lttng-add-trigger(1) ==================== :revdate: 23 April 2021 NAME ---- lttng-add-trigger - Add an LTTng trigger SYNOPSIS -------- [verse] *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *add-trigger* [option:--name='NAME'] [option:--owner-id='UID'] option:--condition='CONDTYPE' ['CONDARGS'] option:--action='ACTTYPE' ['ACTARGS'] [option:--action='ACTTYPE' ['ACTARGS']]... DESCRIPTION ----------- The `lttng add-trigger` command creates and adds an LTTng _trigger_ to the session daemon (see man:lttng-sessiond(8)). A trigger is an association between a _condition_ and one or more _actions_. When the condition of a trigger{nbsp}__T__ is satisfied, LTTng requests to execute the actions of{nbsp}__T__. Depending on the rate policy of an action, an execution request can become an actual execution. A trigger doesn't belong to a specific tracing session: it's global to the session daemon. Within the session daemon, and for a given Unix user, a trigger has a unique name. By default, the `add-trigger` command automatically assigns a name to the added trigger. Use the option:--name option to assign a specific name instead. The `add-trigger` command adds a trigger for your Unix user. If your Unix user is `root`, you can add the trigger as another user with the option:--owner-id option. Specify the condition of the trigger to add with a <> and its actions with one or more <>. The order of the action specifiers is significant: LTTng attempts to execute the actions of a trigger in order. List the available triggers for your Unix user (or for all users if your Unix user is `root`) with the man:lttng-list-triggers(1) command. Remove an existing trigger with the man:lttng-remove-trigger(1) command. [[cond-spec]] Condition specifier ~~~~~~~~~~~~~~~~~~~ Synopsis: [verse] option:--condition='CONDTYPE' ['CONDARGS'] A condition specifier is the option:--condition option, which specifies the type of condition 'CONDTYPE', followed, depending on 'CONDTYPE', with zero or more arguments 'CONDARGS'. The available condition types are: [[er-matches-cond-spec]]`event-rule-matches`:: Synopsis: + [verse] option:--condition=event-rule-matches [nloption:--capture='CDESCR']... 'ERSPEC' {nbsp} + An `event-rule-matches` condition is considered satisfied when the event rule specified with 'ERSPEC' matches an event. + See man:lttng-event-rule(7) to learn how to specify an event rule ('ERSPEC' part). + Capture event record and context fields with one or more nloption:--capture options (see the <> 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{nbsp}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-descr]] Capture descriptor ~~~~~~~~~~~~~~~~~~ A capture descriptor is a textual expression which describes how to read an event record or context field. The argument of a nloption:--capture option, when using an <> (`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`. ++$ctx.++__NAME__:: A statically-known context field named 'NAME'. + List the available statically-known context field names with man:lttng-add-context(1). + Examples: `$ctx.prio`, `$ctx.preemptible`, `$ctx.perf:cpu:stalled-cycles-frontend`. ++$app.++__PROVIDER__++.++__NAME__:: An application-specific context field named 'NAME' from the provider 'PROVIDER'. + See man:lttng-add-context(1) to learn more about application-specific context fields. + Example: `$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-spec]] Action specifier ~~~~~~~~~~~~~~~~ Synopsis: [verse] option:--action='ACTTYPE' ['ACTARGS'] An action specifier is the option:--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: + [verse] option:--action=notify [nloption:--rate-policy='POLICY'] {nbsp} + Sends a notification through the notification mechanism of the session daemon (see man:lttng-session(8)). + The session daemon sends details about the condition evaluation along with the notification. + As of LTTng{nbsp}{lttng_version}, you can write a C/pass:[C++] program to receive LTTng notifications (see the liblttng-ctl C{nbsp}headers). + See below for the nloption:--rate-policy option. Start a tracing session:: Synopsis: + [verse] option:--action=start-session 'SESSION' [nloption:--rate-policy='POLICY'] {nbsp} + Starts the tracing session named 'SESSION' like man:lttng-start(1) would. + If no tracing session has the name 'SESSION' when LTTng is ready to execute the action, LTTng does nothing. + See below for the nloption:--rate-policy option. Stop a tracing session:: Synopsis: + [verse] option:--action=stop-session 'SESSION' [nloption:--rate-policy='POLICY'] {nbsp} + Stops the tracing session named 'SESSION' like man:lttng-stop(1) would. + If no tracing session has the name 'SESSION' when LTTng is ready to execute the action, LTTng does nothing. + See below for the nloption:--rate-policy option. Rotate a tracing session:: Synopsis: + [verse] option:--action=rotate-session 'SESSION' [nloption:--rate-policy='POLICY'] {nbsp} + Archives the current trace chunk of the tracing session named 'SESSION' like man:lttng-rotate(1) would. + If no tracing session has the name 'SESSION' when LTTng is ready to execute the action, LTTng does nothing. + See below for the nloption:--rate-policy option. Take a tracing session snapshot:: Synopsis: + [verse] option:--action=snapshot-session 'SESSION' [nloption:--rate-policy='POLICY'] {nbsp} + Takes a snapshot of the tracing session named 'SESSION' like man:lttng-snapshot(1) would. + When the condition of the trigger is satisfied, the tracing session named 'SESSION', if any, must be a snapshot-mode tracing session (see man:lttng-create(1)). + If no tracing session has the name 'SESSION' when LTTng is ready to execute the action, LTTng does nothing. + See below for the nloption:--rate-policy option. Common action options (as of LTTng{nbsp}{lttng_version}): nloption:--rate-policy='POLICY':: Set the rate policy of the action to 'POLICY'. + 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{nbsp}__A__ first increments the execution request count{nbsp}__C__ of{nbsp}__A__. An execution request can then become an actual execution when{nbsp}__C__ satisfies the rate policy of{nbsp}__A__. + The default action rate policy is `every:1` (always execute{nbsp}__A__). Use this option to specify another rate policy. + 'POLICY' is one of: + -- ++once-after:++__COUNT__:: Only execute{nbsp}__A__ when{nbsp}__C__ is equal to 'COUNT'. + In other words, execute{nbsp}__A__ a single time after 'COUNT' execution requests. ++every:++__COUNT__:: Only execute{nbsp}__A__ when{nbsp}__C__ is a multiple of 'COUNT'. + In other words, execute{nbsp}__A__ every 'COUNT' execution requests. -- + As of LTTng{nbsp}{lttng_version}, you can use this option with any action type, but new action types in the future may not support it. OPTIONS ------- Identification ~~~~~~~~~~~~~~ option:--name='NAME':: Set the unique name of the trigger to add to 'NAME' instead of the `add-trigger` command automatically assigning one. option:--owner-id='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 ~~~~~~~~~ option:--condition='CONDTYPE':: Introductory option for a condition specifier of type 'CONDTYPE'. + See the <> section above to learn more. option:--action='ACTTYPE':: Introductory option for an action specifier of type 'ACTTYPE'. + See the <> section above to learn more. include::common-cmd-help-options.txt[] include::common-cmd-footer.txt[] SEE ALSO -------- man:lttng(1), man:lttng-list-triggers(1), man:lttng-remove-trigger(1)