The other day we discussed how to [**list the installed repositories**][2] in RPM and DEB-based systems. Today, we are going to learn how to delete a repository along with its GPG key in Ubuntu. For those wondering, a repository (shortly **repo** ) is a central place where the developers keep the software packages. The packages in the repositories are thoroughly tested and built specifically for each version by Ubuntu developers. The users can download and install these packages on their Ubuntu system using **Apt****package manager**. Ubuntu has four official repositories namely **Main** , **Universe** , **Restricted** and **Multiverse**.
Apart from the official repositories, there are many unofficial repositories maintained by developers (or package maintainers). The unofficial repositories usually have the packages which are not available in the official repositories. All packages are signed with pair of keys, a public and private key, by the package maintainer. As you already know, the public key is given out to the users and the private must be kept secret. Whenever you add a new repository in the sources list, you should also add the repository key if Apt package manager wants to trust the newly added repository. Using the repository keys, you can ensure that you’re getting the packages from the right person. Hope you got a basic idea about software repositories and repository keys. Now let us go ahead and see how to delete the repository and its key if it is no longer necessary in Ubuntu systems.
### Delete A Repository In Ubuntu
Whenever you add a repository using “add-apt-repository” command, it will be stored in **/etc/apt/sources.list** file.
To delete a software repository from Ubuntu and its derivatives, just open the /etc/apt/sources.list file and look for the repository entry and delete it.
```
$ sudo nano /etc/apt/sources.list
```
As you can see in the below screenshot, I have added [**Oracle Virtualbox**][3] repository in my Ubuntu system.
![][4]
virtualbox repository
To delete this repository, simply remove the entry. Save and close the file.
If you have added PPA repositories, look into **/etc/apt/sources.list.d/** directory and delete the respective entry.
Alternatively, you can delete the repository using “add-apt-repository” command. For example, I am deleting the [**Systemback**][5] repository like below.
```
$ sudo add-apt-repository -r ppa:nemh/systemback
```
Finally, update the software sources list using command:
```
$ sudo apt update
```
### Delete Repository keys
We use “apt-key” command to add the repository keys. First, let us list the added keys using command:
As you can see in the above output, the long (40 characters) hex value is the repository key. If you want APT package manager to stop trusting the key, simply delete it using command:
