docker-docs/_data/glossary.yaml

aufs: |
  aufs (advanced multi layered unification filesystem) is a Linux [filesystem](#filesystem) that
  Docker supports as a storage backend. It implements the
  [union mount](http://en.wikipedia.org/wiki/Union_mount) for Linux file systems.
base image: |
  An image that has no parent is a **base image**.
boot2docker: |
  [boot2docker](http://boot2docker.io/) is a lightweight Linux distribution made
  specifically to run Docker containers. The boot2docker management tool for Mac and Windows was deprecated and replaced by [`docker-machine`](#machine) which you can install with the Docker Toolbox.
btrfs: |
  btrfs (B-tree file system) is a Linux [filesystem](#filesystem) that Docker
  supports as a storage backend. It is a [copy-on-write](http://en.wikipedia.org/wiki/Copy-on-write)
  filesystem.
build: |
  build is the process of building Docker images using a [Dockerfile](#dockerfile).
  The build uses a Dockerfile and a "context". The context is the set of files in the
  directory in which the image is built.
cgroups: |
  cgroups is a Linux kernel feature that limits, accounts for, and isolates
  the resource usage (CPU, memory, disk I/O, network, etc.) of a collection
  of processes. Docker relies on cgroups to control and isolate resource limits.

  *Also known as : control groups*
Compose: |
  [Compose](https://github.com/docker/compose) is a tool for defining and
  running complex applications with Docker. With compose, you define a
  multi-container application in a single file, then spin your
  application up in a single command which does everything that needs to
  be done to get it running.

  *Also known as : docker-compose, fig*
copy-on-write: |
  Docker uses a
  [copy-on-write](/engine/userguide/storagedriver/imagesandcontainers/#/the-copy-on-write-strategy)
  technique and a [union file system](#union-file-system) for both images and
  containers to optimize resources and speed performance. Multiple copies of an
  entity share the same instance and each one makes only specific changes to its
  unique layer.

  Multiple containers can share access to the same image, and make
  container-specific changes on a writable layer which is deleted when
  the container is removed. This speeds up container start times and performance.

  Images are essentially layers of filesystems typically predicated on a base
  image under a writable layer, and built up with layers of differences from the
  base image. This minimizes the footprint of the image and enables shared
  development.

  For more about copy-on-write in the context of Docker, see [Understand images,
  containers, and storage
  drivers](/engine/userguide/storagedriver/imagesandcontainers/).
container: |
  A container is a runtime instance of a [docker image](#image).

  A Docker container consists of

  - A Docker image
  - An execution environment
  - A standard set of instructions

  The concept is borrowed from Shipping Containers, which define a standard to ship
  goods globally. Docker defines a standard to ship software.
Docker: |
  The term Docker can refer to

  - The Docker project as a whole, which is a platform for developers and sysadmins to
  develop, ship, and run applications
  - The docker daemon process running on the host which manages images and containers
  (also called Docker Engine)
Docker Datacenter: |
  The Docker Datacenter is subscription-based service enabling enterprises to leverage a
  platform built by Docker, for Docker. The Docker native tools are integrated to create
  an on premises CaaS platform, allowing organizations to save time and seamlessly take
  applications built in dev to production.
Docker for Mac: |
  [Docker for Mac](/docker-for-mac/) is an easy-to-install,
  lightweight Docker development environment designed specifically for the Mac. A
  native Mac application, Docker for Mac uses the macOS Hypervisor framework,
  networking, and filesystem. It's the best solution if you want to build, debug,
  test, package, and ship Dockerized applications on a Mac. Docker for Mac
  supersedes [Docker Toolbox](#toolbox) as state-of-the-art Docker on macOS.
Docker for Windows: |
  [Docker for Windows](/docker-for-windows/) is an
  easy-to-install, lightweight Docker development environment designed
  specifically for Windows 10 systems that support Microsoft Hyper-V
  (Professional, Enterprise and Education). Docker for Windows uses Hyper-V for
  virtualization, and runs as a native Windows app. It works with Windows Server
  2016, and gives you the ability to set up and run Windows containers as well as
  the standard Linux containers, with an option to switch between the two. Docker
  for Windows is the best solution if you want to build, debug, test, package, and
  ship Dockerized applications from Windows machines. Docker for Windows
  supersedes [Docker Toolbox](#toolbox) as state-of-the-art Docker on Windows.
Docker Hub: |
  The [Docker Hub](https://hub.docker.com/) is a centralized resource for working with
  Docker and its components. It provides the following services:

