Working with Users, Groups and Permissions in Linux

This is a quick guide to show you how to work with Users and Groups in Linux. Concepts will be similar across most distros as well on Macs since they're Unix-based.

Users

By default, a system has a root user which has complete permission over the system. root users can add or remove other users. To add users:

sudo useradd new-user

To log in as the new user, a password must be set up. To do that, use the command

sudo passwd new-user

This blog post does a great job of going in-depth about the user creation process.

Groups

Users belong to groups. By default, root user will be under the sudoers group which will have, as the name implies root previliges. To add a new user to the sudoers group:

usermod -aG sudo new-user

This will give user access to run sudo commands.

To list all the groups available in the system, use the command:

groups

To add a new group

sudo groupadd new_group

You can add new users to this group by simply

usermod -ag new_group new-user

More information on groups and users here.

File Permissions

Deciphering file permissions in linux can seem overwhelming, so here's a crash course.

To see file permissions run this command:

ls -lah

This will show you a result that looks something like drwxrwxrwx with some dashes in the middle. Here's what it means:

• First d if present signifies if this is a directory or not.
• The rwx after show the owner's permissions in the file/directory where r means read, w means write and x means execute. The absence of permission is denoted by a -
• The rwx after that shows permissions for the group.
• The final rwx shows the permissions for all others.

As an example, -rwxrw-r-- means this file has read, write and execute permissions for the owner, read and write permission for the group, and read permission for all others.

Changing owners

Rule of thumb, the owner of a file will have the most permissions regarding reading, writing and executing. So sometimes you might come across a scenario where you might need to transfer ownership. To do that, simply use

chown new_user filename

Optional: Use -R flag for recursively changing all permissions inside a directory.

Bonus: Nuclear option - 777

Not recommended, however, to open up permissions to everyone for a particular file or directory you can use the command:

sudo chmod -R 777 directoryname

Similarly, different codes can be used for specifying different variations of permissions.

Thanks for reading. If you want to go more in-depth, check out this great handbook for Linux SysOps.