I lost all my users and groups as a result of uninstalling a single package (quasar). So now I cannot login because the system does not accept any user name and password. I have created a topic on Ubuntu forum and here in software, but still no luck.

Can anyone tell me where all the info on users and groups is stored. I wonder if I have lost all those files can I replace them with manually created one? Or with some standard files from another machine or installation?

if the same case happen in slackware, I would:

-boot in with slackware cd2
-chroot to the hd
-adduser bla
and/or modify /etc/shadow

(he group file in in /etc/group but I don't you would need to touch it)

if it doesn't work, you can just mount the hdd and copy the data out.

Thanks for the advice. Still have to learn a lot of things: never used chroot before. Can I boot from Ubuntu live cd (or any other recovery cd, because Ubuntu has only one installation cd and another live) and used chroot from there? how should I use it? Is it something like:

chroot /mnt if I mount root partition on /mnt?

Well I have done the following:

1. Installed Ubuntu on my second HD
2. Set up users as they were on my main installation
3. Copied the following files from a new /etc to an old /etc:
group
gshadow
passwd
shadow
sudoers
4. Edited menu.lst to add option to boot my old installation

And pretty much that's it. I had to change ownership of users homes, because they were messed up.

Now it works. Hopefully it will be fine.

The only question left is how to point grub to my old menu.list again, because it now uses menu.list from a second HD?