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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 |
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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 |
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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). |
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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:. | |
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139 | |
140 | * Filter expression (option:--filter option) executed against the | |
141 | dynamic values of event fields at execution time that must evaluate | |
142 | to true. See the <<filter-syntax,Filter expression syntax>> section | |
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 | |
158 | to true. See the <<filter-syntax,Filter expression syntax>> section | |
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)). |
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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 | ||
178 | [[filter-syntax]] | |
179 | Filter expression syntax | |
180 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
181 | Filter expressions can be specified with the option:--filter option | |
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. | |
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 | ||
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190 | The filter expression syntax is very similar to C language conditional |
191 | expressions (expressions that can be evaluated by an `if` statement). | |
192 | ||
193 | The following logical operators are supported: | |
194 | ||
195 | [width="40%",options="header"] | |
196 | |===================================== | |
197 | | Name | Syntax | |
198 | | Logical negation (NOT) | `!a` | |
199 | | Logical conjunction (AND) | `a && b` | |
200 | | Logical disjunction (OR) | `a \|\| b` | |
201 | |===================================== | |
202 | ||
203 | The following comparison operators/relational operators are supported: | |
204 | ||
205 | [width="40%",options="header"] | |
206 | |==================================== | |
207 | | Name | Syntax | |
208 | | Equal to | `a == b` | |
209 | | Not equal to | `a != b` | |
210 | | Greater than | `a > b` | |
211 | | Less than | `a < b` | |
212 | | Greater than or equal to | `a >= b` | |
213 | | Less than or equal to | `a <= b` | |
214 | |==================================== | |
215 | ||
216 | The arithmetic and bitwise operators are :not: supported. | |
217 | ||
218 | The precedence table of the operators above is the same as the one of | |
219 | the C language. Parentheses are supported to bypass this. | |
220 | ||
221 | The dynamic value of an event field is read by using its name as | |
222 | a C identifier. | |
223 | ||
224 | The dynamic value of a statically-known context field is read by | |
225 | prefixing its name with `$ctx.`. Statically-known context fields are | |
226 | context fields added to channels without the `$app.` prefix using the | |
7c1a4458 | 227 | man:lttng-add-context(1) command. |
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228 | |
229 | The dynamic value of an application-specific context field is read by | |
230 | prefixing its name with `$app.` (follows the format used to add such a | |
7c1a4458 | 231 | context field with the man:lttng-add-context(1) command). |
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232 | |
233 | When a comparison includes a non existent event field, the whole filter | |
234 | expression evaluates to false (the event is discarded). | |
235 | ||
236 | C integer and floating point number constants are supported, as well as | |
f69e7997 PP |
237 | literal strings between double quotes (`"`). You can use `*` characters |
238 | at any place in a literal string as wildcards to match zero or more | |
239 | characters. To use a literal `*` character, use :escwc:. | |
