How to get the gpg key for a repository?

Question

When adding a repository through add-apt-repository a new gpg key will be add.

e,g:

sudo add-apt-repository ppa:some-ppa

You will be asked to press Enter to import the gpg key. I need to get the gpg key for ppa:some-ppa without executing add-apt-repository.

Is it possible to get the gpg key before adding the repository (before executing add-apt-repository) from command line?

Answer 1

Here's a procedure that essentially tries to replicate sudo add-apt-repository ppa:owner/name but lets you do all the steps (including downloading the GPG key) manually:

1. Go to the page of the owner/name PPA on Launchpad: https://launchpad.net/~owner/+archive/ubuntu/name.

2. Look for signing key's fingerprint on the page.

   In the page there should be a section "Fingerprint:" with the key fingerprint printed below.

3. Download the PPA key into a specific directory on your system.

   • Download the key via the URL https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x<fingerprint>, where <fingerprint> is the value you found in step 2.
   • Dearmor the key and put it in /etc/apt/trusted.gpg.d/owner_ubuntu_name.gpg.

4. Create a file /etc/apt/sources.list.d/owner-ubuntu-name.list with these contents:

   deb http://ppa.launchpad.net/owner/name/ubuntu <codename> main
   

   where <codename> is what lsb_release -sc gives.

5. Enjoy the new software that the PPA provides!

Example, Safe Eyes (ppa:slgobinath/safeeyes) software

1. Go to https://launchpad.net/~slgobinath/+archive/ubuntu/safeeyes

2. As of 7th March 2023 the page says:

   Fingerprint:

   53A5446DABC1B038506E33F5E71C080343BB5214

3. Run:

   curl -S "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x53A5446DABC1B038506E33F5E71C080343BB5214" \
     | sudo gpg --batch --yes --dearmor --output "/etc/apt/trusted.gpg.d/slgobinath_ubuntu_safeeyes.gpg"
   

4. Run:

   echo "deb https://ppa.launchpadcontent.net/slgobinath/safeeyes/ubuntu $(lsb_release -sc) main" \
     | sudo tee /etc/apt/sources.list.d/slgobinath-ubuntu-safeeyes.list
   

5. Run sudo apt update && sudo apt install safeeyes and enjoy your new software!