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LTTNG-ENABLE-EVENT(1) LTTng Manual LTTNG-ENABLE-EVENT(1)
lttng-enable-event - Create or enable LTTng event rules
Create or enable Linux kernel event rules:
lttng [GENERAL OPTIONS] enable-event --kernel
[--probe=SOURCE | --function=SOURCE | --syscall]
[--filter=EXPR] [--session=SESSION]
[--channel=CHANNEL] EVENT[,EVENT]...
Create or enable an "all" Linux kernel event rule:
lttng [GENERAL OPTIONS] enable-event --kernel --all [--syscall]
[--filter=EXPR] [--session=SESSION] [--channel=CHANNEL]
Create or enable application event rules:
lttng [GENERAL OPTIONS] enable-event
(--userspace | --jul | --log4j | --python)
[--filter=EXPR] [--exclude=EVENT[,EVENT]...]
[--loglevel=LOGLEVEL | --loglevel-only=LOGLEVEL]
[--session=SESSION] [--channel=CHANNEL] (--all | EVENT[,EVENT]...)
The lttng enable-event command can create a new event rule, or enable
one or more existing and disabled ones.
An event rule created by lttng enable-event is a set of conditions
that must be satisfied in order for an actual event to be emitted by
an LTTng tracer when the execution of an application or the Linux
kernel reaches an event source (tracepoint, system call, dynamic
probe). Event sources can be listed with the lttng-list(1) command.
The lttng-disable-event(1) command can be used to disable existing
event rules.
Event rules are always assigned to a channel when they are created.
If the --channel option is omitted, a default channel named channel0
is used (and created automatically if it does not exist for the
specified domain in the selected tracing session).
If the --session option is omitted, the chosen channel is picked from
the current tracing session.
Events can be enabled while tracing is active (use lttng-start(1) to
make a tracing session active).
Event source types
Four types of event sources are available in the Linux kernel tracing
domain (--kernel option):
Tracepoint (--tracepoint option; default)
A Linux kernel tracepoint, that is, a static instrumentation
point placed in the kernel source code. Standard tracepoints are
designed and placed in the source code by developers and record
useful payload fields.
Dynamic probe (--probe option)
A Linux kernel kprobe, that is, an instrumentation point placed
dynamically in the compiled kernel code. Dynamic probe events do
not record any payload field.
Function probe (--function option)
A Linux kernel kretprobe, that is, two instrumentation points
placed dynamically where a function is entered and where it
returns in the compiled kernel code. Function probe events do not
record any payload field.
System call (--syscall option)
A Linux kernel system call. Two instrumentation points are
statically placed where a system call function is entered and
where it returns in the compiled kernel code. System call event
sources record useful payload fields.
The application tracing domains (--userspace, --jul, --log4j, or
--python options) only support tracepoints. In the cases of the JUL,
Apache log4j, and Python domains, the event names correspond to
logger names.
Understanding event rule conditions
When creating an event rule with lttng enable-event, conditions are
specified using options. The logical conjunction (logical AND) of all
those conditions must be true when an event source is reached by an
application or by the Linux kernel in order for an actual event to be
emitted by an LTTng tracer.
Any condition that is not explicitly specified on creation is
considered a don’t care.
For example, consider the following commands:
$ lttng enable-event --userspace hello:world
$ lttng enable-event --userspace hello:world --loglevel=TRACE_INFO
Here, two event rules are created. The first one has a single
condition: the tracepoint name must match hello:world. The second one
has two conditions:
· The tracepoint name must match hello:world, and
· The tracepoint’s defined log level must be at least as severe as
the TRACE_INFO level.
In this case, the second event rule is pointless because the first
one is more general: it does not care about the tracepoint’s log
level. If an event source matching both event rules is reached by the
application’s execution, only one event is emitted.
The available conditions for the Linux kernel domain are:
· Tracepoint/system call name (EVENT argument with --tracepoint or
--syscall options) or dynamic probe/function name/address
(--probe or --function option’s argument) which must match event
source’s equivalent.
You can use * characters at any place in the tracepoint or system
call name as wildcards to match zero or more characters. To use a
literal * character, use \*.
· Filter expression (--filter option) executed against the dynamic
values of event fields at execution time that must evaluate to
true. See the Filter expression syntax section below for more
information.
