No-Post Reboots

One of the things that's always sorta bugged me about Linux was reboots generally required a full reset of the system. That is, if you did an `init 6`, the default bahavior cause your system to drop back down to the boot PROM and go through its POST routines. While on a virtualized system, this is mostly an inconvenience as virtual hardware POST is fairly speedy. However, when you're running on physical hardware, it can be a genuine hardship (the HP-based servers I typically work with can take upwards of ten to fifteen minutes to run its POST routines).
At any rate, a few months back I was just dinking around online and found a nifty method for doing a quick, no-BIOS reboot:

# BOOTOPTS=`cat /proc/cmdline` ; KERNEL=`uname -r` ; \
kexec -l /boot/vmlinuz-$KERNEL --initrd=/boot/initrd-"{$KERNEL}".img \
--append=${BOOTOPTS} ; reboot

Basically, the above:

1. Reads your /proc/cmdline file to get the boot arguments of your most recent bootup and stuffs the value into the BOOTOPTS environmental
2. Grabs your system's currently running kernel release (in case you've got multiple kernels installed and want to boot back into the current one) and stuffs the value into the KERNEL environmental
3. Calls the `kexec` command (a nifty utility for directly booting into a new kernel), leveraging the previously set environmentals to tell `kexec` what to do
4. Finishes with a reboot to the `kexec`-defined kernel (and options)

In testing it on a physical server that normally takes about 15 minutes to reboot (10+ minutes of POST routines) and speeded it up by over 66%. On a VM, it only saves maybe a minute (though that will depend on your VM's configuration settings).