From 319214bfcd528ec9b4a487f36dccaf15a57bb3ea Mon Sep 17 00:00:00 2001 From: darksun Date: Mon, 11 Dec 2017 22:08:47 +0800 Subject: [PATCH] =?UTF-8?q?=E9=80=89=E9=A2=98:=2010=20useful=20ncat=20(nc)?= =?UTF-8?q?=20Command=20Examples=20for=20Linux=20Systems?= MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit --- ...(nc) Command Examples for Linux Systems.md | 200 ++++++++++++++++++ 1 file changed, 200 insertions(+) create mode 100644 sources/tech/20171206 10 useful ncat (nc) Command Examples for Linux Systems.md diff --git a/sources/tech/20171206 10 useful ncat (nc) Command Examples for Linux Systems.md b/sources/tech/20171206 10 useful ncat (nc) Command Examples for Linux Systems.md new file mode 100644 index 0000000000..8264014664 --- /dev/null +++ b/sources/tech/20171206 10 useful ncat (nc) Command Examples for Linux Systems.md @@ -0,0 +1,200 @@ +translating by lujun9972 +10 useful ncat (nc) Command Examples for Linux Systems +====== + [![nc-ncat-command-examples-Linux-Systems](https://www.linuxtechi.com/wp-content/uploads/2017/12/nc-ncat-command-examples-Linux-Systems.jpg)][1] + +ncat or nc is networking utility with functionality similar to cat command but for network. It is a general purpose CLI tool for reading, writing, redirecting data across a network. It is designed to be a reliable back-end tool that can be used with scripts or other programs. It’s also a great tool for network debugging, as it can create any kind of connect one can need. + +ncat/nc can be a port scanning tool, or a security tool, or monitoring tool and is also a simple TCP proxy. Since it has so many features, it is known as a network swiss army knife. It’s one of those tools that every System Admin should know & master. + +In most of Debian distributions ‘nc’ is available and its package is automatically installed during installation. But in minimal CentOS 7 / RHEL 7 installation you will not find nc as a default package. You need to install using the following command. + +``` +[root@linuxtechi ~]# yum install nmap-ncat -y +``` + +System admins can use it audit their system security, they can use it find the ports that are opened & than secure them. Admins can also use it as a client for auditing web servers, telnet servers, mail servers etc, with ‘nc’ we can control every character sent & can also view the responses to sent queries. + +We can also cause it to capture data being sent by client to understand what they are upto. + +In this tutorial, we are going to learn about how to use ‘nc’ command with 10 examples, + +#### Example: 1) Listen to inbound connections + +Ncat can work in listen mode & we can listen for inbound connections on port number with option ‘l’. Complete command is, + +$ ncat -l port_number + +For example, + +``` +$ ncat -l 8080 +``` + +Server will now start listening to port 8080 for inbound connections. + +#### Example: 2) Connect to a remote system + +To connect to a remote system with nc, we can use the following command, + +$ ncat IP_address port_number + +Let’s take an example, + +``` +$ ncat 192.168.1.100 80 +``` + +Now a connection to server with IP address 192.168.1.100 will be made at port 80 & we can now send instructions to server. Like we can get the complete page content with + +GET / HTTP/1.1 + +or get the page name, + +GET / HTTP/1.1 + +or we can get banner for OS fingerprinting with the following, + +HEAD / HTTP/1.1 + +This will tell what software is being used to run the web Server. + +#### Example: 3) Connecting to UDP ports + +By default , the nc utility makes connections only to TCP ports. But we can also make connections to UDP ports, for that we can use option ‘u’, + +``` +$ ncat -l -u 1234 +``` + +Now our system will start listening a udp port ‘1234’, we can verify this using below netstat command, + +``` +$ netstat -tunlp | grep 1234 +udp 0 0 0.0.0.0:1234 0.0.0.0:* 17341/nc +udp6 0 0 :::1234 :::* 17341/nc +``` + +Let’s assume we want to send or test UDP port connectivity to a specific remote host, then use the following command, + +$ ncat -v -u {host-ip} {udp-port} + +example: + +``` +[root@localhost ~]# ncat -v -u 192.168.105.150 53 +Ncat: Version 6.40 ( http://nmap.org/ncat ) +Ncat: Connected to 192.168.105.150:53. +``` + +#### Example: 4) NC as chat tool + +NC can also be used as chat tool, we can configure server to listen to a port & than can make connection to server from a remote machine on same port & start sending message. On server side, run + +``` +$ ncat -l 8080 +``` + +On remote client machine, run + +``` +$ ncat 192.168.1.100 8080 +``` + +Than start sending messages & they will be displayed on server terminal. + +#### Example: 5) NC as a proxy + +NC can also be used as a proxy with a simple command. Let’s take an example, + +``` +$ ncat -l 8080 | ncat 192.168.1.200 80 +``` + +Now all the connections coming to our server on port 8080 will be automatically redirected to 192.168.1.200 server on port 80\. But since we are using a pipe, data can only be transferred & to be able to receive the data back, we need to create a two way pipe. Use the following commands to do so, + +``` +$ mkfifo 2way +$ ncat -l 8080 0<2way | ncat 192.168.1.200 80 1>2way +``` + +Now you will be able to send & receive data over nc proxy. + +#### Example: 6) Copying Files using nc/ncat + +NC can also be used to copy the files from one system to another, though it is not recommended & mostly all systems have ssh/scp installed by default. But none the less if you have come across a system with no ssh/scp, you can also use nc as last ditch effort. + +Start with machine on which data is to be received & start nc is listener mode, + +``` +$ ncat -l 8080 > file.txt +``` + +Now on the machine from where data is to be copied, run the following command, + +``` +$ ncat 192.168.1.100 8080 --send-only < data.txt +``` + +Here, data.txt is the file that has to be sent. –send-only option will close the connection once the file has been copied. If not using this option, than we will have press ctrl+c to close the connection manually. + +We can also copy entire disk partitions using this method, but it should be done with caution. + +#### Example: 7) Create a backdoor via nc/nact + +NC command can also be used to create backdoor to your systems & this technique is actually used by hackers a lot. We should know how it works in order to secure our system. To create a backdoor, the command is, + +``` +$ ncat -l 10000 -e /bin/bash +``` + +‘e‘ flag attaches a bash to port 10000\. Now a client can connect to port 10000 on server & will have complete access to our system via bash, + +``` +$ ncat 192.168.1.100 1000 +``` + +#### Example: 8) Port forwarding via nc/ncat + +We can also use NC for port forwarding with the help of option ‘c’ , syntax for accomplishing port forwarding is, + +``` +$ ncat -u -l 80 -c 'ncat -u -l 8080' +``` + +Now all the connections for port 80 will be forwarded to port 8080. + +#### Example: 9) Set Connection timeouts + +Listener mode in ncat will continue to run & would have to be terminated manually. But we can configure timeouts with option ‘w’, + +``` +$ ncat -w 10 192.168.1.100 8080 +``` + +This will cause connection to be terminated in 10 seconds, but it can only be used on client side & not on server side. + +#### Example: 10) Force server to stay up using -k option in ncat + +When client disconnects from server, after sometime server also stops listening. But we can force server to stay connected & continuing port listening with option ‘k’. Run the following command, + +``` +$ ncat -l -k 8080 +``` + +Now server will stay up, even if a connection from client is broken. + +With this we end our tutorial, please feel free to ask any question regarding this article using the comment box below. + +-------------------------------------------------------------------------------- + +via: https://www.linuxtechi.com/nc-ncat-command-examples-linux-systems/ + +作者：[Pradeep Kumar][a] +译者：[lujun9972](https://github.com/lujun9972) +校对：[校对者ID](https://github.com/校对者ID) + +本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出 + +[a]:https://www.linuxtechi.com/author/pradeep/ +[1]:https://www.linuxtechi.com/wp-content/uploads/2017/12/nc-ncat-command-examples-Linux-Systems.jpg