Fix Mono Repo (apt-key is deprecated)
This works for any “legacy” repository that gives the warning
W: https://download.mono-project.com/repo/ubuntu/dists/stable-focal/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
We will also fix the arch notice
N: Skipping acquire of configured file ‘main/binary-i386/Packages’ as repository ‘https://download.mono-project.com/repo/ubuntu stable-focal InRelease’ doesn’t support architecture ‘i386’
This example will show how to fix the mono-project repository on Ubuntu / Pop!_OS, but you can adapt it to any repository with the same issues.
Locate problematic key
First we need to know what is the mono key in the keyring. I had some trouble to find it, since the name is not obvious in this case. So I went back to the download instructions to be sure.
You can list the keys with
$ sudo apt-key list
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
/etc/apt/trusted.gpg
--------------------
pub rsa4096 2017-06-22 [SC]
63C4 6DF0 140D 7389 6142 9F4E 204D D8AE C33A 7AFF
uid [ unknown] Pop OS (ISO Signing Key) <info@system76.com>
sub rsa4096 2017-06-22 [E]
pub rsa2048 2017-12-19 [SC] [expires: 2023-12-17]
D563 11E5 FF3B 6F39 D5A1 6ABE 18DF 3741 CDFF DE29
uid [ unknown] philandro Software GmbH <info@philandro.com>
sub rsa2048 2017-12-19 [E] [expires: 2023-12-17]
pub rsa2048 2014-08-04 [SC]
3FA7 E032 8081 BFF6 A14D A29A A6A1 9B38 D3D8 31EF
uid [ unknown] Xamarin Public Jenkins (auto-signing) <releng@xamarin.com>
sub rsa2048 2014-08-04 [E]
We are interested in this first block, which shows the keys in /etc/apt/trusted.gpg.
The mono-project key is the Xamarin Public Jenkins key.
This is how the installation instructions shows it
sudo apt install gnupg ca-certificates
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys 3FA7E0328081BFF6A14DA29AA6A19B38D3D831EF
echo "deb https://download.mono-project.com/repo/ubuntu stable-focal main" | sudo tee /etc/apt/sources.list.d/mono-official-stable.list
sudo apt update
Note that the key is the same from the list above
Export key
Now we export the key using the last 8 digits of the key
sudo apt-key export D3D831EF | sudo gpg --dearmour -o /usr/share/keyrings/mono.gpg
If you are doing this for other software, change the key value and the gpg file name above
Edit repository
Now we edit the repository file.
sudo nano /etc/apt/sources.list.d/mono-official-stable.list
We will add the signed-by tag for the key, as well as the arch tag to remove the warning about it not having i386 packages.
Note: If you need i386 packages, just don’t add the arch=amd64 part, but you may need to add trusted=yes as mentioned in my other post. However, they do not build for i386 anymore because Ubuntu does not include the needed packages for that anymore.
deb [arch=amd64 signed-by=/usr/share/keyrings/mono.gpg] https://download.mono-project.com/repo/ubuntu stable-focal main
Delete key from trusted.gpg
sudo apt-key del D3D831EF
Check
Now we just check if all is fine
sudo apt update
This should run without errors or warnings now
Cheers! 🍻
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