Computer Science OpenStack cluster and Virtual Machines

We provide virtual machines (VMs) as needed for students registered for courses in Computer Science. All virtual machines are hosted in an OpenStack cluster located in the basement of the Davis Marksbury Building.


On 2020/10/01, the CS department changed host keys to strengthen security. For more information see SSH Errors. You will probably see warnings from your client, this is expected and the SSH Errors document will show you how to resolve the problem.


The CS OpenStack Cluster is on a private IPv4 network. If you are on a external network you will need to connect to the Campus VPN first. If you are connected to a campus network like Eduroam you can connect directly to the OpenStack Dashboard or to your VM.


While you are on campus, don’t connect from network UK-Guest, ssh access is not allowed from it. Also, don’t use wifiHelp to connect to your VM, please use eduroam Wifi Network.


If you are on eduroam and are unable to access it, there is a good chance you are connected using credentials from another institution. Remove/delete the connection and reconnect with your LinkBlue credentials.


Please read the section titled UK Firewall and External connections when connecting from a external network to avoid connection timeouts.

OpenStack Dashboard


Please do not use your when login on the OpenStack Dashboard, just the username part, For example, if your linkbue ID username is pepe223, use that instead of

You can manage your VM through the OpenStack dashboard. The dashboard is helpful when the VM is non-responsive and needs to be forcefully rebooted or for configuring the network firewall. However, the most efficient method to connect and use your VM is connecting using the instructions detailed in Connecting to your Virtual Machine.

Accessing the dashboard

You can access the dashboard by going to the OpenStack Dashboard. Enter your LinkBlue credentials without the for authentication.

login page

OpenStack calls VMs “instances” and accounts “projects”. Your VM and project, as well as your login account on the VM, are all named after your LinkBlue ID. Upon logging in you should see an overview of your account and, at the bottom, your LinkBlue ID as a hyperlink. This is your VM instance. Click the link to open the management page for the VM. Click on the following picture to see a more detailed view of what you will see once you click on the Instances menu on the left.

Instance Overview

When you click on the Instance Name of your VM, the tabs available give details of the VM as well as its firewall settings (called “Security Groups”), logs, and a console. Use the console only when NoMachine (see below) is not available, because NoMachine provides far better performance for a graphical desktop.


If the console is not responding to keyboard input, either (1) click the blue/grey status bar at the top of the console, or (2) click the “Click here to show only console” message, or (3) refresh the web page in your browser.

Connecting to your Virtual Machine


We create both Linux and Windows VMs. These VMs have a DNS entry setup which you should use to connect to your VM. For Linux VMs the DNS hostname is, for Windows VMs the DNS address is However, in the case of Windows, should also work since the machine is integrated with UK Campus’ Authentication Directory. In both types of VMs you can use your LinkBlue username to login.


When restarting your Linux VM please use sudo reboot via ssh whenever possible. If this is not possible then use the OpenStack Dashboard.

There are different ways to connect to your VM. The method you select will depend on what you need to do on the machine, use the following index to select the most appropiate option for you:

Once your VM is created and it’s running use the following methods to connect. The next two sections will detail how to connect using a graphical client and a SSHv2 client. If you want to explore alternative methods to connect please see the section Other Connection Methods

NoMachine client (Windows/Linux/Mac)

NoMachine provides a great experience when connecting to your VM’s Desktop. You can download it from NoMachine Downloads. There are versions for Windows, Mac and Linux.

Your VM already has NoMachine installed, and it’s accepting connections, for this reason what you need is the client part to be able to connect. Once you have installed NoMachine on your own computer (your laptop, for instance), follow the images below for guidance or check this Video for a quick review of the process.

Click <Click here to create a connection>.

Instance Overview

Make sure the protocol is ‘NX’, then click Continue.

Instance Overview

Enter the name of your VM (its DNS address) on the text field in the next screen.

Choose password authentication.

Instance Overview

Most users do not need to configure a HTTP proxy.

Instance Overview

Enter your LinkBlue credentials.

Instance Overview

Configure the settings.

Instance Overview


Display resolution can have a dramatic affect on performance. 1280x800 is a good initial setting.

