how to check if port is free in linux code example

Example 1: linux how to see ports in use

# Any of the following
sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo lsof -i:22 # see a specific port such as 22
sudo nmap -sTU -O IP-address-Here

Example 2: free port in linux

netstat -tulnap        // list all ports and processes
netstat -anp|grep "port_number"     // show port details
sudo fuser -k Port_Number/tcp       // free the port needed
# or
lsof -n -i :'port-number' | grep LISTEN  // get port details
# sample  response:  java   4744 (PID)  test  364u  IP0 asdasdasda   0t0  TCP *:port-number (LISTEN)
kill -9 PID  // free port

Example 3: check if port is running in ubuntu

# Any of the following
sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo lsof -i:22 # Port
sudo nmap -sTU -O IP-address-Here