On macOS Big Sur and later, use this command:

sudo lsof -i -P | grep LISTEN | grep :$PORT

or to just see just IPv4:

sudo lsof -nP -i4TCP:$PORT | grep LISTEN

On older versions, use one of the following forms:

sudo lsof -nP -iTCP:$PORT | grep LISTEN
sudo lsof -nP -i:$PORT | grep LISTEN

Substitute $PORT with the port number or a comma-separated list of port numbers.

Prepend sudo (followed by a space) if you need information on ports below #1024.

The -n flag is for displaying IP addresses instead of host names. This makes the command execute much faster, because DNS lookups to get the host names can be slow (several seconds or a minute for many hosts).

The -P flag is for displaying raw port numbers instead of resolved names like http, ftp or more esoteric service names like dpserve, socalia.

See the comments for more options.

For completeness, because frequently used together:

To kill the PID:

sudo kill -9 <PID>
# kill -9 60401

Up to macOS 13 Ventura, every version of macOS supports this:

sudo lsof -iTCP -sTCP:LISTEN -n -P

Personally I've end up with this simple function in my ~/.bash_profile:

listening() {
    if [ $# -eq 0 ]; then
        sudo lsof -iTCP -sTCP:LISTEN -n -P
    elif [ $# -eq 1 ]; then
        sudo lsof -iTCP -sTCP:LISTEN -n -P | grep -i --color $1
    else
        echo "Usage: listening [pattern]"
    fi
}

Then listening command gives you a listing of processes listening on some port and listening smth greps this for some pattern.

Having this, it's quite easy to ask about particular process, e.g. listening dropbox, or port, e.g. listening 22.

lsof command has some specialized options for asking about port, protocol, process etc. but personally I've found above function much more handy, since I don't need to remember all these low-level options. lsof is quite powerful tool, but unfortunately not so comfy to use.

You can also use:

sudo lsof -i -n -P | grep TCP

This works in Mavericks.

Update January 2016

Really surprised no-one has suggested:

lsof -i :PORT_NUMBER

to get the basic information required. For instance, checking on port 1337:

lsof -i :1337

Other variations, depending on circumstances:

sudo lsof -i :1337
lsof -i tcp:1337

You can easily build on this to extract the PID itself. For example:

lsof -t -i :1337

which is also equivalent (in result) to this command:

lsof -i :1337 | awk '{ print $2; }' | head -n 2 | grep -v PID

Quick illustration:

For completeness, because frequently used together:

To kill the PID:

kill -9 <PID>
# kill -9 60401

or as a one liner:

kill -9 $(lsof -t -i :1337)

For the LISTEN, ESTABLISHED and CLOSED ports:

sudo lsof -n -i -P | grep TCP

For the LISTEN ports only:

sudo lsof -n -i -P | grep LISTEN

For a specific LISTEN port (e.g. port 80):

sudo lsof -n -i -P | grep ':80 (LISTEN)'

Or if you just want a compact summary [no service/apps described], go by netstat. The good side here is, no sudo needed:

netstat -a -n | grep 'LISTEN '

Explaining the options used

lsof options (for more details see man lsof):

• -n suppress the host name
• -i for IPv4 and IPv6 protocols
• -P omit port names

netstat options (for more details see man netstat):

• -a for all sockets
• -n don't resolve names, show network addresses as numbers

Tested on High Sierra 10.13.3 and Mojave 10.14.3

The last syntax netstat works on Linux too [apt install net-tools]

lsof comes by default on some Linux distribution

on OS X you can use the -v option for netstat to give the associated pid.

type:

netstat -anv | grep [.]PORT

the output will look like this:

tcp46      0      0  *.8080                 *.*                    LISTEN      131072 131072   3105      0

The PID is the number before the last column, 3105 for this case

On macOS, here's an easy way to get the process ID that's listening on a specific port with netstat. This example looks for a process serving content on port 80:

find server running on port 80

netstat -anv | egrep -w [.]80.*LISTEN

sample output

tcp4  0 0  *.80       *.*    LISTEN      131072 131072    715      0

The 2nd from the last column is the PID. In above, it's 715.

options

-a - show all ports, including those used by servers

-n - show numbers, don't look up names. This makes the command a lot faster

-v - verbose output, to get the process IDs

-w - search words. Otherwise the command will return info for ports 8000 and 8001, not just "80"

LISTEN - give info only for ports in LISTEN mode, i.e. servers

On the latest macOS version you can use this command:

lsof -nP -i4TCP:$PORT | grep LISTEN

If you find it hard to remember then maybe you should create a bash function and export it with a friendlier name like so

vi ~/.bash_profile

and then add the following lines to that file and save it.

function listening_on() {
    lsof -nP -i4TCP:"$1" | grep LISTEN
}

Now you can type listening_on 80 in your Terminal and see which process is listening on port 80.

