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1# The Standard Environment {#chap-stdenv} 2 3The standard build environment in the Nix Packages collection provides an environment for building Unix packages that does a lot of common build tasks automatically. In fact, for Unix packages that use the standard `./configure; make; make install` build interface, you don’t need to write a build script at all; the standard environment does everything automatically. If `stdenv` doesn’t do what you need automatically, you can easily customise or override the various build phases. 4 5## Using `stdenv` {#sec-using-stdenv} 6 7To build a package with the standard environment, you use the function `stdenv.mkDerivation`, instead of the primitive built-in function `derivation`, e.g. 8 9```nix 10stdenv.mkDerivation { 11 name = "libfoo-1.2.3"; 12 src = fetchurl { 13 url = "http://example.org/libfoo-1.2.3.tar.bz2"; 14 sha256 = "0x2g1jqygyr5wiwg4ma1nd7w4ydpy82z9gkcv8vh2v8dn3y58v5m"; 15 }; 16} 17``` 18 19(`stdenv` needs to be in scope, so if you write this in a separate Nix expression from `pkgs/all-packages.nix`, you need to pass it as a function argument.) Specifying a `name` and a `src` is the absolute minimum Nix requires. For convenience, you can also use `pname` and `version` attributes and `mkDerivation` will automatically set `name` to `"${pname}-${version}"` by default. Since [RFC 0035](https://github.com/NixOS/rfcs/pull/35), this is preferred for packages in Nixpkgs, as it allows us to reuse the version easily: 20 21```nix 22stdenv.mkDerivation rec { 23 pname = "libfoo"; 24 version = "1.2.3"; 25 src = fetchurl { 26 url = "http://example.org/libfoo-source-${version}.tar.bz2"; 27 sha256 = "0x2g1jqygyr5wiwg4ma1nd7w4ydpy82z9gkcv8vh2v8dn3y58v5m"; 28 }; 29} 30``` 31 32Many packages have dependencies that are not provided in the standard environment. It’s usually sufficient to specify those dependencies in the `buildInputs` attribute: 33 34```nix 35stdenv.mkDerivation { 36 name = "libfoo-1.2.3"; 37 ... 38 buildInputs = [libbar perl ncurses]; 39} 40``` 41 42This attribute ensures that the `bin` subdirectories of these packages appear in the `PATH` environment variable during the build, that their `include` subdirectories are searched by the C compiler, and so on. (See <xref linkend="ssec-setup-hooks" /> for details.) 43 44Often it is necessary to override or modify some aspect of the build. To make this easier, the standard environment breaks the package build into a number of *phases*, all of which can be overridden or modified individually: unpacking the sources, applying patches, configuring, building, and installing. (There are some others; see <xref linkend="sec-stdenv-phases" />.) For instance, a package that doesn’t supply a makefile but instead has to be compiled "manually" could be handled like this: 45 46```nix 47stdenv.mkDerivation { 48 name = "fnord-4.5"; 49 ... 50 buildPhase = '' 51 gcc foo.c -o foo 52 ''; 53 installPhase = '' 54 mkdir -p $out/bin 55 cp foo $out/bin 56 ''; 57} 58``` 59 60(Note the use of `''`-style string literals, which are very convenient for large multi-line script fragments because they don’t need escaping of `"` and `\`, and because indentation is intelligently removed.) 61 62There are many other attributes to customise the build. These are listed in <xref linkend="ssec-stdenv-attributes" />. 63 64While the standard environment provides a generic builder, you can still supply your own build script: 65 66```nix 67stdenv.mkDerivation { 68 name = "libfoo-1.2.3"; 69 ... 70 builder = ./builder.sh; 71} 72``` 73 74where the builder can do anything it wants, but typically starts with 75 76```bash 77source $stdenv/setup 78``` 79 80to let `stdenv` set up the environment (e.g., process the `buildInputs`). If you want, you can still use `stdenv`’s generic builder: 81 82```bash 83source $stdenv/setup 84 85buildPhase() { 86 echo "... this is my custom build phase ..." 87 gcc foo.c -o foo 88} 89 90installPhase() { 91 mkdir -p $out/bin 92 cp foo $out/bin 93} 94 95genericBuild 96``` 97 98## Tools provided by `stdenv` {#sec-tools-of-stdenv} 99 100The standard environment provides the following packages: 101 102- The GNU C Compiler, configured with C and C++ support. 103- GNU coreutils (contains a few dozen standard Unix commands). 104- GNU findutils (contains `find`). 105- GNU diffutils (contains `diff`, `cmp`). 106- GNU `sed`. 107- GNU `grep`. 108- GNU `awk`. 109- GNU `tar`. 110- `gzip`, `bzip2` and `xz`. 111- GNU Make. 112- Bash. This is the shell used for all builders in the Nix Packages collection. Not using `/bin/sh` removes a large source of portability problems. 113- The `patch` command. 114 115On Linux, `stdenv` also includes the `patchelf` utility. 116 117## Specifying dependencies {#ssec-stdenv-dependencies} 118 119As described in the Nix manual, almost any `*.drv` store path in a derivation’s attribute set will induce a dependency on that derivation. `mkDerivation`, however, takes a few attributes intended to, between them, include all the dependencies of a package. This is done both for structure and consistency, but also so that certain other setup can take place. For example, certain dependencies need their bin directories added to the `PATH`. That is built-in, but other setup is done via a pluggable mechanism that works in conjunction with these dependency attributes. See <xref linkend="ssec-setup-hooks" /> for details. 120 121Dependencies can be broken down along three axes: their host and target platforms relative to the new derivation’s, and whether they are propagated. The platform distinctions are motivated by cross compilation; see <xref linkend="chap-cross" /> for exactly what each platform means. [^footnote-stdenv-ignored-build-platform] But even if one is not cross compiling, the platforms imply whether or not the dependency is needed at run-time or build-time, a concept that makes perfect sense outside of cross compilation. By default, the run-time/build-time distinction is just a hint for mental clarity, but with `strictDeps` set it is mostly enforced even in the native case. 122 123The extension of `PATH` with dependencies, alluded to above, proceeds according to the relative platforms alone. The process is carried out only for dependencies whose host platform matches the new derivation’s build platform i.e. dependencies which run on the platform where the new derivation will be built. [^footnote-stdenv-native-dependencies-in-path] For each dependency \<dep\> of those dependencies, `dep/bin`, if present, is added to the `PATH` environment variable. 124 125The dependency is propagated when it forces some of its other-transitive (non-immediate) downstream dependencies to also take it on as an immediate dependency. Nix itself already takes a package’s transitive dependencies into account, but this propagation ensures nixpkgs-specific infrastructure like setup hooks (mentioned above) also are run as if the propagated dependency. 126 127It is important to note that dependencies are not necessarily propagated as the same sort of dependency that they were before, but rather as the corresponding sort so that the platform rules still line up. The exact rules for dependency propagation can be given by assigning to each dependency two integers based one how its host and target platforms are offset from the depending derivation’s platforms. Those offsets are given below in the descriptions of each dependency list attribute. Algorithmically, we traverse propagated inputs, accumulating every propagated dependency’s propagated dependencies and adjusting them to account for the “shift in perspective” described by the current dependency’s platform offsets. This results in sort a transitive closure of the dependency relation, with the offsets being approximately summed when two dependency links are combined. We also prune transitive dependencies whose combined offsets go out-of-bounds, which can be viewed as a filter over that transitive closure removing dependencies that are blatantly absurd. 128 129We can define the process precisely with [Natural Deduction](https://en.wikipedia.org/wiki/Natural_deduction) using the inference rules. This probably seems a bit obtuse, but so is the bash code that actually implements it! [^footnote-stdenv-find-inputs-location] They’re confusing in very different ways so… hopefully if something doesn’t make sense in one presentation, it will in the other! 130 131``` 132let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1) 133 134propagated-dep(h0, t0, A, B) 135propagated-dep(h1, t1, B, C) 136h0 + h1 in {-1, 0, 1} 137h0 + t1 in {-1, 0, 1} 138-------------------------------------- Transitive property 139propagated-dep(mapOffset(h0, t0, h1), 140 mapOffset(h0, t0, t1), 141 A, C) 142``` 143 144``` 145let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1) 146 147dep(h0, _, A, B) 148propagated-dep(h1, t1, B, C) 149h0 + h1 in {-1, 0, 1} 150h0 + t1 in {-1, 0, -1} 151----------------------------- Take immediate dependencies' propagated dependencies 152propagated-dep(mapOffset(h0, t0, h1), 153 mapOffset(h0, t0, t1), 154 A, C) 155``` 156 157``` 158propagated-dep(h, t, A, B) 159----------------------------- Propagated dependencies count as dependencies 160dep(h, t, A, B) 161``` 162 163Some explanation of this monstrosity is in order. In the common case, the target offset of a dependency is the successor to the target offset: `t = h + 1`. That means that: 164 165``` 166let f(h, t, i) = i + (if i <= 0 then h else t - 1) 167let f(h, h + 1, i) = i + (if i <= 0 then h else (h + 1) - 1) 168let f(h, h + 1, i) = i + (if i <= 0 then h else h) 169let f(h, h + 1, i) = i + h 170``` 171 172This is where “sum-like” comes in from above: We can just sum all of the host offsets to get the host offset of the transitive dependency. The target offset is the transitive dependency is simply the host offset + 1, just as it was with the dependencies composed to make this transitive one; it can be ignored as it doesn’t add any new information. 