Motivation
Sometimes a process, like a web server or running Clojure REPL, closes unexpectedly but the port is never released. I'd need to find that process and kill it so that I can rightfully claim my port back.
Find the process
netstat -vanp tcp | grep "*."
It will return something like this (note that the table scrolls to the right):
tcp4 0 0 *.3000 *.* LISTEN 131072 131072 46834 0 0x0100 0x00000106
tcp46 0 0 *.8085 *.* LISTEN 131072 131072 29254 0 0x0100 0x00000006
tcp46 0 0 *.8321 *.* LISTEN 131072 131072 29254 0 0x0100 0x00000006
tcp46 0 0 *.8080 *.* LISTEN 131072 131072 29254 0 0x0100 0x00000006
tcp4 0 0 *.61350 *.* LISTEN 131072 131072 29278 0 0x0100 0x00000006
tcp4 0 0 127.0.0.1.61933 *.* LISTEN 131072 131072 2951 0 0x0100 0x00000106
tcp4 0 0 127.0.0.1.45623 *.* LISTEN 131072 131072 2951 0 0x0100 0x00000106
tcp4 0 0 127.0.0.1.49489 *.* LISTEN 131072 131072 2951 0 0x0100 0x00000106
tcp4 0 0 127.0.0.1.49488 *.* LISTEN 131072 131072 2951 0 0x0100 0x00000106
tcp4 0 0 127.0.0.1.16494 *.* LISTEN 131072 131072 2901 0 0x0000 0x0000020f
tcp4 0 0 127.0.0.1.15393 *.* LISTEN 131072 131072 2901 0 0x0000 0x0000020f
tcp4 0 0 127.0.0.1.15292 *.* LISTEN 131072 131072 2901 0 0x0000 0x0000020f
tcp4 0 0 127.0.0.1.6463 *.* LISTEN 131072 131072 838 0 0x0100 0x00000106
Identify the process
The 3rd column after LISTEN is the pid. Taking the first entry (a process running on :3000), I can safely grab its pid of 46834 and inspect it.
ps aux | grep 46834
It will return something like this:
clarice 46834 0.0 1.3 441950208 219760 s001 S+ 9:06pm 0:25.95 /Users/clarice/.nvm/versions/node/v16.13.0/bin/node /Users/clarice/Workspace/demos/react/node_modules/react-scripts/scripts/start.js
clarice 58003 0.0 0.0 408628368 1632 s010 S+ 4:52am 0:00.00 grep --color=auto --exclude-dir=.bzr --exclude-dir=CVS --exclude-dir=.git --exclude-dir=.hg --exclude-dir=.svn --exclude-dir=.idea --exclude-dir=.tox 46834
Based on this output, the first entry gives me the most information. I can see it's a Node.js application and it's coming from demos/react app. That's the correct one so I can kill it.
The 2nd entry is always present on a terminal grep. I believe it to be the coloured output of the terminal.
Kill the process
Now that I have the right process, I can kill it using kill 46834. If the process is stubborn and keen on staying alive, you can force it by using kill -9 46834
(I think these commands are Unix based so it should work on Linux too)
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