This would be the equivalent of “full mirror” sync mode for yum content. This is not currently implemented for APT content. For technical reasons, we first need to finish with “structured APT for Katello” before we can consider placing a full mirror mode on the roadmap.
In short: This feature may happen one day, but there is currently no ETA, it is some ways off.
Having re-read this old thread, I can say apt list --upgradable with subscription-manager will only work once the “structured APT for Katello” story is done.
Sorry, the error msg is the same but the situation is not, because I don’t use subscription-manager with ubuntu. I have a source.list file with the repository configured.
Broot@linuxform3:~# apt update
…
Ign :2 https://MYSERVER/pulp/content/XXX/Library/custom/Ubuntu jammy InRelease
Ign :3 https://MYSERVER/pulp/content/XXX/Library/custom/Ubuntu jammy-updates InRelease
Atteint :4 http://MYSERVER/pulp/content/XXX/Library/custom/Mozilla_Ubuntu-Debian/Mozilla_Ubuntu-Debian jammy InRelease
Ign :5 https://MYSERVER/pulp/content/XXX/Library/custom/Ubuntu jammy-security InRelease
Err :6 https://MYSERVER/pulp/content/XXX/Library/custom/Ubuntu jammy Release
404 Not Found [IP : … 443]
Err :7 https://MYSERVER/pulp/content/XXX/Library/custom/Ubuntu jammy-updates Release
404 Not Found [IP : … 443]
Err :8 https://MYSERVER/pulp/content/CEA/Library/custom/Ubuntu jammy-security Release
404 Not Found [IP : … 443]
lockquote
All the URL referenced here are OK, and the Release files exists (and are signed) .
But the solution is probably the same.