e9b06e2b PP |
240 | |
241 | LTTng-UST enumeration fields can be compared to integer values (fields | |
242 | or constants). | |
243 | ||
244 | NOTE: Although it is possible to filter the process ID of an event when | |
245 | the `pid` context has been added to its channel using, for example, | |
246 | `$ctx.pid == 2832`, it is recommended to use the PID tracker instead, | |
7c1a4458 | 247 | which is much more efficient (see man:lttng-track(1)). |
e9b06e2b PP |
248 | |
249 | Examples: | |
250 | ||
251 | ---------------------------- | |
252 | msg_id == 23 && size >= 2048 | |
253 | ---------------------------- | |
254 | ||
255 | ------------------------------------------------- | |
256 | $ctx.procname == "lttng*" && (!flag || poel < 34) | |
257 | ------------------------------------------------- | |
258 | ||
259 | --------------------------------------------------------- | |
260 | $app.my_provider:my_context == 17.34e9 || some_enum >= 14 | |
261 | --------------------------------------------------------- | |
262 | ||
f69e7997 PP |
263 | ------------------- |
264 | filename != "*.log" | |
265 | ------------------- | |
266 | ||
e9b06e2b PP |
267 | |
268 | [[log-levels]] | |
269 | Log levels | |
270 | ~~~~~~~~~~ | |
271 | Tracepoints and log statements in applications have an attached log | |
272 | level. Application event rules can contain a _log level_ condition. | |
273 | ||
274 | With the option:--loglevel option, the event source's log level must | |
275 | be at least as severe as the option's argument. With the | |
276 | option:--loglevel-only option, the event source's log level must match | |
277 | the option's argument. | |
278 | ||
279 | The available log levels are: | |
280 | ||
281 | User space domain (option:--userspace option):: | |
282 | Shortcuts such as `system` are allowed. | |
283 | + | |
284 | * `TRACE_EMERG` (0) | |
285 | * `TRACE_ALERT` (1) | |
286 | * `TRACE_CRIT` (2) | |
287 | * `TRACE_ERR` (3) | |
288 | * `TRACE_WARNING` (4) | |
289 | * `TRACE_NOTICE` (5) | |
290 | * `TRACE_INFO` (6) | |
291 | * `TRACE_DEBUG_SYSTEM` (7) | |
292 | * `TRACE_DEBUG_PROGRAM` (8) | |
293 | * `TRACE_DEBUG_PROCESS` (9) | |
294 | * `TRACE_DEBUG_MODULE` (10) | |
295 | * `TRACE_DEBUG_UNIT` (11) | |
296 | * `TRACE_DEBUG_FUNCTION` (12) | |
297 | * `TRACE_DEBUG_LINE` (13) | |
298 | * `TRACE_DEBUG` (14) | |
299 | ||
300 | `java.util.logging` domain (option:--jul option):: | |
301 | Shortcuts such as `severe` are allowed. | |
302 | + | |
303 | * `JUL_OFF` (`INT32_MAX`) | |
304 | * `JUL_SEVERE` (1000) | |
305 | * `JUL_WARNING` (900) | |
306 | * `JUL_INFO` (800) | |
307 | * `JUL_CONFIG` (700) | |
308 | * `JUL_FINE` (500) | |
309 | * `JUL_FINER` (400) | |
310 | * `JUL_FINEST` (300) | |
311 | * `JUL_ALL` (`INT32_MIN`) | |
312 | ||
313 | Apache log4j domain (option:--log4j option):: | |
314 | Shortcuts such as `severe` are allowed. | |
315 | + | |
316 | * `LOG4J_OFF` (`INT32_MAX`) | |
317 | * `LOG4J_FATAL` (50000) | |
318 | * `LOG4J_ERROR` (40000) | |
319 | * `LOG4J_WARN` (30000) | |
320 | * `LOG4J_INFO` (20000) | |
321 | * `LOG4J_DEBUG` (10000) | |
322 | * `LOG4J_TRACE` (5000) | |
323 | * `LOG4J_ALL` (`INT32_MIN`) | |
324 | ||
325 | Python domain (option:--python option):: | |
326 | Shortcuts such as `critical` are allowed. | |
327 | + | |
328 | * `PYTHON_CRITICAL` (50) | |
329 | * `PYTHON_ERROR` (40) | |
330 | * `PYTHON_WARNING` (30) | |
331 | * `PYTHON_INFO` (20) | |
332 | * `PYTHON_DEBUG` (10) | |
333 | * `PYTHON_NOTSET` (0) | |
334 | ||
335 | ||
336 | include::common-cmd-options-head.txt[] | |
337 | ||
338 | ||
339 | Domain | |
340 | ~~~~~~ | |
341 | One of: | |
342 | ||
343 | option:-j, option:--jul:: | |
344 | Create or enable event rules in the `java.util.logging` | |
345 | (JUL) domain. | |
346 | ||
347 | option:-k, option:--kernel:: | |
348 | Create or enable event rules in the Linux kernel domain. | |
349 | ||
350 | option:-l, option:--log4j:: | |
