qubes-doc/reference/glossary.md

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Glossary of Qubes Terminology

Qubes OS

A security-oriented operating system (OS). The main principle of Qubes OS is security by compartmentalization (or isolation), in which activities are compartmentalized (or isolated) in separate qubes.

• The official name is Qubes OS (note the capitalization and spacing). However, in casual conversation this is often shortened to Qubes, and in technical contexts where spaces are not permitted, (e.g., usernames), the space may be omitted, as in QubesOS.

VM

An abbreviation for "virtual machine." A software implementation of a machine (for example, a computer) which executes programs like a physical machine.

Qube

A user-friendly term for a VM in Qubes OS.

• Example: "In Qubes OS, you do your banking in your 'banking' qube and your web surfing in your 'untrusted' qube. That way, if your 'untrusted' qube is compromised, your banking activities will remain secure."

• "Qube" is an informal term intended to make it easier for less technical users to understand Qubes OS and learn how to use it. In technical discussions, the other, more precise terms defined on this page are to be preferred.

• The term "qube" should be lowercase unless it is the first word in a sentence. Note that starting a sentence with the plural of "qube" (i.e., "Qubes...") can be ambiguous, since it may not be clear whether the referent is a collection of qubes or Qubes OS.

Domain

An area or set of activities in one's digital life that has certain security requirements and therefore involves the use of certain qubes. For example, suppose your "email" domain encompasses the activity of sending PGP-encrypted email. This domain may include your email qube and your Split GPG qube. Note that domains and qubes are not the same thing. In this example, your "email" domain includes the use of two qubes. Furthermore, a qube can fall under multiple domains simultaneously. For example, your Split GPG qube may also be part of your "software development" domain if you PGP-sign your Git commits.

Dom0

Domain Zero. Also known as the host domain, dom0 is the initial VM started by the Xen hypervisor on boot. Dom0 runs the Xen management toolstack and has special privileges relative to other domains, such as direct access to most hardware. (Note that the use of "domain" for a synonym for "VM" is specific to Xen. Qubes diverges from this practice. See: domain.)

DomU

Unprivileged Domain. Also known as guest domains, domUs are the counterparts to dom0. All VMs except dom0 are domUs. By default, most domUs lack direct hardware access. (Note that the use of "domain" for a synonym for "VM" is specific to Xen. Qubes diverges from this practice. See: domain.)

TemplateVM

Template Virtual Machine. Any VM which supplies its root filesystem to another VM. TemplateVMs are intended for installing and updating software applications, but not for running them.

• Colloquially, TemplateVMs are often referred to as "templates."

TemplateBasedVM

Any VM which depends on a TemplateVM for its root filesystem.

Standalone(VM)

Standalone (Virtual Machine). In general terms, a VM is described as standalone if and only if it does not depend on any other VM for its root filesystem. (In other words, a VM is standalone if and only if it is not a TemplateBasedVM.) More specifically, a StandaloneVM is a type of VM in Qubes which is created by cloning a TemplateVM. Unlike TemplateVMs, however, StandaloneVMs do not supply their root filesystems to other VMs. (Therefore, while a TemplateVM is a type of standalone VM, it is not a StandaloneVM.)

AppVM

Application Virtual Machine. A VM which is intended for running software applications. Typically a TemplateBasedVM, but may be a StandaloneVM. Never a TemplateVM.

NetVM

Network Virtual Machine. A type of VM which connects directly to a network and provides access to that network to other VMs which connect to the NetVM. A NetVM called sys-net is created by default in most Qubes installations.

Alternatively, "NetVM" may refer to whichever VM is directly connected to a VM for networking purposes. For example, if untrusted is directly connected to sys-firewall for network access, then it is accurate to say, "sys-firewall is untrusted's NetVM," even though sys-firewall is a ProxyVM.

ProxyVM

Proxy Virtual Machine. A type of VM which proxies network access for other VMs. Typically, a ProxyVM sits between a NetVM and another VM (such as an AppVM or a TemplateVM) which requires network access.

FirewallVM

Firewall Virtual Machine. A type of ProxyVM which is used to enforce network-level policies (a.k.a. "firewall rules"). A FirewallVM called sys-firewall is created by default in most Qubes installations.

DispVM

Disposable Virtual Machine. A temporary AppVM which can quickly be created, used, and destroyed.

DVM

An abbreviation of DispVM, typically used to refer to the TemplateVM on which DispVMs are based. By default, a VM named fedora-XX-dvm is created on most Qubes installations (where XX is the current Fedora version).

PV

Paravirtualization. An efficient and lightweight virtualization technique originally introduced by the Xen Project and later adopted by other virtualization platforms. Unlike HVMs, paravirtualized VMs do not require virtualization extensions from the host CPU. However, paravirtualized VMs require a PV-enabled kernel and PV drivers, so the guests are aware of the hypervisor and can run efficiently without emulation or virtual emulated hardware.

HVM

Hardware Virtual Machine. Any fully virtualized, or hardware-assisted, VM utilizing the virtualization extensions of the host CPU. Although HVMs are typically slower than paravirtualized VMs due to the required emulation, HVMs allow the user to create domains based on any operating system.

StandaloneHVM

Any HVM which is standalone (i.e., does not depend on any other VM for its root filesystem). In Qubes, StandaloneHVMs are referred to simply as HVMs.

TemplateHVM

Any HVM which functions as a TemplateVM by supplying its root filesystem to other VMs. In Qubes, TemplateHVMs are referred to as HVM templates.

TemplateBasedHVM

Any HVM that depends on a TemplateVM for its root filesystem.

PVHVM

PV on HVM. To boost performance, fully virtualized HVM guests can use special paravirtual device drivers (PVHVM or PV-on-HVM drivers). These drivers are optimized PV drivers for HVM environments and bypass the emulation for disk and network I/O, thus providing PV-like (or better) performance on HVM systems. This allows for optimal performance on guest operating systems such as Windows.