173 174Because of the bounds checks, the uncommon cases are `h = t` and `h + 2 = t`. In the former case, the motivation for `mapOffset` is that since its host and target platforms are the same, no transitive dependency of it should be able to “discover” an offset greater than its reduced target offsets. `mapOffset` effectively “squashes” all its transitive dependencies’ offsets so that none will ever be greater than the target offset of the original `h = t` package. In the other case, `h + 1` is skipped over between the host and target offsets. Instead of squashing the offsets, we need to “rip” them apart so no transitive dependencies’ offset is that one. 175 176Overall, the unifying theme here is that propagation shouldn’t be introducing transitive dependencies involving platforms the depending package is unaware of. \[One can imagine the dependending package asking for dependencies with the platforms it knows about; other platforms it doesn’t know how to ask for. The platform description in that scenario is a kind of unforagable capability.\] The offset bounds checking and definition of `mapOffset` together ensure that this is the case. Discovering a new offset is discovering a new platform, and since those platforms weren’t in the derivation “spec” of the needing package, they cannot be relevant. From a capability perspective, we can imagine that the host and target platforms of a package are the capabilities a package requires, and the depending package must provide the capability to the dependency. 177 178### Variables specifying dependencies 179#### `depsBuildBuild` {#var-stdenv-depsBuildBuild} 180 181A list of dependencies whose host and target platforms are the new derivation’s build platform. This means a `-1` host and `-1` target offset from the new derivation’s platforms. These are programs and libraries used at build time that produce programs and libraries also used at build time. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it in `nativeBuildInputs` instead. The most common use of this `buildPackages.stdenv.cc`, the default C compiler for this role. That example crops up more than one might think in old commonly used C libraries. 182 183Since these packages are able to be run at build-time, they are always added to the `PATH`, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future. 184 185#### `nativeBuildInputs` {#var-stdenv-nativeBuildInputs} 186 187A list of dependencies whose host platform is the new derivation’s build platform, and target platform is the new derivation’s host platform. This means a `-1` host offset and `0` target offset from the new derivation’s platforms. These are programs and libraries used at build-time that, if they are a compiler or similar tool, produce code to run at run-time—i.e. tools used to build the new derivation. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it here, rather than in `depsBuildBuild` or `depsBuildTarget`. This could be called `depsBuildHost` but `nativeBuildInputs` is used for historical continuity. 188 189Since these packages are able to be run at build-time, they are added to the `PATH`, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future. 190 191#### `depsBuildTarget` {#var-stdenv-depsBuildTarget} 192 193A list of dependencies whose host platform is the new derivation’s build platform, and target platform is the new derivation’s target platform. This means a `-1` host offset and `1` target offset from the new derivation’s platforms. These are programs used at build time that produce code to run with code produced by the depending package. Most commonly, these are tools used to build the runtime or standard library that the currently-being-built compiler will inject into any code it compiles. In many cases, the currently-being-built-compiler is itself employed for that task, but when that compiler won’t run (i.e. its build and host platform differ) this is not possible. Other times, the compiler relies on some other tool, like binutils, that is always built separately so that the dependency is unconditional. 194 195This is a somewhat confusing concept to wrap one’s head around, and for good reason. As the only dependency type where the platform offsets are not adjacent integers, it requires thinking of a bootstrapping stage *two* away from the current one. It and its use-case go hand in hand and are both considered poor form: try to not need this sort of dependency, and try to avoid building standard libraries and runtimes in the same derivation as the compiler produces code using them. Instead strive to build those like a normal library, using the newly-built compiler just as a normal library would. In short, do not use this attribute unless you are packaging a compiler and are sure it is needed. 196 197Since these packages are able to run at build time, they are added to the `PATH`, as described above. But since these packages are only guaranteed to be able to run then, they shouldn’t persist as run-time dependencies. This isn’t currently enforced, but could be in the future. 198 199#### `depsHostHost` {#var-stdenv-depsHostHost} 200 201A list of dependencies whose host and target platforms match the new derivation’s host platform. This means a `0` host offset and `0` target offset from the new derivation’s host platform. These are packages used at run-time to generate code also used at run-time. In practice, this would usually be tools used by compilers for macros or a metaprogramming system, or libraries used by the macros or metaprogramming code itself. It’s always preferable to use a `depsBuildBuild` dependency in the derivation being built over a `depsHostHost` on the tool doing the building for this purpose. 202 203#### `buildInputs` {#var-stdenv-buildInputs} 204 205A list of dependencies whose host platform and target platform match the new derivation’s. This means a `0` host offset and a `1` target offset from the new derivation’s host platform. This would be called `depsHostTarget` but for historical continuity. If the dependency doesn’t care about the target platform (i.e. isn’t a compiler or similar tool), put it here, rather than in `depsBuildBuild`. 206 207These are often programs and libraries used by the new derivation at *run*-time, but that isn’t always the case. For example, the machine code in a statically-linked library is only used at run-time, but the derivation containing the library is only needed at build-time. Even in the dynamic case, the library may also be needed at build-time to appease the linker. 208 209#### `depsTargetTarget` {#var-stdenv-depsTargetTarget} 210 211A list of dependencies whose host platform matches the new derivation’s target platform. This means a `1` offset from the new derivation’s platforms. These are packages that run on the target platform, e.g. the standard library or run-time deps of standard library that a compiler insists on knowing about. It’s poor form in almost all cases for a package to depend on another from a future stage \[future stage corresponding to positive offset\]. Do not use this attribute unless you are packaging a compiler and are sure it is needed. 212 213#### `depsBuildBuildPropagated` {#var-stdenv-depsBuildBuildPropagated} 214 215The propagated equivalent of `depsBuildBuild`. This perhaps never ought to be used, but it is included for consistency \[see below for the others\]. 216 217#### `propagatedNativeBuildInputs` {#var-stdenv-propagatedNativeBuildInputs} 218 219The propagated equivalent of `nativeBuildInputs`. This would be called `depsBuildHostPropagated` but for historical continuity. For example, if package `Y` has `propagatedNativeBuildInputs = [X]`, and package `Z` has `buildInputs = [Y]`, then package `Z` will be built as if it included package `X` in its `nativeBuildInputs`. If instead, package `Z` has `nativeBuildInputs = [Y]`, then `Z` will be built as if it included `X` in the `depsBuildBuild` of package `Z`, because of the sum of the two `-1` host offsets. 220 221#### `depsBuildTargetPropagated` {#var-stdenv-depsBuildTargetPropagated} 222 223The propagated equivalent of `depsBuildTarget`. This is prefixed for the same reason of alerting potential users. 224 225#### `depsHostHostPropagated` {#var-stdenv-depsHostHostPropagated} 226 227The propagated equivalent of `depsHostHost`. 228 229#### `propagatedBuildInputs` {#var-stdenv-propagatedBuildInputs} 230 231The propagated equivalent of `buildInputs`. This would be called `depsHostTargetPropagated` but for historical continuity. 232 233#### `depsTargetTargetPropagated` {#var-stdenv-depsTargetTargetPropagated} 234 235The propagated equivalent of `depsTargetTarget`. This is prefixed for the same reason of alerting potential users. 236 237## Attributes {#ssec-stdenv-attributes} 238 239### Variables affecting `stdenv` initialisation 240 241#### `NIX_DEBUG` {#var-stdenv-NIX_DEBUG} 242 243A natural number indicating how much information to log. If set to 1 or higher, `stdenv` will print moderate debugging information during the build. In particular, the `gcc` and `ld` wrapper scripts will print out the complete command line passed to the wrapped tools. If set to 6 or higher, the `stdenv` setup script will be run with `set -x` tracing. If set to 7 or higher, the `gcc` and `ld` wrapper scripts will also be run with `set -x` tracing. 244 245### Attributes affecting build properties 246 247#### `enableParallelBuilding` {#var-stdenv-enableParallelBuilding} 248 249If set to `true`, `stdenv` will pass specific flags to `make` and other build tools to enable parallel building with up to `build-cores` workers. 