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Merge pull request #8706 from fricklerhandwerk/doc-system-features
document system features
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commit
60a155d01c
4 changed files with 53 additions and 16 deletions
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@ -229,6 +229,8 @@ Derivations can declare some infrequently used optional attributes.
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[`outputHashAlgo`](#adv-attr-outputHashAlgo)
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like for *fixed-output derivations* (see above).
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It also implicitly requires that the machine to build the derivation must have the `ca-derivations` [system feature](@docroot@/command-ref/conf-file.md#conf-system-features).
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- [`passAsFile`]{#adv-attr-passAsFile}\
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A list of names of attributes that should be passed via files rather
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than environment variables. For example, if you have
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@ -335,3 +337,15 @@ Derivations can declare some infrequently used optional attributes.
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This is useful, for example, when generating self-contained filesystem images with
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their own embedded Nix store: hashes found inside such an image refer
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to the embedded store and not to the host's Nix store.
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- [`requiredSystemFeatures`]{#adv-attr-requiredSystemFeatures}\
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If a derivation has the `requiredSystemFeatures` attribute, then Nix will only build it on a machine that has the corresponding features set in its [`system-features` configuration](@docroot@/command-ref/conf-file.md#conf-system-features).
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For example, setting
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```nix
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requiredSystemFeatures = [ "kvm" ];
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```
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ensures that the derivation can only be built on a machine with the `kvm` feature.
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@ -2,7 +2,6 @@
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* On Linux, Nix can now run builds in a user namespace where they run
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as root (UID 0) and have 65,536 UIDs available.
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<!-- FIXME: move this to its own section about system features -->
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This is primarily useful for running containers such as `systemd-nspawn`
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inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn].
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@ -343,7 +343,7 @@ public:
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users in `build-users-group`.
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UIDs are allocated starting at 872415232 (0x34000000) on Linux and 56930 on macOS.
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)"};
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)", {}, true, Xp::AutoAllocateUids};
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Setting<uint32_t> startId{this,
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#if __linux__
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@ -697,19 +697,40 @@ public:
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getDefaultSystemFeatures(),
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"system-features",
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R"(
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A set of system “features” supported by this machine, e.g. `kvm`.
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Derivations can express a dependency on such features through the
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derivation attribute `requiredSystemFeatures`. For example, the
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attribute
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A set of system “features” supported by this machine.
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requiredSystemFeatures = [ "kvm" ];
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This complements the [`system`](#conf-system) and [`extra-platforms`](#conf-extra-platforms) configuration options and the corresponding [`system`](@docroot@/language/derivations.md#attr-system) attribute on derivations.
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ensures that the derivation can only be built on a machine with the
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`kvm` feature.
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A derivation can require system features in the [`requiredSystemFeatures` attribute](@docroot@/language/advanced-attributes.md#adv-attr-requiredSystemFeatures), and the machine to build the derivation must have them.
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This setting by default includes `kvm` if `/dev/kvm` is accessible,
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and the pseudo-features `nixos-test`, `benchmark` and `big-parallel`
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that are used in Nixpkgs to route builds to specific machines.
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System features are user-defined, but Nix sets the following defaults:
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- `kvm`
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Included by default if `/dev/kvm` is accessible.
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- `nixos-test`, `benchmark`, `big-parallel`
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These historical pseudo-features are always enabled for backwards compatibility, as they are used in Nixpkgs to route Hydra builds to specific machines.
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- `ca-derivations`
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Included by default if the [`ca-derivations` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-ca-derivations) is enabled.
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This system feature is implicitly required by derivations with the [`__contentAddressed` attribute](@docroot@/language/advanced-attributes.md#adv-attr-__contentAddressed).
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- `recursive-nix`
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Included by default if the [`recursive-nix` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-recursive-nix) is enabled.
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- `uid-range`
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On Linux, Nix can run builds in a user namespace where they run as root (UID 0) and have 65,536 UIDs available.
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This is primarily useful for running containers such as `systemd-nspawn` inside a Nix build. For an example, see [`tests/systemd-nspawn/nix`][nspawn].
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[nspawn]: https://github.com/NixOS/nix/blob/67bcb99700a0da1395fa063d7c6586740b304598/tests/systemd-nspawn.nix.
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Included by default on Linux if the [`auto-allocate-uids`](#conf-auto-allocate-uids) setting is enabled.
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)", {}, false};
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Setting<Strings> substituters{
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@ -153,19 +153,22 @@ struct StoreConfig : public Config
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Setting<int> priority{this, 0, "priority",
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R"(
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Priority of this store when used as a substituter. A lower value means a higher priority.
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Priority of this store when used as a [substituter](@docroot@/command-ref/conf-file.md#conf-substituters).
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A lower value means a higher priority.
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)"};
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Setting<bool> wantMassQuery{this, false, "want-mass-query",
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R"(
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Whether this store (when used as a substituter) can be
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queried efficiently for path validity.
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Whether this store can be queried efficiently for path validity when used as a [substituter](@docroot@/command-ref/conf-file.md#conf-substituters).
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)"};
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Setting<StringSet> systemFeatures{this, getDefaultSystemFeatures(),
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"system-features",
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"Optional features that the system this store builds on implements (like \"kvm\")."};
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R"(
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Optional [system features](@docroot@/command-ref/conf-file.md#conf-system-features) available on the system this store uses to build derivations.
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Example: `"kvm"`
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)" };
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};
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class Store : public std::enable_shared_from_this<Store>, public virtual StoreConfig
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