Script to create a user-mode linux machine (tested under Debian 7)

create_machine.sh

#!/bin/sh

### functions

f() { echo "Failed."; exit; }

check_packages()
{
  hash linux || apt-get install user-mode-linux || f
  hash debootstrap || apt-get install debootstrap || f
}

setup_net()
{
  echo "Configuring network"
  while :; do
    echo -n "IP address of the UML machine (e.g. 192.168.22.2) > "
    read nw_ip
    [ -z "$nw_ip" ] && nw_ip='192.168.22.2'
    break
  done
  while :; do
    echo -n "Network (e.g. 192.168.22.0) > "
    read nw_network
    [ -z "$nw_network" ] && nw_network='192.168.22.0'
    break
  done
  while :; do
    echo -n "Broadcast address (e.g. 192.168.22.3) > "
    read nw_bcast
    [ -z "$nw_bcast" ] && nw_bcast='192.168.22.3'
    break
  done
  while :; do
    echo -n "Netmask (e.g. 255.255.255.252) > "
    read nw_netmask
    [ -z "$nw_netmask" ] && nw_netmask='255.255.255.252'
    break
  done
  while :; do
    echo -n "Gateway (e.g. 192.168.22.1) > "
    read nw_gw
    [ -z "$nw_gw" ] && nw_gw=192.168.22.1
    break
  done
  while :; do
    if_name=tun-${name:-uml}
    echo -n "Host interface (e.g. $if_name) > "
    read nw_if
    [ -z $nw_if ] && nw_if=$if_name
    break
  done

  echo ""
  echo "You entered:"
  echo "  IP address:        $nw_ip"
  echo "  Network:           $nw_network"
  echo "  Broadcast address: $nw_bcast"
  echo "  Netmask:           $nw_netmask"
  echo "  Gateway:           $nw_gw"
  echo "  Host interface:    $nw_if"

  while :; do
    echo -n "Is this correct? [y/n]: "
    read nw_ok
  
    case "$nw_ok" in
      y | yes)
        break
        ;;
      n | no)
        setup_net
        return
        break
        ;;
      *)
        echo "Please enter 'y' or 'n'"
    esac
  done
}

### our script begins here

check_packages

if [ "`id -u`" != "0" ]; then
  echo "I won't run as user. I need root."
  exit 1
fi

if [ "x$1" = "x" ]; then
  echo "Enter the name of the UML machine or press CTRL+C to abort:"
  echo -n "> "
  read name
fi

if [ "x$name" = "x" ]; then
  echo "Aborting."
  exit 1
fi 


setup_fs()
{
echo
echo ==============================
echo Creating file system
echo ==============================
echo

if [ -e $name/root_fs ]; then
  echo 'Skipped'
  mount | grep -q $name/root_fs || mount -o loop $name/root_fs $name/install || f
  return 1
fi

if [ "x$1" = "x" ]; then
  echo "Enter the size of your root partition in MB"
  echo -n "> "
  read size
fi
if [ "x$size" = "x" ]; then
  echo "Aborting."
  exit 1
fi 
mkdir $name || f
# print this so the user does not think that the script is hanging
echo dd if=/dev/zero of=$name/root_fs count=$size bs=1M
dd if=/dev/zero of=$name/root_fs count=$size bs=1M || f
/sbin/mke2fs -F $name/root_fs || f
mkdir $name/install || f
mount -o loop $name/root_fs $name/install || f
}

setup_base()
{
echo
echo ==============================
echo Installing the base system
echo ==============================
echo 
debootstrap  wheezy $name/install http://ftp.us.debian.org/debian || f

echo
echo ==============================
echo Configuring the base system
echo ==============================
echo 

echo '# /etc/fstab: static file system information.
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/dev/ubd0        /             ext2    defaults                 0    0
proc             /proc         proc    defaults                 0    0' \
> $name/install/etc/fstab


echo '# /etc/inittab: init(8) configuration.
# $Id: inittab,v 1.91 2002/01/25 13:35:21 miquels Exp $

# The default runlevel.
id:2:initdefault:

# Boot-time system configuration/initialization script.
# This is run first except when booting in emergency (-b) mode.
si::sysinit:/etc/init.d/rcS

# What to do in single-user mode.
~:S:wait:/sbin/sulogin

# /etc/init.d executes the S and K scripts upon change
# of runlevel.
#
# Runlevel 0 is halt.
# Runlevel 1 is single-user.
# Runlevels 2-5 are multi-user.
# Runlevel 6 is reboot.

l0:0:wait:/etc/init.d/rc 0
l1:1:wait:/etc/init.d/rc 1
l2:2:wait:/etc/init.d/rc 2
l3:3:wait:/etc/init.d/rc 3
l4:4:wait:/etc/init.d/rc 4
l5:5:wait:/etc/init.d/rc 5
l6:6:wait:/etc/init.d/rc 6
# Normally not reached, but fallthrough in case of emergency.
z6:6:respawn:/sbin/sulogin

# What to do when CTRL-ALT-DEL is pressed.
ca:12345:ctrlaltdel:/sbin/shutdown -t1 -a -r now

# Action on special keypress (ALT-UpArrow).
#kb::kbrequest:/bin/echo "Keyboard Request--edit /etc/inittab to let this work."

