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 linklttng:lttng-list(1) command.
  46
  47 The linklttng: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 linklttng: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 linklttng: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 The filter expression syntax is very similar to C language conditional
 185 expressions (expressions that can be evaluated by an `if` statement).
 186
 187 The following logical operators are supported:
 188
 189 [width="40%",options="header"]
 190 |=====================================
 191 | Name                      | Syntax
 192 | Logical negation (NOT)    | `!a`
 193 | Logical conjunction (AND) | `a && b`
 194 | Logical disjunction (OR)  | `a \|\| b`
 195 |=====================================
 196
 197 The following comparison operators/relational operators are supported:
 198
 199 [width="40%",options="header"]
 200 |====================================
 201 | Name                     | Syntax
 202 | Equal to                 | `a == b`
 203 | Not equal to             | `a != b`
 204 | Greater than             | `a > b`
 205 | Less than                | `a < b`
 206 | Greater than or equal to | `a >= b`
 207 | Less than or equal to    | `a <= b`
 208 |====================================
 209
 210 The arithmetic and bitwise operators are :not: supported.
 211
 212 The precedence table of the operators above is the same as the one of
 213 the C language. Parentheses are supported to bypass this.
 214
 215 The dynamic value of an event field is read by using its name as
 216 a C identifier.
 217
 218 The dynamic value of a statically-known context field is read by
 219 prefixing its name with `$ctx.`. Statically-known context fields are
 220 context fields added to channels without the `$app.` prefix using the
 221 linklttng:lttng-add-context(1) command.
 222
 223 The dynamic value of an application-specific context field is read by
 224 prefixing its name with `$app.` (follows the format used to add such a
 225 context field with the linklttng:lttng-add-context(1) command).
 226
 227 When a comparison includes a non existent event field, the whole filter
 228 expression evaluates to false (the event is discarded).
 229
 230 C integer and floating point number constants are supported, as well as
 231 literal strings between double quotes (`"`). Literal strings can contain
 232 a wildcard character (`*`) at the end to match more than one string.
 233 This wildcard can be escaped using :escwc:.
 234
 235 LTTng-UST enumeration fields can be compared to integer values (fields
 236 or constants).
 237
 238 NOTE: Although it is possible to filter the process ID of an event when
 239 the `pid` context has been added to its channel using, for example,
 240 `$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
 241 which is much more efficient (see linklttng:lttng-track(1)).
 242
 243 Examples:
 244
 245 ----------------------------
 246 msg_id == 23 && size >= 2048
 247 ----------------------------
 248
 249 -------------------------------------------------
 250 $ctx.procname == "lttng*" && (!flag || poel < 34)
 251 -------------------------------------------------
 252
 253 ---------------------------------------------------------
 254 $app.my_provider:my_context == 17.34e9 || some_enum >= 14
 255 ---------------------------------------------------------
 256
 257
 258 [[log-levels]]
 259 Log levels
 260 ~~~~~~~~~~
 261 Tracepoints and log statements in applications have an attached log
 262 level. Application event rules can contain a _log level_ condition.
 263
 264 With the option:--loglevel option, the event source's log level must
 265 be at least as severe as the option's argument. With the
 266 option:--loglevel-only option, the event source's log level must match
 267 the option's argument.
 268
 269 The available log levels are:
 270
 271 User space domain (option:--userspace option)::
 272     Shortcuts such as `system` are allowed.
 273 +
 274 * `TRACE_EMERG` (0)
 275 * `TRACE_ALERT` (1)
 276 * `TRACE_CRIT` (2)
 277 * `TRACE_ERR` (3)
 278 * `TRACE_WARNING` (4)
 279 * `TRACE_NOTICE` (5)
 280 * `TRACE_INFO` (6)
 281 * `TRACE_DEBUG_SYSTEM` (7)
 282 * `TRACE_DEBUG_PROGRAM` (8)
 283 * `TRACE_DEBUG_PROCESS` (9)
 284 * `TRACE_DEBUG_MODULE` (10)
 285 * `TRACE_DEBUG_UNIT` (11)
 286 * `TRACE_DEBUG_FUNCTION` (12)
 287 * `TRACE_DEBUG_LINE` (13)
 288 * `TRACE_DEBUG` (14)
 289
 290 `java.util.logging` domain (option:--jul option)::
 291     Shortcuts such as `severe` are allowed.
 292 +
 293 * `JUL_OFF` (`INT32_MAX`)
 294 * `JUL_SEVERE` (1000)
 295 * `JUL_WARNING` (900)
 296 * `JUL_INFO` (800)
 297 * `JUL_CONFIG` (700)
 298 * `JUL_FINE` (500)
 299 * `JUL_FINER` (400)
 300 * `JUL_FINEST` (300)
 301 * `JUL_ALL` (`INT32_MIN`)
