| 1 | lttng-add-trigger(1) |
| 2 | ===================== |
| 3 | :revdate: 27 May 2020 |
| 4 | |
| 5 | |
| 6 | NAME |
| 7 | ---- |
| 8 | lttng-add-trigger - Create LTTng triggers |
| 9 | |
| 10 | |
| 11 | SYNOPSIS |
| 12 | -------- |
| 13 | |
| 14 | [verse] |
| 15 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *add-trigger* [--id ID] |
| 16 | --condition CONDITION-NAME CONDITION-ARGS |
| 17 | --action ACTION-NAME ACTION-ARGS |
| 18 | [--action ACTION-NAME ACTION-ARGS]... |
| 19 | |
| 20 | |
| 21 | DESCRIPTION |
| 22 | ----------- |
| 23 | |
| 24 | The `lttng add-trigger` command is used to create triggers. A |
| 25 | trigger is an association between a *condition* and one or more |
| 26 | *actions*. When the condition associated to a trigger is met, the |
| 27 | actions associated to that trigger are executed. The tracing does not |
| 28 | have to be active for the conditions to be met, and triggers are |
| 29 | independent from tracing sessions. |
| 30 | |
| 31 | The syntax by which conditions and actions are specified is described |
| 32 | below. |
| 33 | |
| 34 | [[conditions]] |
| 35 | Conditions |
| 36 | ~~~~~~~~~~ |
| 37 | |
| 38 | Conditions are specified with the `--condition` option, followed by a |
| 39 | condition name, and possibly some more arguments, depending on the |
| 40 | specific condition. There must be exactly one condition given in the |
| 41 | `lttng add-trigger` invocation. |
| 42 | |
| 43 | The available conditions are: |
| 44 | |
| 45 | Event rule: `on-event [event rule arguments]`:: |
| 46 | This type of condition is met when the tracer encounters an event |
| 47 | matching the given even rule. The arguments describing the event |
| 48 | rule are the same as those describing the event rules of the |
| 49 | man:lttng-enable-event(1) command, with these exceptions: |
| 50 | |
| 51 | - It is not possible to use filter operands that use values from |
| 52 | the context. |
| 53 | |
| 54 | + |
| 55 | Fields to capture can be specified with the option:--capture option, followed by |
| 56 | a capture expression. Zero or more captures can be configured. See the |
| 57 | <<capture-expr, Capture expression>> section below for more information. |
| 58 | |
| 59 | [[actions]] |
| 60 | Actions |
| 61 | ~~~~~~~ |
| 62 | |
| 63 | Actions are specified with the `--action` option, followed by an action |
| 64 | name, and possibly some more arguments, depending on the specific |
| 65 | action. There must be at least one action given in the |
| 66 | `lttng add-trigger` invocation. |
| 67 | |
| 68 | The available actions are: |
| 69 | |
| 70 | Notify: *notify*:: |
| 71 | This action causes the LTTng session daemon to send a notification, |
| 72 | through its notification mechanism (see man:lttng-sessiond(8)). |
| 73 | Some details about the condition evaluation are sent along with the |
| 74 | notification. |
| 75 | |
| 76 | Start session: *start-session* session-name:: |
| 77 | This action causes the LTTng session daemon to start tracing for the |
| 78 | session with the given name. If no session with the given name exist |
| 79 | at the time the condition is met, nothing is done. |
| 80 | |
| 81 | Stop session: *stop-session* session-name:: |
| 82 | This action causes the LTTng session daemon to stop tracing for the |
| 83 | session with the given name. If no session with the given name exist |
| 84 | at the time the condition is met, nothing is done. |
| 85 | |
| 86 | Rotate session: *rotate-session* session-name:: |
| 87 | This action causes the LTTng session daemon to rotate the session |
| 88 | with the given name. See man:lttng-rotate(1) for more information |
| 89 | about the session rotation concept. If no session with the given |
| 90 | name exist at the time the condition is met, nothing is done. |
| 91 | |
| 92 | Snapshot session: *snapshot-session* session-name:: |
| 93 | This action causes the LTTng session daemon to take a snapshot of the |
| 94 | session with the given name. See man:lttng-snapshot(1) for more |
| 95 | information about the session snapshot concept. If no session with |
| 96 | the given name exist at the time the condition is met, nothing is |
| 97 | done. |
| 98 | |
| 99 | |
| 100 | [[capture-expr]] |
| 101 | Capture expression |
