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e9b06e2b PP |
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] | |
ce19b9ed | 15 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel |
e9b06e2b PP |
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] | |
ce19b9ed | 23 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel option:--all [option:--syscall] |
e9b06e2b PP |
24 | [option:--filter='EXPR'] [option:--session='SESSION'] [option:--channel='CHANNEL'] |
25 | ||
26 | Create or enable application event rules: | |
27 | ||
28 | [verse] | |
ce19b9ed | 29 | *lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* |
e9b06e2b PP |
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). | |
7c1a4458 | 45 | Event sources can be listed with the man:lttng-list(1) command. |
e9b06e2b | 46 | |
7c1a4458 | 47 | The man:lttng-disable-event(1) command can be used to disable |
e9b06e2b PP |
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 | |
7c1a4458 | 59 | (use man:lttng-start(1) to make a tracing session active). |
e9b06e2b PP |
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 | ||
d4f093aa | 109 | [role="term"] |
03c5529d PP |
110 | ---- |
111 | $ lttng enable-event --userspace hello:world | |
112 | $ lttng enable-event --userspace hello:world --loglevel=TRACE_INFO | |
113 | ---- | |
e9b06e2b PP |
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 | + | |
f69e7997 PP |
136 | You can use `*` characters at any place in the tracepoint or system |
137 | call name as wildcards to match zero or more characters. To use a | |
138 | literal `*` character, use :escwc:. | |
e9b06e2b PP |
139 | |
140 | * Filter expression (option:--filter option) executed against the | |
141 | dynamic values of event fields at execution time that must evaluate | |
11613178 | 142 | to true. See the <<filter-expr,Filter expression>> section |
e9b06e2b PP |
143 | below for more information. |
144 | ||
145 | The available conditions for the application domains are: | |
146 | ||
147 | * Tracepoint name ('EVENT' with option:--tracepoint option) which must | |
148 | match event source's equivalent. | |
149 | + | |
f69e7997 PP |
150 | You can use `*` characters at any place in the tracepoint name as |
151 | wildcards to match zero or more characters. To use a literal `*` | |
152 | character, use :escwc:. When you create an event rule with a tracepoint | |
153 | name containing a wildcard, you can exclude specific tracepoint names | |
154 | from the match with the option:--exclude option. | |
e9b06e2b PP |
155 | |
156 | * Filter expression (option:--filter option) executed against the | |
157 | dynamic values of event fields at execution time that must evaluate | |
11613178 | 158 | to true. See the <<filter-expr,Filter expression>> section |
e9b06e2b PP |
159 | below for more information. |
160 | * Event's log level that must be at least as severe as a given | |
161 | log level (option:--loglevel option) or match exactly a given log | |
162 | level (option:--loglevel-only option). | |
163 | ||
164 | When using `lttng enable-event` with a set of conditions that does not | |
165 | currently exist for the chosen tracing session, domain, and channel, | |
166 | a new event rule is created. Otherwise, the existing event rule is | |
167 | enabled if it is currently disabled | |
7c1a4458 | 168 | (see man:lttng-disable-event(1)). |
e9b06e2b PP |
169 | |
170 | The option:--all option can be used alongside the option:--tracepoint | |
171 | or option:--syscall options. When this option is used, no 'EVENT' | |
