Overview
This warning means that a key is stored in /etc/apt/trusted.gpg
which is a deprecated keyring:
W: https://example.com/repo: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
Fixing
Find the offending key:
sudo apt-key list | grep -i <keyword> --before --after 3
Any keys marked
expired
can be ignored.An offending key will be listed under the /etc/apt/trusted.gpg section like this:
pub rsa4096 2015-03-22 [SC] CD66 5CBA 0E2F 88B7 373F 7CB9 9720 3C7B 3ADC A79D uid [ unknown] Plex Inc. sub rsa4096 2015-03-22 [E]
The line we are interested in is
CD66 5CBA 0E2F 88B7 373F 7CB9 9720 3C7B 3ADC A79D
.From the line above, take the last 8 characters and remove the space, resulting in
3ADCA79D
. Import that GPG key in its dedicated file:sudo apt-key export 3ADCA79D | sudo gpg --dearmour -o /etc/apt/trusted.gpg.d/plex.gpg