the groups in Ubuntu

Here are the most commonly used group management command-line tools:

• groupadd—This command creates and adds a new group.

• groupdel—This command removes an existing group.

• groupmod—This command creates a group name or GIDs but doesn't add or delete members from a group.

• gpasswd—This command creates a group password. Every group can have a group password and an administrator. Use the -A argument to assign a user as group administrator.

• useradd -G—The -G argument adds a user to a group during the initial user creation. (More arguments are used to create a user.)

• usermod -G—This command allows you to add a user to a group so long as the user is not logged in at the time.

• grpck—A command for checking the /etc/group file for typos.

As an example, there is a DVD-RW device (/dev/scd0) on our computer that the sysadmin wants a regular user named john to have access to. To grant john that access, we would follow these steps:

1.	Add a new group with the groupadd command: # groupadd dvdrw
2.	Change the group ownership of the device to the new group with the chgrp command: # chgrp dvdrw /dev/scd0
3.	Add the approved user to the group with the usermod command: # usermod -G dvdrw john
4.	Make user john the group administrator with the gpasswd command so that she can add new users to the group: # gpasswd -A john