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OpenSolaris 2009.06 - man page for nc (opensolaris section 1)

nc(1)					  User Commands 				    nc(1)

NAME
       nc - arbitrary TCP and UDP connections and listens

SYNOPSIS
       nc -h

       nc [-46dnrtuvz] [-i interval] [-P proxy_username] [-p port]
	    [-s source_ip_address] [-T ToS] [-w timeout]
	    [-X proxy_protocol] [-x proxy_address[:port]]
	    hostname port_list

       nc -l [-46Ddnrtuvz] [-i interval] [-T ToS] [hostname] port

       nc -l [-46Ddnrtuvz] [-i interval] [-T ToS] -p port

       nc -U [-Ddtvz] [-i interval] [-w timeout] path

       nc -Ul [-46Ddktv] [-i interval] path

DESCRIPTION
       The  nc	(or netcat) utility is used for a variety of tasks associated with TCP or UDP. nc
       can open TCP connections, send UDP packets, listen on arbitrary TCP and UDP ports, perform
       port  scanning, and deal with both IPv4 and IPv6. Unlike telnet(1), nc scripts nicely, and
       separates error messages onto standard error instead of sending them to standard output.

       The nc command is often used for the following tasks:

	   o	  simple TCP proxies

	   o	  shell-script based HTTP clients and servers

	   o	  network daemon testing

	   o	  a SOCKS or HTTP ProxyCommand for ssh(1)

OPTIONS
       The following options are supported:

       -4

	   Force nc to use IPv4 addresses only.

       -6

	   Force nc to use IPv6 addresses only.

       -D

	   Enable debugging on the socket.

       -d

	   Do not attempt to read from stdin.

       -h

	   Print nc help.

       -i interval

	   Specify a delay time of interval between lines of text sent and received. This  option
	   also causes a delay time between connections to multiple ports.

       -k

	   Force nc to listen for another connection after its current connection is closed.

	   It is an error to use this option without the -l option.

       -l

	   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 -s or -z options. Addition-
	   ally, any timeout specified with the -w option is ignored.

       -n

	   Do not do any naming or service lookups on any addresses, hostnames, or ports.

	   Use of this option means that hostname and port arguments are  restricted  to  numeric
	   values.

	   If  used  with -v option all addresses and ports are printed in numeric form, in addi-
	   tion to the restriction imposed on the arguments. This option does not have any effect
	   when used in conjunction with the -U option.

       -P proxy_username

	   Specify a username (proxy_username) to present to a proxy server that requires authen-
	   tication. If proxy_username is not specified, authentication is not	attempted.  Proxy
	   authentication is only supported for HTTP CONNECT proxies at present.

	   It is an error to use this option in conjunction with the -l option.

       -p port

	   When  used without -l option, specify the source port nc should use, subject to privi-
	   lege restrictions and availability. When used with the -l option, set the listen port.

	   This option can be used with -l option only provided global port argument is not spec-
	   ified.

       -r

	   Choose  source or destination ports randomly instead of sequentially within a range or
	   in the order that the system assigns them.

	   It is an error to use this option in conjunction with the -l option.

       -s source_ip_address

	   Specify the IP of the interface which is used to send the packets.

	   It is an error to use this option in conjunction with the -l option.

       -T ToS

	   Specify IP Type of Service (ToS) for the connection.  Valid	values	are  the  tokens:
	   lowdelay, throughput, reliability, or an 8-bit hexadecimal value preceded by 0x.

       -t

	   Cause  nc  to  send RFC 854 DON'T and WON'T responses to RFC 854 DO and WILL requests.
	   This makes it possible to use nc to script telnet sessions.

       -U

	   Specify the use of Unix Domain Sockets. If you specify this option without -l, nc,  it
	   becomes  AF_UNIX  client.  If  you  specify	this option with the -l option, a AF_UNIX
	   server is created.

	   Use of this option requires that a single argument of a valid Unix domain path has  to
	   be provided to nc, not a host name or port.

       -u

	   Use UDP instead of the default option of TCP.

       -v

	   Specify verbose output.

       -w timeout

	   Silently close the connection if a connection and stdin are idle for more than timeout
	   seconds.

	   This option has no effect on the -l option, that is, nc listens forever for a  connec-
	   tion, with or without the -w flag. The default is no timeout.

       -X proxy_protocol

	   Use the specified protocol when talking to the proxy server. Supported protocols are 4
	   (SOCKS v.4), 5 (SOCKS v.5) and connect (HTTP proxy). If the protocol is not specified,
	   SOCKS v. 5 is used.

	   It is an error to use this option in conjunction with the -l option.

       -x proxy_address[:port]

	   Request connection to hostname using a proxy at proxy_address and port. If port is not
	   specified, the well-known port for the proxy protocol is used (1080	for  SOCKS,  3128
	   for HTTP).