The available conditions for the application domains are:
· Tracepoint name (EVENT with --tracepoint option) which must match
event source’s equivalent.
You can use * characters at any place in the tracepoint name as
wildcards to match zero or more characters. To use a literal *
character, use \*. When you create an event rule with a
tracepoint name containing a wildcard, you can exclude specific
tracepoint names from the match with the --exclude option.
· Filter expression (--filter option) executed against the dynamic
values of event fields at execution time that must evaluate to
true. See the Filter expression syntax section below for more
information.
· Event’s log level that must be at least as severe as a given log
level (--loglevel option) or match exactly a given log level
(--loglevel-only option).
When using lttng enable-event with a set of conditions that does not
currently exist for the chosen tracing session, domain, and channel,
a new event rule is created. Otherwise, the existing event rule is
enabled if it is currently disabled (see lttng-disable-event(1)).
The --all option can be used alongside the --tracepoint or --syscall
options. When this option is used, no EVENT argument must be
specified. This option defines a single event rule matching all the
possible events of a given tracing domain for the chosen channel and
tracing session. It is the equivalent of an EVENT argument named *
(wildcard).
Filter expression syntax
A filter expression can be specified with the --filter option when
creating a new event rule. If the filter expression evaluates to true
when executed against the dynamic values of an event’s fields when
tracing, the filtering condition passes.
Note
Make sure to single-quote the filter expression when running the
command from a shell, as filter expressions typically include
characters having a special meaning for most shells.
The filter expression syntax is very similar to C language
conditional expressions (expressions that can be evaluated by an if
statement).
The following logical operators are supported:
┌──────────────────────────┬────────┐
│Name │ Syntax │
├──────────────────────────┼────────┤
│ │ │
│Logical negation (NOT) │ !a │
├──────────────────────────┼────────┤
│ │ │
│Logical conjunction (AND) │ a && b │
├──────────────────────────┼────────┤
│ │ │
│Logical disjunction (OR) │ a || b │
└──────────────────────────┴────────┘
The following comparison operators/relational operators are
supported:
┌─────────────────────────┬────────┐
│Name │ Syntax │
├─────────────────────────┼────────┤
│ │ │
│Equal to │ a == b │
├─────────────────────────┼────────┤
│ │ │
│Not equal to │ a != b │
├─────────────────────────┼────────┤
│ │ │
│Greater than │ a > b │
├─────────────────────────┼────────┤
│ │ │
│Less than │ a < b │
├─────────────────────────┼────────┤
│ │ │
│Greater than or equal to │ a >= b │
├─────────────────────────┼────────┤
│ │ │
│Less than or equal to │ a <= b │
└─────────────────────────┴────────┘
The arithmetic and bitwise operators are NOT supported.
The precedence table of the operators above is the same as the one of
the C language. Parentheses are supported to bypass this.
The dynamic value of an event field is read by using its name as a C
identifier.
The dynamic value of a statically-known context field is read by
prefixing its name with $ctx.. Statically-known context fields are
context fields added to channels without the $app. prefix using the
lttng-add-context(1) command. $ctx.cpu_id is also available as the ID
of the CPU which emits the event.
The dynamic value of an application-specific context field is read by
prefixing its name with $app. (follows the format used to add such a
context field with the lttng-add-context(1) command).
When a comparison includes a non existent event field, the whole
filter expression evaluates to false (the event is discarded).
C integer and floating point number constants are supported, as well
as literal strings between double quotes ("). You can use *
characters at any place in a literal string as wildcards to match
zero or more characters. To use a literal * character, use \*.
LTTng-UST enumeration fields can be compared to integer values
(fields or constants).
Note
Although it is possible to filter the process ID of an event when
the pid context has been added to its channel using, for example,
$ctx.pid == 2832, it is recommended to use the PID tracker
instead, which is much more efficient (see lttng-track(1)).
Examples:
msg_id == 23 && size >= 2048
$ctx.procname == "lttng*" && (!flag || poel < 34)
$app.my_provider:my_context == 17.34e9 || some_enum >= 14
$ctx.cpu_id == 2 && filename != "*.log"
Log levels
Tracepoints and log statements in applications have an attached log
level. Application event rules can contain a log level condition.
