Linux Mint Forums

Came across this when looking through the PCLinuxOS forums -

http://fosswire.com/2007/09/08/fix-a-fr ... ysrq-keys/

Quote from the site:-

You finally got your Linux environment to crash. Ctrl+Alt+Backspace does nothing, nor do the F-keys. You know you shouldn't have installed that bad driver, but you did it anyway.

So you reach for the power button.

Stop.

Mashing in the power button to reboot could cause a problem if your hard drive is still being written to, and usually causes more problems than it solves. The Linux kernel includes a secret method of restarting your PC should it ever stop doing its job.

1. Hold down the Alt and SysRq (Print Screen) keys.
2. While holding those down, type the following in order. Nothing will appear to happen until the last letter is pressed: REISUB
3. Watch your computer reboot magically.

What the individual keys do in that sequence are not as important as what it does as a whole: stops all programs, unmounts all drives, and reboots. A lot safer than just cutting the power.

Here it is again: REISUB. Remember that, as it will save you a lot of time when you are configuring a system and something gets messed up. Need a mnemonic? Try Raising Elephants Is So Utterly Boring.

As an aside, don't try this if you just want to reboot. A normal reboot, if it can be done, should always be used instead of the REISUB keys.

R-E-I-S-U-B.

I know it says you shouldn't, but I tried it anyway - it works

You have to use your little fingers for the Alt and SysRq keys, otherwise you can't type the rest

Edit by Husse: If your keyboard does not have a SysRq key the PrintScreen key probably works

Cheers,

Hugh

Id does not happen often but when it does it's bloody annoying
Good tip!

Husse wrote:Good tip!

Good tip yes, ..... but not really new. It's a very old trick in fact. But it probably can't harm to repeat those things from time to time so others get a chance to see this too.

And just to make sure everyone understands this:
This is for emergencies only, e.g. when the system absolutely locks up + freezes. This is not to be used on potentially still busy machines (e.g. which are still writing stuff to disk) or on machines that could still do a proper shutdown if you only were patient enough to wait. This is only for systems which have already died a horrible death, e.g. power-cycling them is the only way to get them back to life ..... *Then* and only then you may try your luck and use this.

Besides, I am not really sure this works on Ubuntu-based distros ... I read somewhere that they disabled this per default

Works on this Cassandra based laptop, I just need to try it on my wife's PClinux laptop - now that does freeze up regularly, and I can't figure out why.

Cheers,

Hugh

Just tested after making sure there was no disk activity
It worked so it's not disabled...

There could be a lot of different reasons why the computer freezes. It's usually either hardware or drivers related. In the second case if you think your 3D support is dodgy, just go and edit /etc/X11/xorg.conf, comment out "load dri" and "load glx" and replace whatever driver it's using with "vesa". That basically means no 3D at all... but it also could mean no more freezes.

I noticed this on a Compaq Presario 1715AP.

Clem

sonofmoog wrote:I reply to this thread to ask how this works? What is happening when I type REISUB?

Ahemm ... how about reading the first posting in this thread? There is a link to a web site and there is an article and that article explains everything ....

And you don't type 'REISUB' just like that as you would e.g. type text into an editor .... you have to enter this as a command sequence for the 'Magic SysRequest' key, e.g. press the 'magic key' and while pressing it hit the 'R-E-I-S-U-B' keys one after the other ... See above. Wikipedia has an article too, maybe you could read that one as well:
http://en.wikipedia.org/wiki/Magic_SysRq_key

Sorry but I don't understand the problem; the results for the typing of the letters are already in the original post:-

What the individual keys do in that sequence are not as important as what it does as a whole: stops all programs, unmounts all drives, and reboots. A lot safer than just cutting the power.

I simply did not have the info. from that site on what each actual key does.

Although the contents of the web page were reproduced, the link to the actual page was put in to stimulate people to look for themselves.

The Wikipedia page is far more in depth, probably more useful for those with better knowledge than I have

hugh wrote: The Wikipedia page is far more in depth

It's almost overkill ... I use Linux since 1996 but believe me, I didn't know half of the stuff Wikipedia wrote there

You learn something new every day

I used that quite a lot lately when trying to set up an ATI Radeon X1950 card on Celena beta. Saved a lot of time and headache since Celena was installed on an intel fakeraid volume (dual-boot with XP) and if it had gotten hosed, reinstalling would have been a pain.

Nice, clean reboots each time with no errors or fsck needed.

Aloha, Tim

disable compiz and it doesnt freeze anymore

hi

I am using linumint daryna when I insert DVD into my DVD-RW it works perfect but when I insert CD system slows down. It works very very slow. moving mouse from one side of screen to another take 15 sec, my PC P4,1GBramDDR2, 2x SATA HDD , ATI radeon X600, MB MSI. same happen on ASUS notebook - CPU AMD some X2 and N vidia graphick

have anyone same problem? do You know how to fix it?

thanks

I hope you will understand my poor english

a dell laptop(inpiron 2650), the buttons become "Insert/print screen" and "Delete/SysRq" so which one do I press with alt then, and can I use alt Gr instead since that would free the other hand to type the letters, also I hear that REISUO shuts down the computer if that helps B is reboot and O is shutdown.

thanks

I've been freezing lately and I'm trying to debug why.

Is there a log that can help me understand why it's locking up? I looked in messages,syslog but there isn't anything in there at the time of the crash.

Great tip. I sort of find out the Ctrl+Alt+Backspace thing myself when I was "searching" for the key combo to reboot Linux machine (like Ctrl+Alt+Del under windows). So far the only few freeze I had, I could use it to reboot.

Here is my question, I read that Ctrl+Alt+Backspace close x-session, should it be used as the first preferred option?
Am I right to assume that only Ctrl+Alt+Backspace doesn't work, then try this REISUB option?

I'd stick to ALT-backspace in Mint, coz that just restarts the X session.

P.

clem wrote:There could be a lot of different reasons why the computer freezes. It's usually either hardware or drivers related. In the second case if you think your 3D support is dodgy, just go and edit /etc/X11/xorg.conf, comment out "load dri" and "load glx" and replace whatever driver it's using with "vesa". That basically means no 3D at all... but it also could mean no more freezes.

I noticed this on a Compaq Presario 1715AP.

Clem

My HP laptop freezes on the first launch of a movie every day (after reboot it works) just the first movie i launch on any one day will kill the system completely.

REISUB is my only way out of this, no other thing is responded to by the frozen system.

Clem, I followed your advice to edit /etc/X11/xorg.conf but there was no Load dri or Load glx in the file, so commenting them out is not an option as they are not even there :S

that is a good trick, but how can i use it ?
I am using a german keyboard. there are two button F1 with Druck = print and F6 S- Abf = system request but
so i pressed Alt/Alt Gr together with Fn and F1/F6 and typed reisub/REISUB but mint opened a lot of save screenshot windows and my laptop was frozen

so any idea how i can use that trick ?

RESUB is used in the US / international K/Board - can you use ALT-Backspace

I have no idea
I pressed and hold down alt + backspace and at the same time i started to type reisub and REISUB
but nothing happened. (when i typed my computer wasn't frozen, i just tried it)
if i am in firefox then some menu will open like i press the hot key.

could it be that that combi only work when my computer is frozen ? or it simply doesnt work ?