Unix/Linux Go Back    

RedHat 9 (Linux i386) - man page for nc (redhat section 1)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:   man
Select Man Page Set:       apropos Keyword Search (sections above)

NC(1)				   BSD General Commands Manual				    NC(1)

     nc -- arbitrary TCP and UDP connections and listens

     nc [-e command] [-g intermediates] [-G hopcount] [-i interval] [-lnrtuvz] [-o filename]
	[-p source port] [-s ip address] [-w timeout] [hostname] [port[s...]]

     The nc (or netcat) utility is used for just about anything under the sun involving TCP or
     UDP.  It can open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports,
     do port scanning, and source routing.  Unlike telnet(1), nc scripts nicely, and separates
     error messages onto standard error instead of sending them to standard output, as telnet(1)
     does with some.

     Destination ports can be single integers, names as listed in services(5), or ranges.  Ranges
     are in the form nn-mm, and several separate ports and/or ranges may be specified on the com-
     mand line.

     Common uses include:

     o	 simple TCP proxies

     o	 shell-script based HTTP clients and servers

     o	 network daemon testing

     o	 source routing based connectivity testing

     o	 and much, much more

     The options are as follows:

     -e command
	     Execute the specified command, using data from the network for stdin, and sending
	     stdout and stderr to the network.	This option is only present if nc was compiled
	     with the GAPING_SECURITY_HOLE compile time option, since it allows users to make
	     arbitrary programs available to anyone on the network.

     -g intermediate-host
	     Specifies a hop along a loose source routed path.	Can be used more than once to
	     build a chain of hop points.

     -G pointer
	     Positions the "hop counter" within the list of machines in the path of a source
	     routed packet.  Must be a multiple of 4.

     -i seconds
	     Specifies a delay time interval between lines of text sent and received.  Also
	     causes a delay time between connections to multiple ports.

     -l      Is used to specify that nc should listen for an incoming connection, rather than
	     initiate a connection to a remote host.  Any hostname/IP address and port arguments
	     restrict the source of inbound connections to only that address and source port.

     -n      Do not do DNS lookups on any of the specified addresses or hostnames, or names of
	     port numbers from /etc/services.

     -o filename
	     Create a hexadecimal log of data transferred in the specified file.  Each line
	     begins with ``<'' or ``>''.  ``<'' means "from the net" and ``>'' means "to the

     -p port
	     Specifies the source port nc should use, subject to privilege restrictions and

     -r      Specifies that source and/or destination ports should be chosen semi-randomly
	     instead of sequentially within a range or in the order that the system assigns.

     -s hostname/ip-address
	     Specifies the IP of the interface which is used to send the packets.  On some plat-
	     forms, this can be used for UDP spoofing by using ifconfig(8) to bring up a dummy
	     interface with the desired source IP address.

     -t      Causes nc to send RFC854 DON'T and WON'T responses to RFC854 DO and WILL requests.
	     This makes it possible to use nc to script telnet sessions.  The presence of this
	     option can be enabled or disabled as a compile-time option.

     -u      Use UDP instead of TCP.  On most platforms, nc will behave as if a connection is
	     established until it receives an ICMP packet indicating that there is no program
	     listening to what it sends.

     -v      Verbose.  Cause nc to display connection information.  Using -v more than once will
	     cause nc to become even more verbose.

     -w timeout
	     Specifies the number of seconds nc should wait before deciding that an attempt to
	     establish a connection is hopeless.  Also used to specify how long to wait for more
	     network data after standard input closes.

     -z      Specifies that nc should just scan for listening daemons, without sending any data
	     to them.  Diagnostic messages about refused connections will not be displayed unless
	     -v is specified twice.

	Wait for the user to type what would normally be command-line arguments in at stdin.

     nc example.host 42
	Open a TCP connection to port 42 of example.host.  If the connection fails, do not dis-
	play any error messages, but simply exit.

     nc -p 31337 example.host 42
	Open a TCP connection to port 42 of example.host, and use port 31337 as the source port.

     nc -w 5 example.host 42
	Open a TCP connection to port 42 of example.host, and time out after five seconds while
	attempting to connect.

     nc -u example.host 53
	Send any data from stdin to UDP port 53 of example.host, and display any data returned.

     nc -s example.host 42
	Open a TCP connection to port 42 of example.host using as the IP for the local
	end of the connection.

     nc -v example.host 42
	Open a TCP connection to port 42 of example.host, displaying some diagnostic messages on

     nc -v -v example.host 42
	Open a TCP connection to port 42 of example.host, displaying all diagnostic messages on

     nc -v -z example.host 20-30
	Attempt to open TCP connections to ports 20 through 30 of example.host, and report which
	ones nc was able to connect to.

     nc -v -u -z -w 3 example.host 20-30
	Send UDP packets to ports 20-30 of example.host, and report which ones did not respond
	with an ICMP packet after three seconds.

     nc -l -p 3000
	Listen on TCP port 3000, and once there is a connection, send stdin to the remote host,
	and send data from the remote host to stdout.

     echo foobar | nc example.host 1000
	Connect to port 1000 of example.host, send the string "foobar" followed by a newline, and
	move data from port 1000 of example.host to stdout until example.host closes the connec-

     cat(1), telnet(1)

     The netcat README.

     *Hobbit*  [hobbit@avian.org]

BSD					  August 1, 1996				      BSD
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums

All times are GMT -4. The time now is 05:22 PM.