How do I?

VirtualBox says "VT-x is not available" and/or I get error code VERR_VMX_NO_VMX

To run a VM efficiently on your computer, it must support a technology called VT-x. Fortunately, practically all modern computers support VT-x but, by default, this functionality is disabled on the computer, but can be re-enabled by modifying the computer's BIOS settings. The process to do this varies a lot from one computer to another, but you can generally access your computer BIOS setting by pressing F2 or Esc when the computer is booting up (some computers will explicitly show a message like "Press F2 to interrupt normal startup" or something along those lines). Once you are in the BIOS settings, you will need to find a setting called "VT-x" or "Virtualization Extensions", and activate it.

You may also want to simply Google for your computer's model and the words "VT-x" and "BIOS". This will usually take you to one or more pages with instructions that are specific to your computer.

I can't push/pull from the department's GitLab server from inside the VM

If you see any error like this:

ssh: Could not resolve hostname mit.cs.uchicago.edu: Name or
service not known fatal: Could not read from remote repository.

Please make sure you have the correct access rights and the
repository exists.

the most likely cause is that your VM is not connected to the network.

Check that the machine you’re running the VM on has Internet access (you can do this just by opening a browser and going to any page). The VM relies on your machine’s Internet connection to reach the GitLab server so, if your machine doesn’t have Internet access, neither will your VM.

If your machine’s Internet access is working correctly, you should try to restart the VM’s networking. In the top right corner of your VM, there should be an icon with two arrows pointing in opposite directions:

Click on that icon. It should bring up a pull-down menu where one of the options should be “Enable Networking”. That option should have a check mark next to it. Click on it once to disable the VM’s network, and then click on “Enable Networking” again to enable it. This will restart the networking on your VM, and may solve the problem.

If you don’t see the icon with the two arrows, the window your VM is running on may be too small. Either resize the window or scroll horizontally until you can see the icon.

I can't access the Internet from the VM

See answer to the previous question.