172 | argument must be specified. This option defines a single event rule | |
173 | matching _all_ the possible events of a given tracing domain for the | |
174 | chosen channel and tracing session. It is the equivalent of an 'EVENT' | |
175 | argument named `*` (wildcard). | |
176 | ||
177 | ||
11613178 PP |
178 | [[filter-expr]] |
179 | Filter expression | |
180 | ~~~~~~~~~~~~~~~~~ | |
c52365cc | 181 | A filter expression can be specified with the option:--filter option |
11613178 PP |
182 | when creating a new event rule. If the filter expression evaluates |
183 | to true when executed against the dynamic values of an event's fields | |
184 | when tracing, the filtering condition passes. | |
e9b06e2b | 185 | |
60f7980c PP |
186 | NOTE: Make sure to **single-quote** the filter expression when running |
187 | the command from a shell, as filter expressions typically include | |
188 | characters having a special meaning for most shells. | |
189 | ||
11613178 PP |
190 | The filter expression syntax is similar to C language conditional |
191 | expressions (expressions that can be evaluated by an `if` statement), | |
192 | albeit with a few differences: | |
e9b06e2b | 193 | |
11613178 PP |
194 | * C integer and floating point number constants are supported, as well |
195 | as literal strings between double quotes (`"`). You can use `*` | |
196 | characters at any place in a literal string as wildcards to match zero | |
197 | or more characters. To use a literal `*` character, use :escwc:. | |
198 | + | |
199 | Examples: `32`, `-0x17`, `0755`, `12.34`, | |
200 | +"a :escbs:"literal string:escbs:""+, `"src/*/*.h"`. | |
e9b06e2b | 201 | |
11613178 PP |
202 | * The dynamic value of an event field is read by using its name as a C |
203 | identifier. | |
204 | + | |
205 | The dot and square bracket notations are available, like in the C | |
206 | language, to access nested structure and array/sequence fields. | |
207 | Only a constant, positive integer number can be used within square | |
208 | brackets. If the index is out of bounds, the whole filter expression | |
209 | evaluates to false (the event is discarded). | |
210 | + | |
211 | An enumeration field's value is an integer. | |
212 | + | |
213 | When the expression's field does not exist, the whole filter expression | |
214 | evaluates to false. | |
215 | + | |
216 | Examples: `my_field`, `target_cpu`, `seq[7]`, `msg.user[1].data[2][17]`. | |
e9b06e2b | 217 | |
11613178 PP |
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 | man:lttng-add-context(1) command. | |
222 | + | |
223 | When the expression's statically-known context field does not exist, | |
224 | the whole filter expression evaluates to false. | |
225 | + | |
226 | Examples: `$ctx.prio`, `$ctx.preemptible`, | |
227 | `$ctx.perf:cpu:stalled-cycles-frontend`. | |
e9b06e2b | 228 | |
11613178 PP |
229 | * The dynamic value of an application-specific context field is read by |
230 | prefixing its name with `$app.` (follows the format used to add such a | |
231 | context field with the man:lttng-add-context(1) command). | |
232 | + | |
233 | When the expression's application-specific context field does not exist, | |
234 | the whole filter expression evaluates to false. | |
235 | + | |
236 | Example: `$app.server:cur_user`. | |
237 | ||
238 | The following precedence table shows the operators which are supported | |
239 | in a filter expression. In this table, the highest precedence is 1. | |
240 | Parentheses are supported to bypass the default order. | |
241 | ||
242 | IMPORTANT: Unlike the C language, the `lttng enable-event` filter | |
