3.5.3. Updating Group Authentication

The gpasswd command administers /etc/group and /etc/gshadow files. Note that this command works only if run by a group administrator.
Who is a group administrator? A group administrator can add and delete users as well as set, change, or remove the group password. A group can have more than one group administrator. The root user can add group administrators with the gpasswd -A users groupname where users is a comma-separated list of existing users you want to be group administrators (without any spaces between commas).
For changing a group's password, run the gpasswd command with the relevant group name. You will be prompted to type the new password of the group. 
gpasswd groupname

Example 3.20. Changing a Group Password

~]# gpasswd crowd
Changing password for group crowd
New password:
Re-enter new password:
The password for the group crowd has been changed.
You can also remove the password from the named group by using the -r option. 
gpasswd -r schoolmates