Softdog is a watchdog device which comes as a standard piece of the Linux kernel. This is basically a software emulation of a hardware watchdog timer. Recent versions of softdog provide for fine-grained watchdog timing, and for a way to tell the system to reboot on an "ungraceful" exit, or not. To configure softdog into Heartbeat, use the watchdog directive.
Many versions of softdog turn on an option called nowayout which when configured will cause the system to reboot automatically when the softdog device is closed - no matter how nicely the application asks. This is fairly annoying - since it means you cannot shut down Heartbeat or apphbd without causing a near-immediate system reboot.
If your softdog driver is configured into a monolithic kernel, you need to configure your kernel with the option CONFIG_WATCHDOG_NOWAYOUT turned off.
If your softdog driver is configured as a module, you will need to make sure it is loaded with the nowayout=0 option enabled. To do this, the following string needs be added to a couple of system configuration files at boot time.
options softdog nowayout=0
For SUSE LINUX, the files you need to change are /etc/modprobe.conf.local and /etc/modules.conf.local. For other versions of Linux, the filenames may be the same, or they may be different. In addition, you should upgrade to Heartbeat 1.2.1 or later.