Linux netcat - Revision history

Pio2pio: /* Test if UDP port is open: simple UDP server and client */

2020-01-20T15:32:22Z

Test if UDP port is open: simple UDP server and client

← Older revision		Revision as of 17:32, 20 January 2020
Line 54:		Line 54:

	===Test if UDP port is open: simple UDP server and client===		===Test if UDP port is open: simple UDP server and client===
			This test is useful if you have shell access to the server that should be tested, but you do not know whether there is a firewall blocking a specific UDP port on the server. On the <code>server</code> listening host
			<source lang=bash>
			nc -u -l -p 5140
			# note: some of 'nc' instances do not accept -ul syntax
			# some of 'nc' instances do require '-p' <PORT> before port number
			</source>

	~~This test is useful, if you have shell access to the server that should be tested, but you do not know whether there is a firewall blocking a specific UDP port on the server.~~

	On the ~~listening~~ host, i.e. on the ~~server whose port needs to be checked, do~~ the ~~following~~:		On the <code>client</code> sending host, note that <code>fluentd.monitoring.svc.cluster.local</code> is the hostname of the listening host:
			<source lang=bash>
			nc -u fluentd.monitoring.svc.cluster.local 5140
			</source>

	~~nc -ul 7000~~

	~~On the sending host, do the following – note that <code>servname</code> is the hostname of the listening host:~~

	~~nc -u servname 7000~~

	If text typed on the sending host (type something and hit enter) is displayed also on the listening host, then the UDP port 7000 is open. If it is not open, you will get an error such as "Connection refused".		If text typed on the sending host (type something and hit enter) is displayed also on the listening host, then the UDP port 7000 is open. If it is not open, you will get an error such as "Connection refused".

Pio2pio: /* Checking if UDP ports (-u) 80-90 are open on 192.168.0.1 using zero mode I/O (-z) */

2020-01-20T15:24:54Z

Checking if UDP ports (-u) 80-90 are open on 192.168.0.1 using zero mode I/O (-z)

← Older revision		Revision as of 17:24, 20 January 2020
Line 47:		Line 47:
	$ php -S localhost:8000 #start a web server with a default index.html as a home page		$ php -S localhost:8000 #start a web server with a default index.html as a home page

	===~~Checking if~~ UDP ports (-u) 80-90 are open ~~on 192.168.0.1~~ using zero mode I/O (-z)===		===Check UDP ports (-u) 80-90 are open using zero mode I/O (-z)===
			<source lang=bash>
	nc -vzu 192.168.0.1 <nowiki>80-90</nowiki>		nc -vzu 192.168.0.1 <nowiki>80-90</nowiki>
			</source>
	Note that UDP tests will always show as "open". The <code>-uz</code> argument is useless.		Note that UDP tests will always show as "open". The <code>-uz</code> argument is useless.

Pio2pio at 22:02, 13 May 2018

2018-05-13T22:02:52Z

← Older revision		Revision as of 00:02, 14 May 2018
Line 15:		Line 15:
	===Simple one-shoot off web server===		===Simple one-shoot off web server===
	This creates a simple web server		This creates a simple web server
	listen@server1:$ nc -kl 8080 < index.html #works in Chrome		<source lang="bash">
	listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\nContent-Length: $(wc -c <index.html)\r\n\r\n"; cat index.html; } \| nc -l 8080		listen@server1:$ nc -kl 8080 < index.html #works in Chrome
	listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to ~~'''~~a single~~'''~~ HTTP1.1 request		listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\nContent-Length: $(wc -c <index.html)\r\n\r\n"; cat index.html; } \| nc -l 8080
			listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to a single HTTP1.1 request
			</source>

	This is a simple index.html file		This is a simple index.html file
			<source lang="html">
	cat >> index.html <<EOL		cat >> index.html <<EOL
	<html>		<html>
	<head>		<head>
	<title>Test Page</title>		<title>Test Page</title>
	</head>		</head>
	<body>		<body>
	<nowiki><h1>Level 1 header</h1></nowiki>		<nowiki><h1>Level 1 header</h1></nowiki>
	<nowiki><h2>Subheading</h2></nowiki>		<nowiki><h2>Subheading</h2></nowiki>
	<nowiki><p>Normal text here</p></nowiki>		<nowiki><p>Normal text here</p></nowiki>
	</body>		</body>
	</html>		</html>
	EOL		EOL
			</source>
	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.
	<source lang="bash">		<source lang="bash">
	client@server2:$ curl -v --noproxy "server1.example.com" ~~<nowiki>~~http://server1.example.com:8080~~</nowiki>~~ #~~will disable using a~~ proxy ~~for the~~ "server1"		client@server2:$ curl -v --noproxy "server1.example.com" http://server1.example.com:8080 #don't use proxy to access "server1"
	client@server2:$ lynx ~~<nowiki>~~http://server1.example.com:8080~~</nowiki>~~		client@server2:$ lynx http://server1.example.com:8080
	</source>		</source>

