OPTIONS] create [SESSION] --live[=DELAYUS]
[--shm-path=PATH] [--set-url=URL | --ctrl-url=URL --data-url=URL]Description
The lttng create command creates a new tracing session.
A tracing session is a named container of channels, which in turn contain event rules. It is domain-agnostic, in that channels and event rules can be enabled for the user space tracer and/or the Linux kernel tracer.
On execution, an .lttngrc file is created, if it does not exist, in the user’s home directory. This file contains the name of the current tracing session. When creating a new tracing session with lttng create, the current tracing session is set to this new tracing session. The lttng-set-session(1) command can be used to set the current tracing session without manually editing the .lttngrc file.
If SESSION is omitted, a session name is automatically created having this form: auto-YYYYmmdd-HHMMSS. SESSION must not contain the character /.
The --shm-path option can be used to specify the path to the shared memory holding the ring buffers. Specifying a location on an NVRAM file system makes it possible to retrieve the latest recorded trace data when the system reboots after a crash. To view the events of ring buffer files after a system crash, use the lttng-crash(1) utility.
Tracing sessions are destroyed using the lttng-destroy(1) command.
Creation modes
There are four tracing session modes:
- Local mode
-
Traces the local system and writes the trace to the local file system. The --output option specifies the trace path. Using --set-url=file://PATH is the equivalent of using --output=PATH. The file system output can be disabled using the --no-output option.
If none of the options mentioned above are used, then the trace is written locally in the $LTTNG_HOME/lttng-traces directory ($LTTNG_HOME defaults to $HOME).
- Network streaming mode
Traces the local system and sends the trace over the network to a listening relay daemon (see lttng-relayd(8)). The --set-url, or --ctrl-url and --data-url options set the trace output destination (see the URL format section below).
- Snapshot mode
Traces the local system without writing the trace to the local file system (implicit --no-output option). Channels are automatically configured to be snapshot-ready on creation (see lttng-enable-channel(1)). The lttng-snapshot(1) command is used to take snapshots of the current ring buffers. The --set-url, or --ctrl-url and --data-url options set the default snapshot output destination.
- Live mode
Traces the local system, sending trace data to an LTTng relay daemon over the network (see lttng-relayd(8)). The --set-url, or --ctrl-url and --data-url options set the trace output destination. The live output URLs cannot use the file:// protocol (see the URL format section below).
URL format
The --set-url, --ctrl-url, and --data-url options' arguments are URLs.
The format of those URLs is one of:
file://TRACEPATH NETPROTO://(HOST | IPADDR)[:CTRLPORT[:DATAPORT]][/TRACEPATH]
The file:// protocol targets the local file system and can only be used as the --set-url option’s argument when the session is created in local or snapshot mode.
- TRACEPATH
Absolute path to trace files on the local file system.
The other version is available when the session is created in network streaming, snapshot, or live mode.
- NETPROTO
-
Network protocol, amongst:
- net
TCP over IPv4; the default values of CTRLPORT and DATAPORT are respectively 5342 and 5343.
- net6
TCP over IPv6: same default ports as the net protocol.
- tcp
Same as the net protocol; can only be used with the --ctrl-url and --data-url options together.
- tcp6
Same as the net6 protocol; can only be used with the --ctrl-url and --data-url options together.
- (HOST | IPADDR)
Hostname or IP address (IPv6 address must be enclosed in brackets ([ and ]); see RFC 2732 <https://www.ietf.org/rfc/rfc2732.txt>).
- CTRLPORT
Control port.
- DATAPORT
Data port.
- TRACEPATH
Path of trace files on the remote file system. This path is relative to the base output directory set on the relay daemon side; see lttng-relayd(8).
Options
General options are described in lttng(1).
Mode selection
- --live[=DELAYUS]
-
Create the session in live mode.
The optional DELAYUS parameter, given in microseconds, is the maximum time the user can wait for the data to be flushed. This mode can be set with a network URL (options --set-url, or --ctrl-url and --data-url) and must have a relay daemon listening (see lttng-relayd(8)).
By default, DELAYUS is 1000000 and the network URL is set to net://127.0.0.1.
- --snapshot
Create the session in snapshot mode. This is the equivalent of using the --no-output option and creating all the channels of this new tracing session in overwrite mode with an mmap output type.
Output
- --no-output
In local mode, do not output any trace data.
- -o PATH, --output=PATH
In local mode, set trace output path to PATH.
- --shm-path=PATH
Create shared memory holding buffers at PATH.
URL
See the URL format section above for more information about the syntax of the following options' URL argument.
- -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).
- -U URL, --set-url=URL
-
Set URL destination of the trace data to URL. It is persistent for the session lifetime. This option sets both data (--data-url option) and control (--ctrl-url option) URLs at the same time.
In local mode, URL must start with file:// followed by the destination path on the local file system.
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.
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
Referenced By
lttng(1), lttng-add-context(1), lttng-destroy(1), lttng-disable-channel(1), lttng-disable-event(1), lttng-disable-rotation(1), lttng-enable-channel(1), lttng-enable-event(1), lttng-help(1), lttng-list(1), lttng-load(1), lttng-metadata(1), lttng-regenerate(1), lttng-save(1), lttng-sessiond(8), lttng-set-session(1), lttng-snapshot(1), lttng-start(1), lttng-status(1), lttng-stop(1), lttng-track(1), lttng-untrack(1), lttng-version(1), lttng-view(1).