  - Docker image hosting
  - User authentication
  - Automated image builds and work-flow tools such as build triggers and web hooks
  - Integration with GitHub and Bitbucket
Dockerfile: |
  A Dockerfile is a text document that contains all the commands you would
  normally execute manually in order to build a Docker image. Docker can
  build images automatically by reading the instructions from a Dockerfile.
ENTRYPOINT: |
  In a Dockerfile, an `ENTRYPOINT` is an optional definition for the first part
  of the command to be run. If you want your Dockerfile to be runnable without
  specifying additional arguments to the `docker run` command, you must specify
  either `ENTRYPOINT`, `CMD`, or both.

  - If `ENTRYPOINT` is specified, it is set to a single command. Most official
    Docker images have an `ENTRYPOINT` of `/bin/sh` or `/bin/bash`. Even if you
    do not specify `ENTRYPOINT`, you may inherit it from the base image that you
    specify using the `FROM` keyword in your Dockerfile. To override the
    `ENTRYPOINT` at runtime, you can use `--entrypoint`. The following example
    overrides the entrypoint to be `/bin/ls` and sets the `CMD` to `-l /tmp`.

    ```bash
    $ docker run --entrypoint=/bin/ls ubuntu -l /tmp
    ```

  - `CMD` is appended to the `ENTRYPOINT`. The `CMD` can be any arbitrary string
    that is valid in terms of the `ENTRYPOINT`, which allows you to pass
    multiple commands or flags at once. To override the `CMD` at runtime, just
    add it after the container name or ID. In the following example, the `CMD`
    is overridden to be `/bin/ls -l /tmp`.

    ```bash
    $ docker run ubuntu /bin/ls -l /tmp
    ```

  In practice, `ENTRYPOINT` is not often overridden. However, specifying the
  `ENTRYPOINT` can make your images more fiexible and easier to reuse.
filesystem: |
  A file system is the method an operating system uses to name files
  and assign them locations for efficient storage and retrieval.

  Examples :

  - Linux : ext4, aufs, btrfs, zfs
  - Windows : NTFS
  - macOS : HFS+
image: |
  Docker images are the basis of [containers](#container). An Image is an
  ordered collection of root filesystem changes and the corresponding
  execution parameters for use within a container runtime. An image typically
  contains a union of layered filesystems stacked on top of each other. An image
  does not have state and it never changes.
Kitematic: |
  A legacy GUI, bundled with [Docker Toolbox](#toolbox), for managing Docker
  containers. We recommend upgrading to [Docker for Mac](#docker-for-mac) or
  [Docker for Windows](#docker-for-windows/), which have superseded Kitematic.
layer: |
  In an image, a layer is modification to the image, represented by an instruction in the
  Dockerfile. Layers are applied in sequence to the base image to create the final image.
  When an image is updated or rebuilt, only layers that change need to be updated, and
  unchanged layers are cached locally. This is part of why Docker images are so fast
  and lightweight. The sizes of each layer add up to equal the size of the final image.
libcontainer: |
  libcontainer provides a native Go implementation for creating containers with
  namespaces, cgroups, capabilities, and filesystem access controls. It allows
  you to manage the lifecycle of the container performing additional operations
  after the container is created.
libnetwork: |
  libnetwork provides a native Go implementation for creating and managing container
  network namespaces and other network resources. It manage the networking lifecycle
  of the container performing additional operations after the container is created.
link: |
  links provide a legacy interface to connect Docker containers running on the
  same host to each other without exposing the hosts' network ports. Use the
  Docker networks feature instead.
Machine: |
  [Machine](https://github.com/docker/machine) is a Docker tool which
  makes it really easy to create Docker hosts on  your computer, on
  cloud providers and inside your own data center. It creates servers,
  installs Docker on them, then configures the Docker client to talk to them.

