# Qubes Overview

Qubes OS is an operating system which uses the Xen hypervisor to provide strong security for desktop computing through isolated virtual machines. Each VM is called a Qube and you can assign each Qube a level of trust based on its purpose. As Qubes OS provides security by using isolation, and only permitting actions on a per case basis, it is the opposite of badness enumeration.

## How does Qubes OS work?¶

Qubes uses compartmentalization to keep the system secure. Qubes are created from templates, the defaults being for Fedora, Debian and Whonix. Qubes OS also allows you to create once-use disposable virtual machines.

Each Qubes application has a colored border that can help you keep track of the virtual machine it is running in. You could, for example, use a specific color for your banking browser, while using a different color for a general untrusted browser.

## Why Should I use Qubes?¶

Qubes OS is useful if your threat model requires strong compartmentalization and security, such as if you think you'll be opening untrusted files from untrusted sources. A typical reason for using Qubes OS is to open documents from unknown sources.

Qubes OS utilizes Dom0 Xen VM (i.e., an "AdminVM") for controlling other guest VMs or Qubes on the host OS. Other VMs display individual application windows within Dom0's desktop environment. It allows you to color code windows based on trust levels and run apps that can interact with each other with very granular control.

### Copying and Pasting Text¶

You can copy and paste text using qvm-copy-to-vm or the below instructions:

1. Press Ctrl+C to tell the VM you're in that you want to copy something.
2. Press Ctrl+Shift+C to tell the VM to make this buffer available to the global clipboard.
3. Press Ctrl+Shift+V in the destination VM to make the global clipboard available.
4. Press Ctrl+V in the destination VM to paste the contents in the buffer.

### File Exchange¶

To copy and paste files and directories (folders) from one VM to another, you can use the option Copy to Other AppVM... or Move to Other AppVM.... The difference is that the Move option will delete the original file. Either option will protect your clipboard from being leaked to any other Qubes. This is more secure than air-gapped file transfer because an air-gapped computer will still be forced to parse partitions or file systems. That is not required with the inter-qube copy system.

AppVMs or qubes do not have their own file systems

You can copy and move files between Qubes. When doing so the changes aren't immediately made and can be easily undone in case of an accident.

### Inter-VM Interactions¶

The qrexec framework is a core part of Qubes which allows virtual machine communication between domains. It is built on top of the Xen library vchan, which facilitates isolation through policies.