developerWorks: Reboot Linux Faster Using kexec

“As computer systems have become faster and better, one area
that has yet to catch up with the improvements is system reboot
time. In fact, as systems have become more advanced and complex in
terms of processor speeds, memory sizes, and resource capacities,
reboot times have actually become longer. While a longer reboot
time is an irritant for everyone, its impact is critical for
production systems where longer reboot times means reduced uptime.
Besides impacting the availability of a system for its users,
longer reboot times are a major bottleneck for kernel and system
software developers who reboot their machines several times a
day.

“Reboot times are especially long when the system has many
sparsely populated SCSI buses or ECC-checked physical memory. Test
results show that the most time consumed during a reboot process is
during the firmware stage, when the devices attached to the system
are recognized and initialized (for details, see the Resources
section of this article). Naturally, most efforts at reducing
reboot times have targeted this stage of the reboot process. One
such effort has led to the development of kexec, a feature
available for Linux kernels on x86 platforms. With kexec, you can
reboot directly into another kernel, without having to go through
the firmware and bootloader stages. Skipping the lengthiest part of
the sequence reduces the reboot time drastically…”

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