On the other side of cloud

I am trying to install xen on my debian a week ago, but failed because of that damn PAE build-in debian kernel for xen and my poor Pentium-M without PAE. Today I retried to install xen(now the version is 3.0.4) from source. Follow the README in the package, everything goes well except extremely long time waiting for kernel compiling – it filled kernel with all kinds of driver modules…

I went with option KERNELS=”linux-2.6-xen0 linux-2.6-xenU” first, everything goes well. But when I try to customize kernel and build a linux-2.6-xen kernel(not only a dom0, but also a an unprivileged guest kernel), and reboot it, I found I encountered this:

VFS: Cannot open root device “hda7″ or unknown-block(0,0)
Please append a correct “root=” boot option
Kernel panic – not syncing: VFS: Unable to mount root fs on
unknown-block(0,0) (XEN) Domain 0 crashed: rebooting machine in 5
seconds. (XEN) Domain 0 crashed: rebooting machine in 5 seconds.

I double checked my /boot/grub/menu.lst, and it was written correctly. So I looked it for google, and mailing list of xen-users told me that:

The -xen kernel is built with almost all drivers configured as modules; hence you’ll need an initrd including the driver[s] for your scsi or ide controller so you can mount the root filesystem.

So what I have to do is add a initrd for my xen kernel. But later I found that mkinitrd which mentioned in README is out of date. According to the Debian Wiki, debian have switched from initrd to initramfs. So another tool is introduced. Offical debian kernel package needs initramfs to preload modules that the kernel didn’t build in but as a module(e.g. ext3, ide, input device), just like the case linux-2.6-xen.

It’s easy to get a initramfs with yaird(and also mkinitramfs can be used too, which appears to be more widely used). Yaird’s configure file located at /etc/yarid, but almost nothing need modified in my case. So I only run following command as a sudoer:

yaird –verbose –output=/boot/initrd.img-xen 2.6.16.33-xen

And appended the following line to the xen’s section in /boot/grub/menu.lst:

title Xen 3.0.4 / XenLinux 2.6.16.33
root (hd0,6)
kernel /boot/xen-3.0.gz
module /boot/vmlinuz-2.6.16-xen root=/dev/hda7 ro console=tty0
module /boot/initrd.img-xen

Take care of “module”. It isn’t “initrd”, for xen take over the kernel while booting.

And reboot, everything goes well with your customize kernel.