Group management on Linux

/etc/group is the file that defines the groups on the system (man group for details).

Display group membership with the groups command:

$ groups [user]

If user is omitted, the current user's group names are displayed.

The id command provides additional detail, such as the user's UID and associated GIDs:

$ id [user]

To list all groups on the system:

$ cat /etc/group

Create new groups with the groupadd command:

# groupadd [group]

Add users to a group with the gpasswd command:

# gpasswd -a [user] [group]

To delete existing groups:

# groupdel [group]

To remove users from a group:

# gpasswd -d [user] [group]

If the user is currently logged in, he/she must log out and in again for the change to have effect.