APT repositories:

Repositories are groups of software packages that could be used with the "apt" command to install, remove or update software on a system.
We can add new software packages to the APT repository.

We could find the "configuration" files related to the "apt" tool in the below locations:

Under the "sources.list.d" directory, we could create a file, for example "our-respository.list" that would do the same job as the "sources.list" file.

The "sources.list":

Inside the 
"sources.list" file, we could see a lot of repositories - that contain software - that the apt utility could use to install software on a system, for example:

  • https://download.docker.com : address of the repository.
  • linux/debian : folder in the repository.
  • buster : the version of the software.
  • stable : the type of the repository.
Adding a new repository:

We could add a new repository in the "sources.list" file, or create a new file in the "sources.list.d" folder. 
We could create a file named "my_repository.list" for example.


  • stable: version of the software
  • non-free: the type of repository, it could also be "main" or "restricted".
Then we run the below command to update the system:

Adding the GPG key of the repository:

After adding the repository to the system, we would need to add its GPG key.

We can download the GPG key for the repository, and add it to our system using the below command for example:

We can then check, if the key was added properly using the below command:

Then we update the system with our new addition, using the below command:

Now, we are ready to install our software from the new repository using the below command: 

The "ppa" tool:

The "ppa" tool can add a repository and its GPG key in one command, for example: 

This will add the repository to the "sources.list" file, it will also download the GPG key and run the "apt update".

We could then install our software, using the usual command:

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