doc/man/lttng-enable-event.1.txt

   1 lttng-enable-event(1)
   2 =====================
   3
   4
   5 NAME
   6 ----
   7 lttng-enable-event - Create or enable LTTng event rules
   8
   9
  10 SYNOPSIS
  11 --------
  12 Create or enable Linux kernel event rules:
  13
  14 [verse]
  15 *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel
  16       [option:--probe='SOURCE' | option:--function='SOURCE' | option:--syscall]
  17       [option:--filter='EXPR'] [option:--session='SESSION']
  18       [option:--channel='CHANNEL'] 'EVENT'[,'EVENT']...
  19
  20 Create or enable an "all" Linux kernel event rule:
  21
  22 [verse]
  23 *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel option:--all [option:--syscall]
  24       [option:--filter='EXPR'] [option:--session='SESSION'] [option:--channel='CHANNEL']
  25
  26 Create or enable application event rules:
  27
  28 [verse]
  29 *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event*
  30       (option:--userspace | option:--jul | option:--log4j | option:--python)
  31       [option:--filter='EXPR'] [option:--exclude='EVENT'[,'EVENT']...]
  32       [option:--loglevel='LOGLEVEL' | option:--loglevel-only='LOGLEVEL']
  33       [option:--session='SESSION'] [option:--channel='CHANNEL'] (option:--all | 'EVENT'[,'EVENT']...)
  34
  35
  36 DESCRIPTION
  37 -----------
  38 The `lttng enable-event` command can create a new event rule, or enable
  39 one or more existing and disabled ones.
  40
  41 An event rule created by `lttng enable-event` is a set of conditions
  42 that must be satisfied in order for an actual event to be emitted by
  43 an LTTng tracer when the execution of an application or the Linux kernel
  44 reaches an event source (tracepoint, system call, dynamic probe).
  45 Event sources can be listed with the man:lttng-list(1) command.
  46
  47 The man:lttng-disable-event(1) command can be used to disable
  48 existing event rules.
  49
  50 Event rules are always assigned to a channel when they are created. If
  51 the option:--channel option is omitted, a default channel named
  52 `channel0` is used (and created automatically if it does not exist for
  53 the specified domain in the selected tracing session).
  54
  55 If the option:--session option is omitted, the chosen channel is picked
  56 from the current tracing session.
  57
  58 Events can be enabled while tracing is active
  59 (use man:lttng-start(1) to make a tracing session active).
  60
  61
  62 Event source types
  63 ~~~~~~~~~~~~~~~~~~
  64 Four types of event sources are available in the Linux kernel tracing
  65 domain (option:--kernel option):
  66
  67 Tracepoint (option:--tracepoint option; default)::
  68     A Linux kernel tracepoint, that is, a static instrumentation point
  69     placed in the kernel source code. Standard tracepoints are designed
  70     and placed in the source code by developers and record useful
  71     payload fields.
  72
  73 Dynamic probe (option:--probe option)::
  74     A Linux kernel kprobe, that is, an instrumentation point placed
  75     dynamically in the compiled kernel code. Dynamic probe events do not
  76     record any payload field.
  77
  78 Function probe (option:--function option)::
  79     A Linux kernel kretprobe, that is, two instrumentation points placed
  80     dynamically where a function is entered and where it returns in the
  81     compiled kernel code. Function probe events do not record any
  82     payload field.
  83
  84 System call (option:--syscall option)::
  85     A Linux kernel system call. Two instrumentation points are
  86     statically placed where a system call function is entered and where
  87     it returns in the compiled kernel code. System call event sources
  88     record useful payload fields.
  89
  90 The application tracing domains (option:--userspace, option:--jul,
  91 option:--log4j, or option:--python options) only support tracepoints.
  92 In the cases of the JUL, Apache log4j, and Python domains, the event
  93 names correspond to _logger_ names.
  94
  95
  96 Understanding event rule conditions
  97 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  98 When creating an event rule with `lttng enable-event`, conditions are
  99 specified using options. The logical conjunction (logical AND) of all
 100 those conditions must be true when an event source is reached by an
 101 application or by the Linux kernel in order for an actual event
 102 to be emitted by an LTTng tracer.
 103
 104 Any condition that is not explicitly specified on creation is considered
 105 a _don't care_.
