If necessary, this should only be done on a hardwired console (attached keyboard and monitor) connected to a computer. Never log in as root using any kind of GUI environments, such as Gnome and KDE.
This is because with a GUI environment, a user can easily forget that it is logged in as root, and start to use application programs with significant security exposure, such as email and web browsing. The damage of a security breach to a regular user’s account is relatively limited. However, if the breach is to happen to a root account, the system can easily be compromised to a point that the only option is a full reinstallation.
If possible, do not even log in as root using a console terminal! The next sections discusses methods to perform administrative work without having to log in as root.