Linux/Xen/Building Xen DomU images: Difference between revisions

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===[[Linux/Xen/DomU/Ubuntu/Ubuntu 14.04 LTS|Ubuntu 14.04 LTS]]===
===[[Linux/Xen/DomU/Ubuntu/Ubuntu 14.04 LTS|Ubuntu 14.04 LTS]]===
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, SSH server and the full version of vim
apt-get install linux-image
apt-get install openssh-server
apt-get install vim
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.
<syntaxhighlight lang="bash">
# 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
</syntaxhighlight>
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.
<syntaxhighlight lang="diff">
@@ -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}=""
</syntaxhighlight>
Configure your '/etc/network/interfaces' for DHCP
<syntaxhighlight lang="bash">
# 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
</syntaxhighlight>
Configure a basic fstab
<syntaxhighlight lang="bash">
# 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
</syntaxhighlight>
====SSH host keys fix====
Since this image will get cloned and used to create new virtual machines we don't want to re-use the same keys for every virtual machine. Ubuntu won't regenerate SSH host keys if you delete them from /etc/ssh. So we need a script to check the host keys and regenerate them if needed.
Create /lib/init/ssh_gen_key and paste this in,
<syntaxhighlight lang="bash">
#!/bin/sh
# Some variables to make things more readable
KEYGEN=/usr/bin/ssh-keygen
RSA1_KEY=/etc/ssh/ssh_host_key
RSA_KEY=/etc/ssh/ssh_host_rsa_key
DSA_KEY=/etc/ssh/ssh_host_dsa_key
ECDSA_KEY=/etc/ssh/ssh_host_ecdsa_key
do_rsa_keygen() {
        if [ ! -s $RSA_KEY ]; then
                echo -n "Generating SSH2 RSA host key: "
                rm -f $RSA_KEY
                if test ! -f $RSA_KEY && $KEYGEN -q -t rsa -f $RSA_KEY -C '' -N '' >/dev/null; then
                        chmod 600 $RSA_KEY
                        chmod 644 $RSA_KEY.pub
echo "OK"
                else
echo "FAIL"
                        exit 1
                fi
        fi
}
do_dsa_keygen() {
        if [ ! -s $DSA_KEY ]; then
                echo -n "Generating SSH2 DSA host key: "
                rm -f $DSA_KEY
                if test ! -f $DSA_KEY && $KEYGEN -q -t dsa -f $DSA_KEY -C '' -N '' >/dev/null; then
                        chmod 600 $DSA_KEY
                        chmod 644 $DSA_KEY.pub
echo "OK"
                else
echo "FAIL"
                        exit 1
                fi
        fi
}
do_ecdsa_keygen() {
        if [ ! -s $ECDSA_KEY ]; then
                echo -n "Generating SSH2 ECDSA host key: "
                rm -f $ECDSA_KEY
                if test ! -f $ECDSA_KEY && $KEYGEN -q -t ecdsa -f $ECDSA_KEY -C '' -N '' >/dev/null; then
                        chmod 600 $ECDSA_KEY
                        chmod 644 $ECDSA_KEY.pub
echo "OK"
                else
echo "FAIL"
                        exit 1
                fi
        fi
}
do_rsa_keygen
do_dsa_keygen
do_ecdsa_keygen
</syntaxhighlight>
chmod 755 /lib/init/ssh_gen_keys
Edit /etc/init/ssh.conf
<syntaxhighlight lang="bash">
@@ -20,6 +20,7 @@ pre-start script
    test -c /dev/null || { stop; exit 0; }
    mkdir -p -m0755 /var/run/sshd
+    /lib/init/ssh_gen_keys
end script
# if you used to set SSHD_OPTS in /etc/default/ssh, you can change the
</syntaxhighlight>
====Firewall====
<syntaxhighlight lang="bash">
apt-get install iptables
apt-get install ufw
ufw allow OpenSSH
ufw enable
</syntaxhighlight>
====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.
<syntaxhighlight lang="bash">
rm /etc/udev/rules.d/70-persistent-net.rules
rm /etc/ssh/ssh_host_*
</syntaxhighlight>

Revision as of 17:34, 9 May 2014

Debian

Ubuntu

Ubuntu 13.10

Ubuntu 13.10

Ubuntu 14.04 LTS

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