Have you checked borgbackup docs, FAQ, and open Github issues?

Yes

Is this a BUG / ISSUE report or a QUESTION?

QUESTION

Describe the problem you're observing.

What exactly does the following mean?

Running borg init via a borg serve --append-only server will not create an append-only repository.

My understanding is that if the server is configured using the following authorized_keys, when initializing a repo using borg init --encryption=keyfile-blake2 "borg@server:backup", --append-only on the server is ignored.

command="borg serve --append-only --restrict-to-repository /home/borg/backup --storage-quota 10G",restrict ssh-rsa ...

This doesn't feel logical to me as the server config should supersede client (for security reasons). Also, I would like to use two SSH keys, one with --append-only and one without (using a key that requires a YubiKey for increased security).

command="borg serve --append-only --restrict-to-repository /home/borg/backup --storage-quota 10G",restrict ssh-rsa ...

vs

command="borg serve --restrict-to-repository /home/borg/backup --storage-quota 10G",restrict ssh-rsa ...

Can someone please confirm how this works?