那年那日那朵花
".......(o´ω`o)......"
linux强制重启方法(另附SysRq说明)
这个年果然没怎么好好过啊，期间断断续续出了点问题需要处理，今天早上就有台服务器出了问题正常重启不了，最后用了SysRq功能才强制重启。之前都不了解这个SysRq功能，今天算是使用了他的一部分功能了，故这里整理记录下。
场景是这样的，我对一台服务器执行reboot和reboot -f命令都无效没法重启，这里应该是命令的信号被阻塞住了。后来上网查了下，采用SysRq功能重启了
echo 1 > /proc/sys/kernel/sysrq echo b > /proc/sysrq-trigger
- 第一条命令是开启sysrq功能。默认的话是0关闭状态，然后我重启后这里也恢复为0了。
- 第二条命令是发送command key b 给 /proc/sysrq-trigger 接口。这样服务器就重启了。不过我发现这样重启的话/etc/rc.local里面的开机自启动项是不会执行的，需要手动启下。
下面我罗列下具体有哪些command key和具体的功能
| ==commandkey== | ==description== |
|---|---|
| 'b' | Will immediately reboot the system without syncing or unmounting your disks. 重启机器 |
| 'c' | Will perform a system crash by a NULL pointer dereference. A crashdump will be taken if configured.手动让服务器crash |
| 'd' | Shows all locks that are held. |
| 'e' | Send a SIGTERM to all processes, except for init. |
| 'f' | Will call the oom killer to kill a memory hog process, but do not panic if nothing can be killed. |
| 'g' | Used by kgdb (kernel debugger) |
| 'h' | Will display help (actually any other key than those listed here will display help. but 'h' is easy to remember :-) |
| 'i' | Send a SIGKILL to all processes, except for init. |
| 'j' | Forcibly "Just thaw it" - filesystems frozen by the FIFREEZE ioctl. |
| 'k' | Secure Access Key (SAK) Kills all programs on the current virtual console. NOTE: See important comments below in SAK section. |
| 'l' | Shows a stack backtrace for all active CPUs. |
| 'm' | Will dump current memory info to your console. |
| 'n' | Used to make RT tasks nice-able |
| 'o' | Will shut your system off (if configured and supported). |
| 'p' | Will dump the current registers and flags to your console. |
| 'q' | Will dump per CPU lists of all armed hrtimers (but NOT regular timer_list timers) and detailed information about all clockevent devices. |
| 'r' | Turns off keyboard raw mode and sets it to XLATE. |
| 's' | Will attempt to sync all mounted filesystems. |
| 't' | Will dump a list of current tasks and their information to your console. |
| 'u' | Will attempt to remount all mounted filesystems read-only. |
| 'v' | Forcefully restores framebuffer console |
| 'v' | Causes ETM buffer dump [ARM-specific] |
| 'w' | Dumps tasks that are in uninterruptable (blocked) state. |
| 'x' | Used by xmon interface on ppc/powerpc platforms. Show global PMU Registers on sparc64. Dump all TLB entries on MIPS. |
| 'y' | Show global CPU Registers [SPARC-64 specific] |
| 'z' | Dump the ftrace buffer |
| '0'-'9' | Sets the console log level, controlling which kernel messages will be printed to your console. ('0', for example would make it so that only emergency messages like PANICs or OOPSes would make it to your console.) |
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