 302
 303 Apache log4j domain (option:--log4j option)::
 304     Shortcuts such as `severe` are allowed.
 305 +
 306 * `LOG4J_OFF` (`INT32_MAX`)
 307 * `LOG4J_FATAL` (50000)
 308 * `LOG4J_ERROR` (40000)
 309 * `LOG4J_WARN` (30000)
 310 * `LOG4J_INFO` (20000)
 311 * `LOG4J_DEBUG` (10000)
 312 * `LOG4J_TRACE` (5000)
 313 * `LOG4J_ALL` (`INT32_MIN`)
 314
 315 Python domain (option:--python option)::
 316     Shortcuts such as `critical` are allowed.
 317 +
 318 * `PYTHON_CRITICAL` (50)
 319 * `PYTHON_ERROR` (40)
 320 * `PYTHON_WARNING` (30)
 321 * `PYTHON_INFO` (20)
 322 * `PYTHON_DEBUG` (10)
 323 * `PYTHON_NOTSET` (0)
 324
 325
 326 include::common-cmd-options-head.txt[]
 327
 328
 329 Domain
 330 ~~~~~~
 331 One of:
 332
 333 option:-j, option:--jul::
 334     Create or enable event rules in the `java.util.logging`
 335     (JUL) domain.
 336
 337 option:-k, option:--kernel::
 338     Create or enable event rules in the Linux kernel domain.
 339
 340 option:-l, option:--log4j::
 341     Create or enable event rules in the Apache log4j domain.
 342
 343 option:-p, option:--python::
 344     Create or enable event rules in the Python domain.
 345
 346 option:-u, option:--userspace::
 347     Create or enable event rules in the user space domain.
 348
 349
 350 Target
 351 ~~~~~~
 352 option:-c, option:--channel='CHANNEL'::
 353     Create or enable event rules in the channel named 'CHANNEL' instead
 354     of the default channel name `channel0`.
 355
 356 option:-s, option:--session='SESSION'::
 357     Create or enable event rules in the tracing session named 'SESSION'
 358     instead of the current tracing session.
 359
 360
 361 Event source type
 362 ~~~~~~~~~~~~~~~~~
 363 One of:
 364
 365 option:--function='SOURCE'::
 366     Linux kernel kretprobe. Only available with the option:--kernel
 367     domain option. 'SOURCE' is one of:
 368 +
 369 * Function address (`0x` prefix supported)
 370 * Function symbol
 371 * Function symbol and offset (`SYMBOL+OFFSET` format)
 372
 373 option:--probe='SOURCE'::
 374     Linux kernel kprobe. Only available with the option:--kernel
 375     domain option. 'SOURCE' is one of:
 376 +
 377 * Address (`0x` prefix supported)
 378 * Symbol
 379 * Symbol and offset (`SYMBOL+OFFSET` format)
 380
 381 option:--syscall::
 382     Linux kernel system call. Only available with the option:--kernel
 383     domain option.
 384
 385 option:--tracepoint::
 386     Linux kernel or application tracepoint (default).
 387
 388
 389 Log level
 390 ~~~~~~~~~
 391 One of:
 392
 393 option:--loglevel='LOGLEVEL'::
 394     Add log level condition to the event rule: the event source's
 395     defined log level must be at least as severe as 'LOGLEVEL'.
 396     See the <<log-levels,Log levels>> section above for the available
 397     log levels. Only available with application domains.
 398
 399 option:--loglevel-only='LOGLEVEL'::
 400     Add log level condition to the event rule: the event source's
 401     defined log level must match 'LOGLEVEL'. See the
 402     <<log-levels,Log levels>> section above for the available log
 403     levels. Only available with application domains.
 404
 405
 406 Filtering and exclusion
 407 ~~~~~~~~~~~~~~~~~~~~~~~
 408 option:-x, option:--exclude='EVENT'[,'EVENT']...::
 409     Exclude events named 'EVENT' from the event rule. This option
 410     can be used when the command's 'EVENT' argument contains a wildcard
 411     (`*`) to exclude specific names. Only available with application
 412     domains.
 413
 414 option:-f, option:--filter='EXPR'::
 415     Add filter expression condition to the event rule. Expression 'EXPR'
 416     must evaluate to true when executed against the dynamic values of
 417     event fields. See the <<filter-syntax,Filter expression syntax>>
 418     section above for more information.
 419
 420
 421 Shortcuts
 422 ~~~~~~~~~
 423 option:-a, option:--all::
 424     Equivalent to an 'EVENT' argument named `*` (wildcard) when also
 425     using the option:--tracepoint (default) or option:--syscall option.
 426
 427
 428 include::common-cmd-help-options.txt[]
 429
 430
 431 include::common-cmd-footer.txt[]
 432
 433
 434 SEE ALSO
 435 --------
 436 linklttng:lttng-disable-event(1),
 437 linklttng:lttng(1)