note ph713 The Linux kernel has a compile-time option called "The Magic SysRq key" that makes SysRq actually do what it sounds like - request certain functions directly from the "system" (which is the kernel in this case).<p> For example: <p> <ul> <li>Alt-SysRq-S asks the kernel to sync all filesystems.</li> <li>Alt-SysRq-U unmounts all filesystems (actually, remounts them all readonly)</li> <li>Alt-SysRq-B reboots the system immediately</li> </ul> <p> Many vendor-compiled kernels have the compile-time flag on, but disabled at runtime via /proc/sys. Re-enable it with "<code>echo 1 > /proc/sys/kernel/sysrq</code>", or put "<code>kernel.sysrq = 1</code>" in /etc/sysctl.conf. <p> Alt-SysRq-S,U,B (hold down the Alt-SysRq while you sequence through S, U, B) is a safe reboot with no fileystem damage, in cases where the system appears to be locked up, but the kernel is in fact still alive enough to see your SysRq requests. <p> See here: <a href="http://lxr.linux.no/source/Documentation/sysrq.txt">Linux Sysrq docs</a> for more details and all of the other sysrq functions available. 509130 510448