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I'm using Debian 'Jessie'. Sometimes my computer freezes, and then I can't use Ctrl+Alt+Supr to reboot, Ctrl+Alt+Backspace to kill the X Window System nor Ctrl+Alt+F1 to open a new shell. I've read in several sites that in a computer freeze you can use the basic kernel commands that are used pressing Alt+Sysreq (holding Alt+Sysreq and pressing REISUB one key)

But in my computer that 'trick' isn't working when it's frozen. Has the kernel frozen as well? I heard that one of the best things of Linux was that you never had to turn off the computer by holding the power button, but It's not being true for me :/

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up vote 5 down vote accepted

Magic keys tend to be disabled in Debian these days, so you can't just hard-reboot your machine or kill all your X processes by pressing a few keys accidentally.

The X Ctrl+Alt+Backspace key sequence is controlled by the "DontZap" option in /etc/X11/xorg.conf -- man xorg.conf for more details. I think you want this, though:

Section "ServerFlags"
    Option "DontZap" "false"
EndSection

The sysreq keys are controlled by the kernel options during kernel compile time, boot time, and also sysctl options. To enable it on Debian, put

kernel.sysrq=1

into /etc/sysctl.conf, and either reload that file (sysctl -p /etc/sysctl.conf; man sysctl for more), or just edit the file and reboot.

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I'm trying to edit the /etc/X11/xorg.conf file (with nano) but it says it's a new file (that file doesn't seem to exist there) I've also tried with the other locations specified in the man page, but I can't find the file. –  dieortin Apr 12 at 14:35
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@dieortin most modern systems don't have an xorg.conf file by default and instead set everything up using udev. You can simply create a new file at /etc/X11/xorg.conf and edit that. –  terdon Apr 12 at 14:42
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