250 251Unless set to `false`, some build systems with good support for parallel building including `cmake`, `meson`, and `qmake` will set it to `true`. 252 253### Special variables 254 255#### `passthru` {#var-stdenv-passthru} 256 257This is an attribute set which can be filled with arbitrary values. For example: 258 259```nix 260passthru = { 261 foo = "bar"; 262 baz = { 263 value1 = 4; 264 value2 = 5; 265 }; 266} 267``` 268 269Values inside it are not passed to the builder, so you can change them without triggering a rebuild. However, they can be accessed outside of a derivation directly, as if they were set inside a derivation itself, e.g. `hello.baz.value1`. We don’t specify any usage or schema of `passthru` - it is meant for values that would be useful outside the derivation in other parts of a Nix expression (e.g. in other derivations). An example would be to convey some specific dependency of your derivation which contains a program with plugins support. Later, others who make derivations with plugins can use passed-through dependency to ensure that their plugin would be binary-compatible with built program. 270 271#### `passthru.updateScript` {#var-passthru-updateScript} 272 273A script to be run by `maintainers/scripts/update.nix` when the package is matched. It needs to be an executable file, either on the file system: 274 275```nix 276passthru.updateScript = ./update.sh; 277``` 278 279or inside the expression itself: 280 281```nix 282passthru.updateScript = writeScript "update-zoom-us" '' 283 #!/usr/bin/env nix-shell 284 #!nix-shell -i bash -p curl pcre common-updater-scripts 285 286 set -eu -o pipefail 287 288 version="$(curl -sI https://zoom.us/client/latest/zoom_x86_64.tar.xz | grep -Fi 'Location:' | pcregrep -o1 '/(([0-9]\.?)+)/')" 289 update-source-version zoom-us "$version" 290''; 291``` 292 293The attribute can also contain a list, a script followed by arguments to be passed to it: 294 295```nix 296passthru.updateScript = [ ../../update.sh pname "--requested-release=unstable" ]; 297``` 298 299The script will be run with `UPDATE_NIX_ATTR_PATH` environment variable set to the attribute path it is supposed to update. 300 301::: note 302The script will be usually run from the root of the Nixpkgs repository but you should not rely on that. Also note that the update scripts will be run in parallel by default; you should avoid running `git commit` or any other commands that cannot handle that. 303::: 304 305For information about how to run the updates, execute `nix-shell maintainers/scripts/update.nix`. 306 307## Phases {#sec-stdenv-phases} 308 309The generic builder has a number of *phases*. Package builds are split into phases to make it easier to override specific parts of the build (e.g., unpacking the sources or installing the binaries). Furthermore, it allows a nicer presentation of build logs in the Nix build farm. 310 311Each phase can be overridden in its entirety either by setting the environment variable `namePhase` to a string containing some shell commands to be executed, or by redefining the shell function `namePhase`. The former is convenient to override a phase from the derivation, while the latter is convenient from a build script. However, typically one only wants to *add* some commands to a phase, e.g. by defining `postInstall` or `preFixup`, as skipping some of the default actions may have unexpected consequences. The default script for each phase is defined in the file `pkgs/stdenv/generic/setup.sh`. 312 313### Controlling phases {#ssec-controlling-phases} 314 315There are a number of variables that control what phases are executed and in what order: 316 317#### Variables affecting phase control 318 319##### `phases` {#var-stdenv-phases} 320 321Specifies the phases. You can change the order in which phases are executed, or add new phases, by setting this variable. If it’s not set, the default value is used, which is `$prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase installCheckPhase $preDistPhases distPhase $postPhases`. 322 323Usually, if you just want to add a few phases, it’s more convenient to set one of the variables below (such as `preInstallPhases`), as you then don’t specify all the normal phases. 324 325##### `prePhases` {#var-stdenv-prePhases} 326 327Additional phases executed before any of the default phases. 328 329##### `preConfigurePhases` {#var-stdenv-preConfigurePhases} 330 331Additional phases executed just before the configure phase. 332 333##### `preBuildPhases` {#var-stdenv-preBuildPhases} 334 335Additional phases executed just before the build phase. 336 337##### `preInstallPhases` {#var-stdenv-preInstallPhases} 338 339Additional phases executed just before the install phase. 340 341##### `preFixupPhases` {#var-stdenv-preFixupPhases} 342 343Additional phases executed just before the fixup phase. 344 345##### `preDistPhases` {#var-stdenv-preDistPhases} 346 347Additional phases executed just before the distribution phase. 348 349##### `postPhases` {#var-stdenv-postPhases} 350 351Additional phases executed after any of the default phases. 352 353### The unpack phase {#ssec-unpack-phase} 354 355The unpack phase is responsible for unpacking the source code of the package. The default implementation of `unpackPhase` unpacks the source files listed in the `src` environment variable to the current directory. It supports the following files by default: 356 357#### Tar files 358 359These can optionally be compressed using `gzip` (`.tar.gz`, `.tgz` or `.tar.Z`), `bzip2` (`.tar.bz2`, `.tbz2` or `.tbz`) or `xz` (`.tar.xz`, `.tar.lzma` or `.txz`). 360 361#### Zip files 362 363Zip files are unpacked using `unzip`. However, `unzip` is not in the standard environment, so you should add it to `nativeBuildInputs` yourself. 364 365#### Directories in the Nix store 366 367These are simply copied to the current directory. The hash part of the file name is stripped, e.g. `/nix/store/1wydxgby13cz...-my-sources` would be copied to `my-sources`. 368 369Additional file types can be supported by setting the `unpackCmd` variable (see below). 370 371#### Variables controlling the unpack phase 372##### `srcs` / `src` {#var-stdenv-src} 373 374The list of source files or directories to be unpacked or copied. One of these must be set. 375 376##### `sourceRoot` {#var-stdenv-sourceRoot} 377 378After running `unpackPhase`, the generic builder changes the current directory to the directory created by unpacking the sources. If there are multiple source directories, you should set `sourceRoot` to the name of the intended directory. 379 380##### `setSourceRoot` {#var-stdenv-setSourceRoot} 381 382Alternatively to setting `sourceRoot`, you can set `setSourceRoot` to a shell command to be evaluated by the unpack phase after the sources have been unpacked. This command must set `sourceRoot`. 383 384##### `preUnpack` {#var-stdenv-preUnpack} 385 386Hook executed at the start of the unpack phase. 387 388##### `postUnpack` {#var-stdenv-postUnpack} 389 390Hook executed at the end of the unpack phase. 391 392##### `dontUnpack` {#var-stdenv-dontUnpack} 393 394Set to true to skip the unpack phase. 395 396##### `dontMakeSourcesWritable` {#var-stdenv-dontMakeSourcesWritable} 397 398If set to `1`, the unpacked sources are *not* made writable. By default, they are made writable to prevent problems with read-only sources. For example, copied store directories would be read-only without this. 399 400##### `unpackCmd` {#var-stdenv-unpackCmd} 401 402The unpack phase evaluates the string `$unpackCmd` for any unrecognised file. The path to the current source file is contained in the `curSrc` variable. 403 404### The patch phase {#ssec-patch-phase} 405 406The patch phase applies the list of patches defined in the `patches` variable. 407 408#### Variables controlling the patch phase 409 410##### `dontPatch` {#var-stdenv-dontPatch} 411 412Set to true to skip the patch phase. 413 414##### `patches` {#var-stdenv-patches} 415 416The list of patches. They must be in the format accepted by the `patch` command, and may optionally be compressed using `gzip` (`.gz`), `bzip2` (`.bz2`) or `xz` (`.xz`). 417 418##### `patchFlags` {#var-stdenv-patchFlags} 419 420Flags to be passed to `patch`. If not set, the argument `-p1` is used, which causes the leading directory component to be stripped from the file names in each patch. 421 422##### `prePatch` {#var-stdenv-prePatch} 423 424Hook executed at the start of the patch phase. 425 426##### `postPatch` {#var-stdenv-postPatch} 427 428Hook executed at the end of the patch phase. 429 430### The configure phase {#ssec-configure-phase} 431 432The configure phase prepares the source tree for building. The default `configurePhase` runs `./configure` (typically an Autoconf-generated script) if it exists. 433 434#### Variables controlling the configure phase 435 436##### `configureScript` {#var-stdenv-configureScript} 437 438The name of the configure script. It defaults to `./configure` if it exists; otherwise, the configure phase is skipped. This can actually be a command (like `perl ./Configure.pl`). 439 440##### `configureFlags` {#var-stdenv-configureFlags} 441 442A list of strings passed as additional arguments to the configure script. 443 444##### `dontConfigure` {#var-stdenv-dontConfigure} 445 446Set to true to skip the configure phase. 447 448##### `configureFlagsArray` {#var-stdenv-configureFlagsArray} 449 450A shell array containing additional arguments passed to the configure script. You must use this instead of `configureFlags` if the arguments contain spaces. 