Creating a Linux User
To create a user account from a linux shell prompt:
Open a shell prompt. If you are not logged in as root, type the command su - and enter the root password.
Type useradd in linux shell followed by a space and the username for the new account you are creating at the command line (for example, useradd jsmith). Press [Enter]. Often, usernames are variations on the user's name, such as jsmith for John Smith. User account names can be anything from the user's name, initials, or birthplace to something more creative.
Type passwd followed by a space and the username again (for example, passwd jsmith).
At the New password: prompt enter a password for the new user and press [Enter].
At the Retype new password: prompt, enter the same password to confirm your selection.
Try to set password which consists of capital letters,numbers,small letters,special symbols etc.,