2009-05-24

Raising Skinny Elephants

Even with as stable as Linux is, at some point, you will probably run into a situation where your system becomes unresponsive. Most of the time, restarting X by pressing Ctrl + Alt + Backspace will take care of the problem. However, if you are unfortunate enough to find yourself in a situation where your machine will not respond to this, there is still something you may be able to do: Raise the Skinny Elephant.

I know this sounds pretty silly, but it is just a mnemonic device to help you remember what to do. Before I explain that, let's check to make sure your system has the sysrq key enabled:

$ ls /proc/sys/kernel/sysrq

If your system finds this, then it is enabled. On most keyboards, the sysrq key is the same as the Print Screen key. The exception here is on some laptop keyboards, Print Screen and sysrq are mapped to different function keys. This is not the case on the Dell Mini 9, both Print Screen and sysrq keys are mapped to fn + 7. Now onto the mnemonic device:

Raising Skinny Elephants Is Utterly Boring

So, now that we know the mnemonic, what do we do with it? We can type the following key strokes to reboot an unresponsive system:

Alt + sysrq + r
Alt + sysrq + s
Alt + sysrq + e
Alt + sysrq + i
Alt + sysrq + u
Alt + sysrq + b

Between each line, we should wait a couple seconds to let the system finish what we're telling it to do. Speaking of, just what are we telling the system to do?

r - Puts the keyboard in raw mode
s - Syncs the disk
e - Terminates all processes
i - Kills all processes
u - Remounts all filesystems in read only
b - Reboots the system

When your system reboots, fsck will run to check your disk, just let it run.

I just want to restate that this is not something you should do normally, it is there as a failsafe for when everything else fails: when Ctrl + Alt + Backspace or rebooting from the command line do not work.

See you next time.

Edit: Thanks to Scowdich for pointing this out:
Typing Alt+SysReq+r,e,i,s,u,b will do the same thing, but will skip the unnecessary fsck on reboot.

3 comments:

  1. Just wanna point out that Alt+SysReq+r,e,i,s,u,b has the same effect, but allows you to skip any necessary fscks on reboot.

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  2. Scowdich, thanks for the information. I've edited my post to reflect it. I've not heard of a mnemonic to help remember this one.

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  3. Pretty easy mnemonic: it's "busier" spelled backwards.

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