TCP/IP swiss army knife. Simple (yet powerful!) Unix utility that reads and writes data across network connections, using TCP or UDP.
Netcat as a Client
Connect to some port of some host:
nc <host> <port>
- your STDIN is sent to the host
- anything that comes back across network is sent to your STDOUT
- this continues indefinitely, until the network side closes (not until EOF on STDIN like many other apps)
Test remote HTTP server:
nc google.com 80
GET / HTTP/1.0
(press Enter two times after the GET line)
Check UDP port is open:
nc -vu ns.nameserver.tld 53
Make sure no data (zero) is sent to the port you connect to:
nc -v -z host.tld 21-25
Change source port / address (ex. to evade a FW):
nc -p 16000 host.tld 22
nc -s 1.2.3.4 host.tld 8181
Netcat as a Server
Listen for an incoming connection on some port:
nc -l <port>
Send a directory over the network:
.. host A (receiving data)
nc -l 1234 | tar xvf -
.. host B (sending data)
tar cf - </some/dir> | nc -w 3 <hostA> 1234
Send a whole partition over the network:
.. host A (receiving data)
nc -l 1234 | dd of=backup_sda1
.. host B (sending data)
dd if=/dev/sda1 | nc -w 3 <hostA> 1234
Run a command (potentially dangerous!); ex. open a shell access:
.. host A (server)
nc -l 9999 -e /bin/bash
.. host B (client)
nc hostA 9999