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LTTNG-ENABLE-EVENT(1)           LTTng Manual           LTTNG-ENABLE-EVENT(1)

NAME         top

       lttng-enable-event - Create or enable LTTng event rules

SYNOPSIS         top

       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]...)

DESCRIPTION         top

       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.

           Wildcard using the * character are supported at the end of
           tracepoint and system call names.

       ·   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.

           Wildcard using the * character are supported at the end of
           tracepoint names. When creating an event rule with a tracepoint
           name containing a wildcard, specific tracepoint names can be
           excluded from the match using 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
       Filter expressions 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.

       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 ("). Literal strings can
       contain a wildcard character (*) at the end to match more than one
       string. This wildcard can be escaped using \*.

       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

   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)

OPTIONS         top

       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 a wildcard (*)
           to exclude specific names. Only available with application
           domains.

       -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.

ENVIRONMENT VARIABLES         top

       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.

FILES         top

       $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.

EXIT STATUS         top

       0
           Success

       1
           Command error

       2
           Undefined command

       3
           Fatal error

       4
           Command warning (something went wrong during the command)

BUGS         top

       If you encounter any issue or usability problem, please report it on
       the LTTng bug tracker <https://bugs.lttng.org/projects/lttng-tools>.

RESOURCES         top

       ·   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

COPYRIGHTS         top

       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.

THANKS         top

       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.

AUTHORS         top

       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>.

SEE ALSO         top

       lttng-disable-event(1), lttng(1)

COLOPHON         top

       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 2017-04-25.  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 2.10.0-pre                 04/25/2017            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)