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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_EVENT_SET_WATCHDOG(3) sd_event_set_watchdog SD_EVENT_SET_WATCHDOG(3)
sd_event_set_watchdog, sd_event_get_watchdog - Enable event loop
watchdog support
#include <systemd/sd-event.h>
int sd_event_set_watchdog(sd_event *event, int b);
int sd_event_get_watchdog(sd_event *event);
sd_event_set_watchdog() may be used to enable or disable automatic
watchdog notification support in the event loop object specified
in the event parameter. Specifically, depending on the b boolean
argument this will make sure the event loop wakes up in regular
intervals and sends watchdog notification messages to the service
manager, if this was requested by the service manager. Watchdog
support is determined with sd_watchdog_enabled(3), and watchdog
messages are sent with sd_notify(3). See the WatchdogSec= setting
in systemd.service(5) for details on how to enable watchdog
support for a service and the protocol used. The wake-up interval
is chosen as half the watchdog timeout declared by the service
manager via the $WATCHDOG_USEC environment variable. If the
service manager did not request watchdog notifications, or if the
process was not invoked by the service manager this call with a
true b parameter executes no operation. Passing a false b
parameter will disable the automatic sending of watchdog
notification messages if it was enabled before. Newly allocated
event loop objects have this feature disabled.
The first watchdog notification message is sent immediately when
sd_event_set_watchdog() is invoked with a true b parameter.
The watchdog logic is designed to allow the service manager to
automatically detect services that ceased processing of incoming
events, and thus appear "hung". Watchdog notifications are sent
out only at the beginning of each event loop iteration. If an
event source dispatch function blocks for an excessively long time
and does not return execution to the event loop quickly, this
might hence cause the notification message to be delayed, and
possibly result in abnormal program termination, as configured in
the service unit file.
sd_event_get_watchdog() may be used to determine whether watchdog
support was previously requested by a call to
sd_event_set_watchdog() with a true b parameter and successfully
enabled.
On success, sd_event_set_watchdog() and sd_event_get_watchdog()
return a non-zero positive integer if the service manager
requested watchdog support and watchdog support was successfully
enabled. They return zero if the service manager did not request
watchdog support, or if watchdog support was explicitly disabled
with a false b parameter. On failure, they return a negative
errno-style error code.
Errors
Returned errors may indicate the following problems:
-ECHILD
The event loop has been created in a different process,
library or module instance.
-EINVAL
The passed event loop object was invalid.
Functions described here are available as a shared library, which
can be compiled against and linked to with the
libsystemd pkg-config(1) file.
The code described here uses getenv(3), which is declared to be
not multi-thread-safe. This means that the code calling the
functions described here must not call setenv(3) from a parallel
thread. It is recommended to only do calls to setenv() from an
early phase of the program when no other threads have been
started.
sd_event_set_watchdog() and sd_event_get_watchdog() were added in
version 229.
systemd(1), sd-event(3), sd_event_new(3), sd_event_add_io(3),
sd_event_add_time(3), sd_event_add_signal(3),
sd_event_add_child(3), sd_event_add_inotify(3),
sd_event_add_defer(3), sd_watchdog_enabled(3), sd_notify(3),
systemd.service(5)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
[email protected]
systemd 258~rc2 SD_EVENT_SET_WATCHDOG(3)
Pages that refer to this page: sd-event(3), sd_watchdog_enabled(3), systemd.service(5), systemd.directives(7), systemd.index(7)
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HTML rendering created 2025-09-06 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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