 106
 107 For example, consider the following commands:
 108
 109 [role="term"]
 110 ----------------------------------------------------------------
 111 lttng enable-event --userspace hello:world
 112 lttng enable-event --userspace hello:world --loglevel=TRACE_INFO
 113 ----------------------------------------------------------------
 114
 115 Here, two event rules are created. The first one has a single condition:
 116 the tracepoint name must match `hello:world`. The second one has two
 117 conditions:
 118
 119 * The tracepoint name must match `hello:world`, _and_
 120 * The tracepoint's defined log level must be at least as severe as
 121   the `TRACE_INFO` level.
 122
 123 In this case, the second event rule is pointless because the first one
 124 is more general: it does not care about the tracepoint's log level.
 125 If an event source matching both event rules is reached by the
 126 application's execution, only one event is emitted.
 127
 128 The available conditions for the Linux kernel domain are:
 129
 130 * Tracepoint/system call name ('EVENT' argument with
 131   option:--tracepoint or option:--syscall options) or
 132   dynamic probe/function name/address
 133   (option:--probe or option:--function option's argument) which must
 134   match event source's equivalent.
 135 +
 136 Wildcard using the `*` character are supported _at the end_ of
 137 tracepoint and system call names.
 138
 139 * Filter expression (option:--filter option) executed against the
 140   dynamic values of event fields at execution time that must evaluate
 141   to true. See the <<filter-syntax,Filter expression syntax>> section
 142   below for more information.
 143
 144 The available conditions for the application domains are:
 145
 146 * Tracepoint name ('EVENT' with option:--tracepoint option) which must
 147   match event source's equivalent.
 148 +
 149 Wildcard using the `*` character are supported _at the end_ of
 150 tracepoint names. When creating an event rule with a tracepoint name
 151 containing a wildcard, specific tracepoint names can be excluded from
 152 the match using the option:--exclude option.
 153
 154 * Filter expression (option:--filter option) executed against the
 155   dynamic values of event fields at execution time that must evaluate
 156   to true. See the <<filter-syntax,Filter expression syntax>> section
 157   below for more information.
 158 * Event's log level that must be at least as severe as a given
 159   log level (option:--loglevel option) or match exactly a given log
 160   level (option:--loglevel-only option).
 161
 162 When using `lttng enable-event` with a set of conditions that does not
 163 currently exist for the chosen tracing session, domain, and channel,
 164 a new event rule is created. Otherwise, the existing event rule is
 165 enabled if it is currently disabled
 166 (see man:lttng-disable-event(1)).
 167
 168 The option:--all option can be used alongside the option:--tracepoint
 169 or option:--syscall options. When this option is used, no 'EVENT'
 170 argument must be specified. This option defines a single event rule
 171 matching _all_ the possible events of a given tracing domain for the
 172 chosen channel and tracing session. It is the equivalent of an 'EVENT'
 173 argument named `*` (wildcard).
 174
 175
 176 [[filter-syntax]]
 177 Filter expression syntax
 178 ~~~~~~~~~~~~~~~~~~~~~~~~
 179 Filter expressions can be specified with the option:--filter option
 180 when creating a new event rule. If the filter expression evaluates
 181 to true when executed against the dynamic values of an event's fields
 182 when tracing, the filtering condition passes.
 183
 184 NOTE: Make sure to **single-quote** the filter expression when running
 185 the command from a shell, as filter expressions typically include
 186 characters having a special meaning for most shells.
 187
 188 The filter expression syntax is very similar to C language conditional
 189 expressions (expressions that can be evaluated by an `if` statement).
 190
 191 The following logical operators are supported:
 192
 193 [width="40%",options="header"]
 194 |=====================================
 195 | Name                      | Syntax
 196 | Logical negation (NOT)    | `!a`
 197 | Logical conjunction (AND) | `a && b`
 198 | Logical disjunction (OR)  | `a \|\| b`
 199 |=====================================
 200
 201 The following comparison operators/relational operators are supported:
 202
 203 [width="40%",options="header"]
 204 |====================================
 205 | Name                     | Syntax
 206 | Equal to                 | `a == b`
 207 | Not equal to             | `a != b`
 208 | Greater than             | `a > b`
 209 | Less than                | `a < b`
 210 | Greater than or equal to | `a >= b`
 211 | Less than or equal to    | `a <= b`
 212 |====================================
 213
 214 The arithmetic and bitwise operators are :not: supported.
 215
 216 The precedence table of the operators above is the same as the one of
 217 the C language. Parentheses are supported to bypass this.
