Using PV-GRUB on Jessie to boot a domU kernel
By using PV-GRUB from grub2, each domU can boot with its own kernel instead of using the dom0 kernel, which makes life easier for updates and multi distribution ?Xen installs. You need to have first a working domU. The domU /boot FileSystem can be anything that grub2 supports.
The idea is to put a PV-GRUB binary in dom0, which you can use as a kernel to boot domUs instead of a linux kernel. PV-GRUB will thus run inside the domU, and access the domU filesystem to get grub.cfg, and then the kernel installed in the domU filesystem, and boot it from inside the domU.
This PV-GRUB is completely independent from the way you boot dom0 itself.
On the dom0
- You need to install the grub-xen-host package (available on Jessie and later only, but you can easily copy the two files from /usr/lib/grub-xen from a Jessie system (or from the grub-xen-host .deb archive) into a dom0 system running an earlier version of Debian) and modify the domU configuration to use it as a kernel, and give it the domU grub2 configuration file path as "extra" parameter. Do *not* leave any "root" configuration there.
For 64bit domUs, use grub-x86_64-xen.bin, and for 32bit domUs, use grub-i386-xen.bin.
Config snippet:
kernel = /usr/lib/grub-xen/grub-x86_64-xen.bin
extra = '(hd1)/boot/grub/grub.cfg'
root = ''
disk = [
'phy:/dev/vg05/test2.openforce.com-swap,xvda1,w',
'phy:/dev/vg05/test2.openforce.com-disk,xvda2,w',
]If you produce a grub.cfg in the skeleton directory then you don't have to do anything with the domU (forget the rest under On the domU)
mkdir -p /etc/xen-tools/skel/boot/grub vim /etc/xen-tools/skel/boot/grub/grub.cfg
for the above config snippet it should look like:
root='(xen/xvda2)' insmod xzio insmod gzio insmod btrfs insmod ext4 linux /vmlinuz root=/dev/xvda2 ro initrd /initrd.img boot
most likely you have to change the xvda2 to something else
On the domU
Install a standard linux-image-amd64 kernel (since Xen support is in mainline Linux since Linux 2.6.37)
mkdir /boot/grub apt-get install linux-image-amd64
- Install grub2-common, and run update-grub to create /boot/grub/grub.cfg
And you are done
Shutdown your domU completely, re-create it, it should boot grub2 and pick up your domU's grub.cfg to show the menu. Kernels upgrades can now be done from inside the domU by just upgrading the kernel and rebooting, without even having to destroy the domain.
grub1
It is also possible to use a grub1 version of pv-grub, although the support is not maintained so much, so there is no reason to use it instead of grub2, unless your domU really has no way to generate a grub2-like grub.cfg
On the dom0
You need to build xen from source, the pv-grub1 binaries will be available in xen/stubdom/mini-os-x86_32-grub/mini-os.gz and xen/stubdom/mini-os-x86_64-grub/mini-os.gz , which you can copy into /boot/pv-grub1-32.gz and /boot/pv-grub1-64.gz for instance. The configuration file is then grub1-style:
Config snippet:
kernel = /boot/pv-grub1-64.gz
extra = '(hd1)/boot/grub/menu.lst'
root = ''
disk = [
'phy:/dev/vg05/test2.openforce.com-swap,xvda1,w',
'phy:/dev/vg05/test2.openforce.com-disk,xvda2,w',
]
On the domU
Install a standard linux-image-amd64 kernel (since Xen support is in mainline Linux since Linux 2.6.37)
mkdir /boot/grub apt-get install linux-image-amd64
- Install grub-legacy (on Wheezy and before) or pv-grub-menu (on Jessie and after), and run update-grub to create /boot/grub/menu.lst . Edit it to fix the groot= parameter which should be (hd1), not (/dev/xvda2), and run update-grub again to fix the menu.
And you are done
Shutdown your domU completely, re-create it, it should boot grub1 and pick up your domU's menu.lst to show the menu. Kernels upgrades can now be done from inside the domU by just upgrading the kernel and rebooting, without even having to destroy the domain.