Answers for "socket port already in use"

Error: That port is already in use.

# list the running ports
$ netstat -ltnp
# kill specific port in my case for django 8000. kill using PID
$ kill -9 31434

Port 3000 is already in use.

If this error is in nextjs

in package.json, update scripts:
"dev": "PORT=3001 next dev",

you can choose other port, and also change for start.