243 | expression syntax's bitwise AND and OR operators (`&` and `|`) take | |
244 | precedence over relational operators (`<`, `<=`, `>`, `>=`, `==`, and | |
245 | `!=`). This means the filter expression `2 & 2 == 2` is true while the | |
246 | equivalent C expression is false. | |
247 | ||
248 | [options="header"] | |
249 | |=== | |
250 | |Precedence |Operator |Description |Associativity | |
251 | |1 |`-` |Unary minus |Right-to-left | |
252 | |1 |`+` |Unary plus |Right-to-left | |
253 | |1 |`!` |Logical NOT |Right-to-left | |
254 | |1 |`~` |Bitwise NOT |Right-to-left | |
255 | |2 |`<<` |Bitwise left shift |Left-to-right | |
256 | |2 |`>>` |Bitwise right shift |Left-to-right | |
257 | |3 |`&` |Bitwise AND |Left-to-right | |
258 | |4 |`^` |Bitwise XOR |Left-to-right | |
259 | |5 |`\|` |Bitwise OR |Left-to-right | |
260 | |6 |`<` |Less than |Left-to-right | |
261 | |6 |`<=` |Less than or equal to |Left-to-right | |
262 | |6 |`>` |Greater than |Left-to-right | |
263 | |6 |`>=` |Greater than or equal to |Left-to-right | |
264 | |7 |`==` |Equal to |Left-to-right | |
265 | |7 |`!=` |Not equal to |Left-to-right | |
266 | |8 |`&&` |Logical AND |Left-to-right | |
267 | |9 |`\|\|` |Logical OR |Left-to-right | |
268 | |=== | |
269 | ||
270 | The arithmetic operators are :not: supported. | |
271 | ||
272 | All integer constants and fields are first casted to signed 64-bit | |
273 | integers. The representation of negative integers is two's complement. | |
274 | This means that, for example, the signed 8-bit integer field 0xff (-1) | |
275 | becomes 0xffffffffffffffff (still -1) once casted. | |
276 | ||
277 | Before a bitwise operator is applied, all its operands are casted to | |
278 | unsigned 64-bit integers, and the result is casted back to a signed | |
279 | 64-bit integer. For the bitwise NOT operator, it is the equivalent of | |
280 | this C expression: | |
281 | ||
282 | [source,c] | |
283 | ---- | |
284 | (int64_t) ~((uint64_t) val) | |
285 | ---- | |
e9b06e2b | 286 | |
11613178 PP |
287 | For the binary bitwise operators, it is the equivalent of those C |
288 | expressions: | |
e9b06e2b | 289 | |
11613178 PP |
290 | [source,c] |
291 | ---- | |
292 | (int64_t) ((uint64_t) lhs >> (uint64_t) rhs) | |
293 | (int64_t) ((uint64_t) lhs << (uint64_t) rhs) | |
294 | (int64_t) ((uint64_t) lhs & (uint64_t) rhs) | |
295 | (int64_t) ((uint64_t) lhs ^ (uint64_t) rhs) | |
296 | (int64_t) ((uint64_t) lhs | (uint64_t) rhs) | |
297 | ---- | |
e9b06e2b | 298 | |
11613178 PP |
299 | If the right-hand side of a bitwise shift operator (`<<` and `>>`) is |
300 | not in the [0,{nbsp}63] range, the whole filter expression evaluates to | |
301 | false. | |
e9b06e2b PP |
302 | |
303 | NOTE: Although it is possible to filter the process ID of an event when | |
304 | the `pid` context has been added to its channel using, for example, | |
305 | `$ctx.pid == 2832`, it is recommended to use the PID tracker instead, | |
7c1a4458 | 306 | which is much more efficient (see man:lttng-track(1)). |
e9b06e2b | 307 | |
11613178 | 308 | Filter expression examples: |
e9b06e2b PP |
309 | |
310 | ---------------------------- | |
311 | msg_id == 23 && size >= 2048 | |
312 | ---------------------------- | |
313 | ||
314 | ------------------------------------------------- | |
315 | $ctx.procname == "lttng*" && (!flag || poel < 34) | |
316 | ------------------------------------------------- | |
317 | ||
318 | --------------------------------------------------------- | |
319 | $app.my_provider:my_context == 17.34e9 || some_enum >= 14 | |
