+++ /dev/null
-.\" $OpenBSD: nc.1,v 1.60 2012/02/07 12:11:43 lum Exp $
-.\"
-.\" Copyright (c) 1996 David Sacerdote
-.\" All rights reserved.
-.\"
-.\" Redistribution and use in source and binary forms, with or without
-.\" modification, are permitted provided that the following conditions
-.\" are met:
-.\" 1. Redistributions of source code must retain the above copyright
-.\" notice, this list of conditions and the following disclaimer.
-.\" 2. Redistributions in binary form must reproduce the above copyright
-.\" notice, this list of conditions and the following disclaimer in the
-.\" documentation and/or other materials provided with the distribution.
-.\" 3. The name of the author may not be used to endorse or promote products
-.\" derived from this software without specific prior written permission
-.\"
-.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
-.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
-.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
-.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
-.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
-.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
-.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-.\"
-.Dd $Mdocdate: February 7 2012 $
-.Dt NC 1
-.Os
-.Sh NAME
-.Nm nc
-.Nd arbitrary TCP and UDP connections and listens
-.Sh SYNOPSIS
-.Nm nc
-.Bk -words
-.Op Fl 46bCDdhklnrStUuvZz
-.Op Fl I Ar length
-.Op Fl i Ar interval
-.Op Fl O Ar length
-.Op Fl P Ar proxy_username
-.Op Fl p Ar source_port
-.Op Fl q Ar seconds
-.Op Fl s Ar source
-.Op Fl T Ar toskeyword
-.Op Fl V Ar rtable
-.Op Fl w Ar timeout
-.Op Fl X Ar proxy_protocol
-.Oo Xo
-.Fl x Ar proxy_address Ns Oo : Ns
-.Ar port Oc
-.Xc Oc
-.Op Ar destination
-.Op Ar port
-.Ek
-.Sh DESCRIPTION
-The
-.Nm
-(or
-.Nm netcat )
-utility is used for just about anything under the sun involving TCP,
-UDP, or
-.Ux Ns -domain
-sockets.
-It can open TCP connections, send UDP packets, listen on arbitrary
-TCP and UDP ports, do port scanning, and deal with both IPv4 and
-IPv6.
-Unlike
-.Xr telnet 1 ,
-.Nm
-scripts nicely, and separates error messages onto standard error instead
-of sending them to standard output, as
-.Xr telnet 1
-does with some.
-.Pp
-Common uses include:
-.Pp
-.Bl -bullet -offset indent -compact
-.It
-simple TCP proxies
-.It
-shell-script based HTTP clients and servers
-.It
-network daemon testing
-.It
-a SOCKS or HTTP ProxyCommand for
-.Xr ssh 1
-.It
-and much, much more
-.El
-.Pp
-The options are as follows:
-.Bl -tag -width Ds
-.It Fl 4
-Forces
-.Nm
-to use IPv4 addresses only.
-.It Fl 6
-Forces
-.Nm
-to use IPv6 addresses only.
-.It Fl b
-Allow broadcast.
-.It Fl C
-Send CRLF as line-ending.
-.It Fl D
-Enable debugging on the socket.
-.It Fl d
-Do not attempt to read from stdin.
-.It Fl h
-Prints out
-.Nm
-help.
-.It Fl I Ar length
-Specifies the size of the TCP receive buffer.
-.It Fl i Ar interval
-Specifies a delay time interval between lines of text sent and received.
-Also causes a delay time between connections to multiple ports.
-.It Fl k
-Forces
-.Nm
-to stay listening for another connection after its current connection
-is completed.
-It is an error to use this option without the
-.Fl l
-option.
-.It Fl l
-Used to specify that
-.Nm
-should listen for an incoming connection rather than initiate a
-connection to a remote host.
-It is an error to use this option in conjunction with the
-.Fl p ,
-.Fl s ,
-or
-.Fl z
-options.
-Additionally, any timeouts specified with the
-.Fl w
-option are ignored.
-.It Fl n
-Do not do any DNS or service lookups on any specified addresses,
-hostnames or ports.
