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I've got a simple XenServer running here and it suddenly stopped responding (I don't know why, it just doesn't respond to anything, but let's put that aside). I think I need to reboot it, but this server is really just a consumer computer. It has a little hard drive which has been running for over 260 days for now, and I don't think it's safe to just do a hard-stop... The hard drive contains really important files, like emails, financial data, log-ins (Active Directory), and so on...

Any ideas on rebooting this server safely?

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What did exactly stop working? the Xen host itself (Dom0) or a virtual machine (DomU)? – jjmontes Feb 19 '12 at 19:42
The Xen host itself. I wasn't doing anything special, just a simple wget on a virtual machine... However, it now doesn't respond to any pings, and if I try doing something to the server physically by using a keyboard, it just doens't do anything.. – Robbietjuh Feb 19 '12 at 19:44

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Assuming there is no kernel panic and that the filesystems are mounted on the Xen server (and not on any DomU), and that you get no information on any console (CTRL+ALT+F1 to CTRL+ALT+F12), I'd say the only thing that's left to try is to reboot using the kernel sysreq commands.

These are some "magic" key strokes you can use to talk to the kernel directly (assuming they are enabled on your system). There is a well known combination of magic sysreq commands that should allow filesystems and processes to shut down correctly.

The combination you look for is called the 'REISUB' sysreq sequence. Check the information at http://en.wikipedia.org/wiki/Magic_SysRq_key .

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Thanks for your answer. The thing is, I can't see if it's a kernel panic. Trying to switch consoles using CTRL+ALT+Fx doesn't work at all. Any other recommendations? Otherwise, I'll try the sysreq sequence... – Robbietjuh Feb 19 '12 at 19:52
Imho, go for it. Also make sure you follow the boot up process and check if there are any filesystem failures, or dmesg issues regarding any hardware you have, just in case. Good luck! – jjmontes Feb 19 '12 at 19:54
Thanks, but I'm afraid that didn't work. I've done exactly what the wiki says, but nothing happens.. Just a black screen, nothing happens. – Robbietjuh Feb 19 '12 at 19:59
Then I'd just press the hard reset button... :( – jjmontes Feb 19 '12 at 20:01
Any chance of the hard drive (actually, it's a laptop hard drive if I remember correctly.. Yeah, old 'slim' pc) surviving a hard stop? – Robbietjuh Feb 19 '12 at 20:03
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