Unassigned at IANA, with no service name and no convention — identify by banner or not at all.
IANA lists 1009 explicitly as Unassigned. Its neighbour is a small piece of registry folklore: 1008/udp carries the comment "Possibly used by Sun Solaris????", which is as much certainty as this stretch of the registry offers. nmap has 1009/tcp as unknown and very rarely open. Anything answering is a local choice, and because the port is below 1024 the process that bound it had root.
Expose with care
No registration and no convention means no assumptions — fingerprint the listener before treating it as benign.
$ sudo lsof -nP -iTCP:1009 -sTCP:LISTENSeen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.