Error: listen EADDRINUSE :::8081

It means the port 8081 is taken by node daemon, you need to find the PID to kill.

sudo lsof -i :8081
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
node 10038 46916597qq 13u IPv6 0x8c26a6ed2b298fbd 0t0 TCP *:sunproxyadmin (LISTEN)


sudo kill -9 10038


Simple and easy!