Why does npm start gives me an error about the port?
Probably port is already in use. I face similar issue when i first run react-native run-android and then npm start. I solve it like this: First, get the id of the process running in port 8081:
sudo lsof -i :8081
then kill it:
kill -9 ID_SHOWN_FROM_PREVIOUS_CMD
ID_SHOWN_FROM_PREVIOUS_CMD will be something like 25534 So after it, first run npm start and then react-native run-android
Find the port:
netstat -a -n -o | find "8081"
You need to find the pid. Second step, kill that:
taskkill /PID 5952 /F
In this case the pid is "5952".