Magic SysRq key
lxfancy
posted @ 2009年8月26日 00:21
in linux
, 4047 阅读
无意中发现这篇《linux 死机了怎么办》，感觉挺好玩的。google了下，在wikipedia找到详细的介绍。凭借我3.5级的E文水平，整理出来和大家分享。
Magic SysRq key 是linux内核提供的一组按键序列。他们对应一些系统的底层操作，能够在software debug和系统应急方面发挥作用。
要用上这个Magic key，有三个基本条件：
- 键盘上有SysRq键；（呵呵...）
- 所使用的内核，在编译时打开了CONFIG_MAGIC_SYSRQ选项；
# 验证方法
grep -F CONFIG_MAGIC_SYSRQ /boot/config-`uname – r`
# y表示已开启
CONFIG_MAGIC_SYSRQ=y - 系统配置Magic key为可用。
#查看/etc/sysctl.conf，确认
kernel.sysrq = 1
#如果先前为0，更改配置后使用以下代码激活
sysctl -p
使用方法：按住Alt和SysRq键，再逐次按下相应功能键（详见下表）。
公式：Alt + SysRq + 相应功能键（或者按键序列）
按下之前要看清键盘布局，不同的布局按键序列不同。而且按按键序列时，每个功能键之间应该间隔一定时间。
话说通常的键盘SysRq键和截屏键（Print Screen)合在一起。
| Action | QWERTY | Dvorak | AZERTY |
|---|---|---|---|
| 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) |
| Immediately reboot the system, without unmounting partitions or syncing | b | x | b |
| Reboot kexec and output a crashdump | c | j | c |
| Display all currently held Locks | d | e | d |
| Send the SIGTERM signal to all processes except init (PID 1) | e | . | e |
| Call oom_kill, which kills a process to alleviate an OOM condition | f | u | f |
| When using Kernel Mode Setting, provides emergency support for switching back to the kernel's framebuffer console[3] | g | i | g |
| Output a terse help document to the console Any key which is not bound to a command should also do the trick |
h | d | h |
| Send the SIGKILL signal to all processes except init | i | c | i |
| 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 Access Key |
k | t | k |
| Show a stack backtrace of all currently executing tasks | l | n | l |
| Output current memory information to the console | m | m | , |
| Reset the nice level of all high-priority and real-time tasks | n | b | n |
| Shut off the system | o | r | o |
| Output the current registers and flags to the console | p | l | p |
| Display all active high-resolution timers and clock sources. | q | ' | a |
| Switch the keyboard from raw mode, the mode used by programs such as X11 and svgalib, to XLATE mode | r | p | r |
| Sync all mounted filesystems | s | o | s |
| Output a list of current tasks and their information to the console | t | y | t |
| Remount all mounted filesystems in read-only mode | u | g | u |
| Output Voyager SMP processor information | v | k | v |
| Display list of blocked (D state) tasks | w | , | z |
针对系统僵死，需要重启的情况，前人总结了两套功能键按键序列。
一、
unRaw 将键盘控制从 X Server 那里抢回来 tErminate 给所有进程发送 SIGTERM 信号，让他们自己解决善后 kIll 给所有进程发送 SIGKILL 信号，强制他们马上关闭 Sync 将所有数据同步至磁盘 Unmount 将所有分区挂载为只读模式 reBoot 重启
* 记为buisier的反序（busy的比较级），时间控制：R – 1 秒 – E – 30 秒 – I – 10 秒 – S – 5 秒 – U – 5 秒 – B
* 摘自blog.upsuper.org.cn/what-to-do-if-linux-crash/
二、
"Raising Skinny Elephants Is Utterly Boring"
两套序列功能一致，都是尽量让系统的关机正常化。不同在于选择Sync的时机。
话说评论对Magic key用在系统应急上很是不屑，因为很多发行版默认都不开启这项功能。原因是避免快捷键冲突和安全方面的考虑。看来这个又是“砖家"的“砖利”！
感兴趣的同学可以看看这里www.ibm.com/developerworks/cn/linux/l-cn-sysrq/index.html
评论 (0)