The watchdog directive configures Heartbeat to use a watchdog device. In some circumstances, a watchdog device can be used in place of a STONITH device. In any case, it is a reasonable thing to configure if you don't have a STONITH device, or if you wish, in addition to your STONITH device.
It is the purpose of a watchdog device to shut the machine down if Heartbeat does not hear its own heartbeats as often as it thinks it should. This keeps things like scheduler bugs from becoming split-brain configurations.
The general syntax of a watchdog directive is:
A sample watchdog directive is shown below:
The most common watchdog device currently used with general Linux systems is the softdog device. The softdog device is a software-based watchdog device and is usually referred to as /dev/watchdog - although like most UNIX devices, this is a convention not a rule.
Heartbeat tries to set the watchdog device to reboot the system at the next second after it would declare itself dead.
It also tries to ensure that if it is shut down gracefully, that it will keep the system from rebooting when it exits. However, this behavior is out of its hands. It depends on the watchdog device driver. For the softdog driver see the softdog page for details on how you can make this work the way you want it to.