 218
 219 The dynamic value of an event field is read by using its name as
 220 a C identifier.
 221
 222 The dynamic value of a statically-known context field is read by
 223 prefixing its name with `$ctx.`. Statically-known context fields are
 224 context fields added to channels without the `$app.` prefix using the
 225 man:lttng-add-context(1) command.
 226
 227 The dynamic value of an application-specific context field is read by
 228 prefixing its name with `$app.` (follows the format used to add such a
 229 context field with the man:lttng-add-context(1) command).
 230
 231 When a comparison includes a non existent event field, the whole filter
 232 expression evaluates to false (the event is discarded).
 233
 234 C integer and floating point number constants are supported, as well as
 235 literal strings between double quotes (`"`). Literal strings can contain
 236 a wildcard character (`*`) at the end to match more than one string.
 237 This wildcard can be escaped using :escwc:.
 238
 239 LTTng-UST enumeration fields can be compared to integer values (fields
 240 or constants).
 241
 242 NOTE: Although it is possible to filter the process ID of an event when
 243 the `pid` context has been added to its channel using, for example,
 244 `$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
 245 which is much more efficient (see man:lttng-track(1)).
 246
 247 Examples:
 248
 249 ----------------------------
 250 msg_id == 23 && size >= 2048
 251 ----------------------------
 252
 253 -------------------------------------------------
 254 $ctx.procname == "lttng*" && (!flag || poel < 34)
 255 -------------------------------------------------
 256
 257 ---------------------------------------------------------
 258 $app.my_provider:my_context == 17.34e9 || some_enum >= 14
 259 ---------------------------------------------------------
 260
 261
 262 [[log-levels]]
 263 Log levels
 264 ~~~~~~~~~~
 265 Tracepoints and log statements in applications have an attached log
 266 level. Application event rules can contain a _log level_ condition.
 267
 268 With the option:--loglevel option, the event source's log level must
 269 be at least as severe as the option's argument. With the
 270 option:--loglevel-only option, the event source's log level must match
 271 the option's argument.
 272
 273 The available log levels are:
 274
 275 User space domain (option:--userspace option)::
 276     Shortcuts such as `system` are allowed.
 277 +
 278 * `TRACE_EMERG` (0)
 279 * `TRACE_ALERT` (1)
 280 * `TRACE_CRIT` (2)
 281 * `TRACE_ERR` (3)
 282 * `TRACE_WARNING` (4)
 283 * `TRACE_NOTICE` (5)
 284 * `TRACE_INFO` (6)
 285 * `TRACE_DEBUG_SYSTEM` (7)
 286 * `TRACE_DEBUG_PROGRAM` (8)
 287 * `TRACE_DEBUG_PROCESS` (9)
 288 * `TRACE_DEBUG_MODULE` (10)
 289 * `TRACE_DEBUG_UNIT` (11)
 290 * `TRACE_DEBUG_FUNCTION` (12)
 291 * `TRACE_DEBUG_LINE` (13)
 292 * `TRACE_DEBUG` (14)
 293
 294 `java.util.logging` domain (option:--jul option)::
 295     Shortcuts such as `severe` are allowed.
 296 +
 297 * `JUL_OFF` (`INT32_MAX`)
 298 * `JUL_SEVERE` (1000)
 299 * `JUL_WARNING` (900)
 300 * `JUL_INFO` (800)
 301 * `JUL_CONFIG` (700)
 302 * `JUL_FINE` (500)
 303 * `JUL_FINER` (400)
 304 * `JUL_FINEST` (300)
 305 * `JUL_ALL` (`INT32_MIN`)
 306
 307 Apache log4j domain (option:--log4j option)::
 308     Shortcuts such as `severe` are allowed.
 309 +
 310 * `LOG4J_OFF` (`INT32_MAX`)
 311 * `LOG4J_FATAL` (50000)
 312 * `LOG4J_ERROR` (40000)
 313 * `LOG4J_WARN` (30000)
 314 * `LOG4J_INFO` (20000)
 315 * `LOG4J_DEBUG` (10000)
 316 * `LOG4J_TRACE` (5000)
 317 * `LOG4J_ALL` (`INT32_MIN`)
