+ <para>If the <varname>$WATCHDOG_USEC</varname>
+ environment variable is set, and the
+ <varname>$WATCHDOG_PID</varname> 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
+ <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ with a message string of
+ <literal>WATCHDOG=1</literal>.</para>
+