UNIX passwd structure
passwd syntax:
username:password:uid:gid:comment:home-directory:login-shell
username: Contains the user or login name.
password: Contains an x, a placeholder for the encrypted password. The encrypted password is stored in the shadow file.
uid: Contains a user identification (UID) number that identifies the user to the system.
gid: Contains a group identification (GID) number that identifies the user’s primary group.
comment: Usually [...]
