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Your Linux system is locked up. Now what?


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 PostPosted: Tue Jan 11, 2011 8:10 pm   
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Joined: Mon Apr 21, 2003 3:56 pm
Posts: 8309
Your system is locked up. You don't like pulling the plug, you have unsaved data, you have a filesystem that needs to be shutdown properly, and so on. There are many reasons to not pull the plug. This rarely happens, but now you NEED to know what to do.

Now what? How do you shut this Linux box down in a relatively safe manner when nothing on the screen is working?

Use the Magic-SysReq key sequence: REISUB, also known as the word 'busier', spelled backwards. Remember that. Write it on a sticky note and then use duct tape to put that note on the rear of your PC. Now, for each letter, press Alt+SysReq+the letter. The Linux kernel captures this and responds, even if the screen refuses to respond.

Alt+SysReq+R Switch the keyboard to XLATE mode - Essentially, this is saying "Kernel, YOU must now pay attention to the keyboard, I'm talking to YOU, not the input device handlers";
Alt+SysReq+E Send the SIGTERM signal to all processes (except init) - "Programs, we want you to stop properly";
Alt+SysReq+I Send the SIGKILL signal to all processes (except init) - "Programs, you must die now";
Alt+SysReq+S Sync all mounted filesystems - "Filesystems, you now need to properly handle any unwritten data that you have been given;
Alt+SysReq+U Remount all mounted filesystems in read-only mode - "Filesystems, you will stop writing data from here on;
Alt+SysReq+B Reboot the system now, without umounting partitions or syncing - "Since we've already handled all the other stuff, do a shutdown".

The stuff in quotes is my take on what is happening, but if I'm wrong, please be kind.

Issues: ALL of the above information assumes a qwerty keyboard is being used. If your keyboard is arranged as Dvorak or AZERTY, read the wikipedia entry I linked below.

For more possibilities that the ones listed in this post, you can research http://en.wikipedia.org/wiki/Magic_SysRq_key, but remember, you take responsibility for whatever happens when you use that information.


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 PostPosted: Tue Jan 11, 2011 9:29 pm   
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Joined: Sat Nov 15, 2003 10:24 pm
Posts: 2765
Location: The Diamond State
That is exactly the Magic-SysRq-key routine I've used for years. :)
Always works as mmmna says.
I've also seen this:
Reboot
Even
If
System
Utterly
Broken

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PCLinuxOS 2009 -2.6.26.8.tex3


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