systemd · medium · solved in-browser (no VM needed) · 3 tiered hints
Write the socket unit /etc/systemd/system/ftpish.socket that listens on TCP port 2121 and spawns a fresh service instance per connection. In [Socket] set ListenStream=2121 and Accept=yes. Add an [Install] section with WantedBy=sockets.target. (systemd will start ftpish@.service per connection.) (Authored config, graded structurally — the engine isn't run here.)
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