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Kill the process using a port on Linux

The quick way

npx portcheck-cli kill 3000

portcheck lists what is listening on port 3000 and who started it, asks before stopping it, and refuses system processes such as systemd and init. It needs no lsof or net-tools, so it also works in minimal containers. To install it permanently: brew install roystondwork-dev/tap/portcheck, pipx install portcheck-tool, or the .deb, .rpm and .apk packages on the releases page (see Install).

To see what's there without stopping it:

$ portcheck 3000
PORT  PROTO  STATUS  PID    PROCESS  USER
3000  tcp    in-use  41852  node     alice

With built-in tools

ss -ltnp 'sport = :3000'

The users:(("node",pid=41852,...)) part names the process. Then:

kill 41852        # asks it to exit
kill -9 41852     # forces it

fuser 3000/tcp       # print the PID
fuser -k 3000/tcp    # kill it (SIGKILL by default)

lsof -nP -iTCP:3000 -sTCP:LISTEN

No PID shown?

Linux only shows the owner of sockets that belong to your user. If the process column is empty, the port belongs to another user or root: use sudo portcheck 3000 (or sudo ss -ltnp).

systemd services

If the process comes back right after you stop it, a service manager is restarting it. Such processes have no started by in portcheck, because the system started them, not a terminal. Stop the service instead:

systemctl status <name>        # find which service it is
sudo systemctl stop <name>