This article tries to explain how to setup a connection to remote computers. A computer is remote when you are not controlling it with an attached mouse or keyboard but indirectly over some kind of network device.

The network protocol used by most computers to securely communicate with other computers is called SSH, or openSSH. This protocol is available by default on almost all operating systems, such as Linux, MacOS, BSD, Unix,… but Windows. The latter has historical reasons, but will change in the near future of Windows 10, where SSH will be shipped by default.

In any case there are two requirements to connect to a remote computer:

• The remote computer must be in the range of your computer, for most OVGU services, this means you have to be within the university's network (WLAN,VPN,..)
• You must have an account on the remote computer. Otherwise you cannot login into the remote computer.

There are a number of steps (and programs) necessary to set up a remote connection via SSH. Jump to the section windows, in case you are using this OS. In any other case (non-mobile OS) proceed with the Linux section:

• Windows
• Linux

Before continuing with this section, make yourself comfortable with the UNIX command line environment. SSH is a command line tool in its original form. And you'll mostly be only able to work in a command line environment on a remote computer.

the setup should be quite similar to Linux for these OS: Mac/OS, UNIX, BSD

ssh remote_username@remote_host

exit

1. Create a SSH key pair on your local machine with ssh-keygen. Open a Terminal and type the following command (after the $ character). Now press Enter three times to use the default location, and to set no passphrase. E.g. StarCCM+ will not be able to connect to a remote computer if you do set passwords for the key.
   

   ssh-keygen

   Generating public/private rsa key pair.
   Enter file in which to save the key (/home/user/.ssh/id_rsa):     press Enter here (only if you don't have a key pair already!)
   Enter passphrase (empty for no passphrase):                       press Enter here
   Enter same passphrase again:                                      press Enter here
   Your identification has been saved in test.
   Your public key has been saved in test.pub.
   The key fingerprint is:
   SHA256:VbvpxtFz3adfafafasdfasdfp4ScZbiBY+jfh84 user@computer
   The key's randomart image is:
   +---[RSA 2048]----+
   |B.+o........oo   |
   |BOo  . =   . .o  |
   |     E     .. . .|
   |             ..o |
   +----[SHA256]-----+

2. You now have a public key (id_rsa.pub) and a private key (id_rsa) in the hidden .ssh directory in your home directory. Never share the private key.
3. On your local machine, check if the command ssh-copy-id is available. E.g. run

   which ssh-copy-id

   when a path to the command is shown, then it is available.

4. If ssh-copy-id is available run the following command to finish quickly. It is a tool which copies your login credentials to a remote machine.

   ssh-copy-id -i ~/.ssh/id_rsa user@141.44.132.7

   After the argument -i the path to the key pair is expected, by default it should be in ~/.ssh/id_rsa. If you have changed the location, or used a different name for the key pair, insert the respective path here. The next argument is the remote computer's IP address and your account on the remote computer, such as user.

5. If you don't have ssh-copy-id, you have to do a bit more manual work:
   1. Copy the public key (id_rsa.pub) to the remote computer.
      For example:

      scp ~/.ssh/id_rsa.pub user@141.44.132.7:/home/user/ 

      Type your password for the remote computer now, to authorize the file transfer.

   2. Now log into the remote computer via ssh:
      

      ssh user@141.44.132.7 

   3. On the remote computer, add the public key to the authorized_keys file

      cat ~/id_rsa.pub >> ~/.ssh/authorized_keys

   4. Now refresh the authorized_keys using command
      

      chmod 600 .ssh/authorized_keys

   5. To efficiently use remote clusters, there is an additional key pair necessary.
      On the remote computer run the following commands again (copy-paste them):
      1. Create a second keypair. Press enter three times after running this command:

         ssh-keygen

      2. Add the new key to authorized_keys:

         cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

   6. You can log out the remote computer for now by typing:

      exit

For convenience, it is a good idea to save your login details in the config of ssh of your local computer. That way you don't have to type username@141.44.132.7 every time you want to login. Check if a conifg file is already present

ls ~/.ssh/

If it is not there yet, copy the following file to '~/.ssh/config':

config

Host           neumann
HostName       neumann.urz.uni-magdeburg.de 
IdentityFile   ~/.ssh/id_rsa
User           UsernameOnRemote

Replace UsernameOnRemote with your username on the remote machine. Then make sure the 'IdentityFile' directs to your private key. The location ~/.ssh/id_rsa is the default. When you followed the previous section, then there is no need to change this line. If you delete this line, the remote server will persist to ask for you password (if the default option is not used). In case you already have a config file, append the content above to your own ssh config seperated by a empty line.

With this config in place, you can now log in simply with:

ssh neumann
Last login: Wed Sep 27 11:21:56 2017 from  mylocalcomputer
 
Infos/News: http://www-e.uni-magdeburg.de/urzs/t100/
...

