Groups make it easy to associate users with similar access-control requirements, so managing users and groups is a key responsibility for sysadmins. As I mentioned in my article on managing users, I like simple commands with a logical syntax. Such commands are easier to remember, particularly for new administrators.
The three commands used to manage group accounts on Red Hat Enterprise Linux (RHEL) and RHEL-like distributions fit this description nicely:
- Add a group:
groupadd - Modify a group:
groupmod - Delete a group:
groupdel
As in my overview on user account administration, these concepts apply to any distribution of Linux.
Groups make it easier to associate users that have similar access control requirements. Tyler Carrigan's article Managing local group accounts in Linux covers some of this content.
groupadd
Sysadmins are likely to add groups that represent specific and varied needs to Linux servers. Most of these needs center on controlling access to files, directories, or other resources. You can even use groups help manage sudo access.
To create a group, use the following command:
$ sudo groupadd projectA
Note: These commands require root or administrative privileges.
This command adds projectA to the /etc/group file. The file contains the group name, password (if any), group ID, and a list of existing members. The group membership is empty by default. The fields are separated by colons.
There are a few options for groupadd, but a common one is --gid (-g for short), to specify a group ID (GID) number.
[ You might also be interested in the Bash shell scripting cheat sheet. ]
groupmod
Creating a group is only the first step. You might also need to modify the group by using the groupmod command. The most common group modifications consist of name changes.
Note: Adding or removing a user from a group modifies the user, not the group, by using the usermod command.
Group modification options include:
--gid(-g): Change the GID--new-name(-n): Change the group name
Therefore, if you need to update a group name from projectA to projectZ, use:
$ sudo groupmod --new-name projectZ projectA
The projectA string is the command's argument.
After modifying the group, use the tail or cat commands to check the /etc/group file contents to ensure the desired settings are in place.
groupdel
You may need to delete a group. Deleting a group does not delete the user accounts that are members of the group.
To delete the projectA group, type:
$ sudo groupdel projectA
Other than the --help option for help, the other option sysadmins commonly use is --force, which forces the group deletion.
Wrap up
The three commands used to manage groups are quite similar to the user management commands. There are few options to remember, yet these six commands to manage users and groups are logical and straightforward.
- Add a group:
groupadd - Modify a group:
groupmod - Delete a group:
groupdel
To manage users, use:
- Add a user:
useradd - Modify a user:
usermod - Delete a user:
userdel
Because user and group management are such common and important tasks for Linux sysadmins, you would be wise to learn and memorize these commands.
关于作者
Damon Garn owns Cogspinner Coaction, LLC, a technical writing, editing, and IT project company based in Colorado Springs, CO. Damon authored many CompTIA Official Instructor and Student Guides (Linux+, Cloud+, Cloud Essentials+, Server+) and developed a broad library of interactive, scored labs. He regularly contributes to Enable Sysadmin, SearchNetworking, and CompTIA article repositories. Damon has 20 years of experience as a technical trainer covering Linux, Windows Server, and security content. He is a former sysadmin for US Figure Skating. He lives in Colorado Springs with his family and is a writer, musician, and amateur genealogist.
