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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] | |
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']... | |
19 | ||
20 | Create or enable an "all" Linux kernel event rule: | |
21 | ||
22 | [verse] | |
23 | *lttng* ['GENERAL OPTIONS'] *enable-event* option:--kernel option:--all [option:--syscall] | |
24 | [option:--filter='EXPR'] [option:--session='SESSION'] [option:--channel='CHANNEL'] | |
25 | ||
26 | Create or enable application event rules: | |
27 | ||
28 | [verse] | |
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']...) | |
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). | |
45 | Event sources can be listed with the linklttng:lttng-list(1) command. | |
46 | ||
47 | The linklttng:lttng-disable-event(1) command can be used to disable | |
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 | |
59 | (use linklttng:lttng-start(1) to make a tracing session active). | |
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 | ||
109 | ---------------------------------------------------------------- | |
110 | lttng enable-event --userspace hello:world | |
111 | lttng enable-event --userspace hello:world --loglevel=TRACE_INFO | |
112 | ---------------------------------------------------------------- | |
113 | ||
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 | |
116 | conditions: | |
117 | ||
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. | |
121 | ||
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. | |
126 | ||
127 | The available conditions for the Linux kernel domain are: | |
128 | ||
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. | |
134 | + | |
135 | Wildcard using the `*` character are supported _at the end_ of | |
136 | tracepoint and system call names. | |
137 | ||
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. | |
142 | ||
143 | The available conditions for the application domains are: | |
144 | ||
145 | * Tracepoint name ('EVENT' with option:--tracepoint option) which must | |
146 | match event source's equivalent. | |
147 | + | |
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. | |
152 | ||
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). | |
160 | ||
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)). | |
166 | ||
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). | |
173 | ||
174 | ||
175 | [[filter-syntax]] | |
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. | |
182 | ||
183 | The filter expression syntax is very similar to C language conditional | |
184 | expressions (expressions that can be evaluated by an `if` statement). | |
185 | ||
186 | The following logical operators are supported: | |
187 | ||
188 | [width="40%",options="header"] | |
189 | |===================================== | |
190 | | Name | Syntax | |
191 | | Logical negation (NOT) | `!a` | |
192 | | Logical conjunction (AND) | `a && b` | |
193 | | Logical disjunction (OR) | `a \|\| b` | |
194 | |===================================== | |
195 | ||
196 | The following comparison operators/relational operators are supported: | |
197 | ||
198 | [width="40%",options="header"] | |
199 | |==================================== | |
200 | | Name | Syntax | |
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 | |==================================== | |
208 | ||
209 | The arithmetic and bitwise operators are :not: supported. | |
210 | ||
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. | |
213 | ||
214 | The dynamic value of an event field is read by using its name as | |
215 | a C identifier. | |
216 | ||
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. | |
221 | ||
222 | The dynamic value of an application-specific context field is read by | |
223 | prefixing its name with `$app.` (follows the format used to add such a | |
224 | context field with the linklttng:lttng-add-context(1) command). | |
225 | ||
226 | When a comparison includes a non existent event field, the whole filter | |
227 | expression evaluates to false (the event is discarded). | |
228 | ||
229 | C integer and floating point number constants are supported, as well as | |
230 | literal strings between double quotes (`"`). Literal strings can contain | |
231 | a wildcard character (`*`) at the end to match more than one string. | |
232 | This wildcard can be escaped using `\\*`. | |
233 | ||
234 | LTTng-UST enumeration fields can be compared to integer values (fields | |
235 | or constants). | |
236 | ||
237 | NOTE: Although it is possible to filter the process ID of an event when | |
238 | the `pid` context has been added to its channel using, for example, | |
239 | `$ctx.pid == 2832`, it is recommended to use the PID tracker instead, | |
240 | which is much more efficient (see linklttng:lttng-track(1)). | |
241 | ||
242 | Examples: | |
243 | ||
