# Virtual Machine#

A virtual machine is what the name suggests: a machine running virtually inside another machine. With virtual machines, there are two operating systems involved: the host operating system (OS) and the guest OS. The host is your own native OS (maybe Windows). The guest is the OS that runs inside the host.

The virtual machine (VM) we provide here has OCaml pre-installed in an Ubuntu guest OS. Ubuntu is a free Linux OS, and is an ancient African word meaning “humanity to others”. The process we use to create the VM is documented here.

## Installing the VM#

• Download our VM. Don’t worry about the “We’re sorry, the preview didn’t load” message you see. Just click the Download button and save the .ova file wherever you like. It’s about a 6GB file, so the download might take awhile.

• Launch VirtualBox, select File → Import Appliance, and choose the .ova file you just downloaded. Click Next, then Import.

## Starting the VM#

• Select cs3110-2022fa-ubuntu from the list of machines in VirtualBox. Click Start. At this point various errors can occur that depend on your hardware, hence are hard to predict.

• If you get an error about “VT-x/AMD-V hardware acceleration”, you most likely need to access your computer’s BIOS settings and enable virtualization. The details of that will vary depending on the model and manufacturer of your computer. Try googling “enable virtualization [manufacturer] [model]”, substituting for the manufacturer and model of your machine. This Red Hat Linux page might also help.

• If you get an error about “kernel panic” and “attempted to kill the idle task”, then you might need to increase the number of processors provided to it by your host OS. Select the VM in Virtual Box, click Settings, and look at the System → Processor settings. Increase the number of processors from 1 to 2. If the sliders are greyed out and won’t permit adjustment, it means the VM is still running: you can’t change the amount of memory while the guest OS is active; so, shut down the VM (see below) and try again.

• If the machine just freezes or blacks out or aborts, you might need to adjust the memory provided to it by your host OS. Select the VM in Virtual Box, click Settings, and look at the System and Display settings. You might need to adjust the Base Memory (under System → Motherboard) or the Video Memory (under Display → Screen). Those sliders have color coding underneath them to indicate what good amounts might be on your computer. Make sure nothing is in the red zone, and try some lower or higher settings to see if they help. If the sliders are greyed out and won’t permit adjustment, it means the VM is still running: you can’t change the amount of memory while the guest OS is active; so, shut down the VM (see below) and try again.

• If you have a monitor with high pixel density (e.g., an Apple Retina display), the VM window might be incredibly tiny. In VirtualBox go to Settings → Display → Scale Factor and increase it as needed, perhaps to 200%.

• The VM will log you in automatically. The username is camel and the password is camel. To change your password, run passwd from the terminal and follow the prompts. If you’d rather have your own username, you are welcome to go to Settings → Users to create a new account. Just be aware that OPAM and VS Code won’t be installed for that user. You’ll need to follow the install instructions to add them.

## Stopping the VM#

You can use Ubuntu’s own menus to safely shutdown or reboot the VM. But more often you will likely use VirtualBox to close the VM by clicking the VM window’s “X” icon in the host OS. Then you will be presented with three options that VirtualBox doesn’t explain very well:

• Save the machine state. This option is what you normally want. It’s like closing the lid on your laptop: it puts it to sleep, and it can quickly wake.

• Send the shutdown signal. This option is like shutting down a machine you don’t intend to use for a long time, or before unplugging a desktop machine from the wall. When you start the machine again later, it will have to boot from scratch, which takes longer.

• Power off the machine. This option is dangerous. It is the equivalent of pulling the power cord of a desktop machine from the wall while the machine is still running: it causes the operating system to suddenly quit without doing any cleanup. Doing this even just a handful of times could cause the file system to become corrupted, which will cause you to lose all your work and have to reinstall the VM from scratch. You will be very unhappy. So, avoid this option.

## Using the VM#

• There are icons provided for the terminal, VS Code, and the Firefox web browser. They are in the left-hand launcher bar.

• It can be helpful to set up a shared folder between the host and guest OS, so that you can easily copy files between them. With the VM shutdown (i.e., select “send the shutdown signal”), click Settings, then click Shared Folders. Click the little icon on the right that looks like a folder with a plus sign. In the dialog box for Folder Path, select Other, then navigate to the folder on your host OS that you want to share with the guest OS. Let’s assume you created a new folder named vmshared inside your Documents folder, or wherever you like to keep files. The Folder Name in the dialog box will automatically be filled with vmshared. This is the name by which the guest OS will know the folder. You can change it if you like. Check Auto-mount; do not check Read-only. Make the Mount Point /home/camel/vmshared. Click OK, then click OK again. Start the VM again. You should now have a subdirectory named vmshared in your guest OS home directory that is shared between the host OS and the guest OS.

• You might be able to improve the performance of your VM by increasing the amount of memory or CPUs allocated to it, though it depends on how much your actual machine has available and what else you have running at the same time. With the VM shut down, try going in Virtual Box to Settings → System, and tinkering with the Base Memory slider on the Motherboard tab, and the Processors slider on the Processor tab. Then bring up the VM again and see how it does. You might have to play around to find a sweet spot. Later, after you are satisfied the VM is working properly hence you won’t have to re-import it, you can safely delete the .ova file you downloaded to free up some space.