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 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.
187 The filter expression syntax is very similar to C language conditional
188 expressions (expressions that can be evaluated by an `if` statement).
190 The following logical operators are supported:
192 [width="40%",options="header"]
193 |=====================================
195 | Logical negation (NOT) | `!a`
196 | Logical conjunction (AND) | `a && b`
197 | Logical disjunction (OR) | `a \|\| b`
198 |=====================================
200 The following comparison operators/relational operators are supported:
202 [width="40%",options="header"]
203 |====================================
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 |====================================
213 The arithmetic and bitwise operators are :not: supported.
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.
218 The dynamic value of an event field is read by using its name as
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.
226 The dynamic value of an application-specific context field is read by
227 prefixing its name with `$app.` (follows the format used to add such a
228 context field with the linklttng:lttng-add-context(1) command).
230 When a comparison includes a non existent event field, the whole filter
231 expression evaluates to false (the event is discarded).
233 C integer and floating point number constants are supported, as well as
234 literal strings between double quotes (`"`). Literal strings can contain
235 a wildcard character (`*`) at the end to match more than one string.
236 This wildcard can be escaped using `\\*`.
238 LTTng-UST enumeration fields can be compared to integer values (fields
241 NOTE: Although it is possible to filter the process ID of an event when
242 the `pid` context has been added to its channel using, for example,
243 `$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
244 which is much more efficient (see linklttng:lttng-track(1)).
248 ----------------------------
249 msg_id == 23 && size >= 2048
250 ----------------------------
252 -------------------------------------------------
253 $ctx.procname == "lttng*" && (!flag || poel < 34)
254 -------------------------------------------------
256 ---------------------------------------------------------
257 $app.my_provider:my_context == 17.34e9 || some_enum >= 14
258 ---------------------------------------------------------
264 Tracepoints and log statements in applications have an attached log
265 level. Application event rules can contain a _log level_ condition.
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.
272 The available log levels are:
274 User space domain (option:--userspace option)::
275 Shortcuts such as `system` are allowed.
281 * `TRACE_WARNING` (4)
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)
293 `java.util.logging` domain (option:--jul option)::
294 Shortcuts such as `severe` are allowed.
296 * `JUL_OFF` (`INT32_MAX`)
297 * `JUL_SEVERE` (1000)
298 * `JUL_WARNING` (900)
304 * `JUL_ALL` (`INT32_MIN`)
306 Apache log4j domain (option:--log4j option)::
307 Shortcuts such as `severe` are allowed.
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`)
318 Python domain (option:--python option)::
319 Shortcuts such as `critical` are allowed.
321 * `PYTHON_CRITICAL` (50)
322 * `PYTHON_ERROR` (40)
323 * `PYTHON_WARNING` (30)
325 * `PYTHON_DEBUG` (10)
326 * `PYTHON_NOTSET` (0)
329 include::common-cmd-options-head.txt[]
336 option:-j, option:--jul::
337 Create or enable event rules in the `java.util.logging`
340 option:-k, option:--kernel::
341 Create or enable event rules in the Linux kernel domain.
343 option:-l, option:--log4j::
344 Create or enable event rules in the Apache log4j domain.
346 option:-p, option:--python::
347 Create or enable event rules in the Python domain.
349 option:-u, option:--userspace::
350 Create or enable event rules in the user space domain.
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`.
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.
368 option:--function='SOURCE'::
369 Linux kernel kretprobe. Only available with the option:--kernel
370 domain option. 'SOURCE' is one of:
372 * Function address (`0x` prefix supported)
374 * Function symbol and offset (`SYMBOL+OFFSET` format)
376 option:--probe='SOURCE'::
377 Linux kernel kprobe. Only available with the option:--kernel
378 domain option. 'SOURCE' is one of:
380 * Address (`0x` prefix supported)
382 * Symbol and offset (`SYMBOL+OFFSET` format)
385 Linux kernel system call. Only available with the option:--kernel
388 option:--tracepoint::
389 Linux kernel or application tracepoint (default).
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.
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.
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
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.
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.
431 include::common-cmd-help-options.txt[]
434 include::common-cmd-footer.txt[]
439 linklttng:lttng-disable-event(1),