	   It is an error to use this option in conjunction with the -l option.

       -z

	   Scan for listening daemons, without sending any data to them.

	   It is an error to use this option in conjunction with the -l option.

OPERANDS
       The following operands are supported:

       hostname     Specify host name.

		    hostname  can be a numerical IP address or a symbolic hostname (unless the -n
		    option is specified).

		    In general, hostname must be specified, unless the -l option is given  or  -U
		    is used (in which case the argument is a path). If hostname argument is spec-
		    ified with -l option then port argument must be given as well and nc tries to
		    bind  to that address and port. If hostname argument is not specified with -l
		    option then nc tries to listen on a wildcard socket for given port.

       path	    Specify pathname.

       port	    Specify port.
       port_list
		    port_list can be specified as single  integers,  ranges  or  combinations  of
		    both.  Specify  ranges in the form of nn-mm. The port_list must have at least
		    one member, but can have multiple ports/ranges separated by commas.

		    In general, a destination port must be specified, unless  the  -U  option  is
		    given,  in	which case a Unix Domain Socket path must be specified instead of
		    hostname.

USAGE
   Client/Server Model
       It is quite simple to build a very basic client/server model using  nc.	On  one  console,
       start nc listening on a specific port for a connection. For example, the command:

	 $ nc -l 1234

       listens	on port 1234 for a connection. On a second console (or a second machine), connect
       to the machine and port to which nc is listening:

	 $ nc 127.0.0.1 1234

       There should now be a connection between the ports. Anything typed at the  second  console
       is  concatenated  to  the  first, and vice-versa. After the connection has been set up, nc
       does not really care which side is being used as a server and which side is being used  as
       a client. The connection can be terminated using an EOF (Ctrl/d).

   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 is output to the other end, and input
       and output can be easily captured in order to emulate file transfer.

       Start by using nc to listen on a specific port, with output captured into a file:

	 $ nc -l 1234 > filename.out

       Using  a second machine, connect to the listening nc process, feeding it the file which is
       to be transferred:

	 $ nc host.example.com 1234 < filename.in

       After the file has been 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  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:
				  0r0 | nc host.example.com 80
	 $ echo -n "GET / HTTP/1.0

       This also displays the headers sent by the web server. They can be filtered, if necessary,
       by using a tool such as sed(1).

       More  complicated  examples  can  be  built  up when the user knows the format of requests
       required by the server. As another example, an email can be submitted to  an  SMTP  server
       using:

	 $ nc localhost 25 << EOF
	 HELO host.example.com
	 MAIL FROM: <user@host.example.com
	 RCTP TO: <user2@host.example.com
	 DATA
	 Body of email.
	 .
	 QUIT
	 EOF

   Port Scanning
       It  can	be  useful to know which ports are open and running services on a target machine.
       The -z flag can be used to tell nc to report open ports, rather than to initiate a connec-
       tion.

       In this example:

	 $ nc -z 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!

       The port range was specified to limit the search to ports 20 - 30.

       Alternatively, it might be useful to know which server software is running, and which ver-
       sions. 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 -w flag, or perhaps by issuing a QUIT command to the server:

	 $ echo "QUIT" | nc host.example.com 20-30
	 SSH-2.0-Sun_SSH_1.1
	 Protocol mismatch.
	 220 host.example.com IMS SMTP Receiver Version 0.84 Ready

   inetd Capabilities
       One of the possible uses is to create simple services by using inetd(1M).

       The following example creates a redirect from TCP port 8080 to port 80 on host realwww:

	 # cat << EOF >> /etc/services
	 wwwredir    8080/tcp	 # WWW redirect
	 EOF
	 # cat << EOF > /tmp/wwwredir.conf
	 wwwredir stream tcp nowait nobody /usr/bin/nc /usr/bin/nc -w 3 realwww 80
	 EOF
	 # inetconv -i /tmp/wwwredir.conf
	 wwwredir -> /var/svc/manifest/network/wwwredir-tcp.xml
	 Importing wwwredir-tcp.xml ...Done
	 # inetadm -l wwwredir/tcp
	 SCOPE	  NAME=VALUE
	 name="wwwredir"
	 endpoint_type="stream"
	 proto="tcp"
	 isrpc=FALSE
	 wait=FALSE
	 exec="/usr/bin/nc -w 3 realwww 80"
	 arg0="/usr/bin/nc"
	 user="nobody"
	 default  bind_addr=""
	 default  bind_fail_max=-1
	 default  bind_fail_interval=-1
	 default  max_con_rate=-1
	 default  max_copies=-1
	 default  con_rate_offline=-1
	 default  failrate_cnt=40
	 default  failrate_interval=60
	 default  inherit_env=TRUE
	 default  tcp_trace=TRUE
	 default  tcp_wrappers=FALSE

   Privileges
       To  bind to a privileged port number nc needs to be granted the net_privaddr privilege. If
       Solaris Trusted Extensions are configured and the port nc should listen on  is  configured
       as a multi-level port nc also needs the net_bindmlp privilege.