Pio2pio: /* Simple one-shoot off web server */

2018-04-01T09:40:28Z

Simple one-shoot off web server

← Older revision		Revision as of 11:40, 1 April 2018
Line 21:		Line 21:
	This is a simple index.html file		This is a simple index.html file

	cat index.html		cat >> index.html <<EOL
	<html>		<html>
	<head>		<head>
Line 32:		Line 32:
	</body>		</body>
	</html>		</html>
			EOL

	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.

Pio2pio: /* Simple one-shoot off web server */

2018-03-30T22:14:48Z

Simple one-shoot off web server

← Older revision		Revision as of 00:14, 31 March 2018
Line 20:		Line 20:

	This is a simple index.html file		This is a simple index.html file
	~~<source lang="bash">~~
	cat index.html		cat index.html
	<html>		<html>
	<head>		<head>
	<title>Test Page</title>		<title>Test Page</title>
	</head>		</head>
	<body>		<body>
	<h1>Level 1 header</h1>		<nowiki><h1>Level 1 header</h1></nowiki>
	<h2>Subheading</h2>		<nowiki><h2>Subheading</h2></nowiki>
	<p>Normal text here</p>		<nowiki><p>Normal text here</p></nowiki>
	</~~body~~>		</body>
	</~~html~~>		</html>
	</~~source~~>

	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.

Pio2pio: /* Simple web server */

2016-09-29T09:02:33Z

Simple web server

← Older revision		Revision as of 11:02, 29 September 2016
Line 13:		Line 13:
	listen@server1# nc -l 4444 > file1.txt		listen@server1# nc -l 4444 > file1.txt

	===Simple web server===		===Simple one-shoot off web server===
	This creates a simple web server		This creates a simple web server
	listen@server1:$ nc -kl 8080 < index.html #works in Chrome		listen@server1:$ nc -kl 8080 < index.html #works in Chrome
Line 39:		Line 39:
	client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki>		client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki>
	</source>		</source>

			==== PHP simple web server ====
			Since version 5.4.0 PHP also has a built-in web server. If you use an IP address the website will be available over a network
			$ sudo -E apt-get install php5-cli #install PHP
			$ php -S localhost:8000 #start a web server with a default index.html as a home page

	===Checking if UDP ports (-u) 80-90 are open on 192.168.0.1 using zero mode I/O (-z)===		===Checking if UDP ports (-u) 80-90 are open on 192.168.0.1 using zero mode I/O (-z)===

Pio2pio at 08:51, 29 September 2016

2016-09-29T08:51:52Z

← Older revision		Revision as of 10:51, 29 September 2016
Line 1:		Line 1:
	'''Netcat''' in slow translation is the network version of '''cat''' command.		'''Netcat''' in slow translation is the network version of '''cat''' command.

	== Send a string over a network ==		===Send a string over a network===

	Start listening for a connection. The command below listen on TCP port 4444 for a new connections and displays any incoming data to a screen (default STDOUT) then it stops when the connection closes. Use <code>-k</code> to continue listening after a transfer completes.		Start listening for a connection. The command below listen on TCP port 4444 for a new connections and displays any incoming data to a screen (default STDOUT) then it stops when the connection closes. Use <code>-k</code> to continue listening after a transfer completes.
Line 9:		Line 9:
	send@server2# echo "Hello Tom!" \| nc server1.example.com 4444		send@server2# echo "Hello Tom!" \| nc server1.example.com 4444

	== Send Files through Netcat ==		===Send Files through Netcat===
	This example will redirect any incoming data to a file		This example will redirect any incoming data to a file
	listen@server1# nc -l 4444 > file1.txt		listen@server1# nc -l 4444 > file1.txt

	== Simple web server ==		===Simple web server===
	This creates a simple web server		This creates a simple web server
	listen@server1:$ nc -kl 8080 < index.html #works in Chrome		listen@server1:$ nc -kl 8080 < index.html #works in Chrome

Pio2pio: /* Simple web server */

2016-09-29T08:51:19Z

Simple web server

← Older revision		Revision as of 10:51, 29 September 2016
Line 16:		Line 16:
	This creates a simple web server		This creates a simple web server
	listen@server1:$ nc -kl 8080 < index.html #works in Chrome		listen@server1:$ nc -kl 8080 < index.html #works in Chrome
			listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\nContent-Length: $(wc -c <index.html)\r\n\r\n"; cat index.html; } \| nc -l 8080
	listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to '''a single''' HTTP1.1 request		listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to '''a single''' HTTP1.1 request

