I keep getting [Errno 98] Address already in use But the address is not in use. I tried to change the ip and port but It isn't budging. from fastapi import FastAPI app = FastAPI() @app.get("/") async def main(): return {"message": "Helloworld,FastAPI"} if __name__ == '__main__': import uvicorn uvicorn.run(app, host="127.0.0.1", port=8000) uvicorn main:app --reload also tried uvicorn main:app --host=172.0.0.2 --port=5000 then it gives [Errno 99] error while attempting to bind on address ('172.0.0.2', 5000): cannot assign requested address I tried running a flask dev server and it was also running on 172.0.0.1 without a problem? using Arch-Manjaro-Linux I used nmap to see what the fuss was about. But only 2 ports in use on the 127.0.0.1 IP PORT STATE SERVICE 631/tcp open ipp 8000/tcp open http-alt I would use another IP and port but it gives an error that it can't be assigned. Continue reading...