[Gllug] Linux Stops

[itsbruce at uklinux.net]

On Fri, Oct 17, 2003 at 05:26:51PM +0100, Mick Farmer wrote:
> Dear GLLUGers,
> 
> Yesterday, my Red Hat 8.0 system stopped responding to any
> stimulus and required a reboot.  I've checked the majority
> of the log files for clues as to what went wrong but can't
> find anything.  Does anyone know where else I should look?

Were you in X at the time?  Did you try logging in by some other root
(ssh, serial port)?  It is, unfortunately,  possible for X to lock solid
while the rest of your system works fine.  You will see no error
messages in any logs, the only evidence is that you can still log in by
other means and see a running system.

Make sure that you do have a means of access other than the standard kb
and screen (if you have a local network, set up ssh access, otherwise
set up a tty on the serial port that you can access using a laptop or
pda).  Then you can try logging in remotely, next time this happens.  If
you can log in remotely, try killing whatever app is showing on the
screen, or the window manager (but *don't kill X).  If the app dies but
nothing changes on the screen then it is definitely an X lockup.  DO NOT
KILL X and don't use the shutdown command - either of these will simply
cause your machine to lock up completely.  Instead, sync your disks and
reboot.  There is nothing else you can do.

If you cannot set up a remote login, enable the magic SysRQ key (this
may require you to compile your own kernel).  You can then recover from
the lockup by pressing the following key sequence:

Alt-SysRQ-S
Alt-SysRQ-U
Alt-SysRQ-B

which will sync your disks (flushing cached data to disk), remount all
the mounted filesystems as read-only and then reboot your machine.

-- 
Bruce

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