351 | Create or enable event rules in the Apache log4j domain. | |
352 | ||
353 | option:-p, option:--python:: | |
354 | Create or enable event rules in the Python domain. | |
355 | ||
356 | option:-u, option:--userspace:: | |
357 | Create or enable event rules in the user space domain. | |
358 | ||
359 | ||
360 | Target | |
361 | ~~~~~~ | |
59b19c3c | 362 | option:-c 'CHANNEL', option:--channel='CHANNEL':: |
e9b06e2b PP |
363 | Create or enable event rules in the channel named 'CHANNEL' instead |
364 | of the default channel name `channel0`. | |
365 | ||
59b19c3c | 366 | option:-s 'SESSION', option:--session='SESSION':: |
e9b06e2b PP |
367 | Create or enable event rules in the tracing session named 'SESSION' |
368 | instead of the current tracing session. | |
369 | ||
370 | ||
371 | Event source type | |
372 | ~~~~~~~~~~~~~~~~~ | |
373 | One of: | |
374 | ||
375 | option:--function='SOURCE':: | |
376 | Linux kernel kretprobe. Only available with the option:--kernel | |
377 | domain option. 'SOURCE' is one of: | |
378 | + | |
379 | * Function address (`0x` prefix supported) | |
380 | * Function symbol | |
381 | * Function symbol and offset (`SYMBOL+OFFSET` format) | |
382 | ||
383 | option:--probe='SOURCE':: | |
384 | Linux kernel kprobe. Only available with the option:--kernel | |
385 | domain option. 'SOURCE' is one of: | |
386 | + | |
387 | * Address (`0x` prefix supported) | |
388 | * Symbol | |
389 | * Symbol and offset (`SYMBOL+OFFSET` format) | |
390 | ||
391 | option:--syscall:: | |
392 | Linux kernel system call. Only available with the option:--kernel | |
393 | domain option. | |
394 | ||
395 | option:--tracepoint:: | |
396 | Linux kernel or application tracepoint (default). | |
397 | ||
398 | ||
399 | Log level | |
400 | ~~~~~~~~~ | |
401 | One of: | |
402 | ||
403 | option:--loglevel='LOGLEVEL':: | |
404 | Add log level condition to the event rule: the event source's | |
405 | defined log level must be at least as severe as 'LOGLEVEL'. | |
406 | See the <<log-levels,Log levels>> section above for the available | |
407 | log levels. Only available with application domains. | |
408 | ||
409 | option:--loglevel-only='LOGLEVEL':: | |
410 | Add log level condition to the event rule: the event source's | |
411 | defined log level must match 'LOGLEVEL'. See the | |
412 | <<log-levels,Log levels>> section above for the available log | |
413 | levels. Only available with application domains. | |
414 | ||
415 | ||
416 | Filtering and exclusion | |
417 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
59b19c3c | 418 | option:-x 'EVENT'[,'EVENT']..., option:--exclude='EVENT'[,'EVENT']...:: |
e9b06e2b | 419 | Exclude events named 'EVENT' from the event rule. This option |
f69e7997 PP |
420 | can be used when the command's 'EVENT' argument contains at least |
421 | one wildcard star (`*`) to exclude specific names. 'EVENT' can also | |
422 | contain wildcard stars. To use a | |
423 | literal `,` character, use :esccomma:. | |
424 | Only available with the option:--userspace domain. | |
e9b06e2b | 425 | |
59b19c3c | 426 | option:-f 'EXPR', option:--filter='EXPR':: |
e9b06e2b PP |
427 | Add filter expression condition to the event rule. Expression 'EXPR' |
428 | must evaluate to true when executed against the dynamic values of | |
429 | event fields. See the <<filter-syntax,Filter expression syntax>> | |
430 | section above for more information. | |
431 | ||
432 | ||
433 | Shortcuts | |
434 | ~~~~~~~~~ | |
435 | option:-a, option:--all:: | |
436 | Equivalent to an 'EVENT' argument named `*` (wildcard) when also | |
437 | using the option:--tracepoint (default) or option:--syscall option. | |
438 | ||
439 | ||
440 | include::common-cmd-help-options.txt[] | |
441 | ||
442 | ||
443 | include::common-cmd-footer.txt[] | |
444 | ||
445 | ||
446 | SEE ALSO | |
447 | -------- | |
7c1a4458 PP |
448 | man:lttng-disable-event(1), |
449 | man:lttng(1) |