Linux groups are a mechanism to manage a collection users. All Linux users have a user ID (UID) and a group ID (GID). Groups can be assigned users together for a common security, privilege and access purpose. It is the foundation of Linux security and access. Files and devices may be granted access based on a users ID or group ID.

Important files

/etc/group:- This file contains the group information for each account.

/etc/gshadow:- This file contains secure group account information.

Creating groups

Create a new group

# groupadd grp01
#
# tail -1 /etc/group
grp01:x:3461:
#

Creating group force with success status.

# groupadd -f grp02
# tail -1 /etc/group
grp02:x:3462:
#

Creating group with custom GID.

# groupadd -g 5000 grp03
# tail -1 /etc/group
grp03:x:5000:
#

Creating system group

# groupadd -r sysgrp
# tail -1 /etc/group
sysgrp:x:403:
#

Modifying groups

Changing name of the group

# groupmod -n newgrp grp01

Adding and removing user to a group

# gpasswd -M user8,user7 grp03
#
# tail /etc/group | grep grp03
grp03:x:5000:user8,user7
#
# gpasswd -d user6 grp03
#
# tail /etc/group | grep grp03
grp03:x:5000:user8,user7
#

Options:

-M to add multiple users
-A to add group administrator
-a to add single user to group
-d to removing user from a group

Deleting a group

Deleting a group

# groupdel newgrp