Commands
The key combination consists of Alt, SysRq and another key, which controls the command issued (as shown in the table below). Users with a keyboard layout other than QWERTY have to remember that their layout becomes QWERTY when they use one of these combinations. For example, on a Dvorak keyboard, the key below '9' and '0' counts as an 'o', not as an 'r', so it shuts the system down instead of switching the keyboard to raw mode. Furthermore, some keyboards may not provide a separate SysRq key. In this case, a separate "Print Screen" key should be present. Under graphical environments (such as Gnome or KDE) 'Alt'+'PrintScrn/SysRq'+key combination generally only leads to a screenshot being dumped. To avoid this Print Screen feature the magic SysRq combination should include the Ctrl, becoming 'Ctrl'+'Alt'+'SysRq'+key. For the same purposes the AltGr key, if present, can be used in place of the Alt key. On some laptops SysRq is accessible only by pressing 'Fn'. In this case the combination is a bit trickier: hold 'Alt', hold 'Fn', hold 'SysRq', release 'Fn', press key. The magic SysRq can also be accessed from the serial console.
| Action | QWERTY | Dvorak | AZERTY | Colemak |
|---|---|---|---|---|
| Set the console log level, which controls the types of kernel messages that are output to the console | 0 through 9 | 0 through 9 | 0 through 9 (without using shift) |
0 through 9 |
| Immediately reboot the system, without unmounting or syncing filesystems | b | x | b | b |
| Reboot kexec and output a crashdump | c | j | c | c |
| Display all currently held Locks (CONFIG_LOCKDEP kernel option is required) | d | e | d | s |
| Send the SIGTERM signal to all processes except init (PID 1) | e | . | e | f |
| Call oom_kill, which kills a process to alleviate an OOM condition | f | u | f | t |
| When using Kernel Mode Setting, provides emergency support for switching back to the kernel's framebuffer console If the in-kernel debugger 'kdb' is present, enter the debugger. | g | i | g | d |
| Output a terse help document to the console Any key which is not bound to a command should also perform this action |
h | d | h | h |
| Send the SIGKILL signal to all processes except init | i | c | i | u |
| Forcibly "Just thaw it" - filesystems frozen by the FIFREEZE ioctl. | j | h | j | n |
| Kill all processes on the current virtual console (Can be used to kill X and svgalib programs, see below) This was originally designed to imitate a secure attention key |
k | t | k | e |
| Shows a stack backtrace for all active CPUs. | l | n | l | i |
| Output current memory information to the console | m | m | , | m |
| Reset the nice level of all high-priority and real-time tasks | n | b | n | k |
| Shut off the system | o | r | o | y |
| Output the current registers and flags to the console | p | l | p | ; |
| Display all active high-resolution timers and clock sources. | q | ' | a | q |
| Switch the keyboard from raw mode, the mode used by programs such as X11 and svgalib, to XLATE mode | r | p | r | p |
| Sync all mounted filesystems | s | o | s | r |
| Output a list of current tasks and their information to the console | t | y | t | g |
| Remount all mounted filesystems in read-only mode | u | g | u | l |
| Forcefully restores framebuffer console, except for ARM processors, where this key causes ETM buffer dump | v | k | v | v |
| Display list of blocked (D state) tasks | w | , | z | w |
| Used by xmon interface on PPC/PowerPC platforms. | x | q | x | x |
| Show global CPU registers (SPARC-64 specific) | y | f | y | j |
| Dump the ftrace buffer | z | ; | w | z |
Read more about this topic: Magic Sys Rq Key
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