lttng-enable-event.1.txt: document dynamic user space probes
[lttng-tools.git] / doc / man / lttng-enable-event.1.txt
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1lttng-enable-event(1)
2=====================
3
4
5NAME
6----
7lttng-enable-event - Create or enable LTTng event rules
8
9
10SYNOPSIS
11--------
12Create 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:--userspace-probe='SOURCE']
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18 [option:--filter='EXPR'] [option:--session='SESSION']
19 [option:--channel='CHANNEL'] 'EVENT'[,'EVENT']...
20
21Create or enable an "all" Linux kernel event rule:
22
23[verse]
ce19b9ed 24*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event* option:--kernel option:--all [option:--syscall]
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25 [option:--filter='EXPR'] [option:--session='SESSION'] [option:--channel='CHANNEL']
26
b981f450 27Create or enable application/library event rules:
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28
29[verse]
ce19b9ed 30*lttng* ['linkgenoptions:(GENERAL OPTIONS)'] *enable-event*
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31 (option:--userspace | option:--jul | option:--log4j | option:--python)
32 [option:--filter='EXPR'] [option:--exclude='EVENT'[,'EVENT']...]
33 [option:--loglevel='LOGLEVEL' | option:--loglevel-only='LOGLEVEL']
34 [option:--session='SESSION'] [option:--channel='CHANNEL'] (option:--all | 'EVENT'[,'EVENT']...)
35
36
37DESCRIPTION
38-----------
39The `lttng enable-event` command can create a new event rule, or enable
40one or more existing and disabled ones.
41
42An event rule created by `lttng enable-event` is a set of conditions
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43that must be satisfied in order for an actual event to be emitted by an
44LTTng tracer when the execution of an application or a library or the
45Linux kernel reaches an event source (tracepoint, system call, dynamic
46probe). Event sources can be listed with the man:lttng-list(1) command.
e9b06e2b 47
7c1a4458 48The man:lttng-disable-event(1) command can be used to disable
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49existing event rules.
50
51Event rules are always assigned to a channel when they are created. If
52the option:--channel option is omitted, a default channel named
53`channel0` is used (and created automatically if it does not exist for
54the specified domain in the selected tracing session).
55
56If the option:--session option is omitted, the chosen channel is picked
57from the current tracing session.
58
59Events can be enabled while tracing is active
7c1a4458 60(use man:lttng-start(1) to make a tracing session active).
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61
62
63Event source types
64~~~~~~~~~~~~~~~~~~
b981f450 65Five types of event sources are available in the Linux kernel tracing
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66domain (option:--kernel option):
67
68Tracepoint (option:--tracepoint option; default)::
69 A Linux kernel tracepoint, that is, a static instrumentation point
70 placed in the kernel source code. Standard tracepoints are designed
71 and placed in the source code by developers and record useful
72 payload fields.
73
b981f450 74Dynamic kernel probe (option:--probe option)::
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75 A Linux kernel kprobe, that is, an instrumentation point placed
76 dynamically in the compiled kernel code. Dynamic probe events do not
77 record any payload field.
78
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79Dynamic user space probe (option:--userspace-probe option)::
80 A Linux kernel uprobe, that is, an instrumentation point placed
81 dynamically in the compiled user space application/library through
82 the kernel. Dynamic user space probe events do not record any
83 payload field.
84+
85See the <<userspace-probe,Dynamic user space probes>> section for more
86information.
87
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88Function probe (option:--function option)::
89 A Linux kernel kretprobe, that is, two instrumentation points placed
90 dynamically where a function is entered and where it returns in the
91 compiled kernel code. Function probe events do not record any
92 payload field.
93
94System call (option:--syscall option)::
95 A Linux kernel system call. Two instrumentation points are
96 statically placed where a system call function is entered and where
97 it returns in the compiled kernel code. System call event sources
98 record useful payload fields.
99
100The application tracing domains (option:--userspace, option:--jul,
101option:--log4j, or option:--python options) only support tracepoints.
102In the cases of the JUL, Apache log4j, and Python domains, the event
103names correspond to _logger_ names.
104
105
106Understanding event rule conditions
107~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
108When creating an event rule with `lttng enable-event`, conditions are
109specified using options. The logical conjunction (logical AND) of all
110those conditions must be true when an event source is reached by an
111application or by the Linux kernel in order for an actual event
112to be emitted by an LTTng tracer.
113
114Any condition that is not explicitly specified on creation is considered
115a _don't care_.
