Connecting to the Caviness Cluster

Overview

Teaching: 20 min
Exercises: 10 min

Questions

• How do I open a terminal?

• How do I connect to a remote computer?

Objectives

• Remotely connect to the Caviness cluster

Opening a Terminal

Connecting to Caviness must be done through a tool known as “SSH” (Secure SHell) and usually it is run through a terminal. So, to begin using Caviness we need to begin by opening a terminal. Different operating systems have different terminals, none of which are exactly the same in terms of their features and abilities while working on the local operating system. When connected to the remote system the experience between terminals will be identical as each will faithfully present the same experience of the Caviness cluster.

Here is the process for opening a terminal in each operating system.

Linux

There are many different versions (aka “flavors”) of Linux and how to open a terminal window can change between flavors. Fortunately, most Linux users already know how to open a terminal window since it is a common part of the workflow for Linux users. If this is something that you do not know how to do then a quick search on the Internet for “how to open a terminal window in” with your particular Linux flavor appended to the end should quickly give you the directions you need.

A very popular version of Linux is Ubuntu. There are many ways to open a terminal window in Ubuntu but a very fast way is to use the terminal shortcut key sequence: Ctrl+Alt+T.

Mac

Macs have had a terminal built in since the first version of OS X since it is built on a UNIX-like operating system, leveraging many parts from BSD (Berkeley Systems Designs). The terminal can be quickly opened through the use of the Searchlight tool. Hold down the command key and press the spacebar. In the search bar that shows up type “terminal”, choose the terminal app from the list of results (it will look like a tiny, black computer screen) and you will be presented with a terminal window. Alternatively, you can find Terminal under “Utilities” in the Applications menu.

XQuartz

XQuartz is an open-source project thats goal is to bring X.org Window Systems to the Mac operating system. It allows for GUI, images, and other graphical interactions on a remote machine to be viewable on a local machine connected to the remote system. For more information about it or to download it visit the XQuartz sites

Windows

While Windows does have a command-line interface known as the “Command Prompt” that has its roots in MS-DOS (Microsoft Disk Operating System) its built-in SSH tool does not have all the options we need in setting up our SSH connections. To get those additional options we will need to install some 3rd party applications. There are a variety of programs that can be used. Below we will go into the details of two more common ones.

PuTTY

It is strictly speaking not necessary to have a terminal running on your local computer in order to access and use a remote system, only a window into the remote system once connected. PuTTy is likely the oldest, most well-known, and widely used software solution to take this approach.

PuTTY is available for free download from UDeploy or www.putty.org. Through the UDeploy site you will have the option to download and install Putty, Xming, and WinSCP. It is suggested that you download and install all three of these programs. The download and installation process will not be covered in this lesson. For directions on how to download, install, and set up PuTTY can be found in the course’s setup lesson.

Running PuTTY will not initially produce a terminal but instead a window full of connection options. Putting the address of the remote system in the “Host Name (or IP Address)” box and either pressing enter or clicking the “Open” button should begin the connection process. If there is a save session you could alternatively “double click” a on the saved session name, or click to highlight it and then click on the “Open” button to start the connection process.

If this works you will see a terminal window open that prompts you for a username through the “login as:” prompt and then for a password. If both of these are passed correctly then you will be given access to the system and will see a message saying so within the terminal. If you need to escape the authentication process you can hold the Control (ctrl) key and press the C key to exit and start again.

Note that you may want to paste in your password rather than typing it. Use ctrl plus a right-click of the mouse or use shift + insert to paste content from the clipboard to the PuTTY terminal.

For those logging in with PuTTY it would likely be best to cover the terminal basics already mentioned above before moving on to navigating the remote system.

XMing

Xming is an X11 display server for Microsoft Windows operating systems, for Windows XP and later. It can be installed to allow a GUI launched from Caviness to display on your Windows computer. This will allow you to interact with a program’s GUI, such as Matlab, or view images of results such as charts or tables. The download and installation process will not be covered in this lesson. For directions on how to download, install, and set up XMing can be found in the course’s setup lesson.

Logging onto the system

With all of this in mind, let’s make a remote connection. In this workshop, we will connect to Caviness — which is one of three community clusters at University of Delaware. Although it’s unlikely that every system will be exactly like Caviness, it’s a very good example of what you can expect from an HPC installation. To connect to our example computer, we will use SSH (if you are using PuTTY, see above).

SSH allows us to connect to UNIX computers remotely, and use them as if they were our own. The general syntax of the connection command follows the format ssh yourUsername@some.computer.address. Let’s attempt to connect to the HPC system now:

ssh yourUsername@caviness.hpc.udel.edu

$ ssh traine@caviness.hpc.udel.edu
The authenticity of host 'caviness.hpc.udel.edu (128.4.5.164)' can't be established.
ECDSA key fingerprint is SHA256:bmpB4mr7nmeTgtDHts4yjB73BFMEJAfZ/mSoGgj5jGA.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added 'caviness.hpc.udel.edu' (ECDSA) to the list of known hosts.
......................................................................


    Caviness cluster (caviness.hpc.udel.edu)

    This computer system is maintained by University of Delaware
    IT.  Links to documentation and other online resources can be
    found at:

      http://docs.hpc.udel.edu/abstract/caviness/

    For support, please contact consult@udel.edu


......................................................................

traine@caviness.hpc.udel.edu's password:

If you’ve connected successfully, you should see a prompt like the one below. This prompt is informative, and lets you grasp certain information at a glance. (If you don’t understand what these things are, don’t worry! We will cover things in depth as we explore the system further.)

[traine@login00 ~]$ 

Note that Caviness has two login node login00 and login01. The above output could reflect either node.

Telling the Difference between the Local Terminal and the Remote Terminal

You may have noticed that the prompt changed when you logged into the remote system using the terminal (if you logged in using PuTTY this will not apply because it does not offer a local terminal). This change is important because it makes it clear on which system the commands you type will be run when you pass them into the terminal. This change is also a small complication that we will need to navigate throughout the workshop. Exactly what is reported before the $ in the terminal when it is connected to the local system and the remote system will typically be different for every user. We still need to indicate which system we are entering commands on though so we will adopt the following convention:

• [local]$ when the command is to be entered on a terminal connected to your local computer
• [traine@login00 ~]$ when the command is to be entered on a terminal connected to the remote system
• $ when it really doesn’t matter which system the terminal is connected to.

Being certain which system your terminal is connected to

If you ever need to be certain which system a terminal you are using is connected to then use the following command: $ hostname.

Keep two terminal windows open

For Mac and Linux user:

It is strongly recommended that you have two terminals open, one connected to the local system and one connected to the remote system, that you can switch back and forth between. If you only use one terminal window then you will need to reconnect to the remote system using one of the methods above when you see a change from [local]$ to [traine@login00 ~]$ and disconnect when you see the reverse.

Key Points

• Connect to the Caviness cluster by using SSH: ssh yourUsername@caviness.hpc.udel.edu

• Connect to the Caviness cluster by using SSH with X Win (using Xming): ssh -Y yourUsername@caviness.hpc.udel.edu