-.It Fl O Ar length
-Specifies the size of the TCP send buffer.
-.It Fl P Ar proxy_username
-Specifies a username to present to a proxy server that requires authentication.
-If no username is specified then authentication will not be attempted.
-Proxy authentication is only supported for HTTP CONNECT proxies at present.
-.It Fl p Ar source_port
-Specifies the source port
-.Nm
-should use, subject to privilege restrictions and availability.
-.It Fl q Ar seconds
-after EOF on stdin, wait the specified number of seconds and then quit. If
-.Ar seconds
-is negative, wait forever.
-.It Fl r
-Specifies that source and/or destination ports should be chosen randomly
-instead of sequentially within a range or in the order that the system
-assigns them.
-.It Fl S
-Enables the RFC 2385 TCP MD5 signature option.
-.It Fl s Ar source
-Specifies the IP of the interface which is used to send the packets.
-For
-.Ux Ns -domain
-datagram sockets, specifies the local temporary socket file
-to create and use so that datagrams can be received.
-It is an error to use this option in conjunction with the
-.Fl l
-option.
-.It Fl T Ar toskeyword
-Change IPv4 TOS value.
-.Ar toskeyword
-may be one of
-.Ar critical ,
-.Ar inetcontrol ,
-.Ar lowcost ,
-.Ar lowdelay ,
-.Ar netcontrol ,
-.Ar throughput ,
-.Ar reliability ,
-or one of the DiffServ Code Points:
-.Ar ef ,
-.Ar af11 ... af43 ,
-.Ar cs0 ... cs7 ;
-or a number in either hex or decimal.
-.It Fl t
-Causes
-.Nm
-to send RFC 854 DON'T and WON'T responses to RFC 854 DO and WILL requests.
-This makes it possible to use
-.Nm
-to script telnet sessions.
-.It Fl U
-Specifies to use
-.Ux Ns -domain
-sockets.
-.It Fl u
-Use UDP instead of the default option of TCP.
-For
-.Ux Ns -domain
-sockets, use a datagram socket instead of a stream socket.
-If a
-.Ux Ns -domain
-socket is used, a temporary receiving socket is created in
-.Pa /tmp
-unless the
-.Fl s
-flag is given.
-.It Fl V Ar rtable
-Set the routing table to be used.
-The default is 0.
-.It Fl v
-Have
-.Nm
-give more verbose output.
-.It Fl w Ar timeout
-Connections which cannot be established or are idle timeout after
-.Ar timeout
-seconds.
-The
-.Fl w
-flag has no effect on the
-.Fl l
-option, i.e.\&
-.Nm
-will listen forever for a connection, with or without the
-.Fl w
-flag.
-The default is no timeout.
-.It Fl X Ar proxy_protocol
-Requests that
-.Nm
-should use the specified protocol when talking to the proxy server.
-Supported protocols are
-.Dq 4
-(SOCKS v.4),
-.Dq 5
-(SOCKS v.5)
-and
-.Dq connect
-(HTTPS proxy).
-If the protocol is not specified, SOCKS version 5 is used.
-.It Xo
-.Fl x Ar proxy_address Ns Oo : Ns
-.Ar port Oc
-.Xc
-Requests that
-.Nm
-should connect to
-.Ar destination
-using a proxy at
-.Ar proxy_address
-and
-.Ar port .
-If
-.Ar port
-is not specified, the well-known port for the proxy protocol is used (1080
-for SOCKS, 3128 for HTTPS).
-.It Fl Z
-DCCP mode.
-.It Fl z
-Specifies that
-.Nm
-should just scan for listening daemons, without sending any data to them.
-It is an error to use this option in conjunction with the
-.Fl l
-option.
-.El
-.Pp
-.Ar destination
-can be a numerical IP address or a symbolic hostname
-(unless the
-.Fl n
-option is given).
-In general, a destination must be specified,
-unless the
-.Fl l
-option is given
-(in which case the local host is used).
-For
-.Ux Ns -domain
-sockets, a destination is required and is the socket path to connect to
-(or listen on if the
-.Fl l
-option is given).
-.Pp
-.Ar port
-can be a single integer or a range of ports.
