Understanding Group Management in Linux

Group management in Linux is a fundamental aspect of system administration, enabling you to efficiently control access to files and resources based on user roles and permissions. Groups allow you to categorize users with similar privileges, streamlining permission management compared to individual user accounts.

Types of Groups

1. Primary Group

2. Secondary Group

Primary Group

Every user in Linux belongs to exactly one primary group. This group is assigned automatically when the user is created and determines the default permissions for files the user creates.

Secondary Group

A user can be a member of zero or more secondary groups, granting them additional permissions associated with those groups.

System Files

• /etc/passwd: This file stores user account information, including the ^{username, encrypted password, UID, GID, primary group name, home directory, and login shell.} The line for a newly created user will show their username, followed by an x (password is hidden), UID, GID, primary group name, home directory, and login shell (e.g., /bin/bash).

    username:password:UID:GID:comment:home:shell
  

  For More Info:-

  https://cloudcoder.hashnode.dev/local-user-management#heading-passwd-and-shadows

• /etc/group: This file contains information about ^{groups, including the group name, encrypted password (often left blank), GID,} and a comma-separated list of users belonging to the group. The newly created group will have an entry in this file with the same name as the user, their GID, and the user listed as the only member.

    groupname:password:GID:group member
  

  For More Info:-

  https://www.redhat.com/sysadmin/local-group-accounts

Group Management Commands

groups

The groups command displays the groups to which a user belongs.

$ groups username

id

The id command displays the user and group IDs associated with a user account.

$ id username

usermod

The usermod command is used to modify user account properties, including group membership.

• -a: Append the user to the supplementary group(s) listed without removing current group membership.

• -G: Specify supplementary groups for the user.

• -g: Set the primary group for the user.

$ sudo usermod -a -G groupname username

$ sudo usermod -g newprimarygroup username

groupmod

The groupmod command is used to modify group properties, such as the group name.

$ sudo groupmod -n newgroupname oldgroupname

groupdel

The groupdel command is used to delete a group from the system.

$ sudo groupdel groupname

gpasswd

The gpasswd command is used to administer the /etc/group file and manage group passwords.

• -A: Set the group administrator.

• -a: Add a user to the specified group.

• -d: Remove a user from the specified group.

$ sudo gpasswd -A admin groupname
$ sudo gpasswd -a username groupname
$ sudo gpasswd -d username groupname

Note:-

remove all Admins in a group

$ sudo gpasswd -A " " groupname

newgrp

The newgrp command is used to change the current group ID, effectively switching to a new group.

$ newgrp groupname