Send the SIGTERM signal to all processes except init ( PID 1)Ĭall oom_kill, which kills a process to alleviate an OOM condition A crashdump will be taken if it is configured.ĭisplay all currently held Locks ( CONFIG_LOCKDEP kernel option is required) Immediately reboot the system, without unmounting or syncing filesystems Set the console log level, which controls the types of kernel messages that are output to the console Note that some commands may be disabled out of the box as specified in the bitmask value in /proc/sys/kernel/sysrq. See § Other ways to invoke Magic SysRq below. SysRq functionalities can also be accessed without a keyboard. On a ChromeOS device press Alt+ Volume Up (F10)+. on Thinkpad Carbon X1 the SysRq is activated by pressing Alt+ Fn+ S simultaneously, then releasing Fn and S while still holding Alt ( see here). On some devices, notably laptops, the Fn key may need to be pressed to use the magic SysRq key, e.g. In this case, a separate PrtScn key should be present. Furthermore, some keyboards may not provide a separate SysRq key. The combinations always assume the QWERTY keyboard layout for example, on the Dvorak keyboard layout, the combination to shut down the system uses the R key instead of O. SysRq may be released before pressing the command key, as long as Alt remains held down. The key combination consists of Alt+ SysRq and another key, which controls the command issued. The magic SysRq key cannot work under certain conditions, such as a kernel panic or a hardware failure preventing the kernel from running properly. Principal among the offered commands are means to forcibly unmount file systems, kill processes, recover keyboard state, and write unwritten data to disk. In this sense, it can be considered a form of escape sequence.
This key combination provides access to features for disaster recovery. Its effect is similar to the computer's hardware reset button (or power switch) but with many more options and much more control.
It is often used to recover from freezes, or to reboot a computer without corrupting the filesystem. The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system's state.
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