# What to do when the power fails/returns.
pf::powerwait:/etc/init.d/powerfail start
pn::powerfailnow:/etc/init.d/powerfail now
po::powerokwait:/etc/init.d/powerfail stop

# /sbin/getty invocations for the runlevels.
#
# The "id" field MUST be the same as the last
# characters of the device (after "tty").
#
# Format:
#  <id>:<runlevels>:<action>:<process>
#
# Note that on most Debian systems tty7 is used by the X Window System,
# so if you want to add more getty'\''s go ahead but skip tty7 if you run X.
#
0:1235:respawn:/sbin/getty 38400 console linux
#1:2345:respawn:/sbin/getty 38400 tty1
#2:23:respawn:/sbin/getty 38400 tty2
#3:23:respawn:/sbin/getty 38400 tty3
#4:23:respawn:/sbin/getty 38400 tty4
#5:23:respawn:/sbin/getty 38400 tty5
#6:23:respawn:/sbin/getty 38400 tty6

# Example how to put a getty on a serial line (for a terminal)
#
#T0:23:respawn:/sbin/getty -L ttyS0 9600 vt100
#T1:23:respawn:/sbin/getty -L ttyS1 9600 vt100

# Example how to put a getty on a modem line.
#
#T3:23:respawn:/sbin/mgetty -x0 -s 57600 ttyS3' > $name/install/etc/inittab

echo $name > $name/install/etc/hostname

# set up apt
cp /etc/apt/sources.list $name/install/etc/apt/sources.list || f


# install SSH
while :; do
  echo -n "Do you want to install SSH? [y/n]: "
  read nw_config

  case "$nw_config" in
    y | yes)
      chroot $name/install apt-get -y update || f
      chroot $name/install apt-get -y install ssh || f
      break
      ;;
    n | no)
      break
      ;;
    *)
      echo "Please enter 'y' or 'n'"
  esac
done
}
setup_fs && setup_base

# network
while :; do
  echo -n "Do you want to configure the network? [y/n]: "
  read nw_config

  case "$nw_config" in
    y | yes)
      nw_config=1
      break
      ;;
    n | no)
      nw_config=0
      break
      ;;
    *)
      echo "Please enter 'y' or 'n'"
  esac
done
  
if [ "$nw_config" = "1" ]; then
  setup_net
  echo '# Used by ifup(8) and ifdown(8). See the interfaces(5) manpage or
# /usr/share/doc/ifupdown/examples for more information.
auto lo
iface lo inet loopback

# eth0
auto eth0
iface eth0 inet static
   address '$nw_ip'
   netmask '$nw_netmask'
   network '$nw_network'
   broadcast '$nw_bcast'
   gateway '$nw_gw > $name/install/etc/network/interfaces
fi

echo
echo ==============================
echo Create root password
echo ==============================
echo

chroot $name/install su - root -c "usermod -p `mkpasswd` root"


# clean up
umount $name/install
rmdir $name/install

echo
echo ==============================
echo Creating start script
echo ==============================
echo 

while :; do
  echo -n "Enter the amount of memory for the UML machine in MB: "
  read mem
  test $mem && break
done

if [ "$nw_config" = "1" ]; then
echo '#!/bin/sh

MEMORY="'$mem'M"
HOST_IFACE="'$nw_if'"

tunctl -t $HOST_IFACE
ifconfig $HOST_IFACE '$nw_gw' netmask '$nw_netmask' up
mount | grep -q '"'"'shm.*noexec'"'"' && mount /dev/shm -o remount,exec
{ iptables -t nat -S POSTROUTING | grep -q '$nw_ip'; } || iptables -t nat -A POSTROUTING -s '$nw_ip' -j MASQUERADE

linux mem=$MEMORY eth0=tuntap,$HOST_IFACE cgroup_enable=memory' > $name/run
else
echo '#!/bin/sh

MEMORY="'$mem'M"

linux mem=$MEMORY' > $name/run
fi

chmod +x $name/run

echo
echo ==============================
echo Finished
echo ==============================
echo 
echo To launch UML, type:
echo   cd $name
echo   ./run
echo
echo Have a lot of fun!
echo