244 | ---------------------------- | |
245 | msg_id == 23 && size >= 2048 | |
246 | ---------------------------- | |
247 | ||
248 | ------------------------------------------------- | |
249 | $ctx.procname == "lttng*" && (!flag || poel < 34) | |
250 | ------------------------------------------------- | |
251 | ||
252 | --------------------------------------------------------- | |
253 | $app.my_provider:my_context == 17.34e9 || some_enum >= 14 | |
254 | --------------------------------------------------------- | |
255 | ||
256 | ||
257 | [[log-levels]] | |
258 | Log levels | |
259 | ~~~~~~~~~~ | |
260 | Tracepoints and log statements in applications have an attached log | |
261 | level. Application event rules can contain a _log level_ condition. | |
262 | ||
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. | |
267 | ||
268 | The available log levels are: | |
269 | ||
270 | User space domain (option:--userspace option):: | |
271 | Shortcuts such as `system` are allowed. | |
272 | + | |
273 | * `TRACE_EMERG` (0) | |
274 | * `TRACE_ALERT` (1) | |
275 | * `TRACE_CRIT` (2) | |
276 | * `TRACE_ERR` (3) | |
277 | * `TRACE_WARNING` (4) | |
278 | * `TRACE_NOTICE` (5) | |
279 | * `TRACE_INFO` (6) | |
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) | |
287 | * `TRACE_DEBUG` (14) | |
288 | ||
289 | `java.util.logging` domain (option:--jul option):: | |
290 | Shortcuts such as `severe` are allowed. | |
291 | + | |
292 | * `JUL_OFF` (`INT32_MAX`) | |
293 | * `JUL_SEVERE` (1000) | |
294 | * `JUL_WARNING` (900) | |
295 | * `JUL_INFO` (800) | |
296 | * `JUL_CONFIG` (700) | |
297 | * `JUL_FINE` (500) | |
298 | * `JUL_FINER` (400) | |
299 | * `JUL_FINEST` (300) | |
300 | * `JUL_ALL` (`INT32_MIN`) | |
301 | ||
302 | Apache log4j domain (option:--log4j option):: | |
303 | Shortcuts such as `severe` are allowed. | |
304 | + | |
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`) | |
313 | ||
314 | Python domain (option:--python option):: | |
315 | Shortcuts such as `critical` are allowed. | |
316 | + | |
317 | * `PYTHON_CRITICAL` (50) | |
318 | * `PYTHON_ERROR` (40) | |
319 | * `PYTHON_WARNING` (30) | |
320 | * `PYTHON_INFO` (20) | |
321 | * `PYTHON_DEBUG` (10) | |
322 | * `PYTHON_NOTSET` (0) | |
323 | ||
324 | ||
325 | include::common-cmd-options-head.txt[] | |
326 | ||
327 | ||
328 | Domain | |
329 | ~~~~~~ | |
330 | One of: | |
331 | ||
332 | option:-j, option:--jul:: | |
333 | Create or enable event rules in the `java.util.logging` | |
334 | (JUL) domain. | |
335 | ||
336 | option:-k, option:--kernel:: | |
337 | Create or enable event rules in the Linux kernel domain. | |
338 | ||
339 | option:-l, option:--log4j:: | |
340 | Create or enable event rules in the Apache log4j domain. | |
341 | ||
342 | option:-p, option:--python:: | |
343 | Create or enable event rules in the Python domain. | |
344 | ||
345 | option:-u, option:--userspace:: | |
346 | Create or enable event rules in the user space domain. | |
347 | ||
348 | ||
349 | Target | |
350 | ~~~~~~ | |
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`. | |
354 | ||
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. | |
358 | ||
359 | ||
360 | Event source type | |
361 | ~~~~~~~~~~~~~~~~~ | |
362 | One of: | |
363 | ||
364 | option:--function='SOURCE':: | |
365 | Linux kernel kretprobe. Only available with the option:--kernel | |
366 | domain option. 'SOURCE' is one of: | |
367 | + | |
368 | * Function address (`0x` prefix supported) | |
369 | * Function symbol | |
370 | * Function symbol and offset (`SYMBOL+OFFSET` format) | |
371 | ||
372 | option:--probe='SOURCE':: | |
373 | Linux kernel kprobe. Only available with the option:--kernel | |
374 | domain option. 'SOURCE' is one of: | |
375 | + | |
376 | * Address (`0x` prefix supported) | |
377 | * Symbol | |
378 | * Symbol and offset (`SYMBOL+OFFSET` format) | |
379 | ||
380 | option:--syscall:: | |
381 | Linux kernel system call. Only available with the option:--kernel | |
382 | domain option. | |
383 | ||
384 | option:--tracepoint:: | |
385 | Linux kernel or application tracepoint (default). | |
386 | ||
387 | ||
388 | Log level | |
389 | ~~~~~~~~~ | |
390 | One of: | |
391 | ||
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. | |
397 | ||
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. | |
403 | ||
404 | ||
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 | |
411 | domains. | |
412 | ||
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. | |
418 | ||
419 | ||
420 | Shortcuts | |
421 | ~~~~~~~~~ | |
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. | |
425 | ||
426 | ||
427 | include::common-cmd-help-options.txt[] | |
428 | ||
429 | ||
430 | include::common-cmd-footer.txt[] | |
431 | ||
432 | ||
433 | SEE ALSO | |
434 | -------- | |
435 | linklttng:lttng-disable-event(1), | |
436 | linklttng:lttng(1) |