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140 lines
4.5 KiB
XML
140 lines
4.5 KiB
XML
<appendix><title>Glossary</title>
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<glosslist>
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<glossentry id="gloss-derivation"><glossterm>derivation</glossterm>
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<glossdef><para>A description of a build action. The result of a
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derivation is a store object. Derivations are typically specified
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in Nix expressions using the <link
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linkend="ssec-derivation"><function>derivation</function>
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primitive</link>. These are translated into low-level
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<emphasis>store derivations</emphasis> (implicitly by
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<command>nix-env</command> and <command>nix-build</command>, or
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explicitly by <command>nix-instantiate</command>).</para></glossdef>
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</glossentry>
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<glossentry><glossterm>store</glossterm>
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<glossdef><para>The location in the file system where store objects
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live. Typically <filename>/nix/store</filename>.</para></glossdef>
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</glossentry>
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<glossentry><glossterm>store path</glossterm>
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<glossdef><para>The location in the file system of a store object,
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i.e., an immediate child of the Nix store
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directory.</para></glossdef>
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</glossentry>
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<glossentry><glossterm>store object</glossterm>
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<glossdef><para>A file that is an immediate child of the Nix store
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directory. These can be regular files, but also entire directory
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trees. Store objects can be sources (objects copied from outside of
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the store), derivation outputs (objects produced by running a build
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action), or derivations (files describing a build
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action).</para></glossdef>
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</glossentry>
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<glossentry id="gloss-substitute"><glossterm>substitute</glossterm>
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<glossdef><para>A substitute is a command invocation stored in the
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Nix database that describes how to build a store object, bypassing
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normal the build mechanism (i.e., derivations). Typically, the
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substitute builds the store object by downloading a pre-built
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version of the store object from some server.</para></glossdef>
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</glossentry>
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<glossentry><glossterm>purity</glossterm>
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<glossdef><para>The assumption that equal Nix derivations when run
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always produce the same output. This cannot be guaranteed in
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general (e.g., a builder can rely on external inputs such as the
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network or the system time) but the Nix model assumes
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it.</para></glossdef>
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</glossentry>
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<glossentry><glossterm>Nix expression</glossterm>
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<glossdef><para>A high-level description of software components and
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compositions thereof. Deploying software using Nix entails writing
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Nix expressions for your components. Nix expressions are translated
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to derivations that are stored in the Nix store. These derivations
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can then be built.</para></glossdef>
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</glossentry>
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<glossentry id="gloss-reference"><glossterm>reference</glossterm>
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<glossdef><para>A store path <varname>P</varname> is said to have a
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reference to a store path <varname>Q</varname> if the store object
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at <varname>P</varname> contains the path <varname>Q</varname>
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somewhere. This implies than an execution involving
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<varname>P</varname> potentially needs <varname>Q</varname> to be
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present. The <emphasis>references</emphasis> of a store path are
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the set of store paths to which it has a reference.</para></glossdef>
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</glossentry>
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<glossentry id="gloss-closure"><glossterm>closure</glossterm>
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<glossdef><para>The closure of a store path is the set of store
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paths that are directly or indirectly “reachable” from that store
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path; that is, it’s the closure of the path under the <link
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linkend="gloss-reference">references</link> relation. For instance,
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if the store object at path <varname>P</varname> contains a
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reference to path <varname>Q</varname>, then <varname>Q</varname> is
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in the closure of <varname>P</varname>. For correct deployment it
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is necessary to deploy whole closures, since otherwise at runtime
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files could be missing. The command <command>nix-store
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-qR</command> prints out closures of store paths.</para></glossdef>
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</glossentry>
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<glossentry id="gloss-output-path"><glossterm>output path</glossterm>
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<glossdef><para>A store path produced by a derivation.</para></glossdef>
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</glossentry>
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<glossentry id="gloss-deriver"><glossterm>deriver</glossterm>
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<glossdef><para>The deriver of an <link
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linkend="gloss-output-path">output path</link> is the store
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derivation that built it.</para></glossdef>
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</glossentry>
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<glossentry id="gloss-validity"><glossterm>validity</glossterm>
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<glossdef><para>A store path is considered
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<emphasis>valid</emphasis> if it exists in the file system, is
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listed in the Nix database as being valid, and if all paths in its
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closure are also valid.</para></glossdef>
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</glossentry>
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</glosslist>
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</appendix>
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