User Accounts and Groups Management on Linux

User Accounts and Groups

On Red Hat Enterprise Linux, information about user accounts and groups are stored in several text files within the /etc/ directory. When a system administrator creates new user accounts, these files must either be edited manually or applications must be used to make the necessary changes.

root:x:0:0:root:/root:/bin/bash

username:password:userid:groupid:fulluser name:user home directory:user shell

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/etc/passwd

 The /etc/passwd file is world-readable and contains a list of users, each on a separate line. On each line is a colon delimited list containing the following information:

1    Username           — The name the user types when logging into the system.

2    Password           — Contains the encrypted password (or an x if shadow passwords are being used more on this later).

3    User ID (UID)      —The numerical equivalent of the username which is referenced by the system and applications when                 determining access privileges.

4    Group ID (GID)     — The numerical equivalent of the primary group name which is referenced by the system and applications                  when determining access privileges.

5    GECOS              —Named for historical reasons, the GECOS[25] field is optional and is used to store extra    information            (such as the user's full name). Multiple entries can be stored here in a comma delimited list. Utilities such as finger access this field to provide additional user information.

6    Home directory     —The absolute path to the user's home directory, such as /home/juan/.

7    Shell              —The program automatically launched whenever a user logs in. This is usually a command interpreter (often called a shell). Under Red Hat Enterprise Linux, the default value is /bin/bash. If this field is left blank, /bin/sh is used. If it is set to a non-existent file, then the user will be unable to log into the system.

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1.    root:x:0:0:root:/root:/bin/bash ---------------------------------------default user id ----- 0

2.    debashis:x:500:500:Debashis Acharya:/home/debashis:/bin/bash --------- default user id ----- 500

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