doc/man/lttng-add-trigger.1.txt

   1 lttng-add-trigger(1)
   2 ====================
   3 :revdate: 14 June 2021
   4
   5
   6 NAME
   7 ----
   8 lttng-add-trigger - Add an LTTng trigger
   9
  10
  11 SYNOPSIS
  12 --------
  13 [verse]
  14 *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *add-trigger* [option:--name='NAME'] [option:--owner-uid='UID']
  15       option:--condition='CONDTYPE' ['CONDARGS']
  16       option:--action='ACTTYPE' ['ACTARGS'] [option:--action='ACTTYPE' ['ACTARGS']]...
  17
  18 DESCRIPTION
  19 -----------
  20 The `lttng add-trigger` command creates and adds an LTTng _trigger_ to
  21 the connected session daemon (see man:lttng-sessiond(8)).
  22
  23 See man:lttng-concepts(7) to learn more about LTTng triggers.
  24
  25 By default, the `add-trigger` command automatically assigns a name,
  26 unique for a given session daemon and Unix user, to the added trigger.
  27 Assign a custom name with the option:--name.
  28
  29 The `add-trigger` command adds a trigger for your Unix user. If your
  30 Unix user is `root`, you may add the trigger as another user with the
  31 option:--owner-uid option.
  32
  33 Specify the condition of the trigger to add with a <<cond-spec,condition
  34 specifier>> and its actions with one or more <<action-spec,action
  35 specifiers>>. The order of the action specifiers is significant: LTTng
  36 attempts to execute the actions of a firing trigger in this order.
  37
  38 See the ``<<examples,EXAMPLES>>'' section below for usage examples.
  39
  40 List the triggers of your Unix user, or of all users if your
  41 Unix user is `root`, with the man:lttng-list-triggers(1) command.
  42
  43 Remove a trigger with the man:lttng-remove-trigger(1) command.
  44
  45
  46 [[cond-spec]]
  47 Condition specifier
  48 ~~~~~~~~~~~~~~~~~~~
  49 Synopsis:
  50
  51 [verse]
  52 option:--condition='CONDTYPE' ['CONDARGS']
  53
  54 A condition specifier is the option:--condition option, which specifies
  55 the type of condition 'CONDTYPE', followed, depending on 'CONDTYPE',
  56 with zero or more arguments 'CONDARGS'.
  57
  58 The available condition types are:
  59
  60 [[er-matches-cond-spec]]`event-rule-matches`::
  61     Synopsis:
  62 +
  63 [verse]
  64 option:--condition=**event-rule-matches** [nloption:--capture='CDESCR']... 'ERSPEC'
  65 {nbsp}
  66 +
  67 An `event-rule-matches` condition is considered satisfied when the event
  68 rule specified with 'ERSPEC' matches an event.
  69 +
  70 See man:lttng-event-rule(7) to learn how to specify an event rule
  71 ('ERSPEC' part).
  72 +
  73 Capture event record and context fields with one or more
  74 nloption:--capture options (see the ``<<capture-descr,Capture
  75 descriptor>>'' section below to learn more). When an
  76 `event-rule-matches` condition with capture descriptors is satisfied,
  77 the captured field values are available in the evaluation object of the
  78 condition using the liblttng-ctl C{nbsp}API.
  79 +
  80 IMPORTANT: Make sure to **single-quote** 'CDESCR' when you run the
  81 `add-trigger` command from a shell, as capture descriptors can include
  82 characters having a special meaning for most shells.
  83
  84
  85 [[capture-descr]]
  86 Capture descriptor
  87 ~~~~~~~~~~~~~~~~~~
  88 A capture descriptor is a textual expression which describes how to read
  89 an event record or context field.
  90
  91 The argument of a nloption:--capture option, when using an
  92 <<er-matches-cond-spec,``event rule matches'' condition specifier>>
  93 (`event-rule-matches`), is a capture descriptor.
