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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | ENVIRONMENT | FILES | EXAMPLES | RESOURCES | COPYRIGHT | THANKS | SEE ALSO | COLOPHON |
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LTTNG-ADD-TRIGGER(1) LTTng Manual LTTNG-ADD-TRIGGER(1)
lttng-add-trigger - Add an LTTng trigger
lttng [GENERAL OPTIONS] add-trigger [--name=NAME] [--owner-uid=UID]
--condition=CONDTYPE [CONDARGS]
--action=ACTTYPE [ACTARGS] [--action=ACTTYPE [ACTARGS]]...
The lttng add-trigger command creates and adds an LTTng trigger to
the connected session daemon (see lttng-sessiond(8)).
See lttng-concepts(7) to learn more about LTTng triggers.
By default, the add-trigger command automatically assigns a name,
unique for a given session daemon and Unix user, to the added
trigger. Assign a custom name with the --name.
The add-trigger command adds a trigger for your Unix user. If your
Unix user is root, you may add the trigger as another user with
the --owner-uid option.
Specify the condition of the trigger to add with a condition
specifier and its actions with one or more action specifiers. The
order of the action specifiers is significant: LTTng attempts to
execute the actions of a firing trigger in this order.
See the “EXAMPLES” section below for usage examples.
List the triggers of your Unix user, or of all users if your Unix
user is root, with the lttng-list-triggers(1) command.
Remove a trigger with the lttng-remove-trigger(1) command.
Condition specifier
Synopsis:
--condition=CONDTYPE [CONDARGS]
A condition specifier is the --condition option, which specifies
the type of condition CONDTYPE, followed, depending on CONDTYPE,
with zero or more arguments CONDARGS.
The available condition types are:
channel-buffer-usage-ge, channel-buffer-usage-le
Synopses:
--condition=channel-buffer-usage-ge --session=SESSION
--channel=CHANNEL
--domain=(kernel | user | jul | log4j | log4j2 | python)
(--threshold-ratio=RATIO | --threshold-size=SIZE)
--condition=channel-buffer-usage-le --session=SESSION
--channel=CHANNEL
--domain=(kernel | user | jul | log4j | log4j2 | python)
(--threshold-ratio=RATIO | --threshold-size=SIZE)
A channel-buffer-usage-ge or channel-buffer-usage-le condition
is considered satisfied when the ring buffer usage of the
channel CHANNEL (within the recording session SESSION and the
tracing domain specified by --domain) becomes greater/less
than or equal to either:
With the --threshold-size=SIZE option
SIZE bytes.
SIZE supports the k (KiB), M (MiB), and G (GiB) suffixes.
With the --threshold-ratio=RATIO option
RATIO times the total size of the ring buffer of the
targeted channel.
RATIO is a floating point number from 0 to 1.
Every time the monitor timer (see the --monitor-timer option
of lttng-enable-channel(1)) of a channel expires, LTTng
updates its statistics, including its buffer usage. This is
when LTTng tries to evaluate channel-buffer-usage-ge and
channel-buffer-usage-le conditions.
The short options -c, -d, -s, and -t are aliases of --channel,
--domain, --session, and --threshold-size.
event-rule-matches
Synopsis:
--condition=event-rule-matches [--capture=CDESCR]... ERSPEC
An event-rule-matches condition is considered satisfied when
the event rule specified with ERSPEC matches an event.
See lttng-event-rule(7) to learn how to specify an event rule
(ERSPEC part).
Capture event record and context fields with one or more
--capture options (see the “Capture descriptor” section below
to learn more). When an event-rule-matches condition with
capture descriptors is satisfied, the captured field values
are available in the evaluation object of the condition using
the liblttng-ctl C API.
Important
Make sure to single-quote CDESCR when you run the add-
trigger command from a shell, as capture descriptors can
include characters having a special meaning for most
shells.
session-consumed-size-ge
Synopsis:
--condition=session-consumed-size-ge --session=SESSION
--threshold-size=THRESHOLD
A session-consumed-size-ge condition is considered satisfied
when the total consumed size of the tracing data of all the
channels of the recording session SESSION becomes greater than
or equal to THRESHOLD bytes.
Every time the monitor timer (see the --monitor-timer option
of lttng-enable-channel(1)) of a channel expires, LTTng
updates the statistics, like the total consumed tracing data
size, of its owning recording session. This is when LTTng
tries to evaluate session-consumed-size-ge conditions.
THRESHOLD supports the k (KiB), M (MiB), and G (GiB) suffixes.
