sd_watchdog_enabled man page
sd_watchdog_enabled — Check whether the service manager expects watchdog keep-alive notifications from a service
int sd_watchdog_enabled(int unset_environment, uint64_t *usec);
sd_watchdog_enabled() may be called by a service to detect whether the service manager expects regular keep-alive watchdog notification events from it, and the timeout after which the manager will act on the service if it did not get such a notification.
If the $WATCHDOG_USEC environment variable is set, and the $WATCHDOG_PID variable is unset or set to the PID of the current process, the service manager expects notifications from this process. The manager will usually terminate a service when it does not get a notification message within the specified time after startup and after each previous message. It is recommended that a daemon sends a keep-alive notification message to the service manager every half of the time returned here. Notification messages may be sent with sd_notify(3) with a message string of "WATCHDOG=1".
If the unset_environment parameter is non-zero, sd_watchdog_enabled() will unset the $WATCHDOG_USEC and $WATCHDOG_PID environment variables before returning (regardless of whether the function call itself succeeded or not). Those variables are no longer inherited by child processes. Further calls to sd_watchdog_enabled() will also return with zero.
If the usec parameter is non-NULL, sd_watchdog_enabled() will write the timeout in µs for the watchdog logic to it.
To enable service supervision with the watchdog logic, use WatchdogSec= in service files. See systemd.service(5) for details.
Use sd_event_set_watchdog(3) to enable automatic watchdog support in sd-event(3)-based event loops.
On failure, this call returns a negative errno-style error code. If the service manager expects watchdog keep-alive notification messages to be sent, > 0 is returned, otherwise 0 is returned. Only if the return value is > 0, the usec parameter is valid after the call.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.
Internally, this functions parses the $WATCHDOG_PID and $WATCHDOG_USEC environment variable. The call will ignore these variables if $WATCHDOG_PID does not contain the PID of the current process, under the assumption that in that case, the variables were set for a different process further up the process tree.
Set by the system manager for supervised process for which watchdog support is enabled, and contains the PID of that process. See above for details.
Set by the system manager for supervised process for which watchdog support is enabled, and contains the watchdog timeout in µs See above for details.
systemd(1), sd-daemon(3), daemon(7), systemd.service(5), sd_notify(3), sd_event_set_watchdog(3)
sd-daemon(3), sd_event_set_watchdog(3), sd_notify(3), systemd.directives(7), systemd.exec(5), systemd.index(7), systemd.service(5).