plucky (1) lttng-add-trigger.1.gz
NAME
lttng-add-trigger - Add an LTTng trigger
SYNOPSIS
lttng [GENERAL OPTIONS] add-trigger [--name=NAME] [--owner-uid=UID]
--condition=CONDTYPE [CONDARGS]
--action=ACTTYPE [ACTARGS] [--action=ACTTYPE [ACTARGS]]...
DESCRIPTION
The lttng add-trigger command creates and adds an LTTng trigger to the connected session daemon (see
lttng-sessiond(8)).
See lttng-concepts(7) to learn more about LTTng triggers.
By default, the add-trigger command automatically assigns a name, unique for a given session daemon and
Unix user, to the added trigger. Assign a custom name with the --name.
The add-trigger command adds a trigger for your Unix user. If your Unix user is root, you may add the
trigger as another user with the --owner-uid option.
Specify the condition of the trigger to add with a condition specifier and its actions with one or more
action specifiers. The order of the action specifiers is significant: LTTng attempts to execute the
actions of a firing trigger in this order.
See the “EXAMPLES” section below for usage examples.
List the triggers of your Unix user, or of all users if your Unix user is root, with the lttng-list-
triggers(1) command.
Remove a trigger with the lttng-remove-trigger(1) command.
Condition specifier
Synopsis:
--condition=CONDTYPE [CONDARGS]
A condition specifier is the --condition option, which specifies the type of condition CONDTYPE,
followed, depending on CONDTYPE, with zero or more arguments CONDARGS.
The available condition types are:
event-rule-matches
Synopsis:
--condition=event-rule-matches [--capture=CDESCR]... ERSPEC
An event-rule-matches condition is considered satisfied when the event rule specified with ERSPEC
matches an event.
See lttng-event-rule(7) to learn how to specify an event rule (ERSPEC part).
Capture event record and context fields with one or more --capture options (see the “Capture
descriptor” section below to learn more). When an event-rule-matches condition with capture
descriptors is satisfied, the captured field values are available in the evaluation object of the
condition using the liblttng-ctl C API.
Important
Make sure to single-quote CDESCR when you run the add-trigger command from a shell, as capture
descriptors can include characters having a special meaning for most shells.
Capture descriptor
A capture descriptor is a textual expression which describes how to read an event record or context
field.
The argument of a --capture option, when using an “event rule matches” condition specifier (event-rule-
matches), is a capture descriptor.
A capture descriptor expression is one of:
NAME
An event record field named NAME.
The supported event record field types are:
• Integer
• Enumeration (integral value)
• Floating point number
• Static array of integers
• Dynamic array (“sequence”) of integers
• Text string
Examples: my_field, target_cpu, ip.
$ctx.NAME
A statically-known context field named NAME.
List the available statically-known context field names with lttng-add-context(1).
Examples: $ctx.prio, $ctx.preemptible, $ctx.perf:cpu:stalled-cycles-frontend.
$app.PROVIDER.NAME
An application-specific context field named NAME from the provider PROVIDER.
See lttng-add-context(1) to learn more about application-specific context fields.
Example: $app.server:cur_user.
EXPR[INDEX]
The element at index INDEX of the array field (static or dynamic) identified by the expression EXPR.
INDEX must be a constant, positive integral value.
Examples: ip[3], user_ids[15].
If, when an event rule matches, a given capture descriptor doesn’t identify an existing event or context
field, then the captured value is reported as being unavailable. This applies to:
• A nonexistent event record field name.
• A nonexistent statically-known context field name.
• A nonexistent application-specific context field name.
• An out-of-bounds array field index.
Action specifier
Synopsis:
--action=ACTTYPE [ACTARGS]
An action specifier is the --action option, which specifies the type of action ACTTYPE, followed,
depending on ACTTYPE, with zero or more arguments ACTARGS.
The available action types are:
Notify
Synopsis:
--action=notify [--rate-policy=POLICY]
Sends a notification through the notification mechanism of the session daemon (see lttng-
sessiond(8)).
