Diskless boot

Jonathan Andrews jon at jonshouse.co.uk
Thu Sep 30 20:37:55 UTC 2004


On Thu, 2004-09-30 at 21:14, Jeremy Katz wrote:
> On Thu, 2004-09-30 at 21:15 +0100, Jonathan Andrews wrote:
> > Am I chasing my tail ? I used to boot sparcs like this by passing an IP
> > and nfsroot as the kernel arguments, yet every example I find for fedora
> > uses an initrd image with modules in it. Isn't it simpler to waste a few
> > extra kbytes and have a kernel with most common ethernet and NFS
> > compiled in.
> > 
> > I notice a diskless kernel and initrd image in fedora, but its seems to
> > be just an installer, the kernel boots on most things - but remove the
> > initrd and it doesn't stand alone ?
> 
> The upstream kernel is moving towards removing these sorts of things.
> It's far easier to do them in userspace and just have everything
> modular.  
Its a nice idea the kernel may be modular but the modules are not self
contained. The module loading in kernel can lead to some gotchas .....

This is an example. I've got an NFS root copy of a yum upgraded core 1
machine, but no suitable kernel to boot it.

So I install the utils for pxe, syslinux etc. Now I discover that I need
to run makedep on the same version of the kernel as the original machine
(as I read it). Catch 22, can't boot the machine without a valid initrd
image, cant create the machine without that kernel - with yum i cant
downgrade the kernel on the machine im using to build initrd back to the
older one I need to make the system.map .....

None of this would happen if the kernel didn't need system.map and
loaded it modules with intelligence rather than slapping them in the
hole the compiler chose ! Or am I treading on dangerous ground in a
Linux group ? 

> And with initramfs[1] if you, for some strange reason, can only load one
> file, you can cat the initramfs to the end of your kernel image.  I'd
> recommend using a boot loader like pxelinux, though, to make things
> simpler.
> 
Thanks, I like the sound of that. If the ramfs image is stuck on the end
of  the kernel do I need to tell the kernel or will it just see the
extra stuff and try and work it out ?

> Jeremy
> 
> [1] Note that mkinitrd now creates an initramfs image if you're on a 2.6
> kernel, the name notwithstanding
Im still in the 2.4 world, but good to know.

Thanks,
Jon





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