SysRq
With a frozen Linux System, not all is already „done“. If you enable the SysRq Feature BEFORE a crash happens (possible at boot time, but security issue), you can use some low-level kernel commands to shut down your system properly with smaller risk of data losses on your discs or serious problems with your opened files.
openSUSE did not enable it by default, so you have to do it within YAST → Kernel-sttings.
The magic Sysrq key basically has a key combination of <ALT> + <SysRq or Prnt Scrn> + <Command key>.
The command key can be one of the following providing a specific functionality
‘b’ - Will immediately reboot the system without syncing or unmounting your disks. ‘c’ - Will perform a kexec reboot in order to take a crashdump. ‘d’ - Shows all locks that are held. ‘e’ - Send a SIGTERM to all processes, except for init. ‘f’ - Will call oom_kill to kill a memory hog process. ‘g’ - Used by kgdb on ppc and sh platforms. ‘h’ - Will display help (actually any other key than those listed here will display help. but ‘h’ is easy to remember ‘i’ - Send a SIGKILL to all processes, except for init. ‘k’ - Secure Access Key (SAK) Kills all programs on the current virtual console. NOTE: See important comments below in SAK section. ‘m’ - Will dump current memory info to your console. ‘n’ - Used to make RT tasks nice-able ‘o’ - Will shut your system off (if configured and supported). ‘p’ - Will dump the current registers and flags to your console. ‘q’ - Will dump a list of all running timers. ‘r’ - Turns off keyboard raw mode and sets it to XLATE. ’s’ - Will attempt to sync all mounted filesystems. ‘t’ - Will dump a list of current tasks and their information to your console. ‘u’ - Will attempt to remount all mounted filesystems read-only. ‘v’ - Dumps Voyager SMP processor info to your console. ‘w’ - Dumps tasks that are in uninterruptable (blocked) state. ‘x’ - Used by xmon interface on ppc/powerpc platforms.
‘0′-’9′ - Sets the console log level, controlling which kernel messages will be printed to your console. (’0′, for example would make it so that only emergency messages like PANICs or OOPSes would make it to your console.)
The most useful combination is the <ALT>+<SysRq or Prnt Scrn> + R-E-I-S-U-B
And, while most of the time when your system is frozen you cannot access this site, here is a cheat-sheet for printing: