If you have a particular repository you want to use for your Linux VM from within Azure to install packages from, simply follow the below instructions. For our example, we will update the repository for installing Nginx.
First, sudo su to elevate to root.
Next, vim /etc/apt/sources.list (you may use your favorite text editor)
Add the following lines to the file:
*taken from this page here.
Save the file.
cd to /etc/apt/
to download the necessary key to authenticate the repository signature, which is necessary for Debian/Ubuntu.
To add the downloaded key to the apt program keyring, type the following command:
apt-key add nginx_signing.key
Then to complete the install from the new repo, type the following:
apt-get update apt-get install nginx
And that’s it! You should see your install pull from the newly specified repository instead of the default one specified in your sources.list file.