Where Can I Find Socket Shelf in New Bern, Nc

Linux nc command

Updated: 11/06/2021 by Computer Hope

On Unix-like operating systems, the nc command runs Netcat, a utility for sending raw data over a network connection.

This folio covers the Linux version of nc.

Clarification

Netcat is a utility that reads and writes data across network connections, using the TCP or UDP protocol. It is designed to exist a reliable "back-cease" tool, used straight or driven by other programs and scripts. At the same time, it is a feature-rich network debugging and exploration tool since it can create virtually any kind of connectedness you would need and has several interesting born capabilities. Common uses include:

• Simple TCP proxies
• Crush-script based HTTP clients and servers
• Network daemon testing
• A Socks or HTTP ProxyCommand for ssh

Syntax

nc [-46bCDdhklnrStUuvZz] [-I          length] [-i          interval] [-O          length]     [-P          proxy_username] [-p          source_port] [-q          seconds] [-due south          source]     [-T          toskeyword] [-5          rtable] [-w          timeout] [-10          proxy_protocol]     [-x          proxy_address[:port]] [destination] [port]

Options

-four	Forces nc to use IPv4 addresses only.
-6	Forces nc to employ IPv6 addresses simply.
-b	Allow broadcast.
-C	Send CRLF every bit line-ending.
-D	Enable debugging on the socket.
-d	Do not endeavor to read from stdin.
-h	Prints out nc help.
-I length	Specifies the size of the TCP receive buffer.
-i interval	Specifies a filibuster fourth dimension interval between lines of text sent and received. Also, causes a filibuster time between connections to multiple ports.
-k	Forces nc to stay listening for some other connection after its current connection is completed. It is an fault to apply this option without the -50 choice.
-l	Used to specify that nc should heed for an incoming connection rather than initiate a connection to a remote host. It is an error to use this choice in conjunction with the -p, -due south, or -z options. Additionally, any timeouts specified with the -w option are ignored.
-n	Do not do any DNS or service lookups on any specified addresses, hostnames or ports.
-O length	Specifies the size of the TCP send buffer.
-P proxy_username	Specifies a username to present to a proxy server that requires authentication. If no username is specified, so authentication is not attempted. Proxy authentication is simply supported for HTTP CONNECT proxies at present.
-p source_port	Specifies the source port nc should use, field of study to privilege restrictions and availability.
-q seconds	After EOF on stdin, expect the specified number of seconds then quit. If seconds is negative, await forever.
-r	Specifies that source or destination ports should be chosen randomly instead of sequentially in a range or in the order the system assigns them.
-S	Enables the RFC 2385 TCP MD5 signature choice.
-s source	Specifies the IP of the interface used to send the packets. For UNIX-domain datagram sockets, specifies the local temporary socket file to create and use and then that datagrams can be received. It is an error to utilise this selection in conjunction with the -fifty choice.
-T toskeyword	Change IPv4 TOS value. toskeyword may be i of disquisitional, inetcontrol, lowcost, lowdelay, netcontrol, throughput, reliability, or one of the DiffServ Lawmaking Points: ef, af11 ... af43, cs0 ... cs7; or a number in either hex or decimal.
-t	Causes nc to transport RFC 854 DON'T and WON'T responses to RFC 854 Practise and Volition requests. This makes it possible to employ nc to script telnet sessions.
-U	Specifies to use UNIX-domain sockets.
-u	Use UDP instead of the default choice of TCP. For UNIX-domain sockets, use a datagram socket instead of a stream socket. If a UNIX-domain socket is used, a temporary receiving socket is created in /tmp unless the -southward flag is given.
-5 rtable	Fix the routing table to be used. The default is 0.
-v	Have nc give more verbose output.
-w timeout	Connections that cannot exist established or are idle timeout after timeout seconds. The -w flag has no event on the -l option, i.due east., nc listens forever for a connexion, with or without the -w flag. The default is no timeout.
-X proxy_protocol	Requests that nc should employ the specified protocol when talking to the proxy server. Supported protocols are "4" (SOCKS five.4), "v" (SOCKS v.5) and "connect" (HTTPS proxy). If the protocol is not specified, SOCKS version 5 is used.
-x proxy_address[:port]	Requests that nc should connect to destination using a proxy at proxy_address and port. If port is non specified, the well-known port for the proxy protocol is used (1080 for SOCKS, 3128 for HTTPS).
-Z	DCCP mode.
-z	Specifies that nc should only scan for listening daemons, without sending any information to them. Information technology is an mistake to use this option in conjunction with the -l choice.

destination is a numerical IP address or a symbolic hostname (unless the -n option is given). In general, a destination must be specified, unless the -l selection is given (where the local host is used). For UNIX-domain sockets, a destination is required and is the socket path to connect to (or listen on if the -l option is given).

port is a single integer or a range of ports. Ranges are in the class nn-mm. In full general, a destination port must be specified, unless the -U pick is given.

