Remote conversion of 32-bit CentOS 6.3 to 64-bit Ubuntu 13.10

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Pretty much any Linux should be fine as long as you have suitable scratch partition for temp Ubuntu install, in this example we're re-using 6GB swap partition. Process is two step, first we do minimal 32-bit Ubuntu install over swap partition, boot system, hack it to 64-bit and finally do final 64-bit Ubuntu install over old CentOS rootfs. 



# Get debootstrap
mkdir -p /tmp/debootstrap
cd /tmp/debootstrap
wget http://archive.ubuntu.com/ubuntu/pool/main/d/debootstrap/debootstrap_1.0.53ubuntu0.1_all.deb
ar -xf debootstrap_1.0.53ubuntu0.1_all.deb
tar xzf data.tar.gz
tar xzf control.tar.gz

# Perl, GPG and keys are needed too
yum install gpg perl
wget "http://archive.ubuntu.com/ubuntu/pool/main/u/ubuntu-keyring/ubuntu-keyring_2011.11.21.1.tar.gz"
tar xzf ubuntu-keyring_2011.11.21.1.tar.gz

# Turn off swap (see /proc/swaps)
swapoff /dev/sda2

# Create new rootfs
mkfs.ext4 /dev/sda2

# Mount new roots
mkdir -p /mnt/ubuntu32
mount /dev/sda2 /mnt/ubuntu32

# Start install of 32-bit Ubuntu
DEBOOTSTRAP_DIR=/tmp/debootstrap/usr/share/debootstrap \
/tmp/debootstrap/usr/sbin/debootstrap --arch i386 \
--keyring=/tmp/debootstrap/ubuntu-keyring-2011.11.21.1/keyrings/ubuntu-archive-keyring.gpg \
saucy /mnt/ubuntu32 http://fi.archive.ubuntu.com/ubuntu/

# Configure OS
cd /mnt/ubuntu32
# hostname
echo "tempinstall" >etc/hostname
# fstab
echo "proc /proc proc defaults 0 0" >etc/fstab
echo "$(blkid /dev/sda2 -o export|grep UUID) / ext4 defaults,errors=remount-ro 0 1" >>etc/fstab
# network
echo "auto lo" >etc/network/interfaces
echo "iface lo inet loopback" >>etc/network/interfaces
echo "auto eth0" >>etc/network/interfaces
echo "iface eth0 inet static" >>etc/network/interfaces
echo "  address 192.168.8.16" >>etc/network/interfaces
echo "  network 192.168.8.0" >>etc/network/interfaces
echo "  broadcast 192.168.9.255" >>etc/network/interfaces
echo "  gateway 192.168.8.1" >>etc/network/interfaces
echo "  netmask 255.255.254.0" >>etc/network/interfaces
# dns
echo "nameserver 8.8.8.8" >etc/resolv.conf

# Mount proc, sysfs and dev
mount -t proc none  /mnt/ubuntu32/proc
mount -t sysfs none /mnt/ubuntu32/sys
mount -o bind /dev  /mnt/ubuntu32/dev

# Next we chroot to temporary 32-bit Ubuntu install
LANG= chroot /mnt/ubuntu32 /bin/bash

# set root password
passwd

# Install openssh for remote access after boot
apt-get update
apt-get -y install openssh-server

# Allow root over ssh
sed -i.bak -e's/.*PermitRootLogin.*/PermitRootLogin yes/g' /etc/ssh/sshd_config

# Install kernel
apt-get -y install linux-image

# When asked where grub-pc should put boot sector select all disks offered on multidisk system, with just one disk simply pick /dev/sda

# exit chroot and then reboot
exit
reboot
For whatever reason at this point names of disks changed and disk containing root was detected as sdb. Hence change in disk names from now on 
# Next we switch kernel from i386 to x64
dpkg --add-architecture amd64
apt-get update 
apt-get -y install linux-image:amd64
apt-get remove linux-image:i386

# Boot
reboot

# Get debootstrap
apt-get update
apt-get -y install debootstrap

# Create new bootfs and rootfs
mkfs.ext4 /dev/sdb1 # boot
mkfs.ext4 /dev/sdb3 # root

# Mount new boot and root
mkdir -p /mnt/ubuntu64
mount /dev/sdb3 /mnt/ubuntu64
mkdir -p /mnt/ubuntu64/boot
mount /dev/sdb1 /mnt/ubuntu64/boot

