After upgrading Katello from 3.12 to 3.13 I get the following output:
Upgrade Step 4/4: katello:upgrades:3.13:republish_deb_metadata. Input file /var/lib/pulp/0004_deb_repo_republish_candidates.txt was not readable.
You can manually use an alternate input file by running "foreman-rake katello:upgrades:3.13:republish_deb_metadata[<path>]"
foreman-rake upgrade:run finished successfully!
The absence of this file most likely means you do not have any affected repositories.
If you do not have any Debian/Ubuntu repositories (presumably true for the vast majority of users) you don’t have any affected repositories.
If your pulp instance is running on the same machine as your Foreman/Katello (presumably 99% of existing set ups) and the pulp data base migrations were successful, and you don’t have the mentioned file, then you don’t have any affected repositories.
The rake task in question fixes a bug mainly known to affect all Ubuntu repositories with a dash (-) in their name (e.g.: “bionic-updates”), as well as any Debian security repositories. If you don’t have any of those, and you don’t have the mentioned file, then most likely you don’t have any affected repositories.