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 a software watchdog, the ability to reboot will depend on the state of the machines and interrupts.
