How to connect to a Unix socket with Netcat

Local daemons sometimes expose a Unix-domain socket instead of a TCP host and port, so a normal nc 127.0.0.1 9000 probe cannot reach them. Netcat can connect to the socket pathname directly when the installed implementation supports the -U option.

OpenBSD Netcat from netcat-openbsd on Ubuntu 26.04 accepts this command form. A one-shot listener creates /tmp/netcat-demo.sock, a client sends one test line to that pathname, and -N closes the client side after the piped input reaches end-of-file.

The command form uses a stream Unix socket. Add -u only when the target service documents a datagram socket, and avoid sending state-changing protocol messages to a production socket unless the service owner has confirmed the request is safe.

Steps to connect to a Unix socket with Netcat:

Check that the active Netcat build supports Unix-domain sockets.

$ nc -h
OpenBSD netcat (Debian patchlevel 1.234-1)
usage: nc [-46CDdFhklNnrStUuvZz] [-I length] [-i interval] [-M ttl]
##### snipped #####
		-U		Use UNIX domain socket
##### snipped #####

If the help text does not show -U, install OpenBSD Netcat before continuing.

Start a one-shot Unix socket listener in the first terminal.
```
$ nc -lU /tmp/netcat-demo.sock
```
The listener creates /tmp/netcat-demo.sock and waits for one client connection. Leave this terminal open while sending the test line from another terminal.
Confirm that the socket file appeared from the second terminal.
```
$ ls -l /tmp/netcat-demo.sock
srwxr-xr-x 1 root root 0 Jun  7 23:58 /tmp/netcat-demo.sock
```
The leading s in the file mode marks the path as a socket, not a regular file.
Send a test payload to the socket from the second terminal.
```
$ printf 'unix socket check\n' | nc -N -U /tmp/netcat-demo.sock
```
-N lets the listener finish after printf reaches end-of-file.
Confirm that the first terminal printed the payload.
```
$ nc -lU /tmp/netcat-demo.sock
unix socket check
```
The matching line confirms that Netcat reached the Unix-domain socket path.
Remove the temporary socket file.
```
$ rm -f /tmp/netcat-demo.sock
```
Do not remove a production service socket. Deleting its pathname can break local clients until the daemon recreates it.