  94
  95 A capture descriptor expression is one of:
  96
  97 'NAME'::
  98     An event record field named 'NAME'.
  99 +
 100 The supported event record field types are:
 101 +
 102 --
 103 * Integer
 104 * Enumeration (integral value)
 105 * Floating point number
 106 * Static array of integers
 107 * Dynamic array (``sequence'') of integers
 108 * Text string
 109 --
 110 +
 111 Examples: `my_field`, `target_cpu`, `ip`.
 112
 113 ++$ctx.++__NAME__::
 114     A statically-known context field named 'NAME'.
 115 +
 116 List the available statically-known context field names with
 117 man:lttng-add-context(1).
 118 +
 119 Examples: `$ctx.prio`, `$ctx.preemptible`,
 120 `$ctx.perf:cpu:stalled-cycles-frontend`.
 121
 122 ++$app.++__PROVIDER__++.++__NAME__::
 123     An application-specific context field named 'NAME' from the
 124     provider 'PROVIDER'.
 125 +
 126 See man:lttng-add-context(1) to learn more about application-specific
 127 context fields.
 128 +
 129 Example: `$app.server:cur_user`.
 130
 131 __EXPR__++[++__INDEX__++]++::
 132     The element at index 'INDEX' of the array field (static or dynamic)
 133     identified by the expression 'EXPR'.
 134 +
 135 'INDEX' must be a constant, positive integral value.
 136 +
 137 Examples: `ip[3]`, `user_ids[15]`.
 138
 139 If, when an event rule matches, a given capture descriptor doesn't
 140 identify an existing event or context field, then the captured value is
 141 reported as being unavailable. This applies to:
 142
 143 * A nonexistent event record field name.
 144 * A nonexistent statically-known context field name.
 145 * A nonexistent application-specific context field name.
 146 * An out-of-bounds array field index.
 147
 148
 149 [[action-spec]]
 150 Action specifier
 151 ~~~~~~~~~~~~~~~~
 152 Synopsis:
 153
 154 [verse]
 155 option:--action='ACTTYPE' ['ACTARGS']
 156
 157 An action specifier is the option:--action option, which specifies
 158 the type of action 'ACTTYPE', followed, depending on 'ACTTYPE', with zero
 159 or more arguments 'ACTARGS'.
 160
 161 The available action types are:
 162
 163 Notify::
 164     Synopsis:
 165 +
 166 [verse]
 167 option:--action=**notify** [nloption:--rate-policy='POLICY']
 168 {nbsp}
 169 +
 170 Sends a notification through the notification
 171 mechanism of the session daemon (see man:lttng-sessiond(8)).
 172 +
 173 The session daemon sends details about the condition evaluation along
 174 with the notification.
 175 +
 176 As of LTTng{nbsp}{lttng_version}, you can write a C/pass:[C++] program
 177 to receive LTTng notifications (see the liblttng-ctl C{nbsp}headers).
 178 +
 179 See below for the nloption:--rate-policy option.
 180
 181 Start a recording session::
 182     Synopsis:
 183 +
 184 [verse]
 185 option:--action=**start-session** 'SESSION' [nloption:--rate-policy='POLICY']
 186 {nbsp}
 187 +
 188 Starts the recording session named 'SESSION' like man:lttng-start(1)
 189 would.
 190 +
 191 If no recording session has the name 'SESSION' when LTTng is ready to
 192 execute the action, LTTng does nothing.
 193 +
 194 See below for the nloption:--rate-policy option.
 195
 196 Stop a recording session::
 197     Synopsis:
 198 +
 199 [verse]
 200 option:--action=**stop-session** 'SESSION' [nloption:--rate-policy='POLICY']
 201 {nbsp}
 202 +
 203 Stops the recording session named 'SESSION' like man:lttng-stop(1)
 204 would.
 205 +
 206 If no recording session has the name 'SESSION' when LTTng is ready to
 207 execute the action, LTTng does nothing.
