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¶

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.

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.

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.

Added in version 209.

$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.