This will come in handy for the file transfer tools scp, and rsync. Moreover, this step is necessary for StarCCM and possibly other tools to connect to remote computers.

explain locations on remote and local, such as:

scp -r ~/dir1 remoteusername@remote_host:/home/remoteuser/

Setting up the SSH connection in a UNIX environment is relatively easy. On a Windows machine(before v10) there is no SSH program installed by default. This problem can be solved in different ways.

• PuTTY and WinSCP
• Windows Subsystem
• Cygwin

PuTTY

PuTTY is an implementation of an SSH client on windows. To use it follow this short guide:

1. Install PuTTY on your computer. PuTTY contains additional tools such as pageant.exe which holds your key pairs, and puttygen.exe which creates ssl key pairs. Don't skip them.
2. Add the PuTTY installation directory to your system's environment variable PATH (for example C:\Program Files (x86)\PuTTY).
   This is done automatically if you install PuTTY. Jump here if you don't know how to modify the PATH variable. This step is necessary for WinSCP and other advanced tasks.
   Do not skip this step! It has been one of the main reason for questions on PuTTY in the past…
3. Create a public/private key pair.
   1. Start PuTTYgen.exe and select the “SSH-2 RSA” option and set the number of bits in the generated key to be 2048. Click “Generate” and then follow the prompts.
      
   2. Don't set a password protection here for the key! Only do this if you know how to deal with it.
   3. Save the private key without password protection, e.g. with the name mySSHkey.ppk. Do not share the private part of your key at any time.
   4. Save the public key, too. Use the same basename, but the extension .pub, such as: mySSHkey.pub
4. Put the key into your key ring (Pagent)
   1. Open Pagaent (the key manager of PuTTY)
      
   2. Pageant starts minimized in the system tray. Click on Add key in the context menu:
      
   3. Locate your private key on your computer, such as mySSHkey.ppk and press open.
   4. You can now close the window. Check that Pagent remains in the system tray.
5. You'll have to open pageant after restart and load the key each time!
   Optionally, do the following steps to avoid the maunal key adding at every start:
   1. Go to the directory where pagent is saved, e.g. C:\Program Files (x86)\PuTTY\
   2. Right click on pageant.exe, press Create Shortcut (ger: Verknüpfung erstellen). It might be possible, that you are asked to save the shortcut on the desktop. Confirm in that case.
   3. Now, open a new file explorer and go to the directory C:\ProgramData\Microsoft\Windows\Start Menu\Programs\Startup
   4. Move the previously created shortcut to the Startup folder.
   5. Rename it back to a sane name, if necessary.
   6. Right click on the shortcut and open properties
   7. In the menu Shortcut, you'll find the field Target. It's marked by default.
   8. Add the end of the file path enclosed in quotes, add the path to your private key. For example:

      "C:\Program Files (x86)\PuTTY\pageant.exe" C:\Users\user\ssh\mySSHkey.ppk

   9. Press accept or Ok to save and close the property window.

confusion +1, insanity protection +3

In this section we forward you public key to the remote computer, so that the remote computer can recognize your login and doesn't require you to give a pasword.

1. Start PuTTY, for example via the desktop shortcut.
2. In the configuration tree, on the left, make sure to select the section Session.
3. Under connection type, select SSH.
4. In the right half, fill in the Host Name. The host name is the IP address of the remote system or its url.
   For example, the IP address of Neumann is neumann.urz.uni-magdeburg.de
   The LSS's computer laboratory in building 03 has the IP adress 141.44.132.7.
5. For convenience add your username as prefix to the IP address, seperated by an @ symbol.
   For example: engel@141.44.132.7
   
6. Then, go to the Auth subsubsection in the configuration tree which is part of the SSH subsection in the Connection section. \\See below:
   
7. At the buttom of this page, you have to set the location of your private (and public key).
   Press the Browse button to locate the private key (.ppk)
8. Then go to the section Connection/SSH/ X11
9. Make sure, the checkbox Enable X11 forwarding is checked.
   
10. Optionally, follow here to setup an X-server(Xming) on windows
11. Now, return to the section Session (at the top of the config tree).
12. In the entry field just below Saved Session fill in a name for the current setup.
    For example, type Neumann or PC-Cluster.
13. Then press the Save button! This will allow you the load a prepared session without the need to reenter any information for a specific remote computer.

    Test your connection now!
    Select a saved session and press load.
    Make sure once that the settings done above are already set with the session loaded.

14. Then press Open at the buttom of the window to open the connection.
15. Connecting the first time to a new computer will raise a window. It asks you, wether you trust the remote computer's key. Usually it's fine to press accept. Ideally, you would cross-reference the key before.
16. When the username has been entered, by prefix or manually, a prompt will ask you for your password. Type your password and press enter.
    You will not see any cursor movement or masking stars when entering the password. It's UNIX default behavior.
17. Congrats !! You are now connected to the remote computer. The terminal now accepts commands.
18. For setting a passwordless connection we need to do a few further steps:
    1. You need to Copy the public part of your ssh key pair (created in the previous section) to the remote server.
       Use WinSCP, or pscp if you have set it up already, otherwise do these steps:
       1. Open the public key, such as mySSHkey.pub, with Notepad.exe on your (windows) computer.
       2. Copy the content of that text file into your clipboard, e.g. press <CTRL + a> and <CTRL + c> sequentially.
       3. Now open PuTTY, and connect to the remote computer, such as the pccluster.
          Use one of the preset connections you have set up earlier.
       4. In the opened terminal run the command:

          nano mySSHkey.pub

          
          It will open a text editor. Unless you know better press only the keys specified below.

