, F n, where n is the highest number of text consoles set up by the distribution. On distributions that do not include a textmode command, the key command Ctrl+ Alt+ F1 may sometimes be able to force a return to a text console. With modern filesystems, this practice is not encouraged, offering no upsides over straight re Boot, though the default value of kernel.sysrq in such distributions as Ubuntu and Debian remains 176 and 438 respectively.Īnother past use was to kill a frozen graphical program, as the X Window System used to have complete control over graphical mode and input devices. Which avoided a risk of filesystem corruption. Sysrq: HELP : loglevel(0-9) reboot(b) crash(c) terminate-all-tasks(e) memory-full-oom-kill(f) kill-all-tasks(i) thaw-filesystems(j) sak(k) show-backtrace-all-active-cpus(l) show-memory-usage(m) nice-all-RT-tasks(n) poweroff(o) show-registers(p) show-all-timers(q) unraw(r) sync(s) show-task-states(t) unmount(u) force-fb(v) show-blocked-tasks(w) dump-ftrace-buffer(z)īefore the advent of journaled filesystems a common use of the magic SysRq key was to perform a safe reboot of a Linux computer which has otherwise locked up (abbr. Output of the SysRq+ h on a x86_64 kernel: Show global CPU registers (SPARC-64 specific) Used by xmon interface on PowerPC platforms. Remount all mounted filesystems in read-only modeįor ARM processors, cause ETM buffer dump instead.
Output a list of current tasks and their information to the console Switch the keyboard from raw mode, used by programs such as X11 and SVGAlib, to XLATE mode Output the current registers and flags to the consoleĭisplay all active high-resolution timers and clock sources. Reset the nice level of all high-priority and real-time tasks Output current memory information to the console Shows a stack backtrace for all active CPUs. This was originally designed to imitate a secure attention key
Kill all processes on the current virtual console (can kill X and SVGAlib programs, see below) Send the SIGKILL signal to all processes except initįorcibly "Just thaw it" – filesystems frozen by the FIFREEZE ioctl. Output a terse help document to the consoleĪny key which is not bound to a command should also perform this action If the in-kernel debugger kdb is present, enter the debugger. When using Kernel Mode Setting, switch to the kernel's framebuffer console. 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.
0 kommentar(er)
