systemd Developer Lennart Poettering lennart@poettering.net sd_watchdog_enabled 3 sd_watchdog_enabled Check whether the service manager expects watchdog keep-alive notifications from a service #include <systemd/sd-daemon.h> int sd_watchdog_enabled int unset_environment const 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 unset_environment parameter is non-zero, sd_watchdog_enabled() will unset the $WATCHDOG_USEC and $WATCHDOG_PID environment variables before returning (regardless whether the function call itself succeeded or not). Further calls to sd_watchdog_enabled() will then return with zero, but the variable is no longer inherited by child processes. If the usec parameter is non-NULL sd_watchdog_enabled() will return the timeout in µs for the watchdog logic. The service manager will usually terminate a service when it did 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_notify3 with a message string of WATCHDOG=1. To enable service supervision with the watchdog logic use WatchdogSec= in service files. See systemd.service5 for details. 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. This function is provided by the reference implementation of APIs for new-style daemons and distributed with the systemd package. The algorithm it implements is simple, and can easily be reimplemented in daemons if it is important to support this interface without using the reference implementation. Internally, this functions parses the $WATCHDOG_PID and $WATCHDOG_USEC environment variable. The call will ignore these variables if $WATCHDOG_PID does containe 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. For details about the algorithm check the liberally licensed reference implementation sources: and sd_watchdog_enabled() is implemented in the reference implementation's sd-daemon.c and sd-daemon.h files. These interfaces are available as shared library, which can be compiled and linked to with the libsystemd-daemon pkg-config1 file. Alternatively, applications consuming these APIs may copy the implementation into their source tree. For more details about the reference implementation see sd-daemon3. If the reference implementation is used as drop-in files and -DDISABLE_SYSTEMD is set during compilation, these functions will always return 0 and otherwise become a NOP. $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. systemd1, sd-daemon3, daemon7, systemd.service5, sd_notify3