Dangers of not thinking about what you’re typing

Just upgraded a domU to Fedora 15 from F14. As part of the upgrade, init essentially dies, and you have to hard reboot the VM. So I thought “Oh hey, why not use the Magic Sysrq keys to trigger a reboot. After all, I just learnt about xm sysrq.”

The first command, xm sysrq 0 r went ok. People who know the syntax for xm/xl commands will know what I did wrong there. 0. I sent the sysrq command to dom0, the VM host!

I didn’t think about this. I got used to just typing in 0 after the command because I was fooling around with block-attack/detach/list. So I didn’t notice what I’d done. Until I typed in xm sysrq 0 e and took down my SSH session, along with virtually all the daemons on the dom0.

Surprisingly, my domUs were still up. Mostly. Jumping over to the dom0 console, I brought sshd, xend, xenstored and xenconsoled back up. None of the xm commands were giving anything, so I restarted xend. I suppose that brought the domUs down, because none of my domUs were accessible by SSH.

Tried init 3 to see if that’d bring the daemons back up. No dice. Ok… init 5, and back to init 3. “Oh wait, it’s frozen now.”

So I had to reset the dom0 to get stuff back up. At least this is giving my startup scripts a good workout!


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