The short options -s and -t are aliases of --session and
--threshold-size.
session-rotation-starts, session-rotation-finishes
Synopses:
--condition=session-rotation-starts --session=SESSION
--condition=session-rotation-finishes --session=SESSION
A session-rotation-starts or session-rotation-finishes
condition is considered satisfied when the rotation operation
(see lttng-rotate(1)) of the recording session SESSION starts
or finishes.
The short option -s is an alias of --session.
Capture descriptor
A capture descriptor is a textual expression which describes how
to read an event record or context field.
The argument of a --capture option, when using an “event rule
matches” condition specifier (event-rule-matches), is a capture
descriptor.
A capture descriptor expression is one of:
NAME
An event record field named NAME.
The supported event record field types are:
• Integer
• Enumeration (integral value)
• Floating point number
• Static array of integers
• Dynamic array (“sequence”) of integers
• Text string
Examples: my_field, target_cpu, ip.
$ctx.NAME
A statically-known context field named NAME.
List the available statically-known context field names with
lttng-add-context(1). As of LTTng 2.15.1, context field names
starting with perf: aren’t supported.
Examples: $ctx.prio, $ctx.gid, $ctx.preemptible.
$app.PROVIDER.NAME
An application-specific context field named NAME from the
provider PROVIDER.
See lttng-add-context(1) to learn more about
application-specific context fields.
Example: $app.server:cur_user.
EXPR[INDEX]
The element at index INDEX of the array field (static or
dynamic) identified by the expression EXPR.
INDEX must be a constant, positive integral value.
Examples: ip[3], user_ids[15].
If, when an event rule matches, a given capture descriptor doesn’t
identify an existing event or context field, then the captured
value is reported as being unavailable. This applies to:
• A nonexistent event record field name.
• A nonexistent statically-known context field name.
• A nonexistent application-specific context field name.
• An out-of-bounds array field index.
Action specifier
Synopsis:
--action=ACTTYPE [ACTARGS]
An action specifier is the --action option, which specifies the
type of action ACTTYPE, followed, depending on ACTTYPE, with zero
or more arguments ACTARGS.
The available action types are:
Notify
Synopsis:
--action=notify [--rate-policy=POLICY]
Sends a notification through the notification mechanism of the
session daemon (see lttng-sessiond(8)).
The session daemon sends details about the condition
evaluation along with the notification.
As of LTTng 2.15.1, you can write a C/C++ program to receive
LTTng notifications (see the liblttng-ctl C headers).
See below for the --rate-policy option.
Start a recording session
Synopsis:
--action=start-session SESSION [--rate-policy=POLICY]
Starts the recording session named SESSION like lttng-start(1)
would.
If no recording session has the name SESSION when LTTng is
ready to execute the action, LTTng does nothing.
See below for the --rate-policy option.
Stop a recording session
Synopsis:
--action=stop-session SESSION [--rate-policy=POLICY]
Stops the recording session named SESSION like lttng-stop(1)
would.
If no recording session has the name SESSION when LTTng is
ready to execute the action, LTTng does nothing.
See below for the --rate-policy option.
Rotate a recording session
Synopsis:
--action=rotate-session SESSION [--rate-policy=POLICY]
Archives the current trace chunk of the recording session
named SESSION like lttng-rotate(1) would.
If no recording session has the name SESSION when LTTng is
ready to execute the action, LTTng does nothing.
See below for the --rate-policy option.
Take a recording session snapshot
Synopsis:
--action=snapshot-session SESSION [--name=NAME]
[--max-size=SIZE]
[--path=PATH | --url=URL |
(--ctrl-url=URL --data-url=URL)]
[--rate-policy=POLICY]
Takes a snapshot of the recording session named SESSION like
lttng-snapshot(1) would.
When the condition of the trigger is satisfied, the recording
session named SESSION, if any, must be a snapshot-mode
recording session (see lttng-create(1)).
If no recording session has the name SESSION when LTTng is
ready to execute the action, LTTng does nothing.
See the add-output action of the lttng-snapshot(1) command to
learn about the snapshot output options: --name/-n, --max-
size/-m, --url, --ctrl-url/-C, and --data-url/-D. The --path
option specifies to write the snapshot to the local
directory PATH.
See below for the --rate-policy option.
Common action options (as of LTTng 2.15.1):
--rate-policy=POLICY
Set the rate policy of the action to POLICY instead of every:1
(always execute).
A trigger which “fires” (its condition is satisfied) leads to
an execution request for each of its actions, in order. An
execution request of a given action A first increments the
execution request count C of A. An execution request can then
become an actual execution when C satisfies the rate policy
of A.