451 452##### `dontAddPrefix` {#var-stdenv-dontAddPrefix} 453 454By default, the flag `--prefix=$prefix` is added to the configure flags. If this is undesirable, set this variable to true. 455 456##### `prefix` {#var-stdenv-prefix} 457 458The prefix under which the package must be installed, passed via the `--prefix` option to the configure script. It defaults to `$out`. 459 460##### `prefixKey` {#var-stdenv-prefixKey} 461 462The key to use when specifying the prefix. By default, this is set to `--prefix=` as that is used by the majority of packages. 463 464##### `dontAddDisableDepTrack` {#var-stdenv-dontAddDisableDepTrack} 465 466By default, the flag `--disable-dependency-tracking` is added to the configure flags to speed up Automake-based builds. If this is undesirable, set this variable to true. 467 468##### `dontFixLibtool` {#var-stdenv-dontFixLibtool} 469 470By default, the configure phase applies some special hackery to all files called `ltmain.sh` before running the configure script in order to improve the purity of Libtool-based packages [^footnote-stdenv-sys-lib-search-path] . If this is undesirable, set this variable to true. 471 472##### `dontDisableStatic` {#var-stdenv-dontDisableStatic} 473 474By default, when the configure script has `--enable-static`, the option `--disable-static` is added to the configure flags. 475 476If this is undesirable, set this variable to true. 477 478##### `configurePlatforms` {#var-stdenv-configurePlatforms} 479 480By default, when cross compiling, the configure script has `--build=...` and `--host=...` passed. Packages can instead pass `[ "build" "host" "target" ]` or a subset to control exactly which platform flags are passed. Compilers and other tools can use this to also pass the target platform. [^footnote-stdenv-build-time-guessing-impurity] 481 482##### `preConfigure` {#var-stdenv-preConfigure} 483 484Hook executed at the start of the configure phase. 485 486##### `postConfigure` {#var-stdenv-postConfigure} 487 488Hook executed at the end of the configure phase. 489 490### The build phase {#build-phase} 491 492The build phase is responsible for actually building the package (e.g. compiling it). The default `buildPhase` simply calls `make` if a file named `Makefile`, `makefile` or `GNUmakefile` exists in the current directory (or the `makefile` is explicitly set); otherwise it does nothing. 493 494#### Variables controlling the build phase 495 496##### `dontBuild` {#var-stdenv-dontBuild} 497 498Set to true to skip the build phase. 499 500##### `makefile` {#var-stdenv-makefile} 501 502The file name of the Makefile. 503 504##### `makeFlags` {#var-stdenv-makeFlags} 505 506A list of strings passed as additional flags to `make`. These flags are also used by the default install and check phase. For setting make flags specific to the build phase, use `buildFlags` (see below). 507 508```nix 509makeFlags = [ "PREFIX=$(out)" ]; 510``` 511 512::: note 513The flags are quoted in bash, but environment variables can be specified by using the make syntax. 514::: 515 516##### `makeFlagsArray` {#var-stdenv-makeFlagsArray} 517 518A shell array containing additional arguments passed to `make`. You must use this instead of `makeFlags` if the arguments contain spaces, e.g. 519 520```nix 521preBuild = '' 522 makeFlagsArray+=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar") 523''; 524``` 525 526Note that shell arrays cannot be passed through environment variables, so you cannot set `makeFlagsArray` in a derivation attribute (because those are passed through environment variables): you have to define them in shell code. 527 528##### `buildFlags` / `buildFlagsArray` {#var-stdenv-buildFlags} 529 530A list of strings passed as additional flags to `make`. Like `makeFlags` and `makeFlagsArray`, but only used by the build phase. 531 532##### `preBuild` {#var-stdenv-preBuild} 533 534Hook executed at the start of the build phase. 535 536##### `postBuild` {#var-stdenv-postBuild} 537 538Hook executed at the end of the build phase. 539 540You can set flags for `make` through the `makeFlags` variable. 541 542Before and after running `make`, the hooks `preBuild` and `postBuild` are called, respectively. 543 544### The check phase {#ssec-check-phase} 545 546The check phase checks whether the package was built correctly by running its test suite. The default `checkPhase` calls `make check`, but only if the `doCheck` variable is enabled. 547 548#### Variables controlling the check phase 549 550##### `doCheck` {#var-stdenv-doCheck} 551 552Controls whether the check phase is executed. By default it is skipped, but if `doCheck` is set to true, the check phase is usually executed. Thus you should set 553 554```nix 555doCheck = true; 556``` 557 558in the derivation to enable checks. The exception is cross compilation. Cross compiled builds never run tests, no matter how `doCheck` is set, as the newly-built program won’t run on the platform used to build it. 559 560##### `makeFlags` / `makeFlagsArray` / `makefile` 561 562See the [build phase](#var-stdenv-makeFlags) for details. 563 564##### `checkTarget` {#var-stdenv-checkTarget} 565 566The make target that runs the tests. Defaults to `check`. 567 568##### `checkFlags` / `checkFlagsArray` {#var-stdenv-checkFlags} 569 570A list of strings passed as additional flags to `make`. Like `makeFlags` and `makeFlagsArray`, but only used by the check phase. 571 572##### `checkInputs` {#var-stdenv-checkInputs} 573 574A list of dependencies used by the phase. This gets included in `nativeBuildInputs` when `doCheck` is set. 575 576##### `preCheck` {#var-stdenv-preCheck} 577 578Hook executed at the start of the check phase. 579 580##### `postCheck` {#var-stdenv-postCheck} 581 582Hook executed at the end of the check phase. 583 584### The install phase {#ssec-install-phase} 585 586The install phase is responsible for installing the package in the Nix store under `out`. The default `installPhase` creates the directory `$out` and calls `make install`. 587 588#### Variables controlling the install phase 589 590##### `dontInstall` {#var-stdenv-dontInstall} 591 592Set to true to skip the install phase. 593 594##### `makeFlags` / `makeFlagsArray` / `makefile` 595 596See the [build phase](#var-stdenv-makeFlags) for details. 597 598##### `installTargets` {#var-stdenv-installTargets} 599 600The make targets that perform the installation. Defaults to `install`. Example: 601 602```nix 603installTargets = "install-bin install-doc"; 604``` 605 606##### `installFlags` / `installFlagsArray` {#var-stdenv-installFlags} 607 608A list of strings passed as additional flags to `make`. Like `makeFlags` and `makeFlagsArray`, but only used by the install phase. 609 610##### `preInstall` {#var-stdenv-preInstall} 611 612Hook executed at the start of the install phase. 613 614##### `postInstall` {#var-stdenv-postInstall} 615 616Hook executed at the end of the install phase. 617 618### The fixup phase {#ssec-fixup-phase} 619 620The fixup phase performs some (Nix-specific) post-processing actions on the files installed under `$out` by the install phase. The default `fixupPhase` does the following: 621 622- It moves the `man/`, `doc/` and `info/` subdirectories of `$out` to `share/`. 623- It strips libraries and executables of debug information. 624- On Linux, it applies the `patchelf` command to ELF executables and libraries to remove unused directories from the `RPATH` in order to prevent unnecessary runtime dependencies. 625- It rewrites the interpreter paths of shell scripts to paths found in `PATH`. E.g., `/usr/bin/perl` will be rewritten to `/nix/store/some-perl/bin/perl` found in `PATH`. 626 627#### Variables controlling the fixup phase 628 629##### `dontFixup` {#var-stdenv-dontFixup} 630 631Set to true to skip the fixup phase. 632 633##### `dontStrip` {#var-stdenv-dontStrip} 634 635If set, libraries and executables are not stripped. By default, they are. 636 637##### `dontStripHost` {#var-stdenv-dontStripHost} 638 639Like `dontStrip`, but only affects the `strip` command targetting the package’s host platform. Useful when supporting cross compilation, but otherwise feel free to ignore. 640 641##### `dontStripTarget` {#var-stdenv-dontStripTarget} 642 643Like `dontStrip`, but only affects the `strip` command targetting the packages’ target platform. Useful when supporting cross compilation, but otherwise feel free to ignore. 644 645##### `dontMoveSbin` {#var-stdenv-dontMoveSbin} 646 647If set, files in `$out/sbin` are not moved to `$out/bin`. By default, they are. 648 649##### `stripAllList` {#var-stdenv-stripAllList} 650 651List of directories to search for libraries and executables from which *all* symbols should be stripped. By default, it’s empty. Stripping all symbols is risky, since it may remove not just debug symbols but also ELF information necessary for normal execution. 652 653##### `stripAllFlags` {#var-stdenv-stripAllFlags} 654 655Flags passed to the `strip` command applied to the files in the directories listed in `stripAllList`. Defaults to `-s` (i.e. `--strip-all`). 656 657##### `stripDebugList` {#var-stdenv-stripDebugList} 658 659List of directories to search for libraries and executables from which only debugging-related symbols should be stripped. It defaults to `lib lib32 lib64 libexec bin sbin`. 660 661##### `stripDebugFlags` {#var-stdenv-stripDebugFlags} 662 663Flags passed to the `strip` command applied to the files in the directories listed in `stripDebugList`. Defaults to `-S` (i.e. `--strip-debug`). 664 665##### `dontPatchELF` {#var-stdenv-dontPatchELF} 666 667If set, the `patchelf` command is not used to remove unnecessary `RPATH` entries. Only applies to Linux. 668 669##### `dontPatchShebangs` {#var-stdenv-dontPatchShebangs} 670 671If set, scripts starting with `#!` do not have their interpreter paths rewritten to paths in the Nix store. 