  *Also known as : docker-machine*
namespace: |
  A [Linux namespace](http://man7.org/linux/man-pages/man7/namespaces.7.html){: target="_blank" class="_"}
  is a Linux kernel feature that isolates and vitualizes system resources. Processes which restricted to
  a namespace can only interact with resources or processes that are part of the same namespace. Namespaces
  are an important part of Docker's isolation model. Namespaces exist for each type of
  resource, including `net` (networking), `mnt` (storage), `pid` (processes), `uts` (hostname control),
  and `user` (UID mapping). For more information about namespaces, see [Docker run reference](/engine/reference/run.md)
  and [Introduction to user namespaces](https://success.docker.com/KBase/Introduction_to_User_Namespaces_in_Docker_Engine){ :target="_blank" class="_" }.

node: |
  A [node](/engine/swarm/how-swarm-mode-works/nodes/) is a physical or virtual
  machine running an instance of the Docker Engine in swarm mode.

  **Manager nodes** perform swarm management and orchestration duties. By default
  manager nodes are also worker nodes.

  **Worker nodes** execute tasks.
overlay network driver: |
  Overlay network driver provides out of the box multi-host network connectivity
  for docker containers in a cluster.
overlay storage driver: |
  OverlayFS is a [filesystem](#filesystem) service for Linux which implements a
  [union mount](http://en.wikipedia.org/wiki/Union_mount) for other file systems.
  It is supported by the Docker daemon as a storage driver.
registry: |
  A Registry is a hosted service containing [repositories](#repository) of [images](#image)
  which responds to the Registry API.

  The default registry can be accessed using a browser at [Docker Hub](#docker-hub)
  or using the `docker search` command.
repository: |
  A repository is a set of Docker images. A repository can be shared by pushing it
  to a [registry](#registry) server. The different images in the repository can be
  labeled using [tags](#tag).

  Here is an example of the shared [nginx repository](https://hub.docker.com/_/nginx/)
  and its [tags](https://hub.docker.com/r/library/nginx/tags/).
SSH: |
  SSH (secure shell) is a secure protocol for accessing remote machines and applications. It
  provides authentication and encrypts data communication over insecure networks such as the Internet. SSH uses public/private key pairs to authenticate logins.
service: |
  A [service](/engine/swarm/how-swarm-mode-works/services/) is the definition of how
  you want to run your application containers in a swarm. At the most basic level
  a service  defines which container image to run in the swarm and which commands
  to run in the container. For orchestration purposes, the service defines the
  "desired state", meaning how many containers to run as tasks and constraints for
  deploying the containers.

  Frequently a service is a microservice within the context of some larger
  application. Examples of services might include an HTTP server, a database, or
  any other type of executable program that you wish to run in a distributed
  environment.
service discovery: |
  Swarm mode [service discovery](/engine/swarm/networking/#use-swarm-mode-service-discovery) is a DNS component
  internal to the swarm that automatically assigns each service on an overlay
  network in the swarm a VIP and DNS entry. Containers on the network share DNS
  mappings for the service via gossip so any container on the network can access
  the service via its service name.

  You don’t need to expose service-specific ports to make the service available to
  other services on the same overlay network. The swarm’s internal load balancer
  automatically distributes requests to the service VIP among the active tasks.
swarm: |
  A [swarm](/engine/swarm/) is a cluster of one or more Docker Engines running in [swarm mode](#swarm-mode).
Docker Swarm: |
  Do not confuse [Docker Swarm](https://github.com/docker/swarm) with the [swarm mode](#swarm-mode) features in Docker Engine.