POLICY is one of:
once-after:COUNT
Only execute A when C is equal to COUNT.
In other words, execute A a single time after COUNT
execution requests.
every:COUNT
Only execute A when C is a multiple of COUNT.
In other words, execute A every COUNT execution requests.
COUNT must be an integer greater than 0.
As of LTTng 2.15.1, you can use this option with any action
type, but new action types in the future may not support it.
Identification
--name=NAME
Set the unique name of the trigger to add to NAME instead of
the add-trigger command automatically assigning one.
--owner-uid=UID
Add the trigger as the Unix user having the user ID UID.
You may only use this option if your Unix user is root.
Specifier
--condition=CONDTYPE
Introductory option for a condition specifier of type
CONDTYPE.
See the “Condition specifier” section above to learn more.
--action=ACTTYPE
Introductory option for an action specifier of type ACTTYPE.
See the “Action specifier” section above to learn more.
Program information
-h, --help
Show help.
This option attempts to launch /usr/bin/man to view this
manual page. Override the manual pager path with the
LTTNG_MAN_BIN_PATH environment variable.
--list-options
List available command options and quit.
0
Success
1
Command error
2
Undefined command
3
Fatal error
4
Command warning (something went wrong during the command)
LTTNG_ABORT_ON_ERROR
Set to 1 to abort the process after the first error is
encountered.
LTTNG_HOME
Path to the LTTng home directory.
Defaults to $HOME.
Useful when the Unix user running the commands has a
non-writable home directory.
LTTNG_LIST_LEGACY
Set to 1 to use the legacy output format (LTTng 2.14 and
earlier) for the lttng-list(1) command instead of the modern
output format.
Note that the legacy output doesn’t show anything related to
features introduced after LTTng 2.14.
LTTNG_MAN_BIN_PATH
Absolute path to the manual pager to use to read the LTTng
command-line help (with lttng-help(1) or with the --help
option) instead of /usr/bin/man.
LTTNG_NO_UTF_8
Set to 1 to NOT emit multi-byte UTF-8 sequences, even if the
locale claims to support it.
LTTNG_SESSION_CONFIG_XSD_PATH
Path to the directory containing the session.xsd recording
session configuration XML schema.
LTTNG_SESSIOND_PATH
Absolute path to the LTTng session daemon binary (see
lttng-sessiond(8)) to spawn from the lttng-create(1) command.
The --sessiond-path general option overrides this environment
variable.
LTTNG_TERM_COLOR
Controls when to emit terminal SGR codes in the output.
The NO_COLOR environment variable overrides this.
One of:
auto (default)
Only emit SGR codes when the standard output is connected
to a color-capable terminal.
always
Always emit SGR codes.
never
Never emit SGR codes.
NO_COLOR
If set and not empty, then it’s equivalent to setting
LTTNG_TERM_COLOR to never.
See NO_COLOR <https://no-color.org/> to learn more.
$LTTNG_HOME/.lttngrc
Unix user’s LTTng runtime configuration.
This is where LTTng stores the name of the Unix user’s current
recording session between executions of lttng(1).
lttng-create(1) and lttng-set-session(1) set the current
recording session.
$LTTNG_HOME/lttng-traces
Default output directory of LTTng traces in local and snapshot
modes.
Override this path with the --output option of the
lttng-create(1) command.
$LTTNG_HOME/.lttng
Unix user’s LTTng runtime and configuration directory.
$LTTNG_HOME/.lttng/sessions
Default directory containing the Unix user’s saved recording
session configurations (see lttng-save(1) and lttng-load(1)).
/usr/local/etc/lttng/sessions
Directory containing the system-wide saved recording session
configurations (see lttng-save(1) and lttng-load(1)).
Note
$LTTNG_HOME defaults to the value of the HOME environment
variable.
Example 1. Add an “event rule matches” trigger of which the action
is to send a notification.
The event-rule-matches trigger condition below specifies an
event rule which matches any Linux system call entry event
with a name starting with exec.
$ lttng add-trigger --condition=event-rule-matches \
--type=syscall:entry \
--name='exec*' --action=notify
Example 2. Add an “event rule matches” trigger of which the action
is to stop a recording session and then rotate it.
The event-rule-matches trigger condition below specifies an
event rule which matches any user space tracepoint event with
a name starting with my_app: and with a log level at least as
severe as a warning.
The order of the --action options below is significant.
