认识
如果正在从事内核开发、设备驱动程序或运行可能导致 Kernel 崩溃的代码，系统将被冻结（卡死），SysRq 能够帮助我们逃离卡死的局面，其为是 Linux Kernel 中的组合快捷键。
组成
WIP
性质
它允许用户执行各种低级命令（不管系统状态如何）。
组合键由 Alt+SysRq+commandkey 组成。在许多系统中，SysRq 键是 Print Screen 键。
首先，启用：echo “1” > /proc/sys/kernel/sysrq
然后，执行：echo “b” > /proc/sysrq-trigger（实现重启）
常用命令
‘k’ – Kills all the process running on the current virtual console.
‘s’ – This will attempt to sync all the mounted file system.
‘b’ – Immediately reboot the system, without unmounting partitions or syncing.
‘e’ – Sends SIGTERM to all process except init.
‘m’ – Output current memory information to the console.
‘i’ – Send the SIGKILL signal to all processes except init
‘r’ – Switch the keyboard from raw mode (the mode used by programs such as X11), to XLATE mode.
‘s’ – sync all mounted file system.
‘t’ – Output a list of current tasks and their information to the console.
‘u’ – Remount all mounted filesystems in readonly mode.
‘o’ – Shutdown the system immediately.
‘p’ – Print the current registers and flags to the console.
‘0-9’ – Sets the console log level, controlling which kernel messages will be printed to your console.
‘f’ – Will call oom_kill to kill process which takes more memory.
‘h’ – Used to display the help. But any other keys than the above listed will print help.
应用
它通常用于从冻结中恢复（或在不损坏文件系统的情况下）重新启动计算机。
Kernel Panic
存储故障导致文件系统只读，进而无法执行重启命令。
安全重启
r ⇒ unRaw (take control of keyboard back from X11,
e ⇒ tErminate (send SIGTERM to all processes, allowing them to terminate gracefully),
i ⇒ kIll (send SIGILL to all processes, forcing them to terminate immediately),
s ⇒ Sync (flush data to disk),
u ⇒ Unmount (remount all filesystems read-only),
b ⇒ reBoot.