The shadow file provides more secure storage for the user's password (which would otherwise be in /etc/passwd). When the password field of an entry in /etc/passwd is empty, /etc/shadow must contain a corresponding entry with the same user name but a non-empty encrypted password.
username:password:
The following list explains the required fields:
Here is a sample shadow password file entry:
dave:Qs5I6pBb2rJDA: