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NC(1)									 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 connec‐
	   tion 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.  Additionally, any timeout specified with the -w option is
	   ignored.

       -n

	   Do not do any naming or service lookups  on	any  addresses,	 host‐
	   names, 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 addition to the restriction imposed on the argu‐
	   ments. This option does not have any effect when used  in  conjunc‐
	   tion with the -U option.

       -P proxy_username

	   Specify  a  username	 (proxy_username) to present to a proxy server
	   that requires authentication. If proxy_username is  not  specified,
	   authentication  is not attempted. Proxy authentication is only sup‐
	   ported 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 privilege 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 specified.

       -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  tel‐
	   net 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 connection, with or without the -w flag. The  default
	   is no timeout.

       -X proxy_protocol

	   Use	the  specified protocol when talking to the proxy server. Sup‐
	   ported 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 host‐
		    name (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 specified with -l
		    option then port argument must be given  as	 well  and  nc
		    tries  to bind to that address and port. If hostname argu‐
		    ment is not specified with -l option then nc tries to lis‐
		    ten on a wildcard socket for given port.

       path
		    Specify pathname.

       port
       port_list
		    Specify port.

		    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  connec‐
       tion  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  automati‐
       cally.

   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	neces‐
       sary  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:

	 $ echo -n "GET / HTTP/1.0\r\n\r\n" | nc host.example.com 80

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

       More  complicated examples can be built up when the user knows the for‐
       mat 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 connection.

       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 run‐
       ning, 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 -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_pri‐
       vaddr 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 privileges(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 Proxy‐
       Command 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 additional 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 allowing it to listen on any port. To permit a  user  or
       role to use nc only to listen on specific 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 │
       ├────────────────────┼─────────────────┤
       │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 com‐
       mand 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), privileges(5), rbac(5)

AUTHORS
       The  original  implementation  of  nc  was  written  by	Hobbit,	  hob‐
       bit@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, ren‐
       dering the -uz combination of flags relatively useless.

				  Apr 9, 2009				 NC(1)
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