# Start install of 64-bit Ubuntu
debootstrap --arch amd64 saucy /mnt/ubuntu64 http://fi.archive.ubuntu.com/ubuntu/

# Configure OS
cd /mnt/ubuntu64
# hostname
echo "vmbu" >etc/hostname
# fstab
echo "proc /proc proc defaults 0 0" >etc/fstab
echo "$(blkid /dev/sdb3 -o export|grep UUID) / ext4 defaults,errors=remount-ro 0 1" >>etc/fstab
echo "$(blkid /dev/sdb1 -o export|grep UUID) /boot ext4 defaults 0 2" >>etc/fstab
# network
echo "auto lo" >etc/network/interfaces
echo "iface lo inet loopback" >>etc/network/interfaces
echo "auto eth0" >>etc/network/interfaces
echo "iface eth0 inet static" >>etc/network/interfaces
echo "  address 192.168.8.16" >>etc/network/interfaces
echo "  network 192.168.8.0" >>etc/network/interfaces
echo "  broadcast 192.168.9.255" >>etc/network/interfaces
echo "  gateway 192.168.8.1" >>etc/network/interfaces
echo "  netmask 255.255.254.0" >>etc/network/interfaces
# dns
echo "nameserver 8.8.8.8" >etc/resolv.conf
echo "nameserver 8.8.4.4">>etc/resolv.conf

# Mount proc, sysfs and dev
mount -t proc none  /mnt/ubuntu64/proc
mount -t sysfs none /mnt/ubuntu64/sys
mount -o bind /dev  /mnt/ubuntu64/dev

# Next we chroot to final 64-bit Ubuntu install
LANG= chroot /mnt/ubuntu64 /bin/bash

# set root password
passwd

# Install openssh for remote access after boot
apt-get update
apt-get -y install openssh-server

# Allow root over ssh
sed -i.bak -e's/.*PermitRootLogin.*/PermitRootLogin yes/g' /etc/ssh/sshd_config

# Install kernel
apt-get -y install linux-image

# When asked where grub-pc should put boot sector select all disks offered on multidisk system, with just one disk simply pick /dev/sda

# exit chroot and then reboot
exit
reboot

# Now we have our final 64-bit Ubuntu 13.10 install up and running but it still needs a bit fixing to be usable

# Fix locales
locale-gen en_US.UTF-8
echo 'LANG="en_US.UTF-8"' >> /etc/environment
echo 'LANGUAGE="en_US:en"' >> /etc/environment

# Enable swap
mkswap /dev/sdb2
swapon /dev/sdb2
echo "$(blkid /dev/sdb2 -o export|grep UUID) none swap sw 0 0" >>/etc/fstab

# Enable full repos
cat <<_eof_>/etc/apt/sources.list
deb http://fi.archive.ubuntu.com/ubuntu/ saucy main restricted
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy main restricted
deb http://fi.archive.ubuntu.com/ubuntu/ saucy-updates main restricted
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy-updates main restricted
deb http://fi.archive.ubuntu.com/ubuntu/ saucy universe
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy universe
deb http://fi.archive.ubuntu.com/ubuntu/ saucy-updates universe
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy-updates universe
deb http://fi.archive.ubuntu.com/ubuntu/ saucy multiverse
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy multiverse
deb http://fi.archive.ubuntu.com/ubuntu/ saucy-updates multiverse
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy-updates multiverse
deb http://fi.archive.ubuntu.com/ubuntu/ saucy-backports main restricted universe multiverse
deb-src http://fi.archive.ubuntu.com/ubuntu/ saucy-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu saucy-security main restricted
deb-src http://security.ubuntu.com/ubuntu saucy-security main restricted
deb http://security.ubuntu.com/ubuntu saucy-security universe
deb-src http://security.ubuntu.com/ubuntu saucy-security universe
deb http://security.ubuntu.com/ubuntu saucy-security multiverse
deb-src http://security.ubuntu.com/ubuntu saucy-security multiverse
_EOF_

# Install base ubuntu packages and some other useful stuff
apt-get update
apt-get -y install ubuntu-standard joe wget curl screen python perl mtr traceroute build-essential python-software-properties software-properties-common linux-source linux-image-generic linux-headers-generic smartmontools ntp
apt-get -y dist-upgrade

# Reconfigure timezone
dpkg-reconfigure tzdata

# Reboot one last time
reboot

# Whoo! We're done.

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