User`s guide

Troubleshooting 197
Kernel Troubleshooting
Using ALT+SYSRQ Keyboard Sequences
Press ALT+SYSRQ+H (3 keys simultaneously) and check what is printed at the server console,
for example:
SysRq: unRaw Boot Sync Unmount showPc showTasks showMem loglevel0-8 tErm kIll
killalL Calls Oops
This output shows you what ALT+SYSRQ sequences you may use for performing this or that
command. The capital letters in the command names identify the sequence. Thus, if there are
any troubles with the machine and you're about to reboot it, please press the following
sequences before pressing the Power button:
ALT+SYSRQ+M to dump memory info
ALT+SYSRQ+P to dump processes states
ALT+SYSRQ+S to sync disks
ALT+SYSRQ+U to unmount filesystems
ALT+SYSRQ+L to kill all processes
ALT+SYSRQ+U try to unmount once again
ALT+SYSRQ+B to reboot
If the server is not rebooted after that, you can press the Power button.