320 | --------------------------------------------------------- | |
321 | ||
c52365cc PP |
322 | --------------------------------------- |
323 | $ctx.cpu_id == 2 && filename != "*.log" | |
324 | --------------------------------------- | |
f69e7997 | 325 | |
11613178 PP |
326 | ------------------------------------------------ |
327 | eax_reg & 0xff7 == 0x240 && x[4] >> 12 <= 0x1234 | |
328 | ------------------------------------------------ | |
329 | ||
e9b06e2b PP |
330 | |
331 | [[log-levels]] | |
332 | Log levels | |
333 | ~~~~~~~~~~ | |
334 | Tracepoints and log statements in applications have an attached log | |
335 | level. Application event rules can contain a _log level_ condition. | |
336 | ||
337 | With the option:--loglevel option, the event source's log level must | |
338 | be at least as severe as the option's argument. With the | |
339 | option:--loglevel-only option, the event source's log level must match | |
340 | the option's argument. | |
341 | ||
342 | The available log levels are: | |
343 | ||
344 | User space domain (option:--userspace option):: | |
345 | Shortcuts such as `system` are allowed. | |
346 | + | |
347 | * `TRACE_EMERG` (0) | |
348 | * `TRACE_ALERT` (1) | |
349 | * `TRACE_CRIT` (2) | |
350 | * `TRACE_ERR` (3) | |
351 | * `TRACE_WARNING` (4) | |
352 | * `TRACE_NOTICE` (5) | |
353 | * `TRACE_INFO` (6) | |
354 | * `TRACE_DEBUG_SYSTEM` (7) | |
355 | * `TRACE_DEBUG_PROGRAM` (8) | |
356 | * `TRACE_DEBUG_PROCESS` (9) | |
357 | * `TRACE_DEBUG_MODULE` (10) | |
358 | * `TRACE_DEBUG_UNIT` (11) | |
359 | * `TRACE_DEBUG_FUNCTION` (12) | |
360 | * `TRACE_DEBUG_LINE` (13) | |
361 | * `TRACE_DEBUG` (14) | |
362 | ||
363 | `java.util.logging` domain (option:--jul option):: | |
364 | Shortcuts such as `severe` are allowed. | |
365 | + | |
366 | * `JUL_OFF` (`INT32_MAX`) | |
367 | * `JUL_SEVERE` (1000) | |
368 | * `JUL_WARNING` (900) | |
369 | * `JUL_INFO` (800) | |
370 | * `JUL_CONFIG` (700) | |
371 | * `JUL_FINE` (500) | |
372 | * `JUL_FINER` (400) | |
373 | * `JUL_FINEST` (300) | |
374 | * `JUL_ALL` (`INT32_MIN`) | |
375 | ||
376 | Apache log4j domain (option:--log4j option):: | |
377 | Shortcuts such as `severe` are allowed. | |
378 | + | |
379 | * `LOG4J_OFF` (`INT32_MAX`) | |
380 | * `LOG4J_FATAL` (50000) | |
381 | * `LOG4J_ERROR` (40000) | |
382 | * `LOG4J_WARN` (30000) | |
383 | * `LOG4J_INFO` (20000) | |
384 | * `LOG4J_DEBUG` (10000) | |
385 | * `LOG4J_TRACE` (5000) | |
386 | * `LOG4J_ALL` (`INT32_MIN`) | |
387 | ||
388 | Python domain (option:--python option):: | |
389 | Shortcuts such as `critical` are allowed. | |
390 | + | |
391 | * `PYTHON_CRITICAL` (50) | |
392 | * `PYTHON_ERROR` (40) | |
393 | * `PYTHON_WARNING` (30) | |
394 | * `PYTHON_INFO` (20) | |
395 | * `PYTHON_DEBUG` (10) | |
396 | * `PYTHON_NOTSET` (0) | |
397 | ||
398 | ||
399 | include::common-cmd-options-head.txt[] | |
400 | ||
401 | ||
402 | Domain | |
403 | ~~~~~~ | |
404 | One of: | |
405 | ||
406 | option:-j, option:--jul:: | |
407 | Create or enable event rules in the `java.util.logging` | |
408 | (JUL) domain. | |
409 | ||
410 | option:-k, option:--kernel:: | |
411 | Create or enable event rules in the Linux kernel domain. | |
412 | ||
413 | option:-l, option:--log4j:: | |
414 | Create or enable event rules in the Apache log4j domain. | |
415 | ||
416 | option:-p, option:--python:: | |
417 | Create or enable event rules in the Python domain. | |
418 | ||
419 | option:-u, option:--userspace:: | |
420 | Create or enable event rules in the user space domain. | |
421 | ||
422 | ||
423 | Target | |
424 | ~~~~~~ | |
