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
set_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.
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
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systemd 233 SD_EVENT_SET_WATCHDOG(3)