LoadCredential= doesn't fail with 243/CREDENTIALS but silently skips if non-existent ID is specified (without explicit PATH) about systemd

[arianvp]

I guess this is somewhat similar to #27373 by the way (Except this one is for paths instead of unix sockets)

[YHNdnzj]

This is intentional: https://github.com/systemd/systemd/blob/main/src/core/exec-credential.c#L500

[arianvp]

To give an anecdote about why this bit me:

Nix uses the existence of the signing key whether packaging signing is enabled or not after building a package. So a missing credential caused my packages not to be signed. We can brush that off as "Nix made a stupid design choice there" but that's why I ran into this.

I'm fine with documenting this as "expected behaviour" by the way. and perhaps that means we can close #27373 with the same reason

[YHNdnzj]

Hmm, I think #27373 can serve as a valid RFE?

[arianvp]

Well. If we can agree on "Hey it's up to the application to actually check that the credential exists" then we can just make all LoadCredential= stanzas work the same. That is: Always succeed silently if the credential doesn't exist. Then people do not get surprised. And then we do not need to change the AF_UNIX protocol to handle "Credential does not exist" scenario"

[poettering]

This is intended, the idea is that we import creds down the tree that are specified, but gracefully handle the ones that aren't.