http://itnihao.blog.51cto.com/1741976/830374
# Restart your computer now
echo "B" >/proc/sysrq-trigger # Shut down the computer now
echo "O" >/proc/sysrq-trigger # Export memory allocation information (can be viewed with/var/log/message)
echo "M" >/proc/sysrq-trigger # Export current CPU register information and flag bit information
echo "P" >/proc/sysrq-trigger # Export thread state information
echo "T" >/proc/sysrq-trigger to crash the system deliberately
echo "C" >/proc/sysrq-trigger to mount all file systems now
echo "S" >/proc/sysrq-trigger instantly mount all file systems as read-only
echo "U" >/proc/sysrq-triggerdocumentation for SYSRQ.C Based on kernel version 2.6.38. Page generated on 2011-03-22 22:20 EST. 1 Linux Magic System Request Key Hacks 2 documentation for SYSRQ.C 3 4 * what is the Magic sysrq key? 5 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 6 It is a ' Magical ' key combo you can hit which the kernel'll respond to 7 regardless of what Ever else it is doing and unless it is completely locked up. 8 9 * how do I enable the Magic SysRq key? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ You need to say "yes" ' Magic sysrq key (CONFIG_MAGIC_SYSRQ) ' When configuring the kernel. When running a kernel With SysRq compiled, /PROC/SYS/KERNEL/SYSRQ controls the functions allowed to be invoked V IA the SYSRQ key. By default the file contains 1 which means, every possible SYSRQ request is allowed (in OL Der versions SysRq is disabled by default, and your were required to specifically enable it at Run-time But this isn't the case no more. This is the list of possible values in/proc/sys/kernel/sysrq:19 &NB sp; 0-disable SysRq completely 1-enable all functions of SysRq   ; >1-bitmask of allowed SYSRQ functions (for more below ; description): 2-enAble control of console logging level 4-enable Control of keyboard (SAK, Unraw) 8-enable Debugging dumps of processes etc   ; 16-enable Sync command 32- Enable Remount read-only 64-enable Signalling of processes (term, kill, Oom-kill) 128-allow reboot/poweroff 256-allow nicing of a ll RT Tasks You can set the ' value in the ' file by the following COM Mand:33   echo "number" >/PROC/SYS/KERNEL/SYSRQ Note this value of/p Roc/sys/kernel/sysrq influences only the invocation via a keyboard. Invocation of Operation Via/proc/sysrq-trigger is always Notoginseng allowed (by a user with admin PR Ivileges). * how do I use the Magic sysrq key? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ on x86 - Press the key combo ' Alt-sysrq-<command key> '. Note-some keyboards May Have a key labeled ' SYSRQ '. The ' SysRq ' key is also known As the ' Print screen ' key. Also some keyboards cannot handle so many keys being pressed in the same time, so might bsp; have better luck with "press Alt", " Press SYSRQ ", Release SysRq", "Press <command key>", release everything. on Sparc-you Press ' Alt-stop-<command key> ', I believe. on the serial console (PC style standard serial ports only)-51 & nbsp; Your send a break, then within 5 Seconds a command key. Sending break twice is interpreted as a normal break. on PowerPc-press ' alt-print screen (or F13)-<command key>, & nbsp; Print screen (or F13)-<command key> may suffice. on Other-if your know of the key combos for other architectures, Please let me know so I can add them to this section. on all- write a character to/proc/sysrq-trigger. e.g.: echo T >/proc/sysrq-trigger * what are the ' command ' keys? ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ' B ' -would immediately reboot the system without syncing or unmounting &NBSP;&N bsp; your disks. i ' C ' -would perform a system crash by a NUL L pointer dereference. # Restart your computer now echo "B" >/proc/sysrq-trigger # immediately turn off the computer echo "O" >/proc/sysrq-trigger # Export memory allocation information (available/ Var/log/message view) echo "M" >/proc/sysrq-trigger # Export current CPU register information and flag bit information echo "P" >/proc/sysrq-trigger # Export Thread state information echo "T" >/proc/sysrq-trigger # deliberately let the system crash echo "C" >/proc/sysrq-trigger # immediately reload all file systems echo "s" &G T /proc/sysrq-trigger # immediately reload all file systems for read-only echo "U" >/proc/sysrq-trigger