 208 +
 209 See below for the nloption:--rate-policy option.
 210
 211 Rotate a recording session::
 212     Synopsis:
 213 +
 214 [verse]
 215 option:--action=**rotate-session** 'SESSION' [nloption:--rate-policy='POLICY']
 216 {nbsp}
 217 +
 218 Archives the current trace chunk of the recording session named
 219 'SESSION' like man:lttng-rotate(1) would.
 220 +
 221 If no recording session has the name 'SESSION' when LTTng is ready to
 222 execute the action, LTTng does nothing.
 223 +
 224 See below for the nloption:--rate-policy option.
 225
 226 Take a recording session snapshot::
 227     Synopsis:
 228 +
 229 [verse]
 230 option:--action=**snapshot-session** 'SESSION' [nloption:--rate-policy='POLICY']
 231 {nbsp}
 232 +
 233 Takes a snapshot of the recording session named 'SESSION' like
 234 man:lttng-snapshot(1) would.
 235 +
 236 When the condition of the trigger is satisfied, the recording session
 237 named 'SESSION', if any, must be a snapshot-mode recording session
 238 (see man:lttng-create(1)).
 239 +
 240 If no recording session has the name 'SESSION' when LTTng is ready to
 241 execute the action, LTTng does nothing.
 242 +
 243 See below for the nloption:--rate-policy option.
 244
 245 Common action options (as of LTTng{nbsp}{lttng_version}):
 246
 247 nloption:--rate-policy='POLICY'::
 248     Set the rate policy of the action to 'POLICY' instead of
 249     `every:1` (always execute).
 250 +
 251 A trigger which ``fires'' (its condition is satisfied) leads to an
 252 execution request for each of its actions, in order. An execution
 253 request of a given action{nbsp}__A__ first increments the execution
 254 request count{nbsp}__C__ of{nbsp}__A__. An execution request can then
 255 become an actual execution when{nbsp}__C__ satisfies the rate policy
 256 of{nbsp}__A__.
 257 +
 258 'POLICY' is one of:
 259 +
 260 --
 261 ++once-after:++__COUNT__::
 262     Only execute{nbsp}__A__ when{nbsp}__C__ is equal to 'COUNT'.
 263 +
 264 In other words, execute{nbsp}__A__ a single time after 'COUNT' execution
 265 requests.
 266
 267 ++every:++__COUNT__::
 268     Only execute{nbsp}__A__ when{nbsp}__C__ is a multiple of 'COUNT'.
 269 +
 270 In other words, execute{nbsp}__A__ every 'COUNT' execution requests.
 271 --
 272 +
 273 'COUNT' must be an integer greater than{nbsp}0.
 274 +
 275 As of LTTng{nbsp}{lttng_version}, you can use this option with any
 276 action type, but new action types in the future may not support it.
 277
 278
 279 OPTIONS
 280 -------
 281 Identification
 282 ~~~~~~~~~~~~~~
 283 option:--name='NAME'::
 284     Set the unique name of the trigger to add to 'NAME' instead of the
 285     `add-trigger` command automatically assigning one.
 286
 287 option:--owner-uid='UID'::
 288     Add the trigger as the Unix user having the user ID 'UID'.
 289 +
 290 You may only use this option if your Unix user is `root`.
 291
 292
 293 Specifier
 294 ~~~~~~~~~
 295 option:--condition='CONDTYPE'::
 296     Introductory option for a condition specifier of type 'CONDTYPE'.
 297 +
 298 See the ``<<cond-spec,Condition specifier>>'' section above to learn
 299 more.
 300
 301 option:--action='ACTTYPE'::
 302     Introductory option for an action specifier of type 'ACTTYPE'.
 303 +
 304 See the ``<<action-spec,Action specifier>>'' section above to learn
 305 more.
 306
 307
 308 include::common-lttng-cmd-help-options.txt[]
 309
 310
 311 include::common-lttng-cmd-after-options.txt[]
 312
 313
 314 [[examples]]
 315 EXAMPLES
 316 --------
 317 .Add an ``event rule matches'' trigger of which the action is to send a notification.
