Linux

To check the listening ports and applications on Linux:

1. Open a terminal application i.e. shell prompt.
2. Run any one of the following command on Linux to see open ports:

# Variante 1

sudo lsof -i -P -n

Consider the following line from above outputs:

sshd    85379     root    3u  IPv4 0xffff80000039e000      0t0  TCP 10.86.128.138:22 (LISTEN)

• sshd is the name of the application.
• 10.86.128.138 is the IP address to which sshd application bind to (LISTEN)
• 22 is the TCP port that is being used (LISTEN)
• 85379 is the process ID of the sshd process

# Variante 2

sudo ss -tulwn

Where ss command options are as follows:

• -t : Show only TCP sockets on Linux
• -u : Display only UDP sockets on Linux
• -l : Show listening sockets. For example, TCP port 22 is opened by SSHD server.
• -p : List process name that opened sockets
• -n : Don’t resolve service names i.e. don’t use DNS

Windows

netstat -a 

PS-1: To list any process listening to the particular port, for example 8080, in Linux :

lsof -i:8080

PS-2: To kill a process listening on a particular port, for example 8080 (in Linux):

kill -9 $(lsof -t -i:8080)

PS: -9 corresponds to the SIGKILL - terminate immediately/hard kill. It implies the process will be killed forcefully.

Reference :

https://www.cyberciti.biz/