  Docker Swarm is the name of a standalone native clustering tool for Docker.
  Docker Swarm pools together several Docker hosts and exposes them as a single
  virtual Docker host. It serves the standard Docker API, so any tool that already
  works with Docker can now transparently scale up to multiple hosts.

  *Also known as : docker-swarm*
swarm mode: |
  [Swarm mode](/engine/swarm/) refers to cluster management and orchestration
  features embedded in Docker Engine. When you initialize a new swarm (cluster) or
  join nodes to a swarm, the Docker Engine runs in swarm mode.
tag: |
  A tag is a label applied to a Docker image in a [repository](#repository).
  Tags are how various images in a repository are distinguished from each other.

  *Note : This label is not related to the key=value labels set for docker daemon.*
task: |
  A [task](/engine/swarm/how-swarm-mode-works/services/#/tasks-and-scheduling) is the
  atomic unit of scheduling within a swarm. A task carries a Docker container and
  the commands to run inside the container. Manager nodes assign tasks to worker
  nodes according to the number of replicas set in the service scale.

  The diagram below illustrates the relationship of services to tasks and
  containers.

  ![services diagram](/engine/swarm/images/services-diagram.png)
Toolbox: |
  [Docker Toolbox](/toolbox/overview/) is a legacy
  installer for Mac and Windows users. It uses Oracle VirtualBox for
  virtualization.

  For Macs running OS X El Capitan 10.11 and newer macOS releases, [Docker for
  Mac](/docker-for-mac/) is the better solution.

  For Windows 10 systems that support Microsoft Hyper-V (Professional, Enterprise
  and Education), [Docker for
  Windows](/docker-for-windows/) is the better solution.
Union file system: |
  Union file systems implement a [union
  mount](https://en.wikipedia.org/wiki/Union_mount) and operate by creating
  layers. Docker uses union file systems in conjunction with
  [copy-on-write](#copy-on-write) techniques to provide the building blocks for
  containers, making them very lightweight and fast.

  For more on Docker and union file systems, see [Docker and AUFS in
  practice](/engine/userguide/storagedriver/aufs-driver/),
  [Docker and Btrfs in
  practice](/engine/userguide/storagedriver/btrfs-driver/),
  and [Docker and OverlayFS in
  practice](/engine/userguide/storagedriver/overlayfs-driver/).

  Example implementations of union file systems are
  [UnionFS](https://en.wikipedia.org/wiki/UnionFS),
  [AUFS](https://en.wikipedia.org/wiki/Aufs), and
  [Btrfs](https://btrfs.wiki.kernel.org/index.php/Main_Page).
virtual machine: |
  A virtual machine is a program that emulates a complete computer and imitates dedicated hardware.
  It shares physical hardware resources with other users but isolates the operating system. The
  end user has the same experience on a Virtual Machine as they would have on dedicated hardware.

  Compared to containers, a virtual machine is heavier to run, provides more isolation,
  gets its own set of resources and does minimal sharing.

  *Also known as : VM*
volume: |
  A volume is a specially-designated directory within one or more containers
  that bypasses the Union File System. Volumes are designed to persist data,
  independent of the container's life cycle. Docker therefore never automatically
  delete volumes when you remove a container, nor will it "garbage collect"
  volumes that are no longer referenced by a container.
  *Also known as: data volume*

  There are three types of volumes: *host, anonymous, and named*:

  - A **host volume** lives on the Docker host's filesystem and can be accessed from within the container.

  - A **named volume** is a volume which Docker manages where on disk the volume is created,
    but it is given a name.

  - An **anonymous volume** is similar to a named volume, however, it can be difficult, to refer to
    the same volume over time when it is an anonymous volumes. Docker handle where the files are stored.