nc_openbsd

nc_openbsd [options] [hostname] [port ...]

-4
    Forces nc_openbsd to use IPv4 addresses only.

-6
    Forces nc_openbsd to use IPv6 addresses only.

-h
    Displays a help message and exits.

-k
    Forces the server to stay listening for another connection after the current client disconnects. Used with -l.

-l
    Sets nc_openbsd into listen mode, acting as a server.

-N
    Shutdown the network socket after EOF on standard input, rather than waiting for remote shutdown.

-p
    Specifies the source port to use for outgoing connections.

-U
    Uses Unix domain sockets instead of network sockets.

-u
    Uses UDP instead of TCP for connections.

-v
    Enables verbose output, providing more information during operation.

-w
    Sets a timeout for connection attempts and idle connections, in seconds.

-z
    Sets nc_openbsd to zero-I/O mode, primarily used for efficient port scanning without sending data.

nc_openbsd is the OpenBSD variant of the widely-used netcat network utility, renowned for its simplicity and versatility. Often called the "TCP/IP Swiss Army knife," it's a fundamental tool for network debugging, testing, and administration.

It allows users to establish and manage both TCP and UDP connections, acting as either a client connecting to a remote host or a simple server listening for incoming connections. Its capabilities extend to port scanning, file transfer, and even simple proxying or shell binding.

While nc_openbsd primarily works by reading data from standard input and writing it to a network connection, and vice-versa, its command-line options unlock a myriad of use cases. It's an invaluable tool for network engineers, developers, and system administrators for quick diagnostics and custom network operations, often used within scripts for automation.

nc_openbsd on Linux is typically a package like netcat-openbsd or a symlink. It adheres closely to the OpenBSD netcat behavior, which notably lacks the -e (execute) or -c (command) options found in some older or traditional netcat implementations. This design choice enhances security by preventing direct command execution via network connections, making it safer by default but requiring external piping for shell binding or command execution.

While versatile, it should be used with caution in production environments, especially when listening on open ports, to avoid exposing services or sensitive data.

nc_openbsd can function both as a client connecting to a remote host and a server listening for incoming connections. In client mode (default), it connects to a specified hostname and port. In server mode, activated with the -l option, it listens on a designated port, making it useful for simple data transfer or setting up temporary network services.

The -z option enables zero-I/O mode, which is perfect for efficient port scanning. When used, nc_openbsd attempts to establish a connection but immediately closes it after determining if the port is open, without sending any data. This makes it faster and less intrusive than a full connection for simple port availability checks, often combined with verbose output (-v).

nc_openbsd can be easily used for basic file transfer between systems. On the sending side, the file can be piped into nc_openbsd which connects to a listening instance. On the receiving side, nc_openbsd listens on a port and pipes incoming data to a file. For example: Sender: cat file.txt | nc_openbsd <receiver_ip> <port>; Receiver: nc_openbsd -l -p <port> > received_file.txt.

The original netcat was written by Hobbit in 1995, quickly gaining legendary status as the "TCP/IP Swiss Army knife." Its simplicity and raw power made it a favorite for network diagnostics and penetration testing. While netcat saw various forks and implementations, the OpenBSD project developed and maintained its own version, aiming for a cleaner, more secure, and robust codebase. This OpenBSD variant, known as nc, became a de-facto standard due to its reliability and specific features. On many Linux distributions, nc_openbsd or netcat-openbsd refers to this ported OpenBSD implementation, providing a consistent and feature-rich netcat experience, distinct from older "traditional" netcat versions.

netcat(1), ncat(1), socat(1)