672 673##### `dontPruneLibtoolFiles` {#var-stdenv-dontPruneLibtoolFiles} 674 675If set, libtool `.la` files associated with shared libraries won’t have their `dependency_libs` field cleared. 676 677##### `forceShare` {#var-stdenv-forceShare} 678 679The list of directories that must be moved from `$out` to `$out/share`. Defaults to `man doc info`. 680 681##### `setupHook` {#var-stdenv-setupHook} 682 683A package can export a [setup hook](#ssec-setup-hooks) by setting this variable. The setup hook, if defined, is copied to `$out/nix-support/setup-hook`. Environment variables are then substituted in it using `substituteAll`. 684 685##### `preFixup` {#var-stdenv-preFixup} 686 687Hook executed at the start of the fixup phase. 688 689##### `postFixup` {#var-stdenv-postFixup} 690 691Hook executed at the end of the fixup phase. 692 693##### `separateDebugInfo` {#stdenv-separateDebugInfo} 694 695If set to `true`, the standard environment will enable debug information in C/C++ builds. After installation, the debug information will be separated from the executables and stored in the output named `debug`. (This output is enabled automatically; you don’t need to set the `outputs` attribute explicitly.) To be precise, the debug information is stored in `debug/lib/debug/.build-id/XX/YYYY…`, where \<XXYYYY…\> is the \<build ID\> of the binary — a SHA-1 hash of the contents of the binary. Debuggers like GDB use the build ID to look up the separated debug information. 696 697For example, with GDB, you can add 698 699``` 700set debug-file-directory ~/.nix-profile/lib/debug 701``` 702 703to `~/.gdbinit`. GDB will then be able to find debug information installed via `nix-env -i`. 704 705### The installCheck phase {#ssec-installCheck-phase} 706 707The installCheck phase checks whether the package was installed correctly by running its test suite against the installed directories. The default `installCheck` calls `make installcheck`. 708 709#### Variables controlling the installCheck phase 710 711##### `doInstallCheck` {#var-stdenv-doInstallCheck} 712 713Controls whether the installCheck phase is executed. By default it is skipped, but if `doInstallCheck` is set to true, the installCheck phase is usually executed. Thus you should set 714 715```nix 716doInstallCheck = true; 717``` 718 719in the derivation to enable install checks. The exception is cross compilation. Cross compiled builds never run tests, no matter how `doInstallCheck` is set, as the newly-built program won’t run on the platform used to build it. 720 721##### `installCheckTarget` {#var-stdenv-installCheckTarget} 722 723The make target that runs the install tests. Defaults to `installcheck`. 724 725##### `installCheckFlags` / `installCheckFlagsArray` {#var-stdenv-installCheckFlags} 726 727A list of strings passed as additional flags to `make`. Like `makeFlags` and `makeFlagsArray`, but only used by the installCheck phase. 728 729##### `installCheckInputs` {#var-stdenv-installCheckInputs} 730 731A list of dependencies used by the phase. This gets included in `nativeBuildInputs` when `doInstallCheck` is set. 732 733##### `preInstallCheck` {#var-stdenv-preInstallCheck} 734 735Hook executed at the start of the installCheck phase. 736 737##### `postInstallCheck` {#var-stdenv-postInstallCheck} 738 739Hook executed at the end of the installCheck phase. 740 741### The distribution phase {#ssec-distribution-phase} 742 743The distribution phase is intended to produce a source distribution of the package. The default `distPhase` first calls `make dist`, then it copies the resulting source tarballs to `$out/tarballs/`. This phase is only executed if the attribute `doDist` is set. 744 745#### Variables controlling the distribution phase 746 747##### `distTarget` {#var-stdenv-distTarget} 748 749The make target that produces the distribution. Defaults to `dist`. 750 751##### `distFlags` / `distFlagsArray` {#var-stdenv-distFlags} 752 753Additional flags passed to `make`. 754 755##### `tarballs` {#var-stdenv-tarballs} 756 757The names of the source distribution files to be copied to `$out/tarballs/`. It can contain shell wildcards. The default is `*.tar.gz`. 758 759##### `dontCopyDist` {#var-stdenv-dontCopyDist} 760 761If set, no files are copied to `$out/tarballs/`. 762 763##### `preDist` {#var-stdenv-preDist} 764 765Hook executed at the start of the distribution phase. 766 767##### `postDist` {#var-stdenv-postDist} 768 769Hook executed at the end of the distribution phase. 770 771## Shell functions {#ssec-stdenv-functions} 772 773The standard environment provides a number of useful functions. 774 775### `makeWrapper` \<executable\> \<wrapperfile\> \<args\> {#fun-makeWrapper} 776 777Constructs a wrapper for a program with various possible arguments. For example: 778 779```bash 780# adds `FOOBAR=baz` to `$out/bin/foo`’s environment 781makeWrapper $out/bin/foo $wrapperfile --set FOOBAR baz 782 783# prefixes the binary paths of `hello` and `git` 784# Be advised that paths often should be patched in directly 785# (via string replacements or in `configurePhase`). 786makeWrapper $out/bin/foo $wrapperfile --prefix PATH : ${lib.makeBinPath [ hello git ]} 787``` 788 789There’s many more kinds of arguments, they are documented in `nixpkgs/pkgs/build-support/setup-hooks/make-wrapper.sh`. 790 791`wrapProgram` is a convenience function you probably want to use most of the time. 792 793### `substitute` \<infile\> \<outfile\> \<subs\> {#fun-substitute} 794 795Performs string substitution on the contents of \<infile\>, writing the result to \<outfile\>. The substitutions in \<subs\> are of the following form: 796 797#### `--replace` \<s1\> \<s2\> 798 799Replace every occurrence of the string \<s1\> by \<s2\>. 800 801#### `--subst-var` \<varName\> 802 803Replace every occurrence of `@varName@` by the contents of the environment variable \<varName\>. This is useful for generating files from templates, using `@...@` in the template as placeholders. 804 805#### `--subst-var-by` \<varName\> \<s\> 806 807Replace every occurrence of `@varName@` by the string \<s\>. 808 809Example: 810 811```shell 812substitute ./foo.in ./foo.out \ 813 --replace /usr/bin/bar $bar/bin/bar \ 814 --replace "a string containing spaces" "some other text" \ 815 --subst-var someVar 816``` 817 818### `substituteInPlace` \<file\> \<subs\> {#fun-substituteInPlace} 819 820Like `substitute`, but performs the substitutions in place on the file \<file\>. 821 822### `substituteAll` \<infile\> \<outfile\> {#fun-substituteAll} 823 824Replaces every occurrence of `@varName@`, where \<varName\> is any environment variable, in \<infile\>, writing the result to \<outfile\>. For instance, if \<infile\> has the contents 825 826```bash 827#! @bash@/bin/sh 828PATH=@coreutils@/bin 829echo @foo@ 830``` 831 832and the environment contains `bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39` and `coreutils=/nix/store/68afga4khv0w...-coreutils-6.12`, but does not contain the variable `foo`, then the output will be 833 834```bash 835#! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh 836PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin 837echo @foo@ 838``` 839 840That is, no substitution is performed for undefined variables. 841 842Environment variables that start with an uppercase letter or an underscore are filtered out, to prevent global variables (like `HOME`) or private variables (like `__ETC_PROFILE_DONE`) from accidentally getting substituted. The variables also have to be valid bash "names", as defined in the bash manpage (alphanumeric or `_`, must not start with a number). 843 844### `substituteAllInPlace` \<file\> {#fun-substituteAllInPlace} 845 846Like `substituteAll`, but performs the substitutions in place on the file \<file\>. 847 848### `stripHash` \<path\> {#fun-stripHash} 849 850Strips the directory and hash part of a store path, outputting the name part to `stdout`. For example: 851 852```bash 853# prints coreutils-8.24 854stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24" 855``` 856 857If you wish to store the result in another variable, then the following idiom may be useful: 858 859```bash 860name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24" 861someVar=$(stripHash $name) 862``` 863 864### `wrapProgram` \<executable\> \<makeWrapperArgs\> {#fun-wrapProgram} 865 866Convenience function for `makeWrapper` that automatically creates a sane wrapper file. It takes all the same arguments as `makeWrapper`, except for `--argv0`. 867 868It cannot be applied multiple times, since it will overwrite the wrapper file. 869 870## Package setup hooks {#ssec-setup-hooks} 871 872Nix itself considers a build-time dependency as merely something that should previously be built and accessible at build time—packages themselves are on their own to perform any additional setup. In most cases, that is fine, and the downstream derivation can deal with its own dependencies. But for a few common tasks, that would result in almost every package doing the same sort of setup work—depending not on the package itself, but entirely on which dependencies were used. 873 874In order to alleviate this burden, the setup hook mechanism was written, where any package can include a shell script that \[by convention rather than enforcement by Nix\], any downstream reverse-dependency will source as part of its build process. That allows the downstream dependency to merely specify its dependencies, and lets those dependencies effectively initialize themselves. No boilerplate mirroring the list of dependencies is needed. 