nc

Linux · Network · reference only

What it does

Netcat: opens TCP and UDP connections from the command line. It is used to test ports, send data and set up simple servers.

Syntax

nc [opciones] equipo puerto
nc -l [opciones] puerto

Options and parameters

• -z

  Only checks whether the port is open, without sending data.

• -v

  Shows detailed connection information.

• -l

  Listens for incoming connections instead of connecting.

• -u

  Uses UDP instead of TCP.

• -w segundos

  Maximum time to wait for the connection.

• -k

  With -l, keeps listening after a connection closes.

• -n

  Does not resolve names: uses only IP addresses.

Usage examples

• nc -zv localhost 22

  Checks whether port 22 on the machine itself is open.

• nc -zv 192.168.1.10 20-25

  Checks a range of ports on another host.

• nc -l 1234

  Opens a test server on port 1234.

• echo "hola" | nc -w 1 localhost 1234

  Sends the text hola to a server listening on port 1234.

Notes and common mistakes

• There are several netcat variants and not all accept the same options; on Debian the netcat-openbsd package is recommended.
• Only test ports on hosts you own or have permission for.

Related commands

• curl
• dig
• dnsdomainname
• hostname
• ip
• netstat