Missing Signed-By in the sources.list(5)
I came across this error on a DigitalOcean droplet running Ubuntu the other day, when running:
sudo apt update
I found out that I had a file named: third-party.sources.
The contents was:
Types: deb
URIs: http://mirrors.digitalocean.com/ubuntu/
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
In another droplet, the file: /etc/apt/sources.list.d/ubuntu.sources contained a similar entry and:
Types: deb
URIs: http://mirrors.digitalocean.com/ubuntu/
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
## Ubuntu security updates. Aside from URIs and Suites,
## this should mirror your choices in the previous section.
Types: deb
URIs: http://security.ubuntu.com/ubuntu
Suites: noble-security
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Where the same file in the first droplet looked as follow:
Types: deb
URIs: http://mirrors.digitalocean.com/ubuntu/
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
So I copied the contents of third-party.sources to /etc/apt/sources.list.d/ubuntu.sources and removed third-party.sources and the warning went away.