875 876The setup hook mechanism is a bit of a sledgehammer though: a powerful feature with a broad and indiscriminate area of effect. The combination of its power and implicit use may be expedient, but isn’t without costs. Nix itself is unchanged, but the spirit of added dependencies being effect-free is violated even if the letter isn’t. For example, if a derivation path is mentioned more than once, Nix itself doesn’t care and simply makes sure the dependency derivation is already built just the same—depending is just needing something to exist, and needing is idempotent. However, a dependency specified twice will have its setup hook run twice, and that could easily change the build environment (though a well-written setup hook will therefore strive to be idempotent so this is in fact not observable). More broadly, setup hooks are anti-modular in that multiple dependencies, whether the same or different, should not interfere and yet their setup hooks may well do so. 877 878The most typical use of the setup hook is actually to add other hooks which are then run (i.e. after all the setup hooks) on each dependency. For example, the C compiler wrapper’s setup hook feeds itself flags for each dependency that contains relevant libraries and headers. This is done by defining a bash function, and appending its name to one of `envBuildBuildHooks`, `envBuildHostHooks`, `envBuildTargetHooks`, `envHostHostHooks`, `envHostTargetHooks`, or `envTargetTargetHooks`. These 6 bash variables correspond to the 6 sorts of dependencies by platform (there’s 12 total but we ignore the propagated/non-propagated axis). 879 880Packages adding a hook should not hard code a specific hook, but rather choose a variable *relative* to how they are included. Returning to the C compiler wrapper example, if the wrapper itself is an `n` dependency, then it only wants to accumulate flags from `n + 1` dependencies, as only those ones match the compiler’s target platform. The `hostOffset` variable is defined with the current dependency’s host offset `targetOffset` with its target offset, before its setup hook is sourced. Additionally, since most environment hooks don’t care about the target platform, that means the setup hook can append to the right bash array by doing something like 881 882```{.bash} 883addEnvHooks "$hostOffset" myBashFunction 884``` 885 886The *existence* of setups hooks has long been documented and packages inside Nixpkgs are free to use this mechanism. Other packages, however, should not rely on these mechanisms not changing between Nixpkgs versions. Because of the existing issues with this system, there’s little benefit from mandating it be stable for any period of time. 887 888First, let’s cover some setup hooks that are part of Nixpkgs default stdenv. This means that they are run for every package built using `stdenv.mkDerivation`. Some of these are platform specific, so they may run on Linux but not Darwin or vice-versa. 889 890### `move-docs.sh` 891 892This setup hook moves any installed documentation to the `/share` subdirectory directory. This includes the man, doc and info directories. This is needed for legacy programs that do not know how to use the `share` subdirectory. 893 894### `compress-man-pages.sh` 895 896This setup hook compresses any man pages that have been installed. The compression is done using the gzip program. This helps to reduce the installed size of packages. 897 898### `strip.sh` 899 900This runs the strip command on installed binaries and libraries. This removes unnecessary information like debug symbols when they are not needed. This also helps to reduce the installed size of packages. 901 902### `patch-shebangs.sh` 903 904This setup hook patches installed scripts to use the full path to the shebang interpreter. A shebang interpreter is the first commented line of a script telling the operating system which program will run the script (e.g `#!/bin/bash`). In Nix, we want an exact path to that interpreter to be used. This often replaces `/bin/sh` with a path in the Nix store. 905 906### `audit-tmpdir.sh` 907 908This verifies that no references are left from the install binaries to the directory used to build those binaries. This ensures that the binaries do not need things outside the Nix store. This is currently supported in Linux only. 909 910### `multiple-outputs.sh` 911 912This setup hook adds configure flags that tell packages to install files into any one of the proper outputs listed in `outputs`. This behavior can be turned off by setting `setOutputFlags` to false in the derivation environment. See <xref linkend="chap-multiple-output" /> for more information. 913 914### `move-sbin.sh` 915 916This setup hook moves any binaries installed in the `sbin/` subdirectory into `bin/`. In addition, a link is provided from `sbin/` to `bin/` for compatibility. 917 918### `move-lib64.sh` 919 920This setup hook moves any libraries installed in the `lib64/` subdirectory into `lib/`. In addition, a link is provided from `lib64/` to `lib/` for compatibility. 921 922### `move-systemd-user-units.sh` 923 924This setup hook moves any systemd user units installed in the `lib/` subdirectory into `share/`. In addition, a link is provided from `share/` to `lib/` for compatibility. This is needed for systemd to find user services when installed into the user profile. 925 926### `set-source-date-epoch-to-latest.sh` 927 928This sets `SOURCE_DATE_EPOCH` to the modification time of the most recent file. 929 930### Bintools Wrapper 931 932The Bintools Wrapper wraps the binary utilities for a bunch of miscellaneous purposes. These are GNU Binutils when targetting Linux, and a mix of cctools and GNU binutils for Darwin. \[The “Bintools” name is supposed to be a compromise between “Binutils” and “cctools” not denoting any specific implementation.\] Specifically, the underlying bintools package, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the Bintools Wrapper. Packages typically depend on CC Wrapper, which in turn (at run time) depends on the Bintools Wrapper. 933 934The Bintools Wrapper was only just recently split off from CC Wrapper, so the division of labor is still being worked out. For example, it shouldn’t care about the C standard library, but just take a derivation with the dynamic loader (which happens to be the glibc on linux). Dependency finding however is a task both wrappers will continue to need to share, and probably the most important to understand. It is currently accomplished by collecting directories of host-platform dependencies (i.e. `buildInputs` and `nativeBuildInputs`) in environment variables. The Bintools Wrapper’s setup hook causes any `lib` and `lib64` subdirectories to be added to `NIX_LDFLAGS`. Since the CC Wrapper and the Bintools Wrapper use the same strategy, most of the Bintools Wrapper code is sparsely commented and refers to the CC Wrapper. But the CC Wrapper’s code, by contrast, has quite lengthy comments. The Bintools Wrapper merely cites those, rather than repeating them, to avoid falling out of sync. 935 936A final task of the setup hook is defining a number of standard environment variables to tell build systems which executables fulfill which purpose. They are defined to just be the base name of the tools, under the assumption that the Bintools Wrapper’s binaries will be on the path. Firstly, this helps poorly-written packages, e.g. ones that look for just `gcc` when `CC` isn’t defined yet `clang` is to be used. Secondly, this helps packages not get confused when cross-compiling, in which case multiple Bintools Wrappers may simultaneously be in use. [^footnote-stdenv-per-platform-wrapper] `BUILD_`- and `TARGET_`-prefixed versions of the normal environment variable are defined for additional Bintools Wrappers, properly disambiguating them. 937 938A problem with this final task is that the Bintools Wrapper is honest and defines `LD` as `ld`. Most packages, however, firstly use the C compiler for linking, secondly use `LD` anyways, defining it as the C compiler, and thirdly, only so define `LD` when it is undefined as a fallback. This triple-threat means Bintools Wrapper will break those packages, as LD is already defined as the actual linker which the package won’t override yet doesn’t want to use. The workaround is to define, just for the problematic package, `LD` as the C compiler. A good way to do this would be `preConfigure = "LD=$CC"`. 939 940### CC Wrapper 941 942The CC Wrapper wraps a C toolchain for a bunch of miscellaneous purposes. Specifically, a C compiler (GCC or Clang), wrapped binary tools, and a C standard library (glibc or Darwin’s libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by the CC Wrapper. Packages typically depend on the CC Wrapper, which in turn (at run-time) depends on the Bintools Wrapper. 943 944Dependency finding is undoubtedly the main task of the CC Wrapper. This works just like the Bintools Wrapper, except that any `include` subdirectory of any relevant dependency is added to `NIX_CFLAGS_COMPILE`. The setup hook itself contains some lengthy comments describing the exact convoluted mechanism by which this is accomplished. 945 946Similarly, the CC Wrapper follows the Bintools Wrapper in defining standard environment variables with the names of the tools it wraps, for the same reasons described above. Importantly, while it includes a `cc` symlink to the c compiler for portability, the `CC` will be defined using the compiler’s “real name” (i.e. `gcc` or `clang`). This helps lousy build systems that inspect on the name of the compiler rather than run it. 947 948Here are some more packages that provide a setup hook. Since the list of hooks is extensible, this is not an exhaustive list. The mechanism is only to be used as a last resort, so it might cover most uses. 949 950### Perl {#setup-hook-perl} 951 952Adds the `lib/site_perl` subdirectory of each build input to the `PERL5LIB` environment variable. For instance, if `buildInputs` contains Perl, then the `lib/site_perl` subdirectory of each input is added to the `PERL5LIB` environment variable. 