Introduction
Adding and removing users on a Linux system is one of the most important system administration tasks to familiarize yourself with. When you create a new system, you are often only given access to the root account by default.
While running as the root user gives you complete control over a system and its users, it is also dangerous and possibly destructive. For common system administration tasks, it’s a better idea to add an unprivileged user and carry out those tasks without root privileges. You can also create additional unprivileged accounts for any other users you may have on your system. Each user on a system should have their own separate account.
For tasks that require administrator privileges, there is a tool installed on Ubuntu systems called sudo. Briefly, sudo allows you to run a command as another user, including users with administrative privileges. In this guide, you’ll learn how to create user accounts, assign sudo privileges, and delete users.
Prerequisites
To complete this tutorial, you will need access to a server running Ubuntu 18.04. Ensure that you have root access to the server and firewall enabled. To set this up, follow our Initial Server Setup Guide for Ubuntu 18.04.
Adding a User
If you are signed in as the root user, you can create a new user at any time by running the following:
adduser newuser
If you are signed in as a non-root user who has been given sudo privileges, you can add a new user with the following command:
sudo adduser newuser
Either way, you will be required to respond to a series of questions:
Assign and confirm a password for the new user.
Enter any additional information about the new user. This is optional and can be skipped by pressing ENTER if you don’t wish to utilize these fields.
Finally, you’ll be asked to confirm that the information you provided was correct. Press Y to continue.
Your new user is now ready for use and can be logged into with the password that you entered.
If you need your new user to have administrative privileges, continue on to the next section.
Granting a User Sudo Privileges
If your new user should have the ability to execute commands with root (administrative) privileges, you will need to give the new user access to sudo. Let’s examine two approaches to this task: first, adding the user to a pre-defined sudo user group, and second, specifying privileges on a per-user basis in sudo’s configuration.
Adding the New User to the Sudo Group
By default, sudo on Ubuntu 18.04 systems is configured to extend full privileges to any user in the sudo group.
You can view what groups your new user is in with the groups command:
groups newuser
newuser : newuser
By default, a new user is only in their own group because adduser creates this in addition to the user profile. A user and its own group share the same name. In order to add the user to a new group, you can use the usermod command:
usermod -aG sudo newuser
The -aG option tells usermod to add the user to the listed groups.
Please note that the usermod command itself requires sudo privileges. This means that you can only add users to the sudo group if you’re signed in as the root user or as another user that has already been added as a member of the sudo group. In the latter case, you will have to precede this command with sudo, as in this example:
sudo usermod -aG sudo newuser
Specifying Explicit User Privileges in /etc/sudoers
As an alternative to putting your user in the sudo group, you can use the visudo command, which opens a configuration file called /etc/sudoers in the system’s default editor, and explicitly specify privileges on a per-user basis.
Using visudo is the only recommended way to make changes to /etc/sudoers because it locks the file against multiple simultaneous edits and performs a validation check on its contents before overwriting the file. This helps to prevent a situation where you misconfigure sudo and cannot fix the problem because you have lost sudo privileges.
If you are currently signed in as root, run the following:
visudo
If you are signed in as a non-root user with sudo privileges, run the same command with the sudo prefix:
sudo visudo
Traditionally, visudo opened /etc/sudoers in the vi editor, which can be confusing for inexperienced users. By default on new Ubuntu installations, visudo will use the nano text editor, which provides a more convenient and accessible text editing experience. Use the arrow keys to move the cursor, and search for the line that reads like the following:
/etc/sudoers
root ALL=(ALL:ALL) ALL
Below this line, add the following highlighted line. Be sure to change newuser to the name of the user profile that you would like to grant sudo privileges:
/etc/sudoers
root ALL=(ALL:ALL) ALL
newuser ALL=(ALL:ALL) ALL
Add a new line like this for each user that should be given full sudo privileges. When you’re finished, save and close the file by pressing CTRL + X, followed by Y, and then ENTER to confirm.
Testing Your User’s Sudo Privileges
Now your new user is able to execute commands with administrative privileges.
When signed in as the new user, you can execute commands as your regular user by typing commands as normal:
some_command
You can execute the same command with administrative privileges by typing sudo ahead of the command:
sudo some_command
When doing this, you will be prompted to enter the password of the regular user account you are signed in as.
Deleting a User
In the event that you no longer need a user, it’s best to delete the old account.
You can delete the user itself, without deleting any of their files, by running the following command as root:
deluser newuser
If you are signed in as another non-root user with sudo privileges, you would use the following:
sudo deluser newuser
If, instead, you want to delete the user’s home directory when the user is deleted, you can issue the following command as root:
deluser --remove-home newuser
If you’re running this as a non-root user with sudo privileges, you would run the same command with the sudo prefix:
sudo deluser --remove-home newuser
If you previously configured sudo privileges for the user you deleted, you may want to remove the relevant line again:
visudo
Or use the following command if you are a non-root user with sudo privileges:
sudo visudo
/etc/sudoers
root ALL=(ALL:ALL) ALL
newuser ALL=(ALL:ALL) ALL # DELETE THIS LINE
This will prevent a new user created with the same name from being accidentally given sudo privileges.
Conclusion
You should now have a fairly good handle on how to add and remove users from your Ubuntu 18.04 system. Effective user management will allow you to separate users and give them only the access that they are required to do their job.
For more information about how to configure sudo, check out our guide on how to edit the sudoers file.
