sd_event_set_watchdog(3) — Linux manual page

SD_EVENT_SET_WATCHDOG(3)  sd_event_set_watchdog SD_EVENT_SET_WATCHDOG(3)

NAME

       sd_event_set_watchdog, sd_event_get_watchdog - Enable event loop
       watchdog support

SYNOPSIS

       #include <systemd/sd-event.h>

       int sd_event_set_watchdog(sd_event *event, int b);

       int sd_event_get_watchdog(sd_event *event);

DESCRIPTION

       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.

RETURN VALUE

       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.

NOTES

       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.

HISTORY

       sd_event_set_watchdog() and sd_event_get_watchdog() were added in
       version 229.

SEE ALSO

       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)

COLOPHON

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       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 2024-06-14.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2024-06-13.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

systemd 257~devel                               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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