lttng — LTTng 2 tracer control command-line tool
lttng [--group=GROUP] [--mi=TYPE] [--no-sessiond|--sessiond-path=PATH] [--quiet|-v|-vv|-vvv] COMMAND [COMMAND OPTIONS]
The Linux Trace Toolkit: next generation 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:
-j, --jul
Apply command to the java.util.logging (JUL) domain.
-k, --kernel
Apply command to the Linux kernel domain.
-l, --log4j
Apply command to the Apache log4j 1.2 (Java) domain.
-p, --python
Apply command to the Python domain.
-u, --userspace
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.
Note: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.
-g GROUP, --group=GROUP
Use GROUP as Unix tracing group (default: tracing).
-m TYPE, --mi=TYPE
Print the command’s result using the machine interface type 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.
-n, --no-sessiond
Do not automatically spawn a session daemon.
-q, --quiet
Suppress all messages, including warnings and errors.
--sessiond-path=PATH
Set the session daemon binary’s absolute path to PATH.
-v, --verbose
Increase verbosity.
Three levels of verbosity are available, which are triggered by
appending additional v letters to the option
(that is, -vv and -vvv).
-h, --help
Show help.
--list-commands
List available commands.
--list-options
List available general options.
-V, --version
Show version.
The following commands also have their own --help option.
Create a recording session.
Destroy recording sessions.
Load recording session configurations.
Regenerate specific recording session data.
Save recording session configurations.
Set the current recording session.
Add context fields to be recorded.
Disable channels.
Create or enable a channel.
Disable recording event rules.
Create or enable recording event rules.
List recording sessions and instrumentation points.
Show the status of the current recording session.
Take a recording session snapshot.
Start a recording session.
Stop a recording session.
Allow specific processes to record events.
Disallow specific processes to record events.
Show the help of a command.
Show LTTng-tools version information.
Launch a trace reader.
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.