 318 ====
 319 The `event-rule-matches` trigger condition below specifies an event rule
 320 which matches any Linux system call entry event with a name starting
 321 with `exec`.
 322
 323 [role="term"]
 324 ----
 325 $ lttng add-trigger --condition=event-rule-matches \
 326                     --type=syscall:entry \
 327                     --name='exec*' --action=notify
 328 ----
 329 ====
 330
 331 .Add an ``event rule matches'' trigger of which the action is to stop a recording session and then rotate it.
 332 ====
 333 The `event-rule-matches` trigger condition below specifies an event rule
 334 which matches any user space tracepoint event with a name starting with
 335 `my_app:` and with a log level at least as severe as a warning.
 336
 337 The order of the option:--action options below is significant.
 338
 339 [role="term"]
 340 ----
 341 $ lttng add-trigger --condition=event-rule-matches \
 342                     --type=user --name='my_app:*' \
 343                     --log-level=TRACE_WARNING.. \
 344                     --action=stop-session my-session \
 345                     --action=rotate-session my-session
 346 ----
 347
 348 See man:lttng-concepts(7) to learn more about recording sessions and
 349 rotations.
 350 ====
 351
 352 .Add an ``event rule matches'' trigger with a specific name.
 353 ====
 354 The `event-rule-matches` trigger condition below specifies an event rule
 355 which matches events which LTTng creates from the `my-logger` Python
 356 logger.
 357
 358 The added trigger is named `my-trigger`, a unique name for your Unix
 359 user.
 360
 361 See the option:--name option.
 362
 363 [role="term"]
 364 ----
 365 $ lttng add-trigger --name=my-trigger \
 366                     --condition=event-rule-matches \
 367                     --type=python --name=my-logger \
 368                     --action=snapshot-session my-session
 369 ----
 370 ====
 371
 372 .Add an ``event rule matches'' trigger as another Unix user.
 373 ====
 374 The command line below adds a trigger as the `mireille` Unix user.
 375
 376 Your Unix user must be `root` to use the option:--owner-uid option.
 377
 378 The condition of the trigger specifies an event rule which matches LTTng
 379 kernel tracepoint events with a name which starts with `sched`.
 380
 381 [role="term"]
 382 ----
 383 # lttng add-trigger --owner-uid=$(id --user mireille) \
 384                     --condition=event-rule-matches \
 385                     --type=kernel --name='sched*' \
 386                     --action=notify
 387 ----
 388 ====
 389
 390 .Add an ``event rule matches'' trigger with a notification action to be executed every 10{nbsp}times.
 391 ====
 392 The `event-rule-matches` trigger condition below specifies an event rule
 393 which matches all user space tracepoint events.
 394
 395 See the nloption:--rate-policy option above.
 396
 397 [role="term"]
 398 ----
 399 $ lttng add-trigger --condition=event-rule-matches \
 400                     --type=user --action=notify \
 401                     --rate-policy=every:10
 402 ----
 403 ====
 404
 405 .Add an ``event rule matches'' trigger with a recording session starting action to be executed a single time after 40{nbsp}times.
 406 ====
 407 The `event-rule-matches` trigger condition below specifies an event rule
 408 which matches any Linux system call event (entry and exit) of which the
 409 `fd` event record field is less than{nbsp}3.
 410
 411 See the nloption:--rate-policy option above.
 412
 413 [role="term"]
 414 ----
 415 $ lttng add-trigger --condition=event-rule-matches \
 416                     --type=syscall --filter='fd < 3' \
 417                     --action=start-session my-session \
 418                     --rate-policy=once-after:40
 419 ----
 420 ====
 421
 422
 423 include::common-footer.txt[]
 424
 425
 426 SEE ALSO
 427 --------
 428 man:lttng(1),
 429 man:lttng-list-triggers(1),
 430 man:lttng-remove-trigger(1),
 431 man:lttng-concepts(7)