xenial (3) sd_watchdog_enabled.3.gz

Provided by: libsystemd-dev_229-4ubuntu21.31_amd64 bug

NAME
       sd_watchdog_enabled - Check whether the service manager expects watchdog keep-alive notifications from a
       service


SYNOPSIS
       #include <systemd/sd-daemon.h>

       int sd_watchdog_enabled(int unset_environment, uint64_t *usec);


DESCRIPTION
       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.


RETURN VALUE
       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.


NOTES
       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.


ENVIRONMENT
       $WATCHDOG_PID
           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.

       $WATCHDOG_USEC
           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.


HISTORY
       The watchdog functionality and the $WATCHDOG_USEC variable were added in systemd-41.

       sd_watchdog_enabled() function was added in systemd-209. Since that version, the $WATCHDOG_PID variable
       is also set.


SEE ALSO
       systemd(1), sd-daemon(3), daemon(7), systemd.service(5), sd_notify(3), sd_event_set_watchdog(3)