| 102 | ~~~~~~~~~~~~~~~~~~ |
| 103 | |
| 104 | A capture expression can be specified with the option:--capture option when |
| 105 | creating a new on-event condition. If the capture expression corresponds with an |
| 106 | event's field when tracing, the runtime dynamic value corresponding to the |
| 107 | capture expression is captured. |
| 108 | |
| 109 | NOTE: Make sure to **single-quote** the capture expression when running |
| 110 | the command from a shell, as capture expressions typically include |
| 111 | characters having a special meaning for most shells. |
| 112 | |
| 113 | * Supported field types: |
| 114 | - integer, |
| 115 | - unsigned integer, |
| 116 | - floating point value, |
| 117 | - fixed-size array of integers, |
| 118 | - variable-size array of integers (sequence), |
| 119 | - enumeration, |
| 120 | - text string, |
| 121 | - element of any allowing previous type. |
| 122 | |
| 123 | * The dynamic value of an event field is captured by using its name as a C |
| 124 | identifier. |
| 125 | + |
| 126 | The square bracket notation is available, like in the C |
| 127 | language, to access array/sequence field. |
| 128 | Only a constant, positive integer number can be used within square |
| 129 | brackets. If the index is out of bounds, the capture expression |
| 130 | evaluates to `unavailable`. |
| 131 | + |
| 132 | An enumeration field's value is an integer. |
| 133 | + |
| 134 | When the capture's field does not exist, the capture expression |
| 135 | evaluates to `unavailable`. |
| 136 | + |
| 137 | Examples: `my_field`, `target_cpu`, `seq[7]` |
| 138 | |
| 139 | * The dynamic value of a statically-known context field is captured by |
| 140 | prefixing its name with `$ctx.`. See man:lttng-add-context(1) to get a list of |
| 141 | available contexts. |
| 142 | + |
| 143 | When the expression's statically-known context field does not exist, |
| 144 | the capture expression evaluates to `unavailable`. |
| 145 | + |
| 146 | Examples: `$ctx.prio`, `$ctx.preemptible`, |
| 147 | `$ctx.perf:cpu:stalled-cycles-frontend`. |
| 148 | + |
| 149 | NOTE: The statically-known context field does NOT need to be added using the |
| 150 | man:lttng-add-context(1) command. The statically-known context fields are |
| 151 | always available in the context of triggers. |
| 152 | |
| 153 | * The dynamic value of an application-specific context field is captured by |
| 154 | prefixing its name with `$app.` (follows the format used to add such a context |
| 155 | field with the man:lttng-add-context(1) command). |
| 156 | + |
| 157 | When the expression's application-specific context field does not exist, |
| 158 | the capture expression evaluates to `unavailable`. |
| 159 | + |
| 160 | Example: `$app.server:cur_user`. |
| 161 | + |
| 162 | NOTE: The application-specific context field does NOT need to be added using the |
| 163 | man:lttng-add-context(1) command. The application-specific context fields fields |
| 164 | are always available in the context of triggers. |
| 165 | |
| 166 | |
| 167 | OPTIONS |
| 168 | ------- |
| 169 | |
| 170 | option:--condition:: |
| 171 | Define the condition for the trigger. See the |
| 172 | <<conditions,CONDITIONS>> section for more details. |
| 173 | |
| 174 | option:--action:: |
| 175 | Define an action for the trigger. See the <<actions,ACTIONS>> |
| 176 | section for more details. |
| 177 | |
| 178 | option:--id='ID':: |
| 179 | Set the id of the trigger to 'ID'. If omitted, an id will |
| 180 | automatically be assigned to the trigger by the session daemon. |
| 181 | + |
| 182 | If a trigger with the specified 'ID' already exists, the trigger |
| 183 | creation will fail. |
| 184 | |
| 185 | option:--fire-every 'N':: |
| 186 | Execute the trigger's actions every 'N' times the condition is met. |
| 187 | |
| 188 | option:--fire-once-after 'N':: |
| 189 | Execute the trigger's actions once after 'N' times the condition is |
| 190 | met, then never after that. |
| 191 | |
| 192 | include::common-cmd-help-options.txt[] |
| 193 | |
| 194 | |
| 195 | include::common-cmd-footer.txt[] |
| 196 | |
| 197 | |
| 198 | SEE ALSO |
| 199 | -------- |
| 200 | man:lttng-list-triggers(1), |
| 201 | man:lttng-remove-trigger(1), |
| 202 | man:lttng(1) |