Freeze a running server and free its TCP port — without killing it. Resume later with the same PID, memory, and state. park reaches inside the target process and injects close(fd) via ptrace (Linux) or Mach thread injection (macOS) to release the listening socket. Resume recreates the listener at the same fd number. Works with uvicorn, FastAPI, Flask, python http.server, and more. Single binary, no deps. Install: curl -fsSL https://raw.githubusercontent.com/mr-vaibh/park/main/install.sh | sh

Customer.io — Automate Messaging Everywhere — Startups Get 12 Months Free

Automate Messaging Everywhere — Startups Get 12 Months Free

Hey PH! I'm Vaibhav, the maker. I built park because I was tired of killing my uvicorn dev server every time I needed port 8000 for something else. Restarting meant losing in-memory caches, websocket clients, and warm-up time. The core trick: SIGSTOP alone doesn't free the port — the kernel keeps the socket bound. park uses ptrace (Linux) and Mach thread injection (macOS) to reach inside the process and close the listening socket fd. That's what actually releases the port. The macOS implementation was especially tricky — I had to create a brand-new thread inside the target process via Mach APIs because hijacking existing threads corrupted their kernel state. Also had to re-register the listener with kqueue and set O_NONBLOCK so async frameworks like uvicorn survive the roundtrip. Would love to hear what you think. Happy to answer any questions about the internals!

Customer.io — Automate Messaging Everywhere — Startups Get 12 Months Free

Automate Messaging Everywhere — Startups Get 12 Months Free

park

Pause a process and free its TCP port. Resume later.

Pause a process and free its TCP port. Resume later.