The backup server directory changed permissions on me again and I lost password-less login. It changed to 775 instead of 751 as is apparently needed for password-less sftp and rsync to work.
I had been working with it when it happened so I suspected it was something I did. It turns out the kludgy rsync command we are forced to use to delete directories recursively is changing the . directory permissions.
Here is the command that I use to delete full directories on the personal backup server.
The empty source directory I was using to force the deletion had the 775 permission that were being replicated to the backup server. I changed it to 751 and I am no longer losing the password-less ssh permissions.
Why can’t we have ssh into the backup server with a limited command set (mv, rm, cp, chmod, chgrp, etc…) and no outbound network access? Life would be so much simpler…