what's the processing sequence for initramfs during boot?
Mikkel L. Ellertson
mikkel at infinity-ltd.com
Sat Sep 8 14:31:22 UTC 2007
Andy Green wrote:
> New to me... but I do know that having an (external) initrd at all is
> completely optional. You can (and I think Debian does it this way; I
> certainly do it that way on embedded devices) get the kernel to mount
> the filesystem on the /root= partition directly and jump straight into
> the init program found on there. Maybe that is in fact done via this
> mysterious internal cyst of an initrd, I don't know.
This depends on the drivers built into the kernel, and what driver
your root file system needs. If the driver needed to read the root
file system is build into the kernel, you do not need the initrd. IN
simpler times, the standard IDE driver was built into the stock
kernels, as well as the ext2 file system driver, so you only needed
an initrd if you had an unusual IDE controller, if you were using
something like SCSI drives, and/or you were using a different file
system on the root device. (Because ext3 is ext2 with journaling
added, the ext2 driver is enough for booting.) But that has changed.
I have not looked lately, but I think the stock kernel only has
drivers for the initrd, and any hard drive controller drivers need
to be in it. I am not sure about file system drivers, but i suspect
that ext2 is still compiled into the kernel.
If I build my own kernel, I build in the drivers I know I am going
to need. So an initrd is not needed. But I need to build a different
kernel for my laptop, for my desktop, and for my server. (SATA,
PATA, and SCSI controllers.) I don't want to get in to processor
types, or some of the oddball machines around here.
Do not meddle in the affairs of dragons,
for thou art crunchy and taste good with Ketchup!
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