953 954### Python {#setup-hook-python} 955 956Adds the `lib/${python.libPrefix}/site-packages` subdirectory of each build input to the `PYTHONPATH` environment variable. 957 958### pkg-config {#setup-hook-pkg-config} 959 960Adds the `lib/pkgconfig` and `share/pkgconfig` subdirectories of each build input to the `PKG_CONFIG_PATH` environment variable. 961 962### Automake {#setup-hook-automake} 963 964Adds the `share/aclocal` subdirectory of each build input to the `ACLOCAL_PATH` environment variable. 965 966### Autoconf {#setup-hook-autoconf} 967 968The `autoreconfHook` derivation adds `autoreconfPhase`, which runs autoreconf, libtoolize and automake, essentially preparing the configure script in autotools-based builds. Most autotools-based packages come with the configure script pre-generated, but this hook is necessary for a few packages and when you need to patch the package’s configure scripts. 969 970### libxml2 {#setup-hook-libxml2} 971 972Adds every file named `catalog.xml` found under the `xml/dtd` and `xml/xsl` subdirectories of each build input to the `XML_CATALOG_FILES` environment variable. 973 974### teTeX / TeX Live 975 976Adds the `share/texmf-nix` subdirectory of each build input to the `TEXINPUTS` environment variable. 977 978### Qt 4 979 980Sets the `QTDIR` environment variable to Qt’s path. 981 982### gdk-pixbuf {#setup-hook-gdk-pixbuf} 983 984Exports `GDK_PIXBUF_MODULE_FILE` environment variable to the builder. Add librsvg package to `buildInputs` to get svg support. See also the [setup hook description in GNOME platform docs](#ssec-gnome-hooks-gdk-pixbuf). 985 986### GHC 987 988Creates a temporary package database and registers every Haskell build input in it (TODO: how?). 989 990### GNOME platform 991 992Hooks related to GNOME platform and related libraries like GLib, GTK and GStreamer are described in <xref linkend="sec-language-gnome" />. 993 994### autoPatchelfHook {#setup-hook-autopatchelfhook} 995 996This is a special setup hook which helps in packaging proprietary software in that it automatically tries to find missing shared library dependencies of ELF files based on the given `buildInputs` and `nativeBuildInputs`. 997 998You can also specify a `runtimeDependencies` variable which lists dependencies to be unconditionally added to rpath of all executables. This is useful for programs that use dlopen 3 to load libraries at runtime. 999 1000In certain situations you may want to run the main command (`autoPatchelf`) of the setup hook on a file or a set of directories instead of unconditionally patching all outputs. This can be done by setting the `dontAutoPatchelf` environment variable to a non-empty value. 1001 1002By default `autoPatchelf` will fail as soon as any ELF file requires a dependency which cannot be resolved via the given build inputs. In some situations you might prefer to just leave missing dependencies unpatched and continue to patch the rest. This can be achieved by setting the `autoPatchelfIgnoreMissingDeps` environment variable to a non-empty value. 1003 1004The `autoPatchelf` command also recognizes a `--no-recurse` command line flag, which prevents it from recursing into subdirectories. 1005 1006### breakpointHook 1007 1008This hook will make a build pause instead of stopping when a failure happens. It prevents nix from cleaning up the build environment immediately and allows the user to attach to a build environment using the `cntr` command. Upon build error it will print instructions on how to use `cntr`, which can be used to enter the environment for debugging. Installing cntr and running the command will provide shell access to the build sandbox of failed build. At `/var/lib/cntr` the sandboxed filesystem is mounted. All commands and files of the system are still accessible within the shell. To execute commands from the sandbox use the cntr exec subcommand. `cntr` is only supported on Linux-based platforms. To use it first add `cntr` to your `environment.systemPackages` on NixOS or alternatively to the root user on non-NixOS systems. Then in the package that is supposed to be inspected, add `breakpointHook` to `nativeBuildInputs`. 1009 1010```nix 1011nativeBuildInputs = [ breakpointHook ]; 1012``` 1013 1014When a build failure happens there will be an instruction printed that shows how to attach with `cntr` to the build sandbox. 1015 1016::: note 1017::: title 1018Caution with remote builds 1019::: 1020 1021This won’t work with remote builds as the build environment is on a different machine and can’t be accessed by `cntr`. Remote builds can be turned off by setting `--option builders ''` for `nix-build` or `--builders ''` for `nix build`. 1022::: 1023 1024### installShellFiles 1025 1026This hook helps with installing manpages and shell completion files. It exposes 2 shell functions `installManPage` and `installShellCompletion` that can be used from your `postInstall` hook. 1027 1028The `installManPage` function takes one or more paths to manpages to install. The manpages must have a section suffix, and may optionally be compressed (with `.gz` suffix). This function will place them into the correct directory. 1029 1030The `installShellCompletion` function takes one or more paths to shell completion files. By default it will autodetect the shell type from the completion file extension, but you may also specify it by passing one of `--bash`, `--fish`, or `--zsh`. These flags apply to all paths listed after them (up until another shell flag is given). Each path may also have a custom installation name provided by providing a flag `--name NAME` before the path. If this flag is not provided, zsh completions will be renamed automatically such that `foobar.zsh` becomes `_foobar`. A root name may be provided for all paths using the flag `--cmd NAME`; this synthesizes the appropriate name depending on the shell (e.g. `--cmd foo` will synthesize the name `foo.bash` for bash and `_foo` for zsh). The path may also be a fifo or named fd (such as produced by `<(cmd)`), in which case the shell and name must be provided. 1031 1032```nix 1033nativeBuildInputs = [ installShellFiles ]; 1034postInstall = '' 1035 installManPage doc/foobar.1 doc/barfoo.3 1036 # explicit behavior 1037 installShellCompletion --bash --name foobar.bash share/completions.bash 1038 installShellCompletion --fish --name foobar.fish share/completions.fish 1039 installShellCompletion --zsh --name _foobar share/completions.zsh 1040 # implicit behavior 1041 installShellCompletion share/completions/foobar.{bash,fish,zsh} 1042 # using named fd 1043 installShellCompletion --cmd foobar \ 1044 --bash <($out/bin/foobar --bash-completion) \ 1045 --fish <($out/bin/foobar --fish-completion) \ 1046 --zsh <($out/bin/foobar --zsh-completion) 1047''; 1048``` 1049 1050### libiconv, libintl 1051 1052A few libraries automatically add to `NIX_LDFLAGS` their library, making their symbols automatically available to the linker. This includes libiconv and libintl (gettext). This is done to provide compatibility between GNU Linux, where libiconv and libintl are bundled in, and other systems where that might not be the case. Sometimes, this behavior is not desired. To disable this behavior, set `dontAddExtraLibs`. 1053 1054### validatePkgConfig 1055 1056The `validatePkgConfig` hook validates all pkg-config (`.pc`) files in a package. This helps catching some common errors in pkg-config files, such as undefined variables. 1057 1058### cmake 1059 1060Overrides the default configure phase to run the CMake command. By default, we use the Make generator of CMake. In addition, dependencies are added automatically to CMAKE_PREFIX_PATH so that packages are correctly detected by CMake. Some additional flags are passed in to give similar behavior to configure-based packages. You can disable this hook’s behavior by setting configurePhase to a custom value, or by setting dontUseCmakeConfigure. cmakeFlags controls flags passed only to CMake. By default, parallel building is enabled as CMake supports parallel building almost everywhere. When Ninja is also in use, CMake will detect that and use the ninja generator. 1061 1062### xcbuildHook 1063 1064Overrides the build and install phases to run the "xcbuild" command. This hook is needed when a project only comes with build files for the XCode build system. You can disable this behavior by setting buildPhase and configurePhase to a custom value. xcbuildFlags controls flags passed only to xcbuild. 1065 1066### Meson 1067 1068Overrides the configure phase to run meson to generate Ninja files. To run these files, you should accompany Meson with ninja. By default, `enableParallelBuilding` is enabled as Meson supports parallel building almost everywhere. 1069 1070#### Variables controlling Meson 1071 1072##### `mesonFlags` 1073 1074Controls the flags passed to meson. 1075 1076##### `mesonBuildType` 1077 1078Which [`--buildtype`](https://mesonbuild.com/Builtin-options.html#core-options) to pass to Meson. We default to `plain`. 1079 1080##### `mesonAutoFeatures` 1081 1082What value to set [`-Dauto_features=`](https://mesonbuild.com/Builtin-options.html#core-options) to. We default to `enabled`. 1083 1084##### `mesonWrapMode` 1085 1086What value to set [`-Dwrap_mode=`](https://mesonbuild.com/Builtin-options.html#core-options) to. We default to `nodownload` as we disallow network access. 1087 1088##### `dontUseMesonConfigure` 1089 1090Disables using Meson’s `configurePhase`. 1091 1092### ninja 1093 1094Overrides the build, install, and check phase to run ninja instead of make. You can disable this behavior with the `dontUseNinjaBuild`, `dontUseNinjaInstall`, and `dontUseNinjaCheck`, respectively. Parallel building is enabled by default in Ninja. 