Practice
I ran into the following situation: a Supermicro X8SIL-F motherboard in a server running Linux Debian. Both during the installation of this OS and afterward (especially afterward) I noticed strange server behavior - it reboots (spontaneously restarts) for no apparent reason after about 5 minutes of operation. It would be easy to blame buggy hardware, but then a thought crossed my mind - this server used to run Windows Server, after which I reconfigured it and decided to install Xen. To do this I had to dig through the BIOS to make sure all the options needed for the hypervisor were enabled.
I went back into the BIOS and, going through everything, found an interesting option:
Judging by the description, this option reboots the server if its activity disappears for 5 minutes - which is exactly the behavior we are seeing.
Apparently some, and perhaps most, Supermicro motherboards (in my case, the budget X8SIL-F) are not compatible with Linux where the Watchdog is concerned, since it does not see the operating system's activity. Maybe this feature only works on Microsoft's OS - I do not know, but with Debian the motherboard confidently decides that everything has hung and forcibly reboots the server, and none too gently at that.
Disabling the Watchdog option solved the problem.
A watchdog timer (sometimes called a computer operating properly or COP timer, or simply a watchdog ) is an electronic or software timer that is used to detect and recover from computer malfunctions. Watchdog timers are widely used in computers to facilitate automatic correction of temporary hardware faults and to prevent system disruption by erroneous or malicious software.
During normal operation, the computer regularly resets the watchdog timer to prevent it from expiring, or «timing out». If, due to a hardware fault or software bug, the computer fails to reset the watchdog timer, the timer will expire and generate a timeout signal. The timeout signal is used to trigger corrective action. Corrective action usually involves putting the computer and its associated equipment into a safe state and performing a computer reboot.
Microcontrollers often have a built-in watchdog timer. In other computers, the watchdog timer may reside in a neighboring chip that connects directly to the CPU, or it may be located on an external expansion card in the computer's case.
Comments