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I can't reboot my Ubuntu 9.04 x86_64 box. I just see the following, and then nothing happens. I've entered this several times now.

$ sudo reboot
[sudo] password for yang:
Broadcast message from
        (/dev/pts/7) at 4:31 ...

The system is going down for reboot NOW!

Probably relevant information: my amd-managed NFS mounts have gone haywire, after the NFS/NIS servers (same host) became inaccessible for several hours. I can create fresh new NFS mounts just fine, but the existing ones are not responding (or more precisely, barely responding). E.g., ls on the directories hangs for minutes, and then fails with only some of the subdirectories actually getting listed (albeit in red) and others resulting in "No such file or directory" error messages.

It's because my NFS mounts have gone haywire that I'm trying to reboot (I tried unmounting these to no avail). I've been waiting for a reboot for three days now.

I'm running Ubuntu 9.04 with regular updates. I don't have physical access to the computer, so it's important that I be able to reboot it and not simply shut down. And BTW, if anyone knows how to deal with the hung NFS mounts without rebooting, that'd be good to know as well.

Thanks in advance for any help.

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up vote 4 down vote accepted

You could always try "reboot -f" or even "echo b > /proc/sysrq-trigger". That should reboot even the most stubbornly hung system.

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Thanks, reboot -f did the trick, though I'm still curious about what happened with NFS. – Yang Oct 12 '09 at 17:27

Sometimes, you need to get someone with physical access to a machine to help you hit the reset button. That may actually be the fastest way to reboot the machine. As for the NFS issue, it may be a locking issue. Try mounting your NFS with the -o nolock option to see if it helps issues.

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Try unmounting the NFS mounts with:

umount -f /path/to/nfs/share

-f is "force", which is generally a bad idea, but in the case of NFS, not a problem.

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I get: umount.nfs: Server failed to unmount 'harvard:(pid14936,port1022)' umount2: Device or resource busy umount.nfs: /nfshome: device is busy umount.nfs: Server failed to unmount 'harvard:(pid14936,port1022)' – Yang Oct 12 '09 at 17:24
Even with -f? Weird. – wfaulk Oct 12 '09 at 23:21
Yes, that was with -f. – Yang Oct 13 '09 at 6:58

If you have to unmount it, you can use umount -l for a lazy unmount. This can break things. It removes the filesystem immediately and clears up references to the filesystem later and depending on which filesystem you're unmounting can bring the whole system down.

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That command just hangs. – Yang Oct 12 '09 at 17:26

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