The session daemon sends details about the condition evaluation along with the notification.
As of LTTng 2.13.14, you can write a C/C++ program to receive LTTng notifications (see the
liblttng-ctl C headers).
See below for the --rate-policy option.
Start a recording session
Synopsis:
--action=start-session SESSION [--rate-policy=POLICY]
Starts the recording session named SESSION like lttng-start(1) would.
If no recording session has the name SESSION when LTTng is ready to execute the action, LTTng does
nothing.
See below for the --rate-policy option.
Stop a recording session
Synopsis:
--action=stop-session SESSION [--rate-policy=POLICY]
Stops the recording session named SESSION like lttng-stop(1) would.
If no recording session has the name SESSION when LTTng is ready to execute the action, LTTng does
nothing.
See below for the --rate-policy option.
Rotate a recording session
Synopsis:
--action=rotate-session SESSION [--rate-policy=POLICY]
Archives the current trace chunk of the recording session named SESSION like lttng-rotate(1) would.
If no recording session has the name SESSION when LTTng is ready to execute the action, LTTng does
nothing.
See below for the --rate-policy option.
Take a recording session snapshot
Synopsis:
--action=snapshot-session SESSION [--rate-policy=POLICY]
Takes a snapshot of the recording session named SESSION like lttng-snapshot(1) would.
When the condition of the trigger is satisfied, the recording session named SESSION, if any, must be
a snapshot-mode recording session (see lttng-create(1)).
If no recording session has the name SESSION when LTTng is ready to execute the action, LTTng does
nothing.
See below for the --rate-policy option.
Common action options (as of LTTng 2.13.14):
--rate-policy=POLICY
Set the rate policy of the action to POLICY instead of every:1 (always execute).
A trigger which “fires” (its condition is satisfied) leads to an execution request for each of its
actions, in order. An execution request of a given action A first increments the execution request
count C of A. An execution request can then become an actual execution when C satisfies the rate
policy of A.
POLICY is one of:
once-after:COUNT
Only execute A when C is equal to COUNT.
In other words, execute A a single time after COUNT execution requests.
every:COUNT
Only execute A when C is a multiple of COUNT.
In other words, execute A every COUNT execution requests.
COUNT must be an integer greater than 0.
As of LTTng 2.13.14, you can use this option with any action type, but new action types in the future
may not support it.
OPTIONS
Identification
--name=NAME
Set the unique name of the trigger to add to NAME instead of the add-trigger command automatically
assigning one.
--owner-uid=UID
Add the trigger as the Unix user having the user ID UID.
You may only use this option if your Unix user is root.
Specifier
--condition=CONDTYPE
Introductory option for a condition specifier of type CONDTYPE.
See the “Condition specifier” section above to learn more.
--action=ACTTYPE
Introductory option for an action specifier of type ACTTYPE.
See the “Action specifier” section above to learn more.
Program information
-h, --help
Show help.
This option attempts to launch /usr/bin/man to view this manual page. Override the manual pager path
with the LTTNG_MAN_BIN_PATH environment variable.
--list-options
List available command options and quit.
EXIT STATUS
0
Success
1
Command error
2
Undefined command
3
Fatal error
4
Command warning (something went wrong during the command)
ENVIRONMENT
LTTNG_ABORT_ON_ERROR
Set to 1 to abort the process after the first error is encountered.
LTTNG_HOME
Path to the LTTng home directory.
Defaults to $HOME.
Useful when the Unix user running the commands has a non-writable home directory.
LTTNG_MAN_BIN_PATH
Absolute path to the manual pager to use to read the LTTng command-line help (with lttng-help(1) or
with the --help option) instead of /usr/bin/man.
LTTNG_SESSION_CONFIG_XSD_PATH
Path to the directory containing the session.xsd recording session configuration XML schema.
LTTNG_SESSIOND_PATH
Absolute path to the LTTng session daemon binary (see lttng-sessiond(8)) to spawn from the lttng-
create(1) command.
