When stuck in a "freeze", your computer will not respond to commands anymore and input devices like keyboard and mouse seem to be blocked. This is a worst case scenario and could mean that you have a very severe error in either your configuration, your software or your hardware. Here we will show you to deal with this annoying situation.
In the case of a system freeze, your top priority should be trying to shutdown your system properly. Let's assume you are under X, if so, try these steps consecutively:
Try to kill the X server by pressing ALT+CTRL+BACKSPACE simultaneously.
Try to switch to another console with ALT+CTRL+F2. If you succeed, login as root and issue the command: kill -15 $(pidof X) or the command kill -9 $(pidof X), if the first command shows no effect. (Check with top to see if X is still running).
If you are part of a local network, try to ssh into your machine from another box. It is advisable to ssh into the remote machine as an unprivileged user and then use su to become root.
If the system does not respond to any of these steps, you have to go through the "SysRq" ("System Request") sequence. The "SysRq" sequence involves pressing three keys at once, the left ALT key, the SysRq key (labeled PrintScreen on older keyboards) and a letter key.
Left ALT+SysRq+r puts the keyboard in "raw" mode. Now try the pressing ALT+CTRL+BACKSPACE again, to kill the X. If that does not work, carry on.
Left ALT+SysRq+s attempts to write all unsaved data to disk ("sync" the disk).
Left ALT+SysRq+e sends a termination signal to all processes, except for init.
Left ALT+SysRq+i sends a kill signal to all processes, except for init.
Left ALT+SysRq+u attempts to remount all mounted filesystems read-only. This removes the "dirty flag" and will avoid a file system check upon reboot.
Left ALT+SysRq+b reboots the system. You might just as well press the "reset" button on your machine.
![]() | Remember that this is a sequence, i.e. you have to press one combination after the other in the right order: Raw, Sync, tErm, kIll, Umount, reBoot[1]. You will find more on this feature in /usr/src/linux/Documentation/sysrq.txt. |
If none of the above helps, cross fingers and press the "reset" switch on your machine. If you are lucky, GNU/Linux will just run a disk check upon reboot.
By all means, try to find out what causes these lockups because they can do severe damage to the file system. You might also want to consider using ReiserFS, a journaling file system included in Mandrake Linux since 7.0, which handles such failures more gracefully. However, replacing ext2fs with ReiserFS requires reformatting your partitions.
[1] | Mnemonic phrase: "Raising Skinny Elephants Is Utterly Boring" |