116
117For example, consider the following commands:
118
d4f093aa 119[role="term"]
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120----
121$ lttng enable-event --userspace hello:world
122$ lttng enable-event --userspace hello:world --loglevel=TRACE_INFO
123----
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124
125Here, two event rules are created. The first one has a single condition:
126the tracepoint name must match `hello:world`. The second one has two
127conditions:
128
129* The tracepoint name must match `hello:world`, _and_
130* The tracepoint's defined log level must be at least as severe as
131 the `TRACE_INFO` level.
132
133In this case, the second event rule is pointless because the first one
134is more general: it does not care about the tracepoint's log level.
135If an event source matching both event rules is reached by the
136application's execution, only one event is emitted.
137
138The available conditions for the Linux kernel domain are:
139
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140* Tracepoint/system call name ('EVENT' argument with option:--tracepoint
141 or option:--syscall options) or dynamic probe/function name/address
142 (option:--probe, option:--userspace-probe, and option:--function
143 option's argument) which must match event source's equivalent.
e9b06e2b 144+
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145You can use `*` characters at any place in the tracepoint or system
146call name as wildcards to match zero or more characters. To use a
147literal `*` character, use :escwc:.
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148
149* Filter expression (option:--filter option) executed against the
150 dynamic values of event fields at execution time that must evaluate
11613178 151 to true. See the <<filter-expr,Filter expression>> section
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152 below for more information.
153
154The available conditions for the application domains are:
155
156* Tracepoint name ('EVENT' with option:--tracepoint option) which must
157 match event source's equivalent.
158+
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159You can use `*` characters at any place in the tracepoint name as
160wildcards to match zero or more characters. To use a literal `*`
161character, use :escwc:. When you create an event rule with a tracepoint
162name containing a wildcard, you can exclude specific tracepoint names
163from the match with the option:--exclude option.
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164
165* Filter expression (option:--filter option) executed against the
166 dynamic values of event fields at execution time that must evaluate
11613178 167 to true. See the <<filter-expr,Filter expression>> section
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168 below for more information.
169* Event's log level that must be at least as severe as a given
170 log level (option:--loglevel option) or match exactly a given log
171 level (option:--loglevel-only option).
172
173When using `lttng enable-event` with a set of conditions that does not
174currently exist for the chosen tracing session, domain, and channel,
175a new event rule is created. Otherwise, the existing event rule is
176enabled if it is currently disabled
7c1a4458 177(see man:lttng-disable-event(1)).
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178
179The option:--all option can be used alongside the option:--tracepoint
180or option:--syscall options. When this option is used, no 'EVENT'
181argument must be specified. This option defines a single event rule
182matching _all_ the possible events of a given tracing domain for the
183chosen channel and tracing session. It is the equivalent of an 'EVENT'
184argument named `*` (wildcard).
185
186
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187[[filter-expr]]
188Filter expression
189~~~~~~~~~~~~~~~~~
c52365cc 190A filter expression can be specified with the option:--filter option
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191when creating a new event rule. If the filter expression evaluates
192to true when executed against the dynamic values of an event's fields
193when tracing, the filtering condition passes.
e9b06e2b 194
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195NOTE: Make sure to **single-quote** the filter expression when running
196the command from a shell, as filter expressions typically include
197characters having a special meaning for most shells.
198
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199The filter expression syntax is similar to C language conditional
200expressions (expressions that can be evaluated by an `if` statement),
201albeit with a few differences:
e9b06e2b 202
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203* C integer and floating point number constants are supported, as well
204 as literal strings between double quotes (`"`). You can use `*`
205 characters at any place in a literal string as wildcards to match zero
206 or more characters. To use a literal `*` character, use :escwc:.
207+
208Examples: `32`, `-0x17`, `0755`, `12.34`,
209+"a :escbs:"literal string:escbs:""+, `"src/*/*.h"`.
e9b06e2b 210
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211* The dynamic value of an event field is read by using its name as a C
212 identifier.
213+
214The dot and square bracket notations are available, like in the C
215language, to access nested structure and array/sequence fields.
216Only a constant, positive integer number can be used within square
217brackets. If the index is out of bounds, the whole filter expression
218evaluates to false (the event is discarded).
219+
220An enumeration field's value is an integer.
221+
222When the expression's field does not exist, the whole filter expression
223evaluates to false.
224+
225Examples: `my_field`, `target_cpu`, `seq[7]`, `msg.user[1].data[2][17]`.
e9b06e2b 226
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227* The dynamic value of a statically-known context field is read by
228 prefixing its name with `$ctx.`. Statically-known context fields are
229 context fields added to channels without the `$app.` prefix using the
230 man:lttng-add-context(1) command.
