x86: ALT-SysRq-<command key> SPARC: ALT-STOP-<command key> PPC: ALT - Print Screen (or F13) - <command key> 'b' - reboot 'p' - dump the current registers and flags to your console 'r' - take control of keyboard back from X 'e' - send SIGTERM to all processes, except for init 'i' - send SIGKILL to all processes, except for init 's' - attempt to sync all mounted filesystems 'u' - remount all filesystems read-only
You can put one of such line:
$ echo 0 > /proc/sys/kernel/sysrq # disable $ echo 1 > /proc/sys/kernel/sysrq # enable
to your /etc/rc.local or alternativaly place under /etc/sysctl:
kernel.sysrq = 1