lttng [--group=GROUP] [--mi=TYPE] [--no-sessiond | --sessiond-path=PATH]
[--quiet | -v | -vv | -vvv] COMMAND [COMMAND OPTIONS]
The Linux Trace Toolkit: next generation <http://lttng.org/> is an open source software package used for correlated tracing of the Linux kernel, user applications, and user libraries.
LTTng consists of Linux kernel modules (for Linux kernel tracing) and dynamically loaded libraries (for user application and library tracing).
An LTTng session daemon, lttng-sessiond(8), receives commands from the command-line interface lttng to control the LTTng tracers. All interactions with the LTTng tracers happen through the lttng tool or through the liblttng-ctl library shipped with the LTTng-tools package.
A tracing domain is a tracer category. There are five available domains. For some commands, the domain needs to be specified with a command-line option. The domain options are:
- Apply command to the java.util.logging (JUL) domain.
- Apply command to the Linux kernel domain.
- Apply command to the Apache log4j 1.2 <https://logging.apache.org/log4j/1.2/> (Java) domain.
- Apply command to the Python <https://www.python.org/> domain.
- Apply command to the user space domain (application using liblttng-ust directly; see lttng-ust(3)).
The LTTng session daemon is a tracing registry which allows the user to interact with multiple tracers (kernel and user space) within the same container, a tracing session. Traces can be gathered from the Linux kernel and/or from instrumented applications (see lttng-ust(3)). You can aggregate and read the events of LTTng traces using babeltrace(1).
To trace the Linux kernel, the session daemon needs to be running as root. LTTng uses a tracing group to allow specific users to interact with the root session daemon. The default tracing group name is tracing. You can use the --group option to set the tracing group name to use.
Session daemons can coexist. You can have a session daemon running as user Alice that can be used to trace her applications alongside a root session daemon or a session daemon running as user Bob.
It is highly recommended to start the session daemon at boot time for stable and long-term tracing.
User applications instrumented with LTTng automatically register to the root session daemon and to user session daemons. This allows any session daemon to list the available traceable applications and event sources (see lttng-list(1)).
By default, the lttng-create(1) command automatically spawns a user session daemon if none is currently running. The --no-sessiond general option can be set to avoid this.
- Use GROUP as Unix tracing group (default: tracing).
Print the command's result using the machine interface type
instead of a human-readable output.
Supported types: xml.
The machine interface (MI) mode converts the traditional pretty-printing to a machine output syntax. The MI mode provides a change-resistant way to access information generated by the lttng command-line program.
When using the MI mode, the data is printed to the standard output. Errors and warnings are printed on the standard error with the pretty-print default format.
If any error occurs during the execution of a command, the return value of the command will be different than 0. In this case, lttng does NOT guarantee the syntax and data validity of the generated MI output.
For the xml MI type, an XML schema definition (XSD) file used for validation is available: see the src/common/mi_lttng.xsd file in the LTTng-tools source tree.
- Do not automatically spawn a session daemon.
- Suppress all messages, including warnings and errors.
- Set the session daemon binary's absolute path to PATH.
Three levels of verbosity are available, which are triggered by appending additional v letters to the option (that is, -vv and -vvv).
- Show help.
- List available commands.
- List available general options.
- Show version.
The following commands also have their own --help option.
- Create a tracing session.
- Tear down tracing sessions.
- Load tracing session configurations.
- Manage an LTTng tracing session's metadata generation.
- Save tracing session configurations.
- Set current tracing session.
- Add context fields to a channel.
- Disable tracing channels.
- Create or enable tracing channels.
- Disable event rules.
- Create or enable event rules.
- List tracing sessions, domains, channels, and events.
- Get the status of the current tracing session.
- Snapshot buffers of current tracing session.
- Start tracing.
- Stop tracing.
- Track specific system resources.
- Untrack specific system resources.
- Quantify LTTng overhead.
- Display help information about a command.
- Show version information.
- Start trace viewer.
- 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.
$LTTNG_HOME defaults to $HOME when not explicitly set.
- 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 <https://bugs.lttng.org/projects/lttng-tools>.
- • LTTng project website <http://lttng.org>
- • LTTng documentation <http://lttng.org/docs>
- • Git repositories <http://git.lttng.org>
- • GitHub organization <http://github.com/lttng>
- • Continuous integration <http://ci.lttng.org/>
- • 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-tools was originally written by Mathieu Desnoyers, Julien Desfossez, and David Goulet. More people have since contributed to it.
LTTng-tools is currently maintained by Jérémie Galarneau <mailto:[email protected]>.