       5. Insert the content by pressing <SHIFT + Insert>
       6. Save by pressing <CTRL + o>, then confirm with <Enter>
       7. Close by pressing <CTRL + x>
    2. PuTTYgen creates a key pair in a specific format. This has to be converted to an open standard. On the remote UNIX computer run:

       ssh-keygen -i -f mySSHkey.pub > myopenssh_key

    3. Then, add the public key (myopenssh_key) to the authorized_keys file in the ~/.ssh/ directory of the remote server:
       

       cat myopenssh_key >> ~/.ssh/authorized_keys

    4. Now refresh the authorized_keys by using the command
       

       chmod 600 ~/.ssh/authorized_keys

    5. And for good measure, run

       chmod 700 ~/.ssh

Level up! range +15, intelligence +1, persistance +3

As a good measure you should do the following steps on the remote computer:

1. An many clusters there is an additional key pair necessary which is to be used internally only.
   On the remote computer run the following commands (copy-paste them):
   1. Create a second keypair. Press <Enter> three times after running this command:

      ssh-keygen

   2. Add the new key to authorized_keys by running:

      cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

Note, that SSH was set up only for a single direction of connection, from the Windows machine to the Linux machine. The other way is typically not needed and is cumbersome to set up. Avoid it, if neccessary. Go here if unix→windows is neccessary.

WinSCP

You might find the CLI environment to transfer files inconvenient at the moment. For this purpose there are tools with graphical interface available. For example WinSCP. Advanced users might also try MobaXterm. For WinSCP, you ideally have set up PuTTY already. Especially, the PATH system variable should contain the directory of your PuTTY installation.

1. Start up WinSCP
2. In the login window
   • select the transfer protocol SCP
   • enter the server address (such as neumann.urz.uni-magdeburg.de for Neumann, or 141.44.132.7 for the PC Cluster). Remember our HPC servers are only available within the university network. Use VPN if your are connecting from outside.
   • enter your account details, either account and password, or account and key file. See attached images.
3. The first time you have to confirm to add a server to your known hosts.
4. If everything was entered correctly you should see two folder structures now in two columns side-by-side.
5. You can work in a windows-like fashion, such as drag-and-drop of files. Use context menu for advanced features.

For more information, be refered to the documentation of WinSCP.
WinSCP also has shortcuts to an own terminal and PuTTY. Don't use the WinSCP's own terminal! It's plain garbage! Use PuTTY only. PuTTY can be opened from WinSCP, too (Ctrl + P).

Sources: https://winscp.net/eng/docs/getting_started

To transfer files, PuTTY brings the tool pscp which works similar to the linux scp.
pscp runs in the command prompt of windows (DOS prompt). To make pscp available in the prompt, PuTTY needs to be added in the system's PATH variable. See above.

The syntax of pscp is very similar to linux' scp

> pscp [options] [user@]host:source target

An example to copy a file from windows to a remote linux server. The command is run on the windows computer:

> pscp c:/star.sim  username@141.44.132.7:/home/username/myfolder

And the other way; requesting a file from a remote server and save it locally:

> pscp username@neumann.urz.uni-magdeburg.de:/home/username/myfolder/star.sim c:/

The linux subsystem is an interesting feature introduced to windows 10 ( More about here). It can run an ubuntu system natively in windows, and other distributions, such as opensuse. This means you run a bash in windows with (almost) all the features of a native linux system. However, this feature is still beta.

If you installed it, you can follow the instructions for Linux. However, if you want to set up WinSCP too, you might have to setup PuTTY (and it's key pair), too.

Suggested only to advanced users, or users eager to learn how to use it. Don't bother googling it if you “just want to get things done”.

It is simply said a linux environment compiled in the MS windows environment. This has the advantage that you can work in a linux-like environment on windows, and even with other windows programs. However, this comes at a cost, it's a crude environment to setup for the beginner. You sometimes have to fix uncommon issues yourself, or compile rarely used programs yourself. This makes the tool for advanced, or enthusiastic users only. Moreover, cygwin starts to be superseded by the Windows Subsystem available on Windows 10.

For a brief overview anyway have a look at this Cygwin introduction.

The environment installer can be downloaded here:
Cygwin

Most commands from linux are available, such as:

ssh
scp
rsync

therefore, continue with the Linux section.

Others might have to be installed additionally. Use the setup.exe to install openssl, and cygwin/X.