Overview

Updating a debian etch (v4.1) system to lenny (v5.0) also involves an upgrade of xen from v3.0 to v3.2. This can create quite some hassle for specific setups.

The documentation below describes some of the issues, that we ran into, when we upgraded the https://systemausfall.org server.

Problematic details

Update the kernel

Update the kernel link for all domU

To ease the maintenance of the domU kernel during upgrades, we use symlinks in /boot:

thorax:~# ls -l /boot
lrwxrwxrwx 1 root root       35 2008-12-28 05:20 domU-initrd -> /boot/initrd.img-2.6.18-6-xen-amd64
lrwxrwxrwx 1 root root       32 2008-12-28 05:20 domU-kernel -> /boot/vmlinuz-2.6.18-6-xen-amd64
 -- snipped some more details --

Update these links to the new domU kernel:

lrwxrwxrwx 1 root root       35 2008-12-28 05:20 domU-initrd -> /boot/initrd.img-2.6.26-1-xen-amd64
lrwxrwxrwx 1 root root       32 2008-12-28 05:20 domU-kernel -> /boot/vmlinuz-2.6.26-1-xen-amd64

Make sure, that all xen host configuration files (e.g. in /etc/xen/ or /etc/xen/vm/) contain the following lines:

kernel  = '/boot/domU-kernel'
ramdisk = '/boot/domU-initrd'

Update the configuration file of xen-tools (/etc/xen-tools/xen-tools.conf) to use these kernel symlinks by default for new xen hosts:

kernel = /boot/domU-kernel
initrd = /boot/domU-initrd
#kernel      = /boot/vmlinuz-`uname -r`
#initrd      = /boot/initrd.img-`uname -r`

Update the new module directory in all domU

Plain copying

shutdown all xen hosts
mount the system partitions of the xen hosts

copy the new modules directory:

cp -a /lib/modules/`uname -r` $MNT_DIR/lib/modules/

Using a shared read-only blockdevice for all domU

Here we use a separate partition for /lib/modules that is shared among all domU hosts.

create the logical volume (only for LVM - assuming the volume group is named xen-vol):

lvcreate -n xen-shared-modules -L 1G xen-vol
mkfs.ext3 /dev/xen-vol/xen-shared-modules

add this block device (read-only!) to all domU (see disk in /etc/xen/vm/${NAME_OF_HOST}.cfg):
```
        'phy:xen-vol/xen-shared-modules,sda4,r',
```

mount the device in dom0 and copy the module directory:

mount /dev/xen-vol/xen-shared-modules /mnt
cp -a /lib/modules/. /mnt/
umount /mnt

add the following line to /etc/fstab in each domU:

/dev/sda4       /lib/modules    auto    defaults        0       0