$ lttng add-trigger --condition=event-rule-matches \
--type=user --name='my_app:*' \
--log-level=TRACE_WARNING.. \
--action=stop-session my-session \
--action=rotate-session my-session
See lttng-concepts(7) to learn more about recording sessions
and rotations.
Example 3. Add an “event rule matches” trigger with a specific
name.
The event-rule-matches trigger condition below specifies an
event rule which matches events which LTTng creates from the
my-logger Python logger.
The added trigger is named my-trigger, a unique name for your
Unix user.
See the --name option.
$ lttng add-trigger --name=my-trigger \
--condition=event-rule-matches \
--type=python --name=my-logger \
--action=snapshot-session my-session
Example 4. Add an “event rule matches” trigger as another Unix
user.
The command line below adds a trigger as the mireille Unix
user.
Your Unix user must be root to use the --owner-uid option.
The condition of the trigger specifies an event rule which
matches LTTng kernel tracepoint events with a name which
starts with sched.
# lttng add-trigger --owner-uid=$(id --user mireille) \
--condition=event-rule-matches \
--type=kernel --name='sched*' \
--action=notify
Example 5. Add an “event rule matches” trigger with a notification
action to be executed every 10 times.
The event-rule-matches trigger condition below specifies an
event rule which matches all user space tracepoint events.
See the --rate-policy option above.
$ lttng add-trigger --condition=event-rule-matches \
--type=user --action=notify \
--rate-policy=every:10
Example 6. Add an “event rule matches” trigger with a recording
session starting action to be executed a single time after
40 times.
The event-rule-matches trigger condition below specifies an
event rule which matches any Linux system call event (entry
and exit) of which the fd event record field is less than 3.
See the --rate-policy option above.
$ lttng add-trigger --condition=event-rule-matches \
--type=syscall --filter='fd < 3' \
--action=start-session my-session \
--rate-policy=once-after:40
Example 7. Add a “recording session consumed data size becomes
greater than” trigger of which the action is to rotate the
recording session.
The session-consumed-size-ge trigger condition below is
considered satisfied when the total consumed size of the
recording session named my-session becomes greater than or
equal to 100 MiB.
$ lttng add-trigger --condition=session-consumed-size-ge \
--session=my-session --threshold-size=100M \
--action=rotate-session my-session
See lttng-concepts(7) to learn more about recording sessions
and rotations.
Example 8. Add a “channel buffer usage becomes greater than or
equal to” trigger of which the actions are to send a notification
and to rotate the recording session.
The channel-buffer-usage-ge trigger condition below is
considered satisfied when the ring buffer usage of the Linux
kernel channel named my-channel within the recording session
named my-session becomes greater than or equal to 512 KiB.
The order of the --action options below is significant.
$ lttng add-trigger --condition=channel-buffer-usage-ge \
--session=my-session --channel=my-channel \
--domain=kernel --threshold-size=512k \
--action=notify \
--action=rotate-session my-session
See lttng-concepts(7) to learn more about recording sessions,
channels, and rotations.
Example 9. Add a “recording session rotation finishes” trigger of
which the action is to send a notification.
The session-rotation-finishes trigger condition below is
considered satisfied when a rotation of the recording session
named my-session finishes.
$ lttng add-trigger --condition=session-rotation-finishes \
--session=my-session --action=notify
See lttng-concepts(7) to learn more about recording sessions
and rotations.
• LTTng project website <https://lttng.org>
• LTTng documentation <https://lttng.org/docs>
• LTTng bug tracker <https://bugs.lttng.org>
• Git repositories <https://git.lttng.org>
• GitHub organization <https://github.com/lttng>
• Continuous integration <https://ci.lttng.org/>
• Mailing list <https://lists.lttng.org/> for support and
development: lttng-dev@lists.lttng.org
• IRC channel <irc://irc.oftc.net/lttng>: #lttng on irc.oftc.net
• Mastodon <https://mastodon.social/@lttng>
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(1), lttng-list-triggers(1), lttng-remove-trigger(1),
lttng-concepts(7)
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
⟨https://github.com/lttng/lttng-tools.git⟩ on 2026-08-04. (At
that time, the date of the most recent commit that was found in
the repository was 2026-07-30.) 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 2.15.1 9 December 2025 LTTNG-ADD-TRIGGER(1)
Pages that refer to this page: lttng(1), lttng-list-triggers(1), lttng-remove-trigger(1), lttng-rotate(1), lttng-snapshot(1), lttng-start(1), lttng-stop(1), lttng-concepts(7), lttng-event-rule(7)
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HTML rendering created 2026-09-09 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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