With the --loglevel option, the event source’s log level must be at
least as severe as the option’s argument. With the --loglevel-only
option, the event source’s log level must match the option’s
argument.
The available log levels are:
User space domain (--userspace option)
Shortcuts such as system are allowed.
· TRACE_EMERG (0)
· TRACE_ALERT (1)
· TRACE_CRIT (2)
· TRACE_ERR (3)
· TRACE_WARNING (4)
· TRACE_NOTICE (5)
· TRACE_INFO (6)
· TRACE_DEBUG_SYSTEM (7)
· TRACE_DEBUG_PROGRAM (8)
· TRACE_DEBUG_PROCESS (9)
· TRACE_DEBUG_MODULE (10)
· TRACE_DEBUG_UNIT (11)
· TRACE_DEBUG_FUNCTION (12)
· TRACE_DEBUG_LINE (13)
· TRACE_DEBUG (14)
java.util.logging domain (--jul option)
Shortcuts such as severe are allowed.
· JUL_OFF (INT32_MAX)
· JUL_SEVERE (1000)
· JUL_WARNING (900)
· JUL_INFO (800)
· JUL_CONFIG (700)
· JUL_FINE (500)
· JUL_FINER (400)
· JUL_FINEST (300)
· JUL_ALL (INT32_MIN)
Apache log4j domain (--log4j option)
Shortcuts such as severe are allowed.
· LOG4J_OFF (INT32_MAX)
· LOG4J_FATAL (50000)
· LOG4J_ERROR (40000)
· LOG4J_WARN (30000)
· LOG4J_INFO (20000)
· LOG4J_DEBUG (10000)
· LOG4J_TRACE (5000)
· LOG4J_ALL (INT32_MIN)
Python domain (--python option)
Shortcuts such as critical are allowed.
· PYTHON_CRITICAL (50)
· PYTHON_ERROR (40)
· PYTHON_WARNING (30)
· PYTHON_INFO (20)
· PYTHON_DEBUG (10)
· PYTHON_NOTSET (0)
General options are described in lttng(1).
Domain
One of:
-j, --jul
Create or enable event rules in the java.util.logging (JUL)
domain.
-k, --kernel
Create or enable event rules in the Linux kernel domain.
-l, --log4j
Create or enable event rules in the Apache log4j domain.
-p, --python
Create or enable event rules in the Python domain.
-u, --userspace
Create or enable event rules in the user space domain.
Target
-c CHANNEL, --channel=CHANNEL
Create or enable event rules in the channel named CHANNEL instead
of the default channel name channel0.
-s SESSION, --session=SESSION
Create or enable event rules in the tracing session named SESSION
instead of the current tracing session.
Event source type
One of:
--function=SOURCE
Linux kernel kretprobe. Only available with the --kernel domain
option. SOURCE is one of:
· Function address (0x prefix supported)
· Function symbol
· Function symbol and offset (SYMBOL+OFFSET format)
--probe=SOURCE
Linux kernel kprobe. Only available with the --kernel domain
option. SOURCE is one of:
· Address (0x prefix supported)
· Symbol
· Symbol and offset (SYMBOL+OFFSET format)
--syscall
Linux kernel system call. Only available with the --kernel domain
option.
--tracepoint
Linux kernel or application tracepoint (default).
Log level
One of:
--loglevel=LOGLEVEL
Add log level condition to the event rule: the event source’s
defined log level must be at least as severe as LOGLEVEL. See the
Log levels section above for the available log levels. Only
available with application domains.
--loglevel-only=LOGLEVEL
Add log level condition to the event rule: the event source’s
defined log level must match LOGLEVEL. See the Log levels section
above for the available log levels. Only available with
application domains.
Filtering and exclusion
-x EVENT[,EVENT]..., --exclude=EVENT[,EVENT]...
Exclude events named EVENT from the event rule. This option can
be used when the command’s EVENT argument contains at least one
wildcard star (*) to exclude specific names. EVENT can also
contain wildcard stars. To use a literal , character, use \,.
Only available with the --userspace domain.
-f EXPR, --filter=EXPR
Add filter expression condition to the event rule. Expression
EXPR must evaluate to true when executed against the dynamic
values of event fields. See the Filter expression syntax section
above for more information.
