7 lttng-enable-event - Create or enable LTTng event rules
12 Create or enable Linux kernel event rules:
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']...
20 Create or enable an "all" Linux kernel event rule:
23 *lttng* ['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* ['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:
109 ----------------------------------------------------------------
110 lttng enable-event --userspace hello:world
111 lttng enable-event --userspace hello:world --loglevel=TRACE_INFO
112 ----------------------------------------------------------------
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
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.
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.
127 The available conditions for the Linux kernel domain are:
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.
135 Wildcard using the `*` character are supported _at the end_ of
136 tracepoint and system call names.
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.
143 The available conditions for the application domains are:
145 * Tracepoint name ('EVENT' with option:--tracepoint option) which must
146 match event source's equivalent.
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.
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).
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)).
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).
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.
183 The filter expression syntax is very similar to C language conditional
184 expressions (expressions that can be evaluated by an `if` statement).
186 The following logical operators are supported:
188 [width="40%",options="header"]
189 |=====================================
191 | Logical negation (NOT) | `!a`
192 | Logical conjunction (AND) | `a && b`
193 | Logical disjunction (OR) | `a \|\| b`
194 |=====================================
196 The following comparison operators/relational operators are supported:
198 [width="40%",options="header"]
199 |====================================
201 | Equal to | `a == b`
202 | Not equal to | `a != b`
203 | Greater than | `a > b`
204 | Less than | `a < b`
205 | Greater than or equal to | `a >= b`
206 | Less than or equal to | `a <= b`
207 |====================================
209 The arithmetic and bitwise operators are :not: supported.
211 The precedence table of the operators above is the same as the one of
212 the C language. Parentheses are supported to bypass this.
214 The dynamic value of an event field is read by using its name as
217 The dynamic value of a statically-known context field is read by
218 prefixing its name with `$ctx.`. Statically-known context fields are
219 context fields added to channels without the `$app.` prefix using the
220 linklttng:lttng-add-context(1) command.
222 The dynamic value of an application-specific context field is read by
223 prefixing its name with `$app.` (follows the format used to add such a
224 context field with the linklttng:lttng-add-context(1) command).
226 When a comparison includes a non existent event field, the whole filter
227 expression evaluates to false (the event is discarded).
229 C integer and floating point number constants are supported, as well as
230 literal strings between double quotes (`"`). Literal strings can contain
231 a wildcard character (`*`) at the end to match more than one string.
232 This wildcard can be escaped using `\\*`.
234 LTTng-UST enumeration fields can be compared to integer values (fields
237 NOTE: Although it is possible to filter the process ID of an event when
238 the `pid` context has been added to its channel using, for example,
239 `$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
240 which is much more efficient (see linklttng:lttng-track(1)).
244 ----------------------------
245 msg_id == 23 && size >= 2048
246 ----------------------------
248 -------------------------------------------------
249 $ctx.procname == "lttng*" && (!flag || poel < 34)
250 -------------------------------------------------
252 ---------------------------------------------------------
253 $app.my_provider:my_context == 17.34e9 || some_enum >= 14
254 ---------------------------------------------------------
260 Tracepoints and log statements in applications have an attached log
261 level. Application event rules can contain a _log level_ condition.
263 With the option:--loglevel option, the event source's log level must
264 be at least as severe as the option's argument. With the
265 option:--loglevel-only option, the event source's log level must match
266 the option's argument.
268 The available log levels are:
270 User space domain (option:--userspace option)::
271 Shortcuts such as `system` are allowed.
277 * `TRACE_WARNING` (4)
280 * `TRACE_DEBUG_SYSTEM` (7)
281 * `TRACE_DEBUG_PROGRAM` (8)
282 * `TRACE_DEBUG_PROCESS` (9)
283 * `TRACE_DEBUG_MODULE` (10)
284 * `TRACE_DEBUG_UNIT` (11)
285 * `TRACE_DEBUG_FUNCTION` (12)
286 * `TRACE_DEBUG_LINE` (13)
289 `java.util.logging` domain (option:--jul option)::
