How to Kill a Process Using a Specific Port [macOS Big Sur]

A quick way to kill a process that uses a specific port.

This is what you need if you get an EADDRINUSE error, which says that a process can’t bind to a port because it is already in use by another process.

The most likely cause is that a development server hung up or didn’t terminate properly.

Here’s how to kill a process occupying port 3000:

kill -15 $(lsof -t -i :3000)

The lsof -t -i :3000 part returns the process id (if exists) for the process that uses port 3000. lsof is a command line utility to list open files. From the manual (man lsof; I love man, it’s often quicker than a Google search):

NAME
       lsof - list open files
[…]
DESCRIPTION
       Lsof revision 4.91 lists on its standard output file information about files opened by processes for the following UNIX
       dialects:

            Apple Darwin 9 and Mac OS X 10.[567]
            FreeBSD 8.[234], 9.0 and 1[012].0 for AMD64-based systems
            Linux 2.1.72 and above for x86-based systems
            Solaris 9, 10 and 11

       (See the DISTRIBUTION section of this manual page for information on how to obtain the latest lsof revision.)

       An open file may be a regular file, a directory, a block special file, a character special file, an executing text ref-
       erence,  a  library,  a stream or a network file (Internet socket, NFS file or UNIX domain socket.)  A specific file or
       all the files in a file system may be selected by path.

       Instead of a formatted display, lsof will produce output that can be parsed by other  programs.   See  the  -F,  option
       description, and the OUTPUT FOR OTHER PROGRAMS section for more information.
[…]
       -i [i]   selects the listing of files any of whose Internet address matches the address specified in i.  If no  address
                is specified, this option selects the listing of all Internet and x.25 (HP-UX) network files.
[…]
       -t       specifies that lsof should produce terse output with process identifiers only and no header -  e.g.,  so  that
                the output may be piped to kill(1).  -t selects the -w option.
[…]
AUTHORS
       Lsof was written by Victor A.Abell <abe@purdue.edu> of Purdue  University.   Many  others  have  contributed  to  lsof.
       They’re listed in the 00CREDITS file of the lsof distribution.
[…]

So -i :3000 looks for internet addresses that partially match :3000. And -t makes lsof give us only the process id of the process holding that file.

kill -15 $(lsof -t -i :3000) sends a regular termination signal (TERM, -15) (similar to CTRL-C) to the process id that lsof -t -i :3000 returns. $(…) opens a subshell, so kill waits for its result.

If the termination signal was sent successfully, you’ll get a normal 0 exit code. If lsof didn’t find a file with the specified port, it’ll log:

kill: not enough arguments

If you still get an EADDRINUSE error when you try to run your program, the program may be stuck. Change the termination signal to KILL (-9): kill -9 $(lsof -t -i :3000), which immediately halts the program.