Client/server model

Information technology is quite simple to build a very basic client/server model using nc. On one console, kickoff nc listening on a specific port for a connectedness. For example:

nc -l 1234

nc is at present listening on port 1234 for a connexion. On a second panel (or a 2nd machine), connect to the automobile and port being listened on:

nc 127.0.0.i 1234

In that location should at present exist a connectedness betwixt the ports. Anything typed at the second console is concatenated to the first, and vice versa. After the connection was gear up up, nc does not really intendance which side is used as a 'server' and which side is used as a 'client'. The connection may be terminated using an EOF ('^D').

There is no -c or -e option in modern netcat, only you notwithstanding can execute a command after connection is established by redirecting file descriptors. Be cautious here because opening a port and letting anyone connected execute arbitrary commands on your site is DANGEROUS. If y'all need to do this, here is an case:

On 'server' side:

rm -f /tmp/f; mkfifo /tmp/f

cat /tmp/f | /bin/sh -i 2>&1 | nc -l 127.0.0.one 1234 > /tmp/f

On 'client' side:

nc host.case.com 1234

(shell prompt from host.example.com)

By doing this, you lot create a fifo at /tmp/f and brand nc listen at port 1234 of address 127.0.0.1 on 'server' side, when a 'client' establishes a connection successfully to that port, /bin/sh gets executed on 'server' side and the shell prompt is given to 'client' side.

When connection is terminated, nc also quits. Utilise -k if you want it keep listening, only if the command quits, this selection won't restart it or proceed nc running. As well, don't forget to remove the file descriptor one time y'all don't demand it anymore:

rm -f /tmp/f

Information transfer

The instance in the previous section tin be expanded to build a basic data transfer model. Whatever data input to one terminate of the connection is output to the other end, and input and output can exist captured to emulate file transfer.

To start, use nc to mind on a specific port, with output captured into a file:

nc -l 1234 > filename.out

Using a 2d car, connect to the listening nc process, feeding it the file that is to exist transferred:

nc host.example.com 1234 < filename.in

After the file is transferred, the connection closes automatically.

Talking to servers

It is sometimes useful to talk to servers "by hand" rather than through a user interface. It can assistance in troubleshooting, when information technology might be necessary to verify what data a server is sending in response to commands issued past the client. For case, to recollect the homepage of a website:

printf "Become / HTTP/1.0\r\n\r\n" | nc host.example.com lxxx

Notation that this as well displays the headers sent by the web server. They tin be filtered, using a tool like sed, if necessary.

More complicated examples can be congenital upwardly when the user knows the format of requests required by the server. As another case, an email may be submitted to an SMTP server using:

nc [-C] localhost 25 << EOF HELO host.case.com Mail FROM:<[email protected]> RCPT TO:<[email protected]> DATA Body of e-mail. . QUIT EOF

Port scanning

It may be useful to know which ports are open and running services on a target motorcar. The -z flag can tell nc to report open up ports, rather than initiate a connection. Usually, it'south useful to turn on verbose output to stderr using this selection with the -v option.

For example:

nc -zv host.example.com twenty-30

Connection to host.example.com 22 port [tcp/ssh] succeeded! Connection to host.example.com 25 port [tcp/smtp] succeeded!

The port range was specified to limit the search to ports 20 - xxx, and is scanned by increasing order.

Y'all can too specify a list of ports to scan; for example:

nc -zv host.example.com eighty 20 22

nc: connect to host.instance.com 80 (tcp) failed: Connection refused  nc: connect to host.case.com twenty (tcp) failed: Connectedness refused  Connection to host.example.com port [tcp/ssh] succeeded!

The ports are scanned by the club you given.

Alternatively, it might be useful to know which server software is running, and which versions. This information is often contained in the greeting banners. To remember these, information technology is necessary to first make a connection, and then interruption the connexion when the banner was retrieved. This can be achieved past specifying a small timeout with the -w flag, or perhaps by issuing a "QUIT" command to the server:

echo "QUIT" | nc host.instance.com 20-30

SSH-i.99-OpenSSH_3.6.1p2 Protocol mismatch.  220 host.example.com IMS SMTP Receiver Version 0.84 Ready

Examples

nc -p 31337 -w v host.example.com 42

Opens a TCP connection to port 42 of host.instance.com, using port 31337 as the source port, with a timeout of 5 seconds.

nc -u host.example.com 53

Opens a UDP connection to port 53 of host.case.com.

nc -south ten.1.2.three host.instance.com 42

Opens a TCP connectedness to port 42 of host.example.com using 10.1.2.three as the IP for the local terminate of the connectedness.

nc -lU /var/tmp/dsocket

Creates and listens on a UNIX-domain stream socket.

nc -x10.2.3.4:8080 -Xconnect host.example.com 42

Connects to port 42 of host.case.com via an HTTP proxy at ten.2.3.4, port 8080. This example could too be used past ssh.

nc -x10.2.3.iv:8080 -Xconnect -Pruser host.case.com 42

The same as the example above, merely this time enabling proxy hallmark with username "ruser" if the proxy requires information technology.

ifconfig — View or modify the configuration of network interfaces.

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Source: https://www.computerhope.com/unix/nc.htm

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