int sd_watchdog_enabled(int unset_environment, uint64_t *usec);
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.
Internally, this function 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.