NAME
sd_watchdog_enabled - Check whether the service manager expects watchdog keep-alive notifications from a service
SYNOPSIS
#include <systemd/sd-daemon.h>
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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.
Added in version 209.
HISTORY
sd_watchdog_enabled() was added in version 209.
SEE ALSO
systemd(1), sd-daemon(3), daemon(7), systemd.service(5), sd_notify(3), sd_event_set_watchdog(3)