Useful NoMachine Features

This subsection has some examples of what you can do with nomachine. If you need to copy information between the VM and your local machine this will help. For the best experience please play these videos on a computer or laptop.

Your VM is fully connected, for example if you need to submit information to Canvas you can connect with NoMachine and then open the web browser and connect to the site to do the required tasks. Since you have full control of your VM you can opt for a different browser (the default is Firefox) like Google Chrome/Chromium.

Command Line SSH client

If your VM runs Linux, you can connect to it from another Linux/Unix/Mac machine via SSH (Secure Shell). The connection command looks like this:

$ ssh


If you get a Warning like the following:

The ECDSA host key for has changed,
and the key for the corresponding IP address
is unknown. This could either mean that
... lines removed here ...
Please contact your system administrator.
Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /Users/username/.ssh/known_hosts:1
ECDSA host key for has changed and you have requested strict checking.
Host key verification failed.

This is normally due to the fact that your VM was recreated at the start of the semester, if this happens the first time you are connecting to it then it’s safe to edit the file (in this case) /Users/username/.ssh/known_hosts and as can be seen line 1 (Offending ECDSA key in /Users/username/.ssh/known_hosts:1) is the line we need to remove from that text file, in this way our ssh client will not fail the check and create a new entry for your VM.

SSH has the advantages of speed and accessibility, but it lacks a graphical user interface. If you are connecting from a machine running an X server able to receive forwarded X Windows connections over SSH, add -Y as a flag to the ssh command. Now you can run graphical applications on your VM and see them on your own machine. This setting and many more can be configured in an ssh configuration file; an example is included below.

File name: ~/.ssh/config

  KexAlgorithms +diffie-hellman-group1-sha1
  Ciphers aes256-ctr,aes256-cbc
  ForwardX11Trusted yes

In the example above, the first line specifies the host you are making a connection to. The lines immediately following are the configuration options specific to that host. See the man page for ssh_config(5) for more information.

Windows PowerShell SSH client

Recent versions of Windows PowerShell™ have OpenSSH available since Windows 10’s Fall Creators Update (April 2018). The syntax is exactly the same as the Linux/Unix/Mac example from above. Open a PowerShell session and run the command:

ssh example in powershell

Example of an SSH session running in PowerShell

This feature can be added to any version of Windows 10. Contact for assistance adding this feature if it is not included with your version of Windows.

Filezilla (Windows/Linux/Mac)

Filezilla is an excellent FTP client with support for SFTP (SSH File Transfer Protocol). In it’s most basic version, it’s free to use. This software allows you to transfer files easily between your machine and your VM, among other operations. Go to Filezilla Downloads and get the FileZilla Cient. If you are presented with three options, select one that is not the Pro version. If the installation wizard asks if you want additional software, just unselect the checkbox and continue. Once you have installed FileZilla, proceed to open it. You will see a window like the following:

login page

Go to File/Site Manager and use a configuration similar to the one in the next picture. Insert your username (like abc123) and the DNS name for your VM (like; then click OK.

login page

When you connect, you will see the following message:

login page

To connect, you can go to the Site Manager and select your session, or you can simply click the arrow and select your session name, as in the following picture:

login page

And when connected, you will see the directory contents of your VM, showing that your session is established:

login page

PuTTY (Windows)

PuTTY lets you to establish an SSHv2 connection to your VM. To set up a Putty session, you can click here and scroll down to the section titled PuTTY session setup and public key authentication. You don’t need to set up the public authentication part if you don’t want (skip the first image and paragraph); just create the session using your username (like abc123) and the name of the remote host (your VM’s name, such as, or a CS Server’s name if you need/have access) and save the new session as detailed in the document.

Bitvise SSH Client (Windows)

This is an SSH client and also a file-transfer program. Follow these instructions to install the software, configure a profile and establish a connection. Download the software from Bitvise SSH Client. After opening the program for the first time you will see a window like this:

login page

The first step is to make a profile and save it. Click New Profile in the left panel and save the file with the profile information in a convenient folder.

login page

In the Server section, enter your VM’s hostname (like and the port (22). Enter your username (like abc123) in the Authentication section. For initial method, select password, and leave everything else alone. Then click Login. You will see a window like the following:

login page

Type your password. After the connection is established, you will see a terminal window and a file-transfer window, which you can use to interact with your VM.

login page

By default, Bitvise sends keep-alive packets every 20 seconds to the server. This feature prevents your connection from timing out.