	This is a simple index.html file		This is a simple index.html file
	<~~syntaxhighlight~~ lang="bash" ~~line~~>		<source lang="bash">
	cat index.html		cat index.html
	<html>		<html>
Line 31:		Line 32:
	</body>		</body>
	</html>		</html>
	</~~syntaxhighlight~~>		</source>

	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.
			<source lang="bash">
	client@server2:$ curl -v --noproxy "server1.example.com" <nowiki>http://server1.example.com:8080</nowiki> #will disable using a proxy for the "server1"		client@server2:$ curl -v --noproxy "server1.example.com" <nowiki>http://server1.example.com:8080</nowiki> #will disable using a proxy for the "server1"
	client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki>		client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki>
			</source>

			===Checking if UDP ports (-u) 80-90 are open on 192.168.0.1 using zero mode I/O (-z)===

			nc -vzu 192.168.0.1 <nowiki>80-90</nowiki>

			Note that UDP tests will always show as "open". The <code>-uz</code> argument is useless.

			===Test if UDP port is open: simple UDP server and client===

			This test is useful, if you have shell access to the server that should be tested, but you do not know whether there is a firewall blocking a specific UDP port on the server.

			On the listening host, i.e. on the server whose port needs to be checked, do the following:

			nc -ul 7000

			On the sending host, do the following – note that <code>servname</code> is the hostname of the listening host:

			nc -u servname 7000

			If text typed on the sending host (type something and hit enter) is displayed also on the listening host, then the UDP port 7000 is open. If it is not open, you will get an error such as "Connection refused".

			There is a caveat. On some machines, [[IPv6]] may be the default IP version to use by <tt>netcat</tt>. Thus, the host specified by the hostname is contacted using IPv6, and the user might not know about this. Ports may appear closed in the test, even though they would be open when using [[IPv4]]. This can be difficult to notice and may cause the false impression that the port is blocked, while it is actually open. You can force the use of IPv4 by using adding <code>-4</code> to the options of the <code>nc</code> commands.

			= References =
			*[https://en.wikipedia.org/wiki/Netcat Netcat] Wikipedia

Pio2pio: /* Simple web server */

2016-09-29T08:27:00Z

Simple web server

← Older revision		Revision as of 10:27, 29 September 2016
Line 17:		Line 17:
	listen@server1:$ nc -kl 8080 < index.html #works in Chrome		listen@server1:$ nc -kl 8080 < index.html #works in Chrome
	listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to '''a single''' HTTP1.1 request		listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to '''a single''' HTTP1.1 request

	This is a simple index.html file		This is a simple index.html file
	<syntaxhighlight lang="bash" line>		<syntaxhighlight lang="bash" line>
Line 35:		Line 35:
	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.

	client@server2:$ curl -v --noproxy "server1.example.com" http://server1.example.com:~~8888~~ #will disable using a proxy for the "server1"		client@server2:$ curl -v --noproxy "server1.example.com" <nowiki>http://server1.example.com:8080</nowiki> #will disable using a proxy for the "server1"
	client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki> #		client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki>

Pio2pio: /* Simple web server */

2016-09-29T08:25:34Z

Simple web server

← Older revision		Revision as of 10:25, 29 September 2016
Line 15:		Line 15:
	== Simple web server ==		== Simple web server ==
	This creates a simple web server		This creates a simple web server
	listen@server1# nc -kl 80 < index.html		listen@server1:$ nc -kl 8080 < index.html #works in Chrome
			listen@server1:$ { echo -ne "HTTP/1.0 200 OK\r\n\r\n"; cat index.html; } \| nc -l -p 8080 #improved version to correctly respond to '''a single''' HTTP1.1 request

	This is a simple index.html file		This is a simple index.html file
	<syntaxhighlight lang="bash" line>		<syntaxhighlight lang="bash" line>
Line 34:		Line 35:
	Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.		Please be aware that <tt>nc</tt> is not aware of HTTP1.1 specification and is not sending 200 Ok, therefore it will not work out of box in curl, wget or lynx. Therefore please try this in a full flagged web browser like Chrome.

	~~Connect~~ using a ~~web browser~~		client@server2:$ curl -v --noproxy "server1.example.com" http://server1.example.com:8888 #will disable using a proxy for the "server1"
	client@server2 lynx <nowiki>http://server1.example.com:80</nowiki>		client@server2:$ lynx <nowiki>http://server1.example.com:8080</nowiki> #