Linux/Xen/Building Xen DomU images

Ubuntu

Ubuntu 13.10

Start this process on a existing Ubuntu system. Does not have to be a 13.10 system. You will need to have debootstrap installed and may need to update debootstrap so it has the correct script for 13.10.

Create a empty image file and format it with ext3.

dd if=/dev/zero of=ubuntu_saucy.img bs=1M count=1 seek=1024
mkfs.ext3 ubuntu_saucy.img

Create a directory to mount the image on. Using '/mnt/img' for this example.

mkdir /mnt/img
mount -oloop ubuntu_saucy.img /mnt/img

Start the debootstrap process.

debootstrap saucy /mnt/img/

Once that completes, copy your existing /etc/apt/sources.list to the new image so we can run updates.

cp /etc/apt/sources.list /mnt/img/etc/apt/

Mount the necessary system files so that we can enter the new root filesystem with chroot.

mount --bind /dev /mnt/img/dev
mount --bind /dev/pts /mnt/img/dev/pts
mount -t proc proc /mnt/img/proc
mount -t sysfs sys /mnt/img/sys
chroot /mnt/img

Run updates and install a language pack.

apt-get update
apt-get install language-pack-en-base
apt-get upgrade

Configure the system timezone.

dpkg-reconfigure tzdata

Install the kernel image and install SSH server.

apt-get install linux-image
apt-get install openssh-server

To use the Xen console 'xm console (domU)' you need to setup a tty on /dev/hvc0. Create the file '/etc/init/hvc0.conf' with this content.

# This service maintains a getty on hvc0 from the point the system is
# started until it is shut down again.

 start on stopped rc RUNLEVEL=[2345] and (
            not-container or
            container CONTAINER=lxc or
            container CONTAINER=lxc-libvirt)
 
 stop on runlevel [!2345]

 respawn
exec /sbin/getty -8 38400 hvc0

The default udev rules for 13.10 ignore Xen generated MAC addresses so you won't get a '/etc/udev/rules.d/70-persistent-net.rules' This causes your network interfaces not to come up.

Edit '/lib/udev/rules.d/75-persistent-net-generator.rules' and comment these lines. Here's the changes in patch/diff format.

@@ -21,7 +21,7 @@ KERNEL!="eth*|ath*|wlan*[0-9]|msh*|ra*|s
                                        GOTO="persistent_net_generator_end"

 # ignore Xen virtual interfaces
-SUBSYSTEMS=="xen",                     GOTO="persistent_net_generator_end"
+#SUBSYSTEMS=="xen",                    GOTO="persistent_net_generator_end"

 # ignore UML virtual interfaces
 DRIVERS=="uml-netdev",                 GOTO="persistent_net_generator_end"
@@ -75,7 +75,7 @@ ENV{MATCHADDR}=="00:0c:29:*|00:50:56:*|0
 ENV{MATCHADDR}=="00:15:5d:*",          ENV{MATCHADDR}=""
 ENV{MATCHADDR}=="52:54:00:*|54:52:00:*", ENV{MATCHADDR}=""
 ENV{MATCHADDR}=="08:00:27:*",          ENV{MATCHADDR}=""
-ENV{MATCHADDR}=="00:16:3e:*",          ENV{MATCHADDR}=""
+#ENV{MATCHADDR}=="00:16:3e:*",         ENV{MATCHADDR}=""

 # ignore Windows Azure Hyper-V virtual interfaces
 ENV{MATCHADDR}=="00:03:ff:*", ENV{MATCHADDR}=""

Configure your '/etc/network/interfaces' for DHCP

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto eth0
iface eth0 inet dhcp

Configure a basic fstab

# Begin /etc/fstab
# <file system> <mount-point>   <type>   <options>                      <dump> <pass>
/dev/sda1          /             ext3      defaults,errors=remount-ro    0     0
proc               /proc         proc      defaults                      0     0

# End /etc/fstab

Final Cleanup

Remove /etc/udev/rules.d/70-persistent-net.rules so that network comes up clean when the image is booted for the first time.

Remove SSH host keys so that new ones get generated on first boot.

rm /etc/udev/rules.d/70-persistent-net.rules
rm /etc/ssh/ssh_host_*