On Snow Leopard (OS X 10.6.8), running 'man lsof' yields:

lsof -i 4 -a

(actual manual entry is 'lsof -i 4 -a -p 1234')

The previous answers didn't work on Snow Leopard, but I was trying to use 'netstat -nlp' until I saw the use of 'lsof' in the answer by pts.

I am a Linux guy. In Linux it is extremely easy with netstat -ltpn or any combination of those letters. But in Mac OS X netstat -an | grep LISTEN is the most humane. Others are very ugly and very difficult to remember when troubleshooting.

checkout this project/tool: procs

install on MacOs: brew install procs

This allows you control what to display with procs.

To see TCP/UDP Ports, add below to ~/.procs.toml after installing the tool.

[[columns]]
kind = "TcpPort"
style = "BrightYellow|Yellow"
numeric_search = true
nonnumeric_search = false
align = "Left"

[[columns]]
kind = "UdpPort"
style = "BrightGreen|Green"
numeric_search = false
nonnumeric_search = true
align = "Left"

Here is a sample output:

lsof -n -i | awk '{ print $1,$9; }' | sort -u

This displays who's doing what. Remove -n to see hostnames (a bit slower).

I wanted to share this command which works well and prints the headers so you know which column is which:

lsof -iTCP:8080 -sTCP:LISTEN -P -n

Example Output:

This did what I needed.

ps -eaf | grep `lsof -t -i:$PORT`

I made a small script to see not only who is listening where but also to display established connections and to which countries. Works on OSX Siera

#!/bin/bash
printf "\nchecking established connections\n\n"
for i in $(sudo lsof -i -n -P | grep TCP | grep ESTABLISHED | grep -v IPv6 | 
grep -v 127.0.0.1 | cut -d ">" -f2 | cut -d " " -f1 | cut -d ":" -f1); do
    printf "$i : " & curl freegeoip.net/xml/$i -s -S | grep CountryName | 
cut -d ">" -f2 | cut -d"<" -f1
done

printf "\ndisplaying listening ports\n\n"

sudo lsof -i -n -P | grep TCP | grep LISTEN | cut -d " " -f 1,32-35

#EOF

Sample output
checking established connections

107.178.244.155 : United States
17.188.136.186 : United States
17.252.76.19 : United States
17.252.76.19 : United States
17.188.136.186 : United States
5.45.62.118 : Netherlands
40.101.42.66 : Ireland
151.101.1.69 : United States
173.194.69.188 : United States
104.25.170.11 : United States
5.45.62.49 : Netherlands
198.252.206.25 : United States
151.101.1.69 : United States
34.198.53.220 : United States
198.252.206.25 : United States
151.101.129.69 : United States
91.225.248.133 : Ireland
216.58.212.234 : United States

displaying listening ports

mysqld TCP *:3306 (LISTEN)
com.avast TCP 127.0.0.1:12080 (LISTEN)
com.avast TCP [::1]:12080 (LISTEN)
com.avast TCP 127.0.0.1:12110 (LISTEN)
com.avast TCP [::1]:12110 (LISTEN)
com.avast TCP 127.0.0.1:12143 (LISTEN)
com.avast TCP [::1]:12143 (LISTEN)
com.avast TCP 127.0.0.1:12995 (LISTEN)
com.avast [::1]:12995 (LISTEN)
com.avast 127.0.0.1:12993 (LISTEN)
com.avast [::1]:12993 (LISTEN)
Google TCP 127.0.0.1:34013 (LISTEN)

This may be useful to check if you are connected to north-korea! ;-)

This is a good way on macOS High Sierra:

netstat -an |grep -i listen

Inspired by user Brent Self:

lsof -i 4 -a | grep LISTEN

For macOS I use two commands together to show information about the processes listening on the machine and process connecting to remote servers. In other words, to check the listening ports and the current (TCP) connections on a host you could use the two following commands together

1. netstat -p tcp -p udp 

2. lsof -n -i4TCP -i4UDP 

Thought I would add my input, hopefully it can end up helping someone.

Just a slight improvement on Michał Kalinowski's answer (I don't have enough reputation to leave a comment there): if you are trying to find the process listening on a port numbered 255 and below, the grep command might print lines related to the IP address, and which do not correspond to the desired result. For a port with any number, the grep command might also erroneously match the device's MAC address or PID. To improve on this, I suggest changing the command to grep --color ":$1 "