The Linux kernel can reset the system if serious problems are detected. This can be implemented via special watchdog hardware, or via a slightly less reliable software-only watchdog inside the kernel. Either way, there needs to be a daemon that tells the kernel the system is working fine. If the daemon stops doing that, the system is reset.
watchdog is such a daemon. It opens /dev/watchdog, and keeps writing to it often enough to keep the kernel from resetting, at least once per minute. Each write delays the reboot time another minute. After a minute the watchdog hardware will cause the reset. In the case of the software watchdog the ability to reboot will depend on the state of the machines and interrupts.
The watchdog can be stopped without causing a reboot if the device /dev/watchdog is closed correctly, unless your kernel is compiled with the CONFIG_WATCHDOG_NOWAYOUT option enabled.
The watchdog daemon does several tests to check the system status:
# Set run_watchdog to 1 to start watchdog or 0 to disable it. run_watchdog=1 # Specify additional watchdogoptions here (see manpage). watchdog_options="" # If you need verbose message, use following option Specify module to load watchdog_module="geodewdt" # watchdog_module="it87_wdt" # watchdog_module="softdog"
* Edit configuration file /etc/watchdog.conf
The main page of watchdog can be found here http://linux.die.net/man/8/watchdog