invocation. This variable is only supported with
sd_pid_notify_with_fds().
+ WATCHDOG_USEC=...
+ Reset watchdog_usec value during runtime.
+ To reset watchdog_usec value, start the service again.
+ Example: "WATCHDOG_USEC=20000000"
+
Daemons can choose to send additional variables. However, it is
recommended to prefix variable names not listed above with X_.