The add-apt-repository command is used to add a repository to the APT (Advanced Package Tool) system on Ubuntu and Debian Linux systems. If you get an error saying that the add-apt-repository command is not found, it means that the package that provides this command is not installed on your system.
To fix this error, you can install the software-properties-common package, which provides the add-apt-repository command. To do this, open a terminal window and type the following command:
sudo apt-get install software-properties-commonSource:www.lautturi.com
This will install the software-properties-common package and all of its dependencies. Once the installation is complete, you should be able to use the add-apt-repository command without any issues.
Keep in mind that you will need to have root privileges (using the sudo command) to install packages on your system. Additionally, make sure that your system is up-to-date by running the apt-get update command before trying to install the software-properties-common package.