How to add user to a Group on Linux

Managing users is an important activity in Linux. For a Sysadmin, you want different access permissions for developers, maintainers and moderators. Groups are an easy way to categorize users. Rights/permissions given to a group will be applicable to all its members. In this howto, I will tell you how to add users to a group.

I would suggest you to read about the two types of groups - Primary and Secondary, before proceeding.

Add a new group

[root]# groupadd developers

Add a new user to a Secondary Group

[root]# useradd -G developers chia

Please note that the user "chia" didn't exist, we used useradd to first create it and then assign it the developers group.

Add a new user to a Primary group

Use the -g option to change the primary group of a user.

[root]# useradd -g developers chia

Add a new user to multiple Secondary groups

[root]# useradd -G developers,ftp,admin chia

Add an existing user to a Secondary group using usermod

[root]# usermod -a -G developers chia

Its important to use the -a option here, without it you will just overwrite the secondary group setttings leading to only 'developers' in the secondary group. '-a' option tells usermod to append the user to the supplementary/secondary groups, its always used with -G option.

Change the Primary group of a user using usermod

[root]# usermod -g ftp