Where the second Jupyter server lands when 8888 is already taken.
Jupyter servers try their configured port and then walk upward to the next free one, so a machine already running a notebook on 8888 puts the next on 8889. The same happens with any tool that retries the next port. IANA registers 8889 as ddi-tcp-2 (Desktop Data), which is not something you will encounter. Treat it exactly as you would 8888: identify the process, and assume a notebook until proven otherwise.
Do not expose
Same reasoning as 8888 — if this is a notebook server it is arbitrary code execution for anyone who can reach it and get past the token.
$ curl -sI http://127.0.0.1:8889/Seen 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.