Softdog is a watchdog[1] device which comes as a standard piece of the Linux kernel. This is basically a software emulation of a hardware watchdog timer[2]. 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[3], use the watchdog directive[4].
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.
See Also: Softdog wikibook entry[5], How to use a watchdog timer[6]
| [1] | http://gentoo-wiki.com/HOWTO_Watchdog_Timer#Introduction |
| [2] | http://en.wikipedia.org/wiki/Watchdog_timer |
| [3] | http://www.linux-ha.org/HeartbeatProgram |
| [4] | http://www.linux-ha.org/ha.cf/WatchdogDirective |
| [5] | http://en.wikibooks.org/wiki/Linux_Kernel_Drivers_Annotated/Character_Drivers/Softdog_Driver |
| [6] | http://techthoughts.typepad.com/managing_computers/2007/10/how-to-use-a-wa.html |
This information provided courtesy of the Linux-HA project at http://linux-ha.org/