The --sessiond-path general option overrides this environment variable.
FILES
$LTTNG_HOME/.lttngrc
Unix user’s LTTng runtime configuration.
This is where LTTng stores the name of the Unix user’s current recording session between executions
of lttng(1). lttng-create(1) and lttng-set-session(1) set the current recording session.
$LTTNG_HOME/lttng-traces
Default output directory of LTTng traces in local and snapshot modes.
Override this path with the --output option of the lttng-create(1) command.
$LTTNG_HOME/.lttng
Unix user’s LTTng runtime and configuration directory.
$LTTNG_HOME/.lttng/sessions
Default directory containing the Unix user’s saved recording session configurations (see lttng-
save(1) and lttng-load(1)).
/etc/lttng/sessions
Directory containing the system-wide saved recording session configurations (see lttng-save(1) and
lttng-load(1)).
Note
$LTTNG_HOME defaults to the value of the HOME environment variable.
EXAMPLES
Example 1. Add an “event rule matches” trigger of which the action is to send a notification.
The event-rule-matches trigger condition below specifies an event rule which matches any Linux system
call entry event with a name starting with exec.
$ lttng add-trigger --condition=event-rule-matches \
--type=syscall:entry \
--name='exec*' --action=notify
Example 2. Add an “event rule matches” trigger of which the action is to stop a recording session and
then rotate it.
The event-rule-matches trigger condition below specifies an event rule which matches any user space
tracepoint event with a name starting with my_app: and with a log level at least as severe as a
warning.
The order of the --action options below is significant.
$ lttng add-trigger --condition=event-rule-matches \
--type=user --name='my_app:*' \
--log-level=TRACE_WARNING.. \
--action=stop-session my-session \
--action=rotate-session my-session
See lttng-concepts(7) to learn more about recording sessions and rotations.
Example 3. Add an “event rule matches” trigger with a specific name.
The event-rule-matches trigger condition below specifies an event rule which matches events which
LTTng creates from the my-logger Python logger.
The added trigger is named my-trigger, a unique name for your Unix user.
See the --name option.
$ lttng add-trigger --name=my-trigger \
--condition=event-rule-matches \
--type=python --name=my-logger \
--action=snapshot-session my-session
Example 4. Add an “event rule matches” trigger as another Unix user.
The command line below adds a trigger as the mireille Unix user.
Your Unix user must be root to use the --owner-uid option.
The condition of the trigger specifies an event rule which matches LTTng kernel tracepoint events
with a name which starts with sched.
# lttng add-trigger --owner-uid=$(id --user mireille) \
--condition=event-rule-matches \
--type=kernel --name='sched*' \
--action=notify
Example 5. Add an “event rule matches” trigger with a notification action to be executed every 10 times.
The event-rule-matches trigger condition below specifies an event rule which matches all user space
tracepoint events.
See the --rate-policy option above.
$ lttng add-trigger --condition=event-rule-matches \
--type=user --action=notify \
--rate-policy=every:10
Example 6. Add an “event rule matches” trigger with a recording session starting action to be executed a
single time after 40 times.
The event-rule-matches trigger condition below specifies an event rule which matches any Linux system
call event (entry and exit) of which the fd event record field is less than 3.
See the --rate-policy option above.
$ lttng add-trigger --condition=event-rule-matches \
--type=syscall --filter='fd < 3' \
--action=start-session my-session \
--rate-policy=once-after:40
RESOURCES
• LTTng project website <https://lttng.org>
• LTTng documentation <https://lttng.org/docs>
• LTTng bug tracker <https://bugs.lttng.org>
• Git repositories <https://git.lttng.org>
• GitHub organization <https://github.com/lttng>
• Continuous integration <https://ci.lttng.org/>
• Mailing list <https://lists.lttng.org/> for support and development: lttng-dev@lists.lttng.org
• IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net
COPYRIGHT
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
lttng(1), lttng-list-triggers(1), lttng-remove-trigger(1), lttng-concepts(7)