--- layout: doc title: Glossary permalink: /doc/glossary/ redirect_from: - /en/doc/glossary/ - /doc/Glossary/ - /wiki/Glossary/ --- 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`. Qube ---- A user-friendly term for a **domain** (i.e., 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 ------ A synonym for **virtual machine (VM)**. A software implementation of a machine (for example, a computer) which executes programs like a physical machine. Dom0 ---- Domain Zero. Also known as the **host** domain, dom0 is the initial domain 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. DomU ---- Unprivileged Domain. Also known as **guest** domains, domUs are the counterparts to dom0. All domains except dom0 are domUs. By default, most domUs lack direct hardware access. 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**. PVH --- 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.