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