Other Connection Methods

Newer versions of Windows have both ssh and scp installed and accessible from a command window.

On a Mac, you might want to use the terminal app along with XQuartz.

On Windows, you might want to use Xming or Cygwin/X or MobaXterm.

OpenStack Network Firewall

The default firewall settings for your VM block all ports except for the ones used by the SSH server and the NoMachine server. Although you may adjust your VM’s firewall settings, please contact for assistance. Open ports can be a security risk.

Creating Firewall rules on your VM

One of the reasons to create a new firewall rule is to allow ingress traffic directed to your VM to a specific port. Let’s say that you need to open port 1280/tcp on your VM because you are working on an application that needs to bind to a specific port and you need to test it, etc.


Creating a firewall rule could lead to unauthorized access to non-secured applications that are listening on a socket. Make sure you don’t expose any sensitive or private information from your application (the one listening on the network port)

The Computer Science OpenStack Cluster’s networking runs using a Private IPv4 subnet, this means that external network access (Internet) it’s not allowed directly to the VMs, and this protects the VMs further from internet attacks, etc., however the VMs are still accessible all over campus so it’s always good practice to exercise care on services listening on sockets.

By default any incoming connection to most ports are not allowed, to create a rule (using the port 1280/tcp as an example) to allow this traffic execute the following steps:

  • Login on the OpenStack Dashboard

  • On the left, look for the menu Network and click on it, then click on Security Groups.

  • You will see your Security Group(s). Normally there is only one that is called default. You need to select the checkbox on the left of it and click on Manage Rules on the right to see all your security rules (firewall rules) that are applied for your VM from the OpenStack’s network functions.

  • To create a rule to allow incoming traffic to port 1280/tcp do the following.

    • Click on Add Rule
    • Under Rule * Select the protocol, the next example assume you use the option Custom TCP Rule
    • Put a description (can be anything that describes the purpose of your rule)
    • Select the Direction, here we need to allow incoming traffic to port 1280 so we select Ingress
    • By default Port is selected and below that we must specify which port is the destination, in this case we write 1280 in the text field.
    • On Remote leave it as CIRD, in the text field below leave it as if you want to allow traffic from all remote IP addresses. Otherwise, you will neeed to specify the remote address, something like to specify a single IP address or to specify a subnet, for example.
    • EtherType is by default at IPv4 since the Computer Science OpenStack cluster don’t use IPv6.
    • Click the Add button to submit the rule and it will take effect inmediately. Proceed to your VM for further testing.

Your VM should now receive incoming traffic if the rule was correctly specified. All other options to create rules are very similar, make sure you exercise care when creating firewall rules.

UK Firewall and External connections

The UK edge Firewall timeout idle connections, this means that if you are connecting from a network outside UK and your session is idle for a few minutes this connection will drop, causing a disconnection. To make sure your external connections won’t timeout follow these steps.

For Linux/Unix/Mac

If you prefer to connect using the command line use the following configuration.

Edit the file ~/.ssh/config and add the following:

Host *
    ServerAliveInterval 60
    ServerAliveCountMax 3

For Windows/Unix/Mac (PuTTY)

If you are using PuTTY you should have a session saved and you use this session to connect to the server(s). Click your session name (if you have more than one please repeat these steps on all your UK sessions) and click Load.

On the left panel, scroll down and click Connection, in the right side of the Window look at the top, it will say Seconds between keepalives, it’s by default on 0 which is disabled. Write a reasonable number of seconds, 60 seems to be a good number, in this way the ssh client will send keep alives packets to the server keeping the connection up.

PuTTY keep alive

To save the new configuration, on the left panel scroll up to Session and click the session you modified, then click Save. The next time you use the session to ssh into a remote host this keep alive configuration will prevent connection timeouts by sending periodic (based on the number of seconds set) SSH NULL packets to the server, in this way the UK firewall will refresh the timeout timer for your connection and it will not be droppped at the edge of the ingress network.