7 lttng-enable-event - Create or enable LTTng event rules
12 Create or enable Linux kernel event rules:
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']...
20 Create or enable an "all" Linux kernel event rule:
23 *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel option:--all [option:--syscall]
24 [option:--filter='EXPR'] [option:--session='SESSION'] [option:--channel='CHANNEL']
26 Create or enable application event rules:
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']...)
38 The `lttng enable-event` command can create a new event rule, or enable
39 one or more existing and disabled ones.
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.
47 The linklttng:lttng-disable-event(1) command can be used to disable
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).
55 If the option:--session option is omitted, the chosen channel is picked
56 from the current tracing session.
58 Events can be enabled while tracing is active
59 (use linklttng:lttng-start(1) to make a tracing session active).
64 Four types of event sources are available in the Linux kernel tracing
65 domain (option:--kernel option):
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
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.
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
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.
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.
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.
104 Any condition that is not explicitly specified on creation is considered
107 For example, consider the following commands:
110 ----------------------------------------------------------------
111 lttng enable-event --userspace hello:world
112 lttng enable-event --userspace hello:world --loglevel=TRACE_INFO
113 ----------------------------------------------------------------
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
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.
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.
128 The available conditions for the Linux kernel domain are:
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.
136 Wildcard using the `*` character are supported _at the end_ of
137 tracepoint and system call names.
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.
144 The available conditions for the application domains are:
146 * Tracepoint name ('EVENT' with option:--tracepoint option) which must
147 match event source's equivalent.
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.
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).
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)).
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).
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.
184 The filter expression syntax is very similar to C language conditional
185 expressions (expressions that can be evaluated by an `if` statement).
187 The following logical operators are supported:
189 [width="40%",options="header"]
190 |=====================================
192 | Logical negation (NOT) | `!a`
193 | Logical conjunction (AND) | `a && b`
194 | Logical disjunction (OR) | `a \|\| b`
195 |=====================================
197 The following comparison operators/relational operators are supported:
199 [width="40%",options="header"]
200 |====================================
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 |====================================
210 The arithmetic and bitwise operators are :not: supported.
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.
215 The dynamic value of an event field is read by using its name as
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.
223 The dynamic value of an application-specific context field is read by
224 prefixing its name with `$app.` (follows the format used to add such a
225 context field with the linklttng:lttng-add-context(1) command).
227 When a comparison includes a non existent event field, the whole filter
228 expression evaluates to false (the event is discarded).
230 C integer and floating point number constants are supported, as well as
231 literal strings between double quotes (`"`). Literal strings can contain
232 a wildcard character (`*`) at the end to match more than one string.
233 This wildcard can be escaped using :escwc:.
235 LTTng-UST enumeration fields can be compared to integer values (fields
238 NOTE: Although it is possible to filter the process ID of an event when
239 the `pid` context has been added to its channel using, for example,
240 `$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
241 which is much more efficient (see linklttng:lttng-track(1)).
245 ----------------------------
246 msg_id == 23 && size >= 2048
247 ----------------------------
249 -------------------------------------------------
250 $ctx.procname == "lttng*" && (!flag || poel < 34)
251 -------------------------------------------------
253 ---------------------------------------------------------
254 $app.my_provider:my_context == 17.34e9 || some_enum >= 14
255 ---------------------------------------------------------
261 Tracepoints and log statements in applications have an attached log
262 level. Application event rules can contain a _log level_ condition.
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.
269 The available log levels are:
271 User space domain (option:--userspace option)::
272 Shortcuts such as `system` are allowed.
278 * `TRACE_WARNING` (4)
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)
290 `java.util.logging` domain (option:--jul option)::
291 Shortcuts such as `severe` are allowed.
293 * `JUL_OFF` (`INT32_MAX`)
294 * `JUL_SEVERE` (1000)
295 * `JUL_WARNING` (900)
301 * `JUL_ALL` (`INT32_MIN`)
303 Apache log4j domain (option:--log4j option)::
304 Shortcuts such as `severe` are allowed.
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`)
315 Python domain (option:--python option)::
316 Shortcuts such as `critical` are allowed.
318 * `PYTHON_CRITICAL` (50)
319 * `PYTHON_ERROR` (40)
320 * `PYTHON_WARNING` (30)
322 * `PYTHON_DEBUG` (10)
323 * `PYTHON_NOTSET` (0)
326 include::common-cmd-options-head.txt[]
333 option:-j, option:--jul::
334 Create or enable event rules in the `java.util.logging`
337 option:-k, option:--kernel::
338 Create or enable event rules in the Linux kernel domain.
340 option:-l, option:--log4j::
341 Create or enable event rules in the Apache log4j domain.
343 option:-p, option:--python::
344 Create or enable event rules in the Python domain.
346 option:-u, option:--userspace::
347 Create or enable event rules in the user space domain.
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`.
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.
365 option:--function='SOURCE'::
366 Linux kernel kretprobe. Only available with the option:--kernel
367 domain option. 'SOURCE' is one of:
369 * Function address (`0x` prefix supported)
371 * Function symbol and offset (`SYMBOL+OFFSET` format)
373 option:--probe='SOURCE'::
374 Linux kernel kprobe. Only available with the option:--kernel
375 domain option. 'SOURCE' is one of:
377 * Address (`0x` prefix supported)
379 * Symbol and offset (`SYMBOL+OFFSET` format)
382 Linux kernel system call. Only available with the option:--kernel
385 option:--tracepoint::
386 Linux kernel or application tracepoint (default).
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.
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.
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
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.
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.
428 include::common-cmd-help-options.txt[]
431 include::common-cmd-footer.txt[]
436 linklttng:lttng-disable-event(1),