I've recently setup a simple UML instance on debian. What I find truly great is, that utilizing rootstrap and slirp, I can create, configure and run a user-mode-linux instance without once needing root access (that is, after the required packages are installed).
First we need some additional debian packages:
$ sudo aptitude install user-mode-linux uml-utilities slirp rootstrap
Then edit /etc/rootstrap/rootstrap.conf and remove the comments for the 'slirp' paragraph in the '[network]' section.
After this, a new debian-etch filesystem can easily be build using rootstrap:
$ dd if=/dev/zero of=root bs=1 count=0 seek=256M $ /sbin/mke2fs -F root $ dd if=/dev/zero of=swap bs=1M count=128 $ /sbin/mkswap swap $ rootstrap root
Now we can boot into the new instance and configure the system. Since I don't like logging in using xterms or whatever, I want to login on the terminal where I started the uml instance. To do this, we need to change '/etc/inittab' within the uml. We boot UML into single user mode
$ linux.uml con=nul con0=fd:0,fd:1 ubda=root ubdb=swap \
root=/dev/ubda eth0=slirp,,slirp-fullbolt s
in single user mode within the UML we edit /etc/inittab:
UML# vi /etc/inittab
We comment out all '/sbin/getty' lines except the first and replace the terminal 'tty1' in the first '/sbin/getty' line with 'tty0'. We exit vi and add 'tty0' as a valid secure terminal and reload the inittab.
UML# echo 'tty0' >>/etc/securetty UML# init q
Next we add the swap partition:
UML# echo '/dev/ubdb swap swap defaults 0 0' >>/etc/fstab UML# swapon -a
Then change the hostname to something meaningful:
UML# echo 'myuml' >/etc/hostname UML# hostname -F /etc/hostname UML# echo "127.0.0.1 localhost.localdomain localhost `hostname`" >/etc/hosts
That's it. We can exit single user mode and continue to boot into runlevel 2. There we can then login as root (no password).
UML# <Ctrl-D>
Use 'shutdown' to exit the UML.
UML# shutdown -h now
A 256M partition is large enough to install a minimal etch system but not much more. To resize the filesystem, use resize2fs:
$ /sbin/e2fsck -f root $ dd if=/dev/zero of=var/root bs=1 seek=1G count=0 $ /sbin/resize2fs root 1G
Will resize the root filesystem to 1G (sparsely). The same procedure may be used to shrink a filesystem. Shrinking and then re-enlarging a filesystem can help save space since it will recreate unused space in the image as sparse regions.