Ubuntu Manpage: sd_event_set_watchdog, sd_event_get_watchdog

Provided by: libsystemd-dev_255.4-1ubuntu8.4_amd64

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