We have a linux VM running under XenServer that reboots itself with no apparent reason. Checking the /var/log files in Xen we noticed that it's sending a force shutdown to the VM, like this:
messages:Dec 6 15:01:07 XenSrvDell2 BLKTAP-DAEMON[7309]: /local/domain/0/backend/tap/19/51728: got start/shutdown watch on /local/domain/0/backend/tap/19/51728/tapdisk-request
What we can't find is the reason why the force-shutdown was initiated. Is there any "higher level log" that might tell us who or why triggered the shutdown?
It could happen if Dom0 runs out of memory and starts crashing for example. Or if there was a device in dispute - shared for writing by multiple machines - but I guess that these are not the circumstances here. Let's hope nobody hacked your box and is playing with you. Or maybe some kind of simple watchdog/heartbeat sensor reseting your machine because it failed to report. In general more information could shed more light on this.