How do I close an open port from the terminal on the Mac?

Question

1. Find out the process ID (PID) which is occupying the port number (e.g., 5955) you would like to free

   sudo lsof -i :5955
   

2. Kill the process which is currently using the port using its PID

   sudo kill -9 PID
   

To find the process try:

sudo lsof -i :portNumber

Kill the process which is currently using the port using its PID

kill PID

and then check to see if the port closed. If not, try:

kill -9 PID

I would only do the following if the previous didnt work

sudo kill -9 PID

Just to be safe. Again depending on how you opened the port, this may not matter.

In 2018 here is what worked for me using MacOS HighSierra:

sudo lsof -nPi :yourPortNumber

then:

sudo kill -9 yourPIDnumber

very simple find port 5900:

sudo lsof -i :5900

then considering 59553 as PID

sudo kill 59553

However you opened the port, you close it in the same way. For example, if you created a socket, bound it to port 0.0.0.0:5955, and called listen, close that same socket.

You can also just kill the process that has the port open.

If you want to find out what process has a port open, try this:

lsof -i :5955

If you want to know whether a port is open, you can do the same lsof command (if any process has it open, it's open; otherwise, it's not), or you can just try to connect to it, e.g.:

nc localhost 5955

If it returns immediately with no output, the port isn't open.

It may be worth mentioning that, technically speaking, it's not a port that's open, but a host:port combination. For example, if you're plugged into a LAN as 10.0.1.2, you could bind a socket to 127.0.0.1:5955, or 10.0.1.2:5955, without either one affecting the other, or you could bind to 0.0.0.0:5955 to handle both at once. You can see all of your computer's IPv4 and IPv6 addresses with the ifconfig command.

One liner is best

kill -9 $(lsof -i:PORT -t) 2> /dev/null

Example : On mac, wanted to clear port 9604. Following command worked like a charm

 kill -9 $(lsof -i:9604 -t) 2> /dev/null