usage of nc

zsgd

               
NC     Linux and Unix命令手册
本命令手册以实用，简洁为原则，对于已经消化的内容，不附加详细的注解。
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参考资料
＊《Unix 技术手册》
＊ Solaris 8 date 命令帮助
＊《鸟哥的 Linux 私房菜》之 "开机关机、在线求助与指令下达方式"
功能
nc---arbitrary TCP and UDP connections and listens
     The nc (or netcat) utility is used for just about anything under the sun involving TCP or UDP.  It can open TCP con-
     nections, send UDP packets, listen on arbitrary TCP and UDP ports, do port scanning, and source routing.  Unlike
     telnet(1), nc scripts nicely, and separates error messages onto standard error instead of sending them to standard
     output, as telnet(1) does with some.
语法


常用用法
-simple TCP proxies
-shell-script based HTTP clients and servers
-network daemon testing
-source routing based connectivity testing
-
重要参数：

打开TCP连接：
nc -v
10.50.57.21
79
10.50.57.21: inverse host lookup failed: Host name lookup failure
(UNKNOWN) [
10.50.57.21
] 79 (finger) open
辅助的参数有-p 31337，-w 5等

打开UDP连接：
[root@oracle ~]# nc -v -u   
10.50.48.16
22
10.50.48.16: inverse host lookup failed: Host name lookup failure
(UNKNOWN) [
10.50.48.16
] 22 (ssh) open
      
使用IP欺骗，部分系统可用
nc -v -s
10.50.44.1
  
10.50.48.16
22
                     

扫描端口：
# nc -v -z  
10.50.57.21
1-100
10.50.57.21: inverse host lookup failed: Host name lookup failure
(UNKNOWN) [
10.50.57.21
] 79 (finger) open
(UNKNOWN) [
10.50.57.21
] 25 (smtp) open
(UNKNOWN) [
10.50.57.21
] 23 (telnet) open
(UNKNOWN) [
10.50.57.21
] 22 (ssh) open
(UNKNOWN) [
10.50.57.21
] 21 (ftp) open

＊    man –k 查找关键字
# man -k vmstat
vmstat               (8)  - Report virtual memory statistics

命令参考
NC(1)                     BSD General Commands Manual                    NC(1)

NAME
     nc - arbitrary TCP and UDP connections and listens

SYNOPSIS
     nc [-e command] [-g intermediates] [-G hopcount] [-i interval] [-lnrtuvz]
        [-o filename] [-p source port] [-s ip address] [-w timeout] [hostname]
        [port[s...]]

DESCRIPTION
     The nc (or netcat) utility is used for just about anything under the sun
     involving TCP or UDP.  It can open TCP connections, send UDP packets,
     listen on arbitrary TCP and UDP ports, do port scanning, and source rout-
     ing. Unlike telnet(1), nc scripts nicely, and separates error messages
     onto standard error instead of sending them to standard output, as
     telnet(1) does with some.

     Destination ports can be single integers, names as listed in services(5),
     or ranges. Ranges are in the form nn-mm, and several separate ports
     and/or ranges may be specified on the command line.

     Common uses include:

     ? simple TCP proxies

     ? shell-script based HTTP clients and servers

     ? network daemon testing

     ? source routing based connectivity testing

     ? and much, much more

     The options are as follows:

     -e command
             Execute the specified command, using data from the network for
             stdin, and sending stdout and stderr to the network.  This option
             is only present if nc was compiled with the GAPING_SECURITY_HOLE
             compile time option, since it allows users to make arbitrary pro-
             grams available to anyone on the network.

     -g intermediate-host
             Specifies a hop along a loose source routed path.  Can be used
             more than once to build a chain of hop points.

     -G pointer
             Positions the "hop counter" within the list of machines in the
             path of a source routed packet.  Must be a multiple of 4.

     -i seconds
             Specifies a delay time interval between lines of text sent and received. Also causes a delay time between
             connections to multiple ports.

     -l     Is used to specify that nc should listen for an incoming connection, rather than initiate a connection to a
             remote host.  Any hostname/IP address and port arguments restrict the source of inbound connections to only
             that address and source port.

     -n     Do not do DNS lookups on any of the specified addresses or hostnames, or names of port numbers from /etc/ser-
             vices.

     -o filename
             Create a hexadecimal log of data transferred in the specified file.  Each line begins with ‘‘’’.
             ‘‘’’ means "to the net".

     -p port
             Specifies the source port nc should use, subject to privilege restrictions and availability.

     -r     Specifies that source and/or destination ports should be chosen semi-randomly instead of sequentially within
             a range or in the order that the system assigns.

     -s hostname/ip-address
             Specifies the IP of the interface which is used to send the packets.  On some platforms, this can be used for
             UDP spoofing by using ifconfig(8) to bring up a dummy interface with the desired source IP address.

     -t     Causes nc to send RFC854 DON’T and WON’T responses to RFC854 DO and WILL requests.  This makes it possible to
             use nc to script telnet sessions.  The presence of this option can be enabled or disabled as a compile-time
             option.

     -u     Use UDP instead of TCP.  On most platforms, nc will behave as if a connection is established until it
             receives an ICMP packet indicating that there is no program listening to what it sends.

     -v     Verbose.  Cause nc to display connection information.  Using -v more than once will cause nc to become even
             more verbose.

     -w timeout
             Specifies the number of seconds nc should wait before deciding that an attempt to establish a connection is
             hopeless.  Also used to specify how long to wait for more network data after standard input closes.

     -z     Specifies that nc should just scan for listening daemons, without sending any data to them.  Diagnostic mes-
             sages about refused connections will not be displayed unless -v is specified twice.

EXAMPLES
     nc
        Wait for the user to type what would normally be command-line arguments in at stdin.

     nc example.host 42
        Open a TCP connection to port 42 of example.host.  If the connection fails, do not display any error messages, but
        simply exit.

     nc -p 31337 example.host 42
        Open a TCP connection to port 42 of example.host, and use port 31337 as the source port.

     nc -w 5 example.host 42
        Open a TCP connection to port 42 of example.host, and time out after five seconds while attempting to connect.

     nc -u example.host 53
        Send any data from stdin to UDP port 53 of example.host, and display any data returned.

     nc -s
10.1.2.3
example.host 42
        Open a TCP connection to port 42 of example.host using
10.1.2.3
as the IP for the local end of the connection.

     nc -v example.host 42
        Open a TCP connection to port 42 of example.host, displaying some diagnostic messages on stderr.

     nc -v -v example.host 42
        Open a TCP connection to port 42 of example.host, displaying all diagnostic messages on stderr.

     nc -v -z example.host 20-30
        Attempt to open TCP connections to ports 20 through 30 of example.host, and report which ones nc was able to con-
        nect to.

     nc -v -u -z -w 3 example.host 20-30
        Send UDP packets to ports 20-30 of example.host, and report which ones did not respond with an ICMP packet after
        three seconds.

     nc -l -p 3000
        Listen on TCP port 3000, and once there is a connection, send stdin to the remote host, and send data from the
        remote host to stdout.

     echo foobar | nc example.host 1000
        Connect to port 1000 of example.host, send the string "foobar" followed by a newline, and move data from port 1000
        of example.host to stdout until example.host closes the connection.

SEE ALSO
     cat(1), telnet(1)

     The netcat README.

AUTHOR
     *Hobbit* [
hobbit@avian.org
]

BSD                                                  August 1, 1996                                                  BSD
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