TableOfContents

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

No terminal for ssh login

Behaviour

Login to domU hosts via ssh fails with the following output:

PTY allocation request failed on channel 0
stdin: is not a tty

Even xm console $HOST_NAME stops before the login prompt.

Workaround

A [http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502798 debian bug #502798] suggests to add the following lines to the configuration file of each domU:

# necessary for ssh login since lenny
# see http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=502798
extra   = "console=hvc0"

This allows to login via ssh, but xm console still does not work.