Groups on CentOS
On a CentOS system, groups are used to manage user access to system resources. A group is a collection of users that share common access permissions to resources such as files, directories, and devices.
Groups are created and managed with the
groupdel commands. Each user on the system is a member of at least one group and can be a member of additional groups. By default, a user is a member of the group with the same name as the user’s username.
Groups are used to control access to resources through the use of permissions. When you create a file or directory, you can assign permissions to the file or directory that specify which users and groups have access to the resource. For example, you can give read and write permissions to the group
developers for a specific directory, allowing all members of the
developers group to read and write to the directory.
Groups are also used to manage access to certain system commands and settings. For example, the
sudo command allows users in the
wheel group to execute commands with root privileges.
How to Add User to Group on CentOS
To add a user to a group on a CentOS system, you can use the
usermod command. Here’s an example of the basic syntax:
usermod -a -G group_name username
This command will add the user
username to the group
-a option tells
usermod to append the user to the group, rather than replacing the user’s current group membership.
Here’s an example of how to use
usermod to add the user
john to the group
usermod -a -G developers john
To make the change effective, you may need to log out and log back in or reboot the system.
Alternatively, you can use the
gpasswd command to add a user to a group. The syntax for
gpasswd is similar to
usermod, but you need to specify the group name with the
-a option, like this:
gpasswd -a username group_name
For example, to add the user
john to the group
gpasswd, you would run the following command:
gpasswd -a john developers
Again, you may need to log out and log back in or reboot the system to make the change effective.