Users on Linux

It's necessary to elaborate a bit how users and permissions work on Linux systems.

The most important user present on every Linux distribution is the root user, sometimes called as a superuser. This guy is the master and can do basically everything. As a consequence of this fact is extermaly important to not let anyone get root access to your server since then he can do everything. It's also quite dangerous work as a root all the time, since you can e.g. mistakenly erase your system partition and so on. For that we are going to create new user which will get the permissions only when he asks for them. For this purpose we will use package called sudo (from superuser do).

Every file (and virtually everything is a file in Linux) specify permissions for owner, group and others. There are three types of permissions: read, write and execute. More about permissions can be found out e.g. here.

Before that, we need to explain some theory from elementary security and cryptography.

Storing passwords

Users are authenticated by passwords. We've learned from past that storing passwords cannot be done in plain text, since when someone steal this text, he automatically gets access to all accounts listed there. For that reason we hash the passwords and store them in hashed form. Furthermore, the salt is used while hashing. The file with stored hashes is usually in /etc/passwd.

For changing a password for a current user passwd is used. Type passwd and change the main root password to something reasonably strong. You are not going to type this password a lot, since we are going to use other user for common system maintenance.


Here we just need to realize that you just don't want anyone to read some confidential file which don't belong to them or execute some malicious script. For this purpose there is an idea of sandboxing. That means that we separate environments of different users - he could touch only what he creates and cannot touch anything which we don't explicitly allow. This scheme will be recurring once more when we will setting up e.g. web server.

Creating a new user

Now we need to install first necessary package. You have to be logged as the root and have internet connection. Update the system by pacman -Syu and then install sudo package by running pacman -S sudo.

We now want to add regular user (think about it as a god who is creating humans). This can be done by: useradd -m -G wheel Bob. It will create user called “Bob”. There are also some other switches in command. -m is for creating bob’s sandbox for his files in /home/bob and -G adds him to the wheel group.

Why? Remember that sudo can grant you superusers privileges. Every user who is in wheel group will have the ability to use sudo. For that we need to edit sudo configuration file. Type: visudo, find this line: # %wheel ALL=(ALL) ALL and delete # character (for future reference, this means to “uncomment line”). It will look like this %wheel ALL=(ALL) ALL. Save and exit. We now need to set password for bob. Do it by typing passwd bob. From now you should be always working as a bob instead of root. When you'll want to do something what only root can do, e.g. this_command, you'll have to type sudo this_command and insert bob's password (not the root one!). It's annoying, but save.