59b19c3c | 425 | option:-c 'CHANNEL', option:--channel='CHANNEL':: |
e9b06e2b PP |
426 | Create or enable event rules in the channel named 'CHANNEL' instead |
427 | of the default channel name `channel0`. | |
428 | ||
59b19c3c | 429 | option:-s 'SESSION', option:--session='SESSION':: |
e9b06e2b PP |
430 | Create or enable event rules in the tracing session named 'SESSION' |
431 | instead of the current tracing session. | |
432 | ||
433 | ||
434 | Event source type | |
435 | ~~~~~~~~~~~~~~~~~ | |
436 | One of: | |
437 | ||
438 | option:--function='SOURCE':: | |
439 | Linux kernel kretprobe. Only available with the option:--kernel | |
440 | domain option. 'SOURCE' is one of: | |
441 | + | |
442 | * Function address (`0x` prefix supported) | |
443 | * Function symbol | |
444 | * Function symbol and offset (`SYMBOL+OFFSET` format) | |
445 | ||
446 | option:--probe='SOURCE':: | |
447 | Linux kernel kprobe. Only available with the option:--kernel | |
448 | domain option. 'SOURCE' is one of: | |
449 | + | |
450 | * Address (`0x` prefix supported) | |
451 | * Symbol | |
452 | * Symbol and offset (`SYMBOL+OFFSET` format) | |
453 | ||
454 | option:--syscall:: | |
455 | Linux kernel system call. Only available with the option:--kernel | |
456 | domain option. | |
457 | ||
458 | option:--tracepoint:: | |
459 | Linux kernel or application tracepoint (default). | |
460 | ||
461 | ||
462 | Log level | |
463 | ~~~~~~~~~ | |
464 | One of: | |
465 | ||
466 | option:--loglevel='LOGLEVEL':: | |
467 | Add log level condition to the event rule: the event source's | |
468 | defined log level must be at least as severe as 'LOGLEVEL'. | |
469 | See the <<log-levels,Log levels>> section above for the available | |
470 | log levels. Only available with application domains. | |
471 | ||
472 | option:--loglevel-only='LOGLEVEL':: | |
473 | Add log level condition to the event rule: the event source's | |
474 | defined log level must match 'LOGLEVEL'. See the | |
475 | <<log-levels,Log levels>> section above for the available log | |
476 | levels. Only available with application domains. | |
477 | ||
478 | ||
479 | Filtering and exclusion | |
480 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
59b19c3c | 481 | option:-x 'EVENT'[,'EVENT']..., option:--exclude='EVENT'[,'EVENT']...:: |
e9b06e2b | 482 | Exclude events named 'EVENT' from the event rule. This option |
f69e7997 PP |
483 | can be used when the command's 'EVENT' argument contains at least |
484 | one wildcard star (`*`) to exclude specific names. 'EVENT' can also | |
485 | contain wildcard stars. To use a | |
486 | literal `,` character, use :esccomma:. | |
487 | Only available with the option:--userspace domain. | |
e9b06e2b | 488 | |
59b19c3c | 489 | option:-f 'EXPR', option:--filter='EXPR':: |
e9b06e2b PP |
490 | Add filter expression condition to the event rule. Expression 'EXPR' |
491 | must evaluate to true when executed against the dynamic values of | |
11613178 | 492 | event fields. See the <<filter-expr,Filter expression>> |
e9b06e2b PP |
493 | section above for more information. |
494 | ||
495 | ||
496 | Shortcuts | |
497 | ~~~~~~~~~ | |
498 | option:-a, option:--all:: | |
499 | Equivalent to an 'EVENT' argument named `*` (wildcard) when also | |
500 | using the option:--tracepoint (default) or option:--syscall option. | |
501 | ||
502 | ||
503 | include::common-cmd-help-options.txt[] | |
504 | ||
505 | ||
506 | include::common-cmd-footer.txt[] | |
507 | ||
508 | ||
509 | SEE ALSO | |
510 | -------- | |
7c1a4458 PP |
511 | man:lttng-disable-event(1), |
512 | man:lttng(1) |