Scripts for building a Minimal Ubuntu on a flash drive

File: rooter.sh

#!/bin/bash

# This script is expected to run on a clean ubuntu install that
# has the locale settings that are required in the final system.
# For best results and to avoid risking your main system run this
# script from with a virtual machine.
# To avoid typeing add an entry to visudo:
#    %sudo   ALL=(ALL)  NOPASSWD:ALL
# assuming you are in the sudo group.


# This script takes an optional name, that will be used for the
# image name and the host name for the new system.
NAME=${1:-root}
FILE=${NAME}.img
HOST=${NAME}
echo "Install to ${FILE}"
echo "With user ${USER}"
echo "With host name ${HOST}"

# Make a loop image with a size of 1G as the deboot install is 
# quite small.
dd if=/dev/zero of=${FILE} bs=1G count=1
sudo mkfs.ext4 ${FILE}

# Mount the loop device and copy over some files from the
# source system. This again assumes that the final system will
# use the same source list as the host system.
sudo mkdir -p /mnt/installer
sudo mount ${FILE} /mnt/installer
sudo debootstrap vivid /mnt/installer
sudo cp /etc/apt/sources.list /mnt/installer/etc/apt/
sudo cp /etc/localtime /mnt/installer/etc
sudo cp /etc/default/locale /mnt/installer/etc/default/locale

# This script will be run withtin the new system chroot and 
# is used to set up the new system. Note the hard coded locale settings
# and the assumption that overlayroot will be used to make a tmpfs
# filesystem overlay.
sudo cat << EOF > /mnt/installer/tmp/script.sh
echo "${HOST}" > /etc/hostname
locale-gen en_GB.UTF-8
dpkg-reconfigure tzdata
apt-get update
apt-get upgrade -y
apt-get install -y ssh overlayroot nano
sed -i -e 's/overlayroot=""/overlayroot="tmpfs"/' /etc/overlayroot.conf 
KERNEL=$(apt-cache search linux-image-[0-9].*generic | awk '{print $1}' | tail -n 1)
apt-get install -y ${KERNEL}
adduser ${USER}
gpasswd -a ${USER} sudo
apt-get autoclean
rm -rf /tmp/*

cat << XXX >> /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp
XXX

EOF

# Bind special resources into the install dir, and run the setup 
# script as chroot.
sudo mount --bind /dev /mnt/installer/dev
sudo mount --bind /dev/pts /mnt/installer/dev/pts
sudo mount -t proc proc /mnt/installer/proc
sudo mount -t sysfs sys /mnt/installer/sys
sudo chroot /mnt/installer /bin/bash /tmp/script.sh

# Now try to unmount, though this may not work so well if the 
# bound mounts are in use.
sudo umount /mnt/installer/sys
sudo umount /mnt/installer/dev/pts
sudo umount /mnt/installer/dev
sudo umount /mnt/installer/proc
sudo umount /mnt/installer

echo "Done"

File: squash.sh

#!/bin/bash

# This script squashes a root image and prepares an initrd image
# in the host system for a bootable drive.

# The script takes the name of the image to squash.
IMG=$1

echo "Compress ${IMG}"

# Make sure the squashfs tools are available.
sudo apt-get install -y squashfs-tools 
if [ -z "$(grep squashfs /etc/initramfs-tools/modules)" ]
then
 sudo sh -c 'echo "squashfs" >> /etc/initramfs-tools/modules'
fi

# Update the local inirtd image.
sudo update-initramfs -ck all

# Mount the image
mkdir -p /tmp/root
sudo mount ${IMG} /tmp/root

# Squash it.
sudo mksquashfs /tmp/root ${IMG}.squashfs -noappend -always-use-fragments
sudo umount /tmp/root
rmdir /tmp/root

File: booter.sh

#!/bin/bash

# This script makes a bootable use from a root file system image.

# This script takes the usb device, an optional image name and an 
# optional file system type
DEV=$1
IMG=${2:-root.img}
FSTYPE=${3:-ext4}

echo "USB ${DEV}"

# Make sure the device is not mounted and format the first fat partition
sudo umount ${DEV}1
sudo mkfs.fat -F32 ${DEV}1
sudo parted ${DEV} set 1 boot on

# Set up the usb with syslinux
sudo apt-get install -y syslinux
sudo dd conv=notrunc bs=440 count=1 if=/usr/lib/SYSLINUX/mbr.bin of=${DEV}
sync
sudo mkdir -p /tmp/usb
sudo mount ${DEV}1 /tmp/usb
sudo mkdir -p /tmp/usb/boot/syslinux
sudo syslinux -i -d /boot/syslinux ${DEV}1

# Make sure overlay root is installed for the local initrd image.
sudo apt-get install -y overlayroot

# Copy the local kernel and initrd image to the usb.
KERNEL=$(ls /boot/vmlinuz-* | tail -n 1)
INITRD=$(ls /boot/initrd.img-* | tail -n 1)
sudo cp -v ${KERNEL} /tmp/usb/boot/vmlinuz
sudo cp -v ${INITRD} /tmp/usb/boot/initrd.img
sudo cp -v ${IMG} /tmp/usb/boot/root.img

# Set the boot options.
UUID=$(sudo blkid ${DEV}1 | awk '{print $2}' | sed -e 's/"//g')
sudo sh -c "cat << EOF > /tmp/usb/boot/syslinux/syslinux.cfg
DEFAULT linux

LABEL linux
 KERNEL /boot/vmlinuz
 INITRD /boot/initrd.img
 APPEND root=${UUID} rw loop=/boot/root.img loopfstype=${FSTYPE}
EOF"

echo "Unmounting..."
sudo umount /tmp/usb
sudo rmdir /tmp/usb
echo "Done."