in reply to The most useless key on my keyboard is:

I had to vote for "SysRq," since not only have I never pressed it, but I've never had any idea what it was for, ever since I first saw one in 1987. Although, I do use "Print Scrn," which is on the same physical key, to take screenshots under Windows pretty often.

I'm surprised that nobody has mentioned the "Application" key (the one with a little picture of a drop-down menu and a cursor) on Windows keyboards. Surely that is more useless than the Windows logo key, which allows Win+R, Win+L ("Lock Workstation" on Windows XP), etc. I know it's supposed to bring up a context menu, but it's easier for me to just press Shift+F10. I guess I could remap it to something else, like I already did with Ctrl/Caps Lock and Esc/~ for Vim.

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Re^2: The most useless key on my keyboard is:
by ph713 (Pilgrim) on Nov 21, 2005 at 22:48 UTC
    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).

    For example:

    • Alt-SysRq-S asks the kernel to sync all filesystems.
    • Alt-SysRq-U unmounts all filesystems (actually, remounts them all readonly)
    • Alt-SysRq-B reboots the system immediately

    Many vendor-compiled kernels have the compile-time flag on, but disabled at runtime via /proc/sys. Re-enable it with "echo 1 > /proc/sys/kernel/sysrq", or put "kernel.sysrq = 1" in /etc/sysctl.conf.

    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.

    See here: Linux Sysrq docs for more details and all of the other sysrq functions available.