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Merge pull request #7066 from fricklerhandwerk/architecture-overview
manual: architecture overview
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Théophane Hufschmitt
GitHub
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@manpages@
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@manpages@
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- [Files](command-ref/files.md)
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- [Files](command-ref/files.md)
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- [nix.conf](command-ref/conf-file.md)
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- [nix.conf](command-ref/conf-file.md)
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- [Architecture](architecture/architecture.md)
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- [Glossary](glossary.md)
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- [Glossary](glossary.md)
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- [Contributing](contributing/contributing.md)
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- [Contributing](contributing/contributing.md)
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- [Hacking](contributing/hacking.md)
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- [Hacking](contributing/hacking.md)
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115
doc/manual/src/architecture/architecture.md
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115
doc/manual/src/architecture/architecture.md
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# Architecture
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This chapter describes how Nix works.
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It should help users understand why Nix behaves as it does, and it should help developers understand how to modify Nix and how to write similar tools.
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## Overview
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Nix consists of [hierarchical layers].
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[hierarchical layers]: https://en.m.wikipedia.org/wiki/Multitier_architecture#Layers
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The following [concept map] shows its main components (rectangles), the objects they operate on (rounded rectangles), and their interactions (connecting phrases):
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[concept map]: https://en.m.wikipedia.org/wiki/Concept_map
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```
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.----------------.
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| Nix expression |----------.
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'----------------' |
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| passed to
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+----------|-------------------|--------------------------------+
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| Nix | V |
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| | +-------------------------+ |
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| | | commmand line interface |------. |
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| | +-------------------------+ | |
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| evaluated by calls manages |
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| | V | |
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| | +--------------------+ | |
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| '-------->| language evaluator | | |
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| +--------------------+ | |
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| produces | |
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| | V |
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| +----------------------------|------------------------------+ |
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| | store | | |
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| | referenced by V builds | |
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| | .-------------. .------------. .--------------. | |
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| | | build input |----->| build plan |----->| build result | | |
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| | '-------------' '------------' '--------------' | |
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| +-------------------------------------------------|---------+ |
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+---------------------------------------------------|-----------+
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represented as
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V
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.---------------.
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| file |
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'---------------'
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```
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At the top is the [command line interface](../command-ref/command-ref.md) that drives the underlying layers.
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The [Nix language](../language/index.md) evaluator transforms Nix expressions into self-contained *build plans*, which are used to derive *build results* from referenced *build inputs*.
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The command line interface and Nix expressions are what users deal with most.
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> **Note**
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> The Nix language itself does not have a notion of *packages* or *configurations*.
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> As far as we are concerned here, the inputs and results of a build plan are just data.
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Underlying the command line interface and the Nix language evaluator is the [Nix store](../glossary.md#gloss-store), a mechanism to keep track of build plans, data, and references between them.
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It can also execute build plans to produce new data, which are made available to the operating system as files.
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A build plan itself is a series of *build tasks*, together with their build inputs.
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> **Important**
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> A build task in Nix is called [derivation](../glossary#gloss-derivation).
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Each build task has a special build input executed as *build instructions* in order to perform the build.
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The result of a build task can be input to another build task.
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The following [data flow diagram] shows a build plan for illustration.
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Build inputs used as instructions to a build task are marked accordingly:
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[data flow diagram]: https://en.m.wikipedia.org/wiki/Data-flow_diagram
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```
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+--------------------------------------------------------------------+
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| build plan |
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| .-------------. |
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| | build input |---------. |
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| '-------------' | |
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| instructions |
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| v |
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| .-------------. .----------. |
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| | build input |-->( build task )-------. |
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| '-------------' '----------' | |
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| instructions |
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| v |
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| .-------------. .----------. .--------------. |
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| | build input |---------. ( build task )--->| build result | |
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| '-------------' | '----------' '--------------' |
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| instructions ^ |
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| v | |
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| .-------------. .----------. | |
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| | build input |-->( build task )-------' |
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| '-------------' '----------' |
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| ^ |
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| .-------------. | |
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| | build input |---------' |
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| '-------------' |
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+--------------------------------------------------------------------+
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```
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