On any system someone must be able to kill any runaway program, purge corrupted files, reset passwords when users forget them, remove users' permission to use the system, and a myriad of other system management tasks.

On UNIX this special user is known as superuser or root (not to be confused with the root directory). Superuser can override file security and do almost anything he/she wants on the system (he/she cannot see your password, since it is encrypted, but he/she can change it). In fact, any user with a useridof 0 is a superuser. Naturally, such users should always have a password.It is not good practice for the system administrator to always logon as superuser. It is too easy to make a trivial mistake and damage the system, perhaps by rm * in an important directory. Instead, logon as a regular user, then switch to superuser with the su command when you need it.