To instal webmin on ubuntu use
sudo apt-get install webmin webmin-core
The problem i faced was that I could not login for the first time. The solution is
1.
add line
username:x:0
(where username is a valid user of your system) to your/etc/webmin/miniserv.users file
2.
modify file /etc/webmin/webmin.acl
make the line
root: acl change-users [...]