orphaned UID (numeric owner)

A file whose owner id matches no account on this machine: ls -l has no name to print and shows the number instead, -rw-r----- 1 998 998 config.php. Ownership does not travel inside the archive the way people assume. tar records both the number and the name; extracted by root, it restores owners by looking the name up among the local accounts, and falls back to the bare number when that account does not exist yet. On the original machine the distinction is invisible. On a rebuilt machine it decides everything: adduser --system hands out the first free UID, so the order the accounts were created in changes the answer. Hence the rule — accounts before files. ls -ln is the command that asks the question, and a service that can no longer read its own configuration is the symptom that does not explain itself.