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My Ubuntu box recently started hanging during reboot. It occurs during the "shutdown" process - before the machine actually resets (bios screen flashing by?). I have to force a shutdown with the power button in order to get out of this state.

Strangely, a standard shutdown does not result in a hang up, only a reboot does.

I haven't been able to identify any culprits by watching the output during the reboot. I've tried several of the items in this post to no avail. But I did notice in that post he mentions "The logs don't show anything unusual."

Are there some kind of system logs that I can view that will give me more information about what might be happening? Any other methods I can use to troubleshoot this?

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Have a look at /var/log/, specifically messages and maybe pm-suspend.log. Also try disabling networking (sudo service networking stop on Ubuntu I think) and then rebooting. Does it still hang? – terdon Jul 5 '13 at 18:23
    
Great info! Turns out it was an entry for a samba mount in my fstab. (the machine on which the network share exists was no longer up). I'd like to give you credit for your answer somehow? – dtmland Jul 5 '13 at 19:31
    
I fleshed it out a bit and posted as an answer. If the machine in question is sometimes available, have a look at autofs and its soft mount option. – terdon Jul 5 '13 at 23:08
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This kind of problem is often the result of the system waiting for a response from a network. For example, mounted network drives and the like. The first step in debugging this kind of hang is to try and reboot after stopping all network services.

If that solves the problem, try and figure out what exactly was causing it, what was not responding. If it is indeed a network drive, you can either remove it from /etc/fstab if it is no longer relevant or you can tweak the scripts in /etc/rc6.d/ to make sure that the network is shutdown early in the process.

Another option is to use autofs to mount volumes only when necessary and to mount them with the soft option to allow them to fail gracefully.

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