-Ranges are in the form nn-mm.
-In general,
-a destination port must be specified,
-unless the
-.Fl U
-option is given.
-.Sh CLIENT/SERVER MODEL
-It is quite simple to build a very basic client/server model using
-.Nm .
-On one console, start
-.Nm
-listening on a specific port for a connection.
-For example:
-.Pp
-.Dl $ nc -l 1234
-.Pp
-.Nm
-is now listening on port 1234 for a connection.
-On a second console
-.Pq or a second machine ,
-connect to the machine and port being listened on:
-.Pp
-.Dl $ nc 127.0.0.1 1234
-.Pp
-There should now be a connection between the ports.
-Anything typed at the second console will be concatenated to the first,
-and vice-versa.
-After the connection has been set up,
-.Nm
-does not really care which side is being used as a
-.Sq server
-and which side is being used as a
-.Sq client .
-The connection may be terminated using an
-.Dv EOF
-.Pq Sq ^D .
-.Pp
-There is no
-.Fl c
-or
-.Fl e
-option in this netcat, but you still can execute a command after connection
-being established by redirecting file descriptors. Be cautious here because
-opening a port and let anyone connected execute arbitrary command on your
-site is DANGEROUS. If you really need to do this, here is an example:
-.Pp
-On
-.Sq server
-side:
-.Pp
-.Dl $ rm -f /tmp/f; mkfifo /tmp/f
-.Dl $ cat /tmp/f | /bin/sh -i 2>&1 | nc -l 127.0.0.1 1234 > /tmp/f
-.Pp
-On
-.Sq client
-side:
-.Pp
-.Dl $ nc host.example.com 1234
-.Dl $ (shell prompt from host.example.com)
-.Pp
-By doing this, you create a fifo at /tmp/f and make nc listen at port 1234
-of address 127.0.0.1 on
-.Sq server
-side, when a
-.Sq client
-establishes a connection successfully to that port, /bin/sh gets executed
-on
-.Sq server
-side and the shell prompt is given to
-.Sq client
-side.
-.Pp
-When connection is terminated,
-.Nm
-quits as well. Use
-.Fl k
-if you want it keep listening, but if the command quits this option won't
-restart it or keep
-.Nm
-running. Also don't forget to remove the file descriptor once you don't need
-it anymore:
-.Pp
-.Dl $ rm -f /tmp/f
-.Pp
-.Sh DATA TRANSFER
-The example in the previous section can be expanded to build a
-basic data transfer model.
-Any information input into one end of the connection will be output
-to the other end, and input and output can be easily captured in order to
-emulate file transfer.
-.Pp
-Start by using
-.Nm
-to listen on a specific port, with output captured into a file:
-.Pp
-.Dl $ nc -l 1234 \*(Gt filename.out
-.Pp
-Using a second machine, connect to the listening
-.Nm
-process, feeding it the file which is to be transferred:
-.Pp
-.Dl $ nc host.example.com 1234 \*(Lt filename.in
-.Pp
-After the file has been transferred, the connection will close automatically.
-.Sh TALKING TO SERVERS
-It is sometimes useful to talk to servers
-.Dq by hand
-rather than through a user interface.
-It can aid in troubleshooting,
-when it might be necessary to verify what data a server is sending
-in response to commands issued by the client.
-For example, to retrieve the home page of a web site:
-.Bd -literal -offset indent
-$ printf "GET / HTTP/1.0\er\en\er\en" | nc host.example.com 80
-.Ed
-.Pp
-Note that this also displays the headers sent by the web server.
-They can be filtered, using a tool such as
-.Xr sed 1 ,
-if necessary.
-.Pp
-More complicated examples can be built up when the user knows the format
-of requests required by the server.
-As another example, an email may be submitted to an SMTP server using:
-.Bd -literal -offset indent
-$ nc [\-C] localhost 25 \*(Lt\*(Lt EOF
-HELO host.example.com
-MAIL FROM:\*(Ltuser@host.example.com\*(Gt
-RCPT TO:\*(Ltuser2@host.example.com\*(Gt
-DATA
-Body of email.