 318
 319 Python domain (option:--python option)::
 320     Shortcuts such as `critical` are allowed.
 321 +
 322 * `PYTHON_CRITICAL` (50)
 323 * `PYTHON_ERROR` (40)
 324 * `PYTHON_WARNING` (30)
 325 * `PYTHON_INFO` (20)
 326 * `PYTHON_DEBUG` (10)
 327 * `PYTHON_NOTSET` (0)
 328
 329
 330 include::common-cmd-options-head.txt[]
 331
 332
 333 Domain
 334 ~~~~~~
 335 One of:
 336
 337 option:-j, option:--jul::
 338     Create or enable event rules in the `java.util.logging`
 339     (JUL) domain.
 340
 341 option:-k, option:--kernel::
 342     Create or enable event rules in the Linux kernel domain.
 343
 344 option:-l, option:--log4j::
 345     Create or enable event rules in the Apache log4j domain.
 346
 347 option:-p, option:--python::
 348     Create or enable event rules in the Python domain.
 349
 350 option:-u, option:--userspace::
 351     Create or enable event rules in the user space domain.
 352
 353
 354 Target
 355 ~~~~~~
 356 option:-c, option:--channel='CHANNEL'::
 357     Create or enable event rules in the channel named 'CHANNEL' instead
 358     of the default channel name `channel0`.
 359
 360 option:-s, option:--session='SESSION'::
 361     Create or enable event rules in the tracing session named 'SESSION'
 362     instead of the current tracing session.
 363
 364
 365 Event source type
 366 ~~~~~~~~~~~~~~~~~
 367 One of:
 368
 369 option:--function='SOURCE'::
 370     Linux kernel kretprobe. Only available with the option:--kernel
 371     domain option. 'SOURCE' is one of:
 372 +
 373 * Function address (`0x` prefix supported)
 374 * Function symbol
 375 * Function symbol and offset (`SYMBOL+OFFSET` format)
 376
 377 option:--probe='SOURCE'::
 378     Linux kernel kprobe. Only available with the option:--kernel
 379     domain option. 'SOURCE' is one of:
 380 +
 381 * Address (`0x` prefix supported)
 382 * Symbol
 383 * Symbol and offset (`SYMBOL+OFFSET` format)
 384
 385 option:--syscall::
 386     Linux kernel system call. Only available with the option:--kernel
 387     domain option.
 388
 389 option:--tracepoint::
 390     Linux kernel or application tracepoint (default).
 391
 392
 393 Log level
 394 ~~~~~~~~~
 395 One of:
 396
 397 option:--loglevel='LOGLEVEL'::
 398     Add log level condition to the event rule: the event source's
 399     defined log level must be at least as severe as 'LOGLEVEL'.
 400     See the <<log-levels,Log levels>> section above for the available
 401     log levels. Only available with application domains.
 402
 403 option:--loglevel-only='LOGLEVEL'::
 404     Add log level condition to the event rule: the event source's
 405     defined log level must match 'LOGLEVEL'. See the
 406     <<log-levels,Log levels>> section above for the available log
 407     levels. Only available with application domains.
 408
 409
 410 Filtering and exclusion
 411 ~~~~~~~~~~~~~~~~~~~~~~~
 412 option:-x, option:--exclude='EVENT'[,'EVENT']...::
 413     Exclude events named 'EVENT' from the event rule. This option
 414     can be used when the command's 'EVENT' argument contains a wildcard
 415     (`*`) to exclude specific names. Only available with application
 416     domains.
 417
 418 option:-f, option:--filter='EXPR'::
 419     Add filter expression condition to the event rule. Expression 'EXPR'
 420     must evaluate to true when executed against the dynamic values of
 421     event fields. See the <<filter-syntax,Filter expression syntax>>
 422     section above for more information.
 423
 424
 425 Shortcuts
 426 ~~~~~~~~~
 427 option:-a, option:--all::
 428     Equivalent to an 'EVENT' argument named `*` (wildcard) when also
 429     using the option:--tracepoint (default) or option:--syscall option.
 430
 431
 432 include::common-cmd-help-options.txt[]
 433
 434
 435 include::common-cmd-footer.txt[]
 436
 437
 438 SEE ALSO
 439 --------
 440 man:lttng-disable-event(1),
 441 man:lttng(1)