I just noticed this post in an oldish Kernel Traffic. I got the following
timing for booting a uml kernel to an IDE root disk:
time ./linux ubd0=/dev/hda6 init=/sbin/halt >/dev/null
real 0m3.146s
user 0m0.310s
sys 0m0.040s
This includes shutdown, and the IDE disk is only 5400 RPM (1 GHz PIII). UML
isn't initializing any physical devices, which would account for most of the
delay on a native kernel. It doesn't do any decompression either. On the
other hand, there are ways to trim the boot time further, e.g., with run-time
precedence relations to control task start order. As others have mentioned,
the limiting factor is likely to be hard disk spin-up time.
To cut down the bios initialization time, use Linux Bios:
http://www.linuxbios.org/index.html
Claimed fastest boot time is 3 seconds, which sounds like they are talking
about a full kernel boot as opposed to just bios start.
I suppose a cold start time in the one second range is achievable without
major hacking of the kernel, using a flash disk, Linux Bios, and minimal
startup scripts.
Regards,
Daniel
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