Group Management in Linux

Group Management :

 

• A user can be participated to more than one group at the same time.
• A user who is member of a group can change to that group without password but a user NOT member can only change to that group if the group password exist and the user gives it.
• One of more users can become group administrators for specific groups.
• Group Administrators can:

1.     add/change/delete the password of the group

2.     add/delete users to the group

3.     reserve the group to members-only.

Types of Group:

• Primary group: Every user must be a member of at least one group, which is identified by the numeric GID in /etc/passwd.
• Secondary group: A user may be listed as member of additional group in the relevant entries in the /etc/group.
• User private group: Created whenever a new user is added to the system and has the same name as the user for which it was created.

Example:

$ id

uid=501(linuxcare) gid=502(linuxcare) groups=502(linuxcare),506(rax)

Group Management Commands:

• groupadd - adding group

      # groupadd admin

      # groupadd -r admin            //start group id 101 and increase up to GID 499

      # groupadd -g 600 admin

• groupmod - modifying group

      # groupmod [-g new gid] [-n new name] group

      # groupmod -g 600 -n networkcare linuxcare

• groupdel - deleting group

      # groupdel networkcare

• gpasswd - administer /etc/group and /etc/gshadow

      # gpasswd networkcare                                   // making new password for networkcare

      # gpasswd -A linuxcare networkcare               // administrator for networkcare

      # gpasswd -R networkcare                             // restrict non-members login

      # gpasswd -r networkcare                              // delete group password

$ gpasswd -a linuxcare networkcare                    // adding new member

$ gpasswd -d linuxcare networkcare                    // deleting group member

• chgrp - Changes the group ownership of a file or directory.

      # chgrp linuxcare /home/linuxcare

So In this way group can be managed in Linux.

By Linux Care