Troubleshooting

Address already in use

You can easily kill the Flask application and restart it, but sometimes you will get an error that the address is already in use. To recover from this problem, run the lsof program to see which program that applies the 5000 port (Flask runs its server on http://127.0.0.1:5000, which means that it uses the 5000 port). Find the PID of the program that occupies the port and force abortion of that program:

Terminal> lsof -i :5000
COMMAND   PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
python  48824  hpl    3u  IPv4 1128848      0t0  TCP ...
Terminal> kill -9 48824
You are now ready to restart a Flask application.