290 Shortcuts such as `severe` are allowed.
292 * `JUL_OFF` (`INT32_MAX`)
293 * `JUL_SEVERE` (1000)
294 * `JUL_WARNING` (900)
300 * `JUL_ALL` (`INT32_MIN`)
302 Apache log4j domain (option:--log4j option)::
303 Shortcuts such as `severe` are allowed.
305 * `LOG4J_OFF` (`INT32_MAX`)
306 * `LOG4J_FATAL` (50000)
307 * `LOG4J_ERROR` (40000)
308 * `LOG4J_WARN` (30000)
309 * `LOG4J_INFO` (20000)
310 * `LOG4J_DEBUG` (10000)
311 * `LOG4J_TRACE` (5000)
312 * `LOG4J_ALL` (`INT32_MIN`)
314 Python domain (option:--python option)::
315 Shortcuts such as `critical` are allowed.
317 * `PYTHON_CRITICAL` (50)
318 * `PYTHON_ERROR` (40)
319 * `PYTHON_WARNING` (30)
321 * `PYTHON_DEBUG` (10)
322 * `PYTHON_NOTSET` (0)
325 include::common-cmd-options-head.txt[]
332 option:-j, option:--jul::
333 Create or enable event rules in the `java.util.logging`
336 option:-k, option:--kernel::
337 Create or enable event rules in the Linux kernel domain.
339 option:-l, option:--log4j::
340 Create or enable event rules in the Apache log4j domain.
342 option:-p, option:--python::
343 Create or enable event rules in the Python domain.
345 option:-u, option:--userspace::
346 Create or enable event rules in the user space domain.
351 option:-c, option:--channel='CHANNEL'::
352 Create or enable event rules in the channel named 'CHANNEL' instead
353 of the default channel name `channel0`.
355 option:-s, option:--session='SESSION'::
356 Create or enable event rules in the tracing session named 'SESSION'
357 instead of the current tracing session.
364 option:--function='SOURCE'::
365 Linux kernel kretprobe. Only available with the option:--kernel
366 domain option. 'SOURCE' is one of:
368 * Function address (`0x` prefix supported)
370 * Function symbol and offset (`SYMBOL+OFFSET` format)
372 option:--probe='SOURCE'::
373 Linux kernel kprobe. Only available with the option:--kernel
374 domain option. 'SOURCE' is one of:
376 * Address (`0x` prefix supported)
378 * Symbol and offset (`SYMBOL+OFFSET` format)
381 Linux kernel system call. Only available with the option:--kernel
384 option:--tracepoint::
385 Linux kernel or application tracepoint (default).
392 option:--loglevel='LOGLEVEL'::
393 Add log level condition to the event rule: the event source's
394 defined log level must be at least as severe as 'LOGLEVEL'.
395 See the <<log-levels,Log levels>> section above for the available
396 log levels. Only available with application domains.
398 option:--loglevel-only='LOGLEVEL'::
399 Add log level condition to the event rule: the event source's
400 defined log level must match 'LOGLEVEL'. See the
401 <<log-levels,Log levels>> section above for the available log
402 levels. Only available with application domains.
405 Filtering and exclusion
406 ~~~~~~~~~~~~~~~~~~~~~~~
407 option:-x, option:--exclude='EVENT'[,'EVENT']...::
408 Exclude events named 'EVENT' from the event rule. This option
409 can be used when the command's 'EVENT' argument contains a wildcard
410 (`*`) to exclude specific names. Only available with application
413 option:-f, option:--filter='EXPR'::
414 Add filter expression condition to the event rule. Expression 'EXPR'
415 must evaluate to true when executed against the dynamic values of
416 event fields. See the <<filter-syntax,Filter expression syntax>>
417 section above for more information.
422 option:-a, option:--all::
423 Equivalent to an 'EVENT' argument named `*` (wildcard) when also
424 using the option:--tracepoint (default) or option:--syscall option.
427 include::common-cmd-help-options.txt[]
430 include::common-cmd-footer.txt[]
435 linklttng:lttng-disable-event(1),