Ubuntu is a user friendly distribution based on debian.
Using debootstrap, then tweaking as necessary (see x86 and amd64 scripts)
These images are on an ext4 filesystem and use 1GB of disk space when uncompressed.
root_fs (32-bit ~50MB) MD5 SHA
root_fs (64-bit ~50MB) MD5 SHA
(last updated on the 2015-05-20)
Since Ubuntu is based on debian, keeping it up to date is as simple as running:
apt-get update apt-get upgrade
This filesystem will not boot to a login prompt when used with UML.
Plymouth should be disabled and /dev should be mounted by the fstab as per these instructions
That's still not enough to make it boot to a prompt... so maybe these will be useful:
* debugging startup problems on Ubuntu
* Debugging Upstart