Debian and Ubuntu provide a rootstrap command that can build a
Ubuntu (or Debian) filesystem for you to use with User-Mode Linux

1. On your computer, install the packages user-mode-linux, slirp and rootstrap.




2. Note that rootstrap earlier than 0.3.24-6 does not run with Python >= 2.6
   You need to apply the patch provided at:
   http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=585352
   if you are running an old version of rootstrap.
   (The version shipped with Ubuntu 11.10 "oneiric" is OK.)




3. Create a rootstrap.conf configuration file (you can use the one
   provided in /etc/rootstrap/rootstrap.conf as a reference):

   
   
   

   [global]
   
   # Initial size of the filesystem image (in MBs). It will be created
   
   # sparsely, so additional space is not allocated until it is used.
   
   initialsize=1024
   
   # the filesystem to create
   
   fstype=ext2
   
   # rootstrap modules to run to create the initial image
   
   modules=network mkfs mount debian uml umount
   
   # rootstraps' defaults are too low for installing recent Ubuntu/Debian
   
   umlargs= mem=512M
   
   
   
   [network]
   
   # name of the network interface inside the UML
   
   interface=eth0
   
   transport=slirp
   
   # note: the following settings were copied verbatim from
   
   # /etc/rootstrap/rootstrap.conf; they're slirp's defaults, tho
   
   host=
   
   uml=10.0.2.15
   
   nameserver=10.0.2.3
   
   gateway=10.0.2.2
   
   netmask=255.255.0.0
   
   slirp=slirp-fullbolt
   
   
   
   [debian]
   
   dist=oneiric
   
   mirror=http://archive.ubuntu.com/
   
   




4. Now run the command rootstrap in the same directory where you
   created the configuration file:

   
   
   

   rootstrap my-disk-image.img
   
   

You can read more about the use of rootstrap in its man page.