Shortcuts
-a, --all
Equivalent to an EVENT argument named * (wildcard) when also
using the --tracepoint (default) or --syscall option.
Program information
-h, --help
Show command help.
This option, like lttng-help(1), attempts to launch /usr/bin/man
to view the command’s man page. The path to the man pager can be
overridden by the LTTNG_MAN_BIN_PATH environment variable.
--list-options
List available command options.
LTTNG_ABORT_ON_ERROR
Set to 1 to abort the process after the first error is
encountered.
LTTNG_HOME
Overrides the $HOME environment variable. Useful when the user
running the commands has a non-writable home directory.
LTTNG_MAN_BIN_PATH
Absolute path to the man pager to use for viewing help
information about LTTng commands (using lttng-help(1) or lttng
COMMAND --help).
LTTNG_SESSION_CONFIG_XSD_PATH
Path in which the session.xsd session configuration XML schema
may be found.
LTTNG_SESSIOND_PATH
Full session daemon binary path.
The --sessiond-path option has precedence over this environment
variable.
Note that the lttng-create(1) command can spawn an LTTng session
daemon automatically if none is running. See lttng-sessiond(8) for
the environment variables influencing the execution of the session
daemon.
$LTTNG_HOME/.lttngrc
User LTTng runtime configuration.
This is where the per-user current tracing session is stored
between executions of lttng(1). The current tracing session can
be set with lttng-set-session(1). See lttng-create(1) for more
information about tracing sessions.
$LTTNG_HOME/lttng-traces
Default output directory of LTTng traces. This can be overridden
with the --output option of the lttng-create(1) command.
$LTTNG_HOME/.lttng
User LTTng runtime and configuration directory.
$LTTNG_HOME/.lttng/sessions
Default location of saved user tracing sessions (see
lttng-save(1) and lttng-load(1)).
/usr/local/etc/lttng/sessions
System-wide location of saved tracing sessions (see lttng-save(1)
and lttng-load(1)).
Note
$LTTNG_HOME defaults to $HOME when not explicitly set.
0
Success
1
Command error
2
Undefined command
3
Fatal error
4
Command warning (something went wrong during the command)
If you encounter any issue or usability problem, please report it on
the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-tools>.
· LTTng project website <http://lttng.org>
· LTTng documentation <http://lttng.org/docs>
· Git repositories <http://git.lttng.org>
· GitHub organization <http://github.com/lttng>
· Continuous integration <http://ci.lttng.org/>
· Mailing list <http://lists.lttng.org> for support and
development: lttng-dev@lists.lttng.org
· IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net
This program is part of the LTTng-tools project.
LTTng-tools is distributed under the GNU General Public License
version 2 <http://www.gnu.org/licenses/old-licenses/gpl-2.0.en.html>.
See the LICENSE <https://github.com/lttng/lttng-
tools/blob/master/LICENSE> file for details.
Special thanks to Michel Dagenais and the DORSAL laboratory
<http://www.dorsal.polymtl.ca/> at École Polytechnique de Montréal
for the LTTng journey.
Also thanks to the Ericsson teams working on tracing which helped us
greatly with detailed bug reports and unusual test cases.
LTTng-tools was originally written by Mathieu Desnoyers, Julien
Desfossez, and David Goulet. More people have since contributed to
it.
LTTng-tools is currently maintained by Jérémie Galarneau
<mailto:jeremie.galarneau@efficios.com>.
lttng-disable-event(1), lttng(1)
This page is part of the LTTng-Tools ( LTTng tools) project.
Information about the project can be found at ⟨http://lttng.org/⟩.
It is not known how to report bugs for this man page; if you know,
please send a mail to man-pages@man7.org. This page was obtained
from the project's upstream Git repository
⟨git://git.lttng.org/lttng-tools.git⟩ on 2018-02-02. (At that time,
the date of the most recent commit that was found in the repository
was 2018-02-01.) If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-to-
date source for the page, or you have corrections or improvements to
the information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
LTTng 2.11.0-pre 02/02/2018 LTTNG-ENABLE-EVENT(1)
Pages that refer to this page: lttng(1), lttng-disable-event(1), lttng-enable-channel(1), lttng-track(1), lttng-ust(3), tracef(3), tracelog(3), babeltrace-filter.lttng-utils.debug-info(7)
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