       Privileges  can	be  assigned  to  the  user  or  role directly, by specifying them in the
       account's default privilege set in user_attr(4). However, this means that any  application
       that  this  user or role starts have these additional privileges. To only grant the privi-
       leges(5) when nc is invoked, the recommended approach is to create and assign  an  rbac(5)
       rights profile. See EXAMPLES for additional information.

EXAMPLES
       Example 1 Using nc

       Open  a TCP connection to port 42 of host.example.com, using port 3141 as the source port,
       with a timeout of 5 seconds:

	 $ nc -p 3141 -w 5 host.example.com 42

       Open a UDP connection to port 53 of host.example.com:

	 $ nc -u host.example.com 53

       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:

	 $ nc -s 10.1.2.3 host.example.com 42

       Use a list of ports and port ranges for a port scan on various ports:

	 $ nc -z host.example.com 21-25,53,80,110-120,443

       Create and listen on a Unix Domain Socket:

	 $ nc -lU /var/tmp/dsocket

       Create and listen on a UDP socket with associated port 8888:

	 $ nc -u -l -p 8888

       which is the same as:

	 $ nc -u -l 8888

       Create  and listen on a TCP socket with associated port 2222 and bind to address 127.0.0.1
       only:

	 $ nc -l 127.0.0.1 2222

       Connect to port 42 of host.example.com using an HTTP proxy at 10.2.3.4,	port  8080.  This
       example	could also be used by ssh(1). See the ProxyCommand directive in ssh_config(4) for
       more information.

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

       The same example again, this time enabling proxy authentication with username ruser if the
       proxy requires it:

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

       To  run	nc  with the smallest possible set of privileges as a user or role that has addi-
       tional privileges (such as the default root account) it can be invoked using  ppriv(1)  as
       well.  For  example,  limiting  it  to only run with the privilege to bind to a privileged
       port:

	 $ ppriv -e -sA=basic,!file_link_any,!proc_exec,!proc_fork,\
	 !proc_info,!proc_session,net_privaddr nc -l 42

       To allow a user or role to use only nc with the net_privaddr privilege, a  rights  profile
       needs to be created:

	 /etc/security/exec_attr
	 Netcat privileged:solaris:cmd:::/usr/bin/nc:privs=net_privaddr

	 /etc/security/prof_attr
	 Netcat privileged:::Allow nc to bind to privileged ports:help=None.html

       Assigning this rights profile using user_attr(4) permits the user or role to run nc allow-
       ing it to listen on any port. To permit a user or role to use nc only to  listen  on  spe-
       cific ports a wrapper script should be specified in the rights profiles:

	 /etc/security/exec_attr
	 Netcat restricted:solaris:cmd:::/usr/bin/nc-restricted:privs=net_privaddr

	 /etc/security/prof_attr
	 Netcat restricted:::Allow nc to bind to privileged ports:help=None.html

       and  write  a  shell  script that restricts the permissible options, for example, one that
       permits one to bind only on ports between 42 and 64 (non-inclusive):

	 /usr/bin/nc-restricted:

	 #!/bin/sh
	 [ $# -eq 1 ] && [ $1 -gt 42 -a $1 -lt 64 ] && /usr/bin/nc -l -p "$1"

       This grants the extra privileges when the user or role invokes nc using the wrapper script
       from a profile shell. See pfsh(1), pfksh(1), pfcsh(1), and pfexec(1).

       Invoking  nc  directly  does  not  run it with the additional privileges, and neither does
       invoking the script without using pfexec or a profile shell.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWnetcat		   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |See below.		   |
       +-----------------------------+-----------------------------+

       The package name is Committed. The command line syntax is Committed for the  -4,  -6,  -l,
       -n,  -p ,-u, and -w options and their arguments (if any). The name and port list arguments
       are Committed. The port range syntax is Uncommitted. The interface stability level for all
       other command line options and their arguments is Uncommitted.

SEE ALSO
       cat(1),	pfcsh(1),  pfexec(1),  pfksh(1),  pfsh(1),  ppriv(1),  sed(1), ssh(1), telnet(1),
       inetadm(1M), inetconv(1M), inetd(1M), ssh_config(4), user_attr(4),  attributes(5),  privi-
       leges(5), rbac(5)

AUTHORS
       The original implementation of nc was written by Hobbit, hobbit@avian.org.

       nc was rewritten with IPv6 support by Eric Jackson, ericj@monkey.org.

NOTES
       UDP  port scans always succeeds, that is, reports the port as open, rendering the -uz com-
       bination of flags relatively useless.

SunOS 5.11				    5 Jan 2009					    nc(1)


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