--- name: "lttng-add-trigger" section: "1" platform: "linux" package: "lttng-tools" version: "2.13.15-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/lttng-add-trigger" --- # lttng-add-trigger(1) Add an LTTng trigger ## 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)](/lttng-sessiond/8.md)). See [**lttng-concepts**(7)](/lttng-concepts/7.md) 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)](/lttng-list-triggers/1.md) command. Remove a trigger with the [**lttng-remove-trigger**(1)](/lttng-remove-trigger/1.md) 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)](/lttng-event-rule/7.md) 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**. **$ctx.***NAME* A statically-known context field named *NAME*. List the available statically-known context field names with [**lttng-add-context**(1)](/lttng-add-context/1.md). Examples: **$ctx.prio**, **$ctx.preemptible**, **$ctx.perf:cpu:stalled-cycles-frontend**. **$app.***PROVIDER***.***NAME* An application-specific context field named *NAME* from the provider *PROVIDER*. See [**lttng-add-context**(1)](/lttng-add-context/1.md) to learn more about application-specific context fields. Example: **$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)](/lttng-sessiond/8.md)). The session daemon sends details about the condition evaluation along with the notification. As of LTTng 2.13.15, 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)](/lttng-start/1.md) 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)](/lttng-stop/1.md) 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)](/lttng-rotate/1.md) 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)](/lttng-snapshot/1.md) 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)](/lttng-create/1.md)). 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 2.13.15): - **--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 2.13.15, 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 **$HOME**. Useful when the Unix user running the commands has a non-writable home directory. **LTTNG\_MAN\_BIN\_PATH** Absolute path to the manual pager to use to read the LTTng command-line help (with [**lttng-help**(1)](/lttng-help/1.md) or with the **--help** option) instead of **/usr/bin/man**. **LTTNG\_SESSION\_CONFIG\_XSD\_PATH** Path to the directory containing the **session.xsd** recording session configuration XML schema. **LTTNG\_SESSIOND\_PATH** Absolute path to the LTTng session daemon binary (see [**lttng-sessiond**(8)](/lttng-sessiond/8.md)) to spawn from the [**lttng-create**(1)](/lttng-create/1.md) command. The **--sessiond-path** general option overrides this environment variable. ## FILES **$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/1.md). [**lttng-create**(1)](/lttng-create/1.md) and [**lttng-set-session**(1)](/lttng-set-session/1.md) set the current recording session. **$LTTNG\_HOME/lttng-traces** Default output directory of LTTng traces in local and snapshot modes. Override this path with the **--output** option of the [**lttng-create**(1)](/lttng-create/1.md) command. **$LTTNG\_HOME/.lttng** Unix user’s LTTng runtime and configuration directory. **$LTTNG\_HOME/.lttng/sessions** Default directory containing the Unix user’s saved recording session configurations (see [**lttng-save**(1)](/lttng-save/1.md) and [**lttng-load**(1)](/lttng-load/1.md)). **/etc/lttng/sessions** Directory containing the system-wide saved recording session configurations (see [**lttng-save**(1)](/lttng-save/1.md) and [**lttng-load**(1)](/lttng-load/1.md)). **Note**\ **$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)](/lttng-concepts/7.md) 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 \ • LTTng documentation \ • LTTng bug tracker \ • Git repositories \ • GitHub organization \ • Continuous integration \ • Mailing list \ for support and development: **lttng-dev@lists.lttng.org** • IRC channel \: **#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 \. See the **LICENSE** \ file for details. ## THANKS 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. ## SEE ALSO [**lttng**(1)](/lttng/1.md), [**lttng-list-triggers**(1)](/lttng-list-triggers/1.md), [**lttng-remove-trigger**(1)](/lttng-remove-trigger/1.md), [**lttng-concepts**(7)](/lttng-concepts/7.md)