[Wylug-help] Root device / pivot_root question

[James Holden]

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Hello All,

I'm trying to bootstrap a system with it's root filesystem on tmpfs. I
understand that this is possible.

Here's the process. The thing boots from an IDE flash disk using
syslinux.

1) The initrd loads and /linuxrc is executed.

2) /linuxrc does the following:

mount -t msdos /dev/hda1 /disk
mount -t tmpfs none /realroot
tar xjpf /disk/rootfs.tbz -C /realroot

There is now a base filesystem (less /usr) in /realroot

mount -t proc none /realroot/proc
mount -t devfs none /realroot/dev

The /proc and /dev are now mounted in the eventual filesystem root.

umount /disk  (not needed just now, but will be later to load /usr)

cd realroot
mkdir old_root
pivot_root . old_root

This leaves me in / in the 'real' root filesystem, in the tmpfs.

But then, when I:

exec chroot . /sbin/init < dev/console >dev/console 2>&1

...I get:

Usage: init 0123456SsQqAaBbCcUu
VFS: Cannot open root device "rd/0" or unknown-block(0,0)
Please append a correct "root=" boot option
Kernel panic: VFS Unable to mount root fs on unknown-block(0,0)

I think the problem is with init not working. Once init bombs, the old
change_root method kicks in, but finds it doesn't have a root to mount.

The problem appears to be that init is failing, but I don't know why.
There exists an /etc/inittab in the 'real' root fs.

Any ideas anyone?

James

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