231+
232When the expression's statically-known context field does not exist,
233the whole filter expression evaluates to false.
234+
235Examples: `$ctx.prio`, `$ctx.preemptible`,
236`$ctx.perf:cpu:stalled-cycles-frontend`.
e9b06e2b 237
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238* The dynamic value of an application-specific context field is read by
239 prefixing its name with `$app.` (follows the format used to add such a
240 context field with the man:lttng-add-context(1) command).
241+
242When the expression's application-specific context field does not exist,
243the whole filter expression evaluates to false.
244+
245Example: `$app.server:cur_user`.
246
247The following precedence table shows the operators which are supported
248in a filter expression. In this table, the highest precedence is 1.
249Parentheses are supported to bypass the default order.
250
251IMPORTANT: Unlike the C language, the `lttng enable-event` filter
252expression syntax's bitwise AND and OR operators (`&` and `|`) take
253precedence over relational operators (`<`, `<=`, `>`, `>=`, `==`, and
254`!=`). This means the filter expression `2 & 2 == 2` is true while the
255equivalent C expression is false.
256
257[options="header"]
258|===
259|Precedence |Operator |Description |Associativity
260|1 |`-` |Unary minus |Right-to-left
261|1 |`+` |Unary plus |Right-to-left
262|1 |`!` |Logical NOT |Right-to-left
263|1 |`~` |Bitwise NOT |Right-to-left
264|2 |`<<` |Bitwise left shift |Left-to-right
265|2 |`>>` |Bitwise right shift |Left-to-right
266|3 |`&` |Bitwise AND |Left-to-right
267|4 |`^` |Bitwise XOR |Left-to-right
268|5 |`\|` |Bitwise OR |Left-to-right
269|6 |`<` |Less than |Left-to-right
270|6 |`<=` |Less than or equal to |Left-to-right
271|6 |`>` |Greater than |Left-to-right
272|6 |`>=` |Greater than or equal to |Left-to-right
273|7 |`==` |Equal to |Left-to-right
274|7 |`!=` |Not equal to |Left-to-right
275|8 |`&&` |Logical AND |Left-to-right
276|9 |`\|\|` |Logical OR |Left-to-right
277|===
278
279The arithmetic operators are :not: supported.
280
281All integer constants and fields are first casted to signed 64-bit
282integers. The representation of negative integers is two's complement.
283This means that, for example, the signed 8-bit integer field 0xff (-1)
284becomes 0xffffffffffffffff (still -1) once casted.
285
286Before a bitwise operator is applied, all its operands are casted to
287unsigned 64-bit integers, and the result is casted back to a signed
28864-bit integer. For the bitwise NOT operator, it is the equivalent of
289this C expression:
290
291[source,c]
292----
293(int64_t) ~((uint64_t) val)
294----
e9b06e2b 295
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296For the binary bitwise operators, it is the equivalent of those C
297expressions:
e9b06e2b 298
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299[source,c]
300----
301(int64_t) ((uint64_t) lhs >> (uint64_t) rhs)
302(int64_t) ((uint64_t) lhs << (uint64_t) rhs)
303(int64_t) ((uint64_t) lhs & (uint64_t) rhs)
304(int64_t) ((uint64_t) lhs ^ (uint64_t) rhs)
305(int64_t) ((uint64_t) lhs | (uint64_t) rhs)
306----
e9b06e2b 307
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308If the right-hand side of a bitwise shift operator (`<<` and `>>`) is
309not in the [0,{nbsp}63] range, the whole filter expression evaluates to
310false.
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311
312NOTE: Although it is possible to filter the process ID of an event when
313the `pid` context has been added to its channel using, for example,
314`$ctx.pid == 2832`, it is recommended to use the PID tracker instead,
7c1a4458 315which is much more efficient (see man:lttng-track(1)).
e9b06e2b 316
11613178 317Filter expression examples:
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318
319----------------------------
320msg_id == 23 && size >= 2048
321----------------------------
322
323-------------------------------------------------
324$ctx.procname == "lttng*" && (!flag || poel < 34)
325-------------------------------------------------
326
327---------------------------------------------------------
328$app.my_provider:my_context == 17.34e9 || some_enum >= 14
329---------------------------------------------------------
330
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331---------------------------------------
332$ctx.cpu_id == 2 && filename != "*.log"
333---------------------------------------
f69e7997 334
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335------------------------------------------------
336eax_reg & 0xff7 == 0x240 && x[4] >> 12 <= 0x1234
337------------------------------------------------
338
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339
340[[log-levels]]
341Log levels
342~~~~~~~~~~
343Tracepoints and log statements in applications have an attached log
344level. Application event rules can contain a _log level_ condition.
