Using Grub 2 as a bootloader for Xen PV guests on Debian Jessie

Sun, 18 Jan 2015 09:23:35 +0000
debian, grub, xen

I recently wrote a blog post on using grub 2 as a Xen PV bootloader for work. See Using Grub 2 as a bootloader for Xen PV guests over on https://blog.xenproject.org.

Rather than repeat the whole thing here I'll just briefly cover the stuff which is of interest for Debian users (if you want all full background and the stuff on building grub from source etc then see the original post).

TL;DR: With Jessie, install grub-xen-host in your domain 0 and grub-xen in your PV guests then in your guest configuration, depending on whether you want a 32- or 64-bit PV guest write either:

kernel = "/usr/lib/grub-xen/grub-i386-xen.bin"

or

kernel = "/usr/lib/grub-xen/grub-x86_64-xen.bin"

(instead of bootloader = ... or other kernel = ..., also omit ramdisk = ... and any command line related stuff (e.g. root = ..., extra = ..., cmdline = ... ) and your guests will boot using Grub 2, much like on native.

In slightly more detail:

The forthcoming Debian 8.0 (Jessie) release will contain support for both host and guest pvgrub2. This was added in version 2.02~beta2-17 of the package (bits were present before then, but -17 ties it all together).

The package grub-xen-host contains grub binaries configured for the host, these will attempt to chainload an in-guest grub image (following the Xen x86 PV Bootloader Protocol) and fall back to searching for a grub.cfg in the guest filesystems. grub-xen-host is Recommended by the Xen meta-packages in Debian or can be installed by hand.

The package grub-xen-bin contains the grub binaries for both the i386-xen and x86_64-xen platforms, while the grub-xen package integrates this into the running system by providing the actual pvgrub2 image (i.e. running grub-install at the appropriate times to create an image tailored to the system) and integration with the kernel packages (i.e. running update-grub at the right times), so it is the grub-xen which should be installed in Debian guests.

At this time the grub-xen package is not installed in a guest automatically so it will need to be done manually (something which perhaps could be addressed for Stretch).