SSH Tutorial for Linux Support Documentation. This document covers the SSH client on the Linux Operating System and other OSes that use Open. SSH. If you use Windows, please read the document SSH Tutorial for Windows If you use Mac OS X or other Unix based system, you should already have Open. SSH installed and can use this document as a reference. This article is one of the top tutorials covering SSH on the Internet. It was originally written back in 1. As of October, 2. Googles search results for SSH Tutorial and Linux SSH. What Is SSH There are a couple of ways that you can access a shell command line remotely on most LinuxUnix systems. One of the older ways is to use the telnet program, which is available on most network capable operating systems. Accessing a shell account through the telnet method though poses a danger in that everything that you send or receive over that telnet session is visible in plain text on your local network, and the local network of the machine you are connecting to. So anyone who can sniff the connection in between can see your username, password, email that you read, and commands that you run. For these reasons you need a more sophisticated program than telnet to connect to a remote host. SSH, which is an acronym for Secure SHell, was designed and created to provide the best security when accessing another computer remotely. Not only does it encrypt the session, it also provides better authentication facilities, as well as features like secure file transfer, X session forwarding, port forwarding and more so that you can increase the security of other protocols. It can use different forms of encryption ranging anywhere from 5. AES Advanced Encryption Scheme, Triple DES, Blowfish, CAST1. Arcfour. Of course, the higher the bits, the longer it will take to generate and use keys as well as the longer it will take to pass data over the connection. The upgrade to Windows 10 has been smooth for most, but some users will always encounter issues. Whether its a flashing screen, network connectivity issues, or. These two diagrams on the left show how a telnet session can be viewed by anyone on the network by using a sniffing program like Ethereal now called Wireshark or tcpdump. It is really rather trivial to do this and so anyone on the network can steal your passwords and other information. The first diagram shows user jsmith logging in to a remote server through a telnet connection. Roland Dt 1 V Drums Tutor more. He types his username jsmith and password C0lts. The second diagram shows how the data in an encrypted connection like SSH is encrypted on the network and so cannot be read by anyone who doesnt have the session negotiated keys, which is just a fancy way of saying the data is scrambled. The server still can read the information, but only after negotiating the encrypted session with the client. When I say scrambled, I dont mean like the old cable pay channels where you can still kinda see things and hear the sound, I mean really scrambled. Usually encryption means that the data has been changed to such a degree that unless you have the key, its really hard to crack the code with a computer. It will take on the order of years for commonly available computer hardware to crack the encrypted data. The premise being that by the time you could crack it, the data is worthless. Getting Started This tutorial isnt going to cover how to install SSH, but will cover how to use it for a variety of tasks. Consult your Linux distributions document for information on how to setup Open. SSH. Chances are that if you are using a version of Linux that was released after 2. Open. SSH installed. The version of SSH that you will want to use on Linux is called Open. SSH. As of this writing October 2. Gentoo Serial Terminal Program' title='Gentoo Serial Terminal Program' />If you are using anything lower than version 3. Id strongly advise you to upgrade it. Open. SSH can be obtained from http www. To really make ssh useful, you need a shell account on a remote machine, such as on a Suso account. The first thing well do is simply connect to a remote machine. This is accomplished by running ssh hostname on your local machine. The hostname that you supply as an argument is the hostname of the remote machine that you want to connect to. By default ssh will assume that you want to authenticate as the same user you use on your local machine. Codecs Windows Movie Maker Avi Files more. To override this and use a different user, simply use remoteusernamehostname as the argument. Such as in this example. The first time around it will ask you if you wish to add the remote host to a list of knownhosts, go ahead and say yes. The authenticity of host arvo. RSA key fingerprint is 5. Are you sure you want to continue connecting yesno Warning Permanently added arvo. Gentoo Serial Terminal Program' title='Gentoo Serial Terminal Program' />RSA to the list of known hosts. It is important to pay attention to this question however because this is one of SSHs major features. Host validation. To put it simply, ssh will check to make sure that you are connecting to the host that you think you are connecting to. That way if someone tries to trick you into logging into their machine instead so that they can sniff your SSH session, you will have some warning, like this. WARNING POSSIBLE DNS SPOOFING DETECTED The RSA host key for arvo. Latest trending topics being covered on ZDNet including Reviews, Tech Industry, Security, Hardware, Apple, and Windows. IP address 2. 16. This could either mean that. DNS SPOOFING is happening or the IP address for the host. Offending key for IP in homesuso. WARNING REMOTE HOST IDENTIFICATION HAS CHANGED IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY Someone could be eavesdropping on you right now man in the middle attack It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is. Please contact your system administrator. Add correct host key in homesuso. Offending key in homesuso. RSA host key for arvo. Host key verification failed. If you ever get a warning like this, you should stop and determine if there is a reason for the remote servers host key to change such as if SSH was upgraded or the server itself was upgraded. Battlefield Bad Company 2 Demo Chip there. If there is no good reason for the host key to change, then you should not try to connect to that machine until you have contacted its administrator about the situation. If this is your own machine that you are trying to connect to, you should do some computer forensics to determine if the machine was hacked yes, Linux can be hacked. Or maybe your home computers IP address has changed such as if you have a dynamic IP address for DSL. One time I received this message when trying to connect to my home machines DSL line. I thought it was odd since I hadnt upgraded SSH or anything on my home machine and so I choose not to try to override the cached key. It was a good thing that I didnt try because I found out that my dynamic IP address had changed and that out of chance, another Linux machine running Open. SSH took my old IP. After saying yes, it will prompt you for your password on the remote system. If the username that you specified exists and you type in the remote password for it correctly then the system should let you in. If it doesnt, try again and if it still fails, you might check with the administrator that you have an account on that machine and that your username and password is correct. Generating a key Now that you have spent all that time reading and are now connected, go ahead and logout. Once youre back to your local computers command prompt enter the command ssh keygen b 4. It should begin spitting out the following. Generating publicprivate rsa key pair. Enter file in which to save the key homelocaluser. Enter passphrase empty for no passphrase. Enter same passphrase again. Your identification has been saved in homelocaluser.