345
346With the option:--loglevel option, the event source's log level must
347be at least as severe as the option's argument. With the
348option:--loglevel-only option, the event source's log level must match
349the option's argument.
350
351The available log levels are:
352
353User space domain (option:--userspace option)::
354 Shortcuts such as `system` are allowed.
355+
356* `TRACE_EMERG` (0)
357* `TRACE_ALERT` (1)
358* `TRACE_CRIT` (2)
359* `TRACE_ERR` (3)
360* `TRACE_WARNING` (4)
361* `TRACE_NOTICE` (5)
362* `TRACE_INFO` (6)
363* `TRACE_DEBUG_SYSTEM` (7)
364* `TRACE_DEBUG_PROGRAM` (8)
365* `TRACE_DEBUG_PROCESS` (9)
366* `TRACE_DEBUG_MODULE` (10)
367* `TRACE_DEBUG_UNIT` (11)
368* `TRACE_DEBUG_FUNCTION` (12)
369* `TRACE_DEBUG_LINE` (13)
370* `TRACE_DEBUG` (14)
371
372`java.util.logging` domain (option:--jul option)::
373 Shortcuts such as `severe` are allowed.
374+
375* `JUL_OFF` (`INT32_MAX`)
376* `JUL_SEVERE` (1000)
377* `JUL_WARNING` (900)
378* `JUL_INFO` (800)
379* `JUL_CONFIG` (700)
380* `JUL_FINE` (500)
381* `JUL_FINER` (400)
382* `JUL_FINEST` (300)
383* `JUL_ALL` (`INT32_MIN`)
384
385Apache log4j domain (option:--log4j option)::
386 Shortcuts such as `severe` are allowed.
387+
388* `LOG4J_OFF` (`INT32_MAX`)
389* `LOG4J_FATAL` (50000)
390* `LOG4J_ERROR` (40000)
391* `LOG4J_WARN` (30000)
392* `LOG4J_INFO` (20000)
393* `LOG4J_DEBUG` (10000)
394* `LOG4J_TRACE` (5000)
395* `LOG4J_ALL` (`INT32_MIN`)
396
397Python domain (option:--python option)::
398 Shortcuts such as `critical` are allowed.
399+
400* `PYTHON_CRITICAL` (50)
401* `PYTHON_ERROR` (40)
402* `PYTHON_WARNING` (30)
403* `PYTHON_INFO` (20)
404* `PYTHON_DEBUG` (10)
405* `PYTHON_NOTSET` (0)
406
407
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408[[userspace-probe]]
409Dynamic user space probes
410~~~~~~~~~~~~~~~~~~~~~~~~~
411With the option:--userspace-probe option, you can instrument function
412entries of any user space binary (application or library) using either
413an available symbol name or a SystemTap SDT probe's provider and probe
414names.
415
416The option:--userspace-probe option must be specified with the
417option:--kernel option because it uses Linux's uprobe feature to
418dynamically instrument a user space application or library.
419
420As of this version, dynamic probe events do not record any payload
421field.
422
423The two available option:--userspace-probe option's argument formats
424are:
425
426option:--userspace-probe=`[elf:]PATH:SYMBOL`::
427 Dynamically instrument an available symbol within a user space
428 executable.
429+
430--
431'PATH'::
432 Application or library path.
433+
434This can be:
435+
436* An absolute path.
437* A relative path.
438* An executable's name as found in the directories listed in the
439 `PATH` environment variable.
440
441'SYMBOL'::
442 Symbol name of the function of which to instrument the entry.
443+
444This can be any defined code symbol listed by the man:nm(1) command
445(including with its nloption:--dynamic option which lists dynamic
446symbols).
447--
448+
449As of this version, not specifying `elf:` is equivalent to specifying
450it.
451+
452Examples:
453+
454* `--userspace-probe=/usr/lib/libc.so.6:malloc`
455* `--userspace-probe=./myapp:createUser`
456* `--userspace-probe=httpd:ap_run_open_htaccess`
457
458option:--userspace-probe=`sdt:PATH:PROVIDER:NAME`::
459 Dynamically instrument an SDT probe within a user space executable.
460+
461--
462'PATH'::
463 Application or library path.
464+
465This can be:
466+
467* An absolute path.
468* A relative path.