-\&.
-QUIT
-EOF
-.Ed
-.Sh PORT SCANNING
-It may be useful to know which ports are open and running services on
-a target machine.
-The
-.Fl z
-flag can be used to tell
-.Nm
-to report open ports,
-rather than initiate a connection. Usually it's useful to turn on verbose
-output to stderr by use this option in conjunction with
-.Fl v
-option.
-.Pp
-For example:
-.Bd -literal -offset indent
-$ nc \-zv host.example.com 20-30
-Connection to host.example.com 22 port [tcp/ssh] succeeded!
-Connection to host.example.com 25 port [tcp/smtp] succeeded!
-.Ed
-.Pp
-The port range was specified to limit the search to ports 20 \- 30, and is
-scanned by increasing order.
-.Pp
-You can also specify a list of ports to scan, for example:
-.Bd -literal -offset indent
-$ nc \-zv host.example.com 80 20 22
-nc: connect to host.example.com 80 (tcp) failed: Connection refused
-nc: connect to host.example.com 20 (tcp) failed: Connection refused
-Connection to host.example.com port [tcp/ssh] succeeded!
-.Ed
-.Pp
-The ports are scanned by the order you given.
-.Pp
-Alternatively, it might be useful to know which server software
-is running, and which versions.
-This information is often contained within the greeting banners.
-In order to retrieve these, it is necessary to first make a connection,
-and then break the connection when the banner has been retrieved.
-This can be accomplished by specifying a small timeout with the
-.Fl w
-flag, or perhaps by issuing a
-.Qq Dv QUIT
-command to the server:
-.Bd -literal -offset indent
-$ echo "QUIT" | nc host.example.com 20-30
-SSH-1.99-OpenSSH_3.6.1p2
-Protocol mismatch.
-220 host.example.com IMS SMTP Receiver Version 0.84 Ready
-.Ed
-.Sh EXAMPLES
-Open a TCP connection to port 42 of host.example.com, using port 31337 as
-the source port, with a timeout of 5 seconds:
-.Pp
-.Dl $ nc -p 31337 -w 5 host.example.com 42
-.Pp
-Open a UDP connection to port 53 of host.example.com:
-.Pp
-.Dl $ nc -u host.example.com 53
-.Pp
-Open a TCP connection to port 42 of host.example.com using 10.1.2.3 as the
-IP for the local end of the connection:
-.Pp
-.Dl $ nc -s 10.1.2.3 host.example.com 42
-.Pp
-Create and listen on a
-.Ux Ns -domain
-stream socket:
-.Pp
-.Dl $ nc -lU /var/tmp/dsocket
-.Pp
-Connect to port 42 of host.example.com via an HTTP proxy at 10.2.3.4,
-port 8080.
-This example could also be used by
-.Xr ssh 1 ;
-see the
-.Cm ProxyCommand
-directive in
-.Xr ssh_config 5
-for more information.
-.Pp
-.Dl $ nc -x10.2.3.4:8080 -Xconnect host.example.com 42
-.Pp
-The same example again, this time enabling proxy authentication with username
-.Dq ruser
-if the proxy requires it:
-.Pp
-.Dl $ nc -x10.2.3.4:8080 -Xconnect -Pruser host.example.com 42
-.Sh SEE ALSO
-.Xr cat 1 ,
-.Xr ssh 1
-.Sh AUTHORS
-Original implementation by *Hobbit*
-.Aq hobbit@avian.org .
-.br
-Rewritten with IPv6 support by
-.An Eric Jackson Aq ericj@monkey.org .
-.br
-Modified for Debian port by Aron Xu
-.Aq aron@debian.org .
-.Sh CAVEATS
-UDP port scans using the
-.Fl uz
-combination of flags will always report success irrespective of
-the target machine's state.
-However,
-in conjunction with a traffic sniffer either on the target machine
-or an intermediary device,
-the
-.Fl uz
-combination could be useful for communications diagnostics.
-Note that the amount of UDP traffic generated may be limited either
-due to hardware resources and/or configuration settings.
~mdw / termux-packages / commitdiff