Re: Re: [gentoo-user] /dev/sda* missing at boot

Em 19/08/2011 10:48, Alan McKinnon <alan.mckinnon@×××××.com> escreveu:
> On Fri 19 August 2011 13:12:25 frares@×××××.com did opine thusly:

> > I the case I don't need a initram, I guess that the grub line for
> > parameter passing to the kernel would be empty. Am I wrong?

> Yes.

> Using or not using kernel parameters has nothing to do with whether
> you use an initramfs or not.

> It's the initrd line in grub you do not need.

> >
> > I was just looking on how to build my own initram. What is it
> > supposed to do anyway?

> First, it's initramfs (the previous incarnation was initrd). You
> should use the correct name.

> An initramfs is a filesystems image stored on disk in a place that
> grub can find. It contains a kernel, essential drivers and other bits
> and pieces. When booting, grub finds the image, bangs it into memory
> and instructs the cpu to start executing at a known point.

> Why is this useful?

> For Gentoo it usually isn't (there are times when it is - see below).
> Binary distros like Ubuntu and Fedora absolutely require this. These
> distros do not know what hardware you have and what drivers you
> require, so they supply drivers for everything. But Ubuntu cannot
> possibly compile into the kernel every possible driver you might need
> to boot as the list would be huge (every known floppy, CD, USB, every
> known MFM, IDE, SATA, SCSI, netboot, Fibre and more driver for a
> start), so what they do instead is probe the hardware at boot time,
> find out what you have, and load the driver modules you DO need.

> This is the problem. The kernel wants to load disk drivers so that it
> can access the disk and continue booting. Where are the drivers? Well,
> they are on the disk. Oops, circular problem.

> The difficulty is not finding and loading drivers, it's how do you get
> the disk driver off the disk before you have the disk driver in
> memory? (think chicken and egg here).

> An initramfs solves this nicely. Grub shoved a disk image into memory
> when it booted. The kernel knows how to access it's memory it doesn't
> need a driver for that. And now the files containing the needed
> drivers are on a virtual disk *in memory*. The kernel loads them, and
> can now access the real physical disks.

> Lots more complicated stuff then happens, like getting rid of the
> virtual filesystem from the initramfs and mounting the real filesystem
> from disk at /, but that's beyond the scope of this mail.

> Gentoo mostly doesn't need any of this because you do know your
> hardware and can just compile your disk drivers into the kernel - this
> is the very thing that Ubuntu cannot do.

> Some Gentoo users still need an initramfs, such as booting off drives
> in a RAID configuration. They need the RAID drivers first to read the
> disks so use an initramfs to fix this little problem exactly as Ubunut
> fixes their problem.

> Make sense?


Completely! Thanks a lot.

So I guess that my problem is to find an appropriate pair of driver and  
hard disk operating mode.

> --
> alan dot mckinnon at gmail dot com


Thanks again
Francisco