469* An executable's name as found in the directories listed in the
470 `PATH` environment variable.
471
472__PROVIDER__:__NAME__::
473 SDT provider and probe names.
474+
475For example, with the following SDT probe:
476+
477[source,c]
478----
479DTRACE_PROBE2("server", "accept_request",
480 request_id, ip_addr);
481----
482+
483The provider/probe name pair is `server:accept_request`.
484--
485+
486Example:
487+
488* `--userspace-probe=sdt:./build/server:server:accept_request`
489
490
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491include::common-cmd-options-head.txt[]
492
493
494Domain
495~~~~~~
496One of:
497
498option:-j, option:--jul::
499 Create or enable event rules in the `java.util.logging`
500 (JUL) domain.
501
502option:-k, option:--kernel::
503 Create or enable event rules in the Linux kernel domain.
504
505option:-l, option:--log4j::
506 Create or enable event rules in the Apache log4j domain.
507
508option:-p, option:--python::
509 Create or enable event rules in the Python domain.
510
511option:-u, option:--userspace::
512 Create or enable event rules in the user space domain.
513
514
515Target
516~~~~~~
59b19c3c 517option:-c 'CHANNEL', option:--channel='CHANNEL'::
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518 Create or enable event rules in the channel named 'CHANNEL' instead
519 of the default channel name `channel0`.
520
59b19c3c 521option:-s 'SESSION', option:--session='SESSION'::
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522 Create or enable event rules in the tracing session named 'SESSION'
523 instead of the current tracing session.
524
525
526Event source type
527~~~~~~~~~~~~~~~~~
528One of:
529
530option:--function='SOURCE'::
531 Linux kernel kretprobe. Only available with the option:--kernel
532 domain option. 'SOURCE' is one of:
533+
534* Function address (`0x` prefix supported)
535* Function symbol
536* Function symbol and offset (`SYMBOL+OFFSET` format)
537
538option:--probe='SOURCE'::
539 Linux kernel kprobe. Only available with the option:--kernel
540 domain option. 'SOURCE' is one of:
541+
542* Address (`0x` prefix supported)
543* Symbol
544* Symbol and offset (`SYMBOL+OFFSET` format)
545
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546option:--userspace-probe='SOURCE'::
547 Linux kernel uprobe. Only available with the option:--kernel
548 domain option.
549+
550See the <<userspace-probe,Dynamic user space probes>> section for more
551information about the option's argument 'SOURCE'.
552
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553option:--syscall::
554 Linux kernel system call. Only available with the option:--kernel
555 domain option.
556
557option:--tracepoint::
558 Linux kernel or application tracepoint (default).
559
560
561Log level
562~~~~~~~~~
563One of:
564
565option:--loglevel='LOGLEVEL'::
566 Add log level condition to the event rule: the event source's
567 defined log level must be at least as severe as 'LOGLEVEL'.
568 See the <<log-levels,Log levels>> section above for the available
569 log levels. Only available with application domains.
570
571option:--loglevel-only='LOGLEVEL'::
572 Add log level condition to the event rule: the event source's
573 defined log level must match 'LOGLEVEL'. See the
574 <<log-levels,Log levels>> section above for the available log
575 levels. Only available with application domains.
576
577
578Filtering and exclusion
579~~~~~~~~~~~~~~~~~~~~~~~
59b19c3c 580option:-x 'EVENT'[,'EVENT']..., option:--exclude='EVENT'[,'EVENT']...::
e9b06e2b 581 Exclude events named 'EVENT' from the event rule. This option
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582 can be used when the command's 'EVENT' argument contains at least
583 one wildcard star (`*`) to exclude specific names. 'EVENT' can also
584 contain wildcard stars. To use a
585 literal `,` character, use :esccomma:.
586 Only available with the option:--userspace domain.
e9b06e2b 587
59b19c3c 588option:-f 'EXPR', option:--filter='EXPR'::
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589 Add filter expression condition to the event rule. Expression 'EXPR'
590 must evaluate to true when executed against the dynamic values of
11613178 591 event fields. See the <<filter-expr,Filter expression>>
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592 section above for more information.
593
594
595Shortcuts
596~~~~~~~~~
597option:-a, option:--all::
598 Equivalent to an 'EVENT' argument named `*` (wildcard) when also
599 using the option:--tracepoint (default) or option:--syscall option.
600
601
602include::common-cmd-help-options.txt[]
603
604
605include::common-cmd-footer.txt[]
606
607
608SEE ALSO
609--------
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610man:lttng-disable-event(1),
611man:lttng(1)
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