linux command to check port occupancy and solve port occupancy

For example, check whether the 4200 port number is occupied.
Enter the command
sudo lsof -i: 4200 in the terminal .
If the port is occupied, the PID value will appear, otherwise there will be no

sudo lsof -i:4200
appears after pressing enter:

COMMAND     PID USER   FD   TYPE  DEVICE SIZE/OFF NODE NAME
ng\x20ser 26462 root   23u  IPv4 6676157      0t0  TCP localhost:4200 (LISTEN)
ng\x20ser 26462 root   28u  IPv4 6680806      0t0  TCP localhost:4200->localhost:60652 (FIN_WAIT2)
ng\x20ser 26462 root   30u  IPv4 6786256      0t0  TCP localhost:4200->localhost:42774 (ESTABLISHED)
electron  26572 root  110u  IPv4 6784563      0t0  TCP localhost:42774->localhost:4200 (ESTABLISHED)
node      26731 root  124u  IPv4 6680805      0t0  TCP localhost:60652->localhost:4200 (CLOSE_WAIT)

Then kill the process and enter the command

sudo kill 26462

Explain that 26462 is the PID value that appears above sudo lsof -i:4200