Port forwarding with ssh

• open a port to it on my local machine ssh -N -L 5050:localhost:5000 cmslpc307.fnal.gov

• Can check which ports are in use with

  lsof -iTCP -sTCP:LISTEN -P -n
  

  That lists every port something is listening on, with the process and PID. The flags: -P keeps ports numeric (no :http aliasing), -n skips DNS so it's instant, -sTCP:LISTEN filters to listeners (drops the noise of established connections).

  Check one specific port — the question you'll actually ask most ("is 5000 taken?"):

  lsof -i :5000
  

  Which ports to use?

"pick something for my app" zone is the 8000s and the 3000–9000 range generally — 8080, 8000, 8888, 5000, 3000 are all common dev defaults precisely because they're memorable and rarely conflict with system services.