1095 1096### unzip 1097 1098This setup hook will allow you to unzip .zip files specified in `$src`. There are many similar packages like `unrar`, `undmg`, etc. 1099 1100### wafHook 1101 1102Overrides the configure, build, and install phases. This will run the “waf” script used by many projects. If `wafPath` (default `./waf`) doesn’t exist, it will copy the version of waf available in Nixpkgs. `wafFlags` can be used to pass flags to the waf script. 1103 1104### scons 1105 1106Overrides the build, install, and check phases. This uses the scons build system as a replacement for make. scons does not provide a configure phase, so everything is managed at build and install time. 1107 1108## Purity in Nixpkgs {#sec-purity-in-nixpkgs} 1109 1110*Measures taken to prevent dependencies on packages outside the store, and what you can do to prevent them.* 1111 1112GCC doesn’t search in locations such as `/usr/include`. In fact, attempts to add such directories through the `-I` flag are filtered out. Likewise, the linker (from GNU binutils) doesn’t search in standard locations such as `/usr/lib`. Programs built on Linux are linked against a GNU C Library that likewise doesn’t search in the default system locations. 1113 1114## Hardening in Nixpkgs {#sec-hardening-in-nixpkgs} 1115 1116There are flags available to harden packages at compile or link-time. These can be toggled using the `stdenv.mkDerivation` parameters `hardeningDisable` and `hardeningEnable`. 1117 1118Both parameters take a list of flags as strings. The special `"all"` flag can be passed to `hardeningDisable` to turn off all hardening. These flags can also be used as environment variables for testing or development purposes. 1119 1120The following flags are enabled by default and might require disabling with `hardeningDisable` if the program to package is incompatible. 1121 1122### `format` 1123 1124Adds the `-Wformat -Wformat-security -Werror=format-security` compiler options. At present, this warns about calls to `printf` and `scanf` functions where the format string is not a string literal and there are no format arguments, as in `printf(foo);`. This may be a security hole if the format string came from untrusted input and contains `%n`. 1125 1126This needs to be turned off or fixed for errors similar to: 1127 1128``` 1129/tmp/nix-build-zynaddsubfx-2.5.2.drv-0/zynaddsubfx-2.5.2/src/UI/guimain.cpp:571:28: error: format not a string literal and no format arguments [-Werror=format-security] 1130 printf(help_message); 1131 ^ 1132cc1plus: some warnings being treated as errors 1133``` 1134 1135### `stackprotector` 1136 1137Adds the `-fstack-protector-strong --param ssp-buffer-size=4` compiler options. This adds safety checks against stack overwrites rendering many potential code injection attacks into aborting situations. In the best case this turns code injection vulnerabilities into denial of service or into non-issues (depending on the application). 1138 1139This needs to be turned off or fixed for errors similar to: 1140 1141``` 1142bin/blib.a(bios_console.o): In function `bios_handle_cup': 1143/tmp/nix-build-ipxe-20141124-5cbdc41.drv-0/ipxe-5cbdc41/src/arch/i386/firmware/pcbios/bios_console.c:86: undefined reference to `__stack_chk_fail' 1144``` 1145 1146### `fortify` 1147 1148Adds the `-O2 -D_FORTIFY_SOURCE=2` compiler options. During code generation the compiler knows a great deal of information about buffer sizes (where possible), and attempts to replace insecure unlimited length buffer function calls with length-limited ones. This is especially useful for old, crufty code. Additionally, format strings in writable memory that contain `%n` are blocked. If an application depends on such a format string, it will need to be worked around. 1149 1150Additionally, some warnings are enabled which might trigger build failures if compiler warnings are treated as errors in the package build. In this case, set `NIX_CFLAGS_COMPILE` to `-Wno-error=warning-type`. 1151 1152This needs to be turned off or fixed for errors similar to: 1153 1154``` 1155malloc.c:404:15: error: return type is an incomplete type 1156malloc.c:410:19: error: storage size of 'ms' isn't known 1157 1158strdup.h:22:1: error: expected identifier or '(' before '__extension__' 1159 1160strsep.c:65:23: error: register name not specified for 'delim' 1161 1162installwatch.c:3751:5: error: conflicting types for '__open_2' 1163 1164fcntl2.h:50:4: error: call to '__open_missing_mode' declared with attribute error: open with O_CREAT or O_TMPFILE in second argument needs 3 arguments 1165``` 1166 1167### `pic` 1168 1169Adds the `-fPIC` compiler options. This options adds support for position independent code in shared libraries and thus making ASLR possible. 1170 1171Most notably, the Linux kernel, kernel modules and other code not running in an operating system environment like boot loaders won’t build with PIC enabled. The compiler will is most cases complain that PIC is not supported for a specific build. 1172 1173This needs to be turned off or fixed for assembler errors similar to: 1174 1175``` 1176ccbLfRgg.s: Assembler messages: 1177ccbLfRgg.s:33: Error: missing or invalid displacement expression `private_key_len@GOTOFF' 1178``` 1179 1180### `strictoverflow` 1181 1182Signed integer overflow is undefined behaviour according to the C standard. If it happens, it is an error in the program as it should check for overflow before it can happen, not afterwards. GCC provides built-in functions to perform arithmetic with overflow checking, which are correct and faster than any custom implementation. As a workaround, the option `-fno-strict-overflow` makes gcc behave as if signed integer overflows were defined. 1183 1184This flag should not trigger any build or runtime errors. 1185 1186### `relro` 1187 1188Adds the `-z relro` linker option. During program load, several ELF memory sections need to be written to by the linker, but can be turned read-only before turning over control to the program. This prevents some GOT (and .dtors) overwrite attacks, but at least the part of the GOT used by the dynamic linker (.got.plt) is still vulnerable. 1189 1190This flag can break dynamic shared object loading. For instance, the module systems of Xorg and OpenCV are incompatible with this flag. In almost all cases the `bindnow` flag must also be disabled and incompatible programs typically fail with similar errors at runtime. 1191 1192### `bindnow` 1193 1194Adds the `-z bindnow` linker option. During program load, all dynamic symbols are resolved, allowing for the complete GOT to be marked read-only (due to `relro`). This prevents GOT overwrite attacks. For very large applications, this can incur some performance loss during initial load while symbols are resolved, but this shouldn’t be an issue for daemons. 1195 1196This flag can break dynamic shared object loading. For instance, the module systems of Xorg and PHP are incompatible with this flag. Programs incompatible with this flag often fail at runtime due to missing symbols, like: 1197 1198``` 1199intel_drv.so: undefined symbol: vgaHWFreeHWRec 1200``` 1201 1202The following flags are disabled by default and should be enabled with `hardeningEnable` for packages that take untrusted input like network services. 1203 1204### `pie` 1205 1206Adds the `-fPIE` compiler and `-pie` linker options. Position Independent Executables are needed to take advantage of Address Space Layout Randomization, supported by modern kernel versions. While ASLR can already be enforced for data areas in the stack and heap (brk and mmap), the code areas must be compiled as position-independent. Shared libraries already do this with the `pic` flag, so they gain ASLR automatically, but binary .text regions need to be build with `pie` to gain ASLR. When this happens, ROP attacks are much harder since there are no static locations to bounce off of during a memory corruption attack. 1207 1208For more in-depth information on these hardening flags and hardening in general, refer to the [Debian Wiki](https://wiki.debian.org/Hardening), [Ubuntu Wiki](https://wiki.ubuntu.com/Security/Features), [Gentoo Wiki](https://wiki.gentoo.org/wiki/Project:Hardened), and the [Arch Wiki](https://wiki.archlinux.org/index.php/DeveloperWiki:Security). 1209 1210[^footnote-stdenv-ignored-build-platform]: The build platform is ignored because it is a mere implementation detail of the package satisfying the dependency: As a general programming principle, dependencies are always *specified* as interfaces, not concrete implementation. 1211[^footnote-stdenv-native-dependencies-in-path]: Currently, this means for native builds all dependencies are put on the `PATH`. But in the future that may not be the case for sake of matching cross: the platforms would be assumed to be unique for native and cross builds alike, so only the `depsBuild*` and `nativeBuildInputs` would be added to the `PATH`. 1212[^footnote-stdenv-find-inputs-location]: The `findInputs` function, currently residing in `pkgs/stdenv/generic/setup.sh`, implements the propagation logic. 1213[^footnote-stdenv-sys-lib-search-path]: It clears the `sys_lib_*search_path` variables in the Libtool script to prevent Libtool from using libraries in `/usr/lib` and such. 1214[^footnote-stdenv-build-time-guessing-impurity]: Eventually these will be passed building natively as well, to improve determinism: build-time guessing, as is done today, is a risk of impurity. 1215[^footnote-stdenv-per-platform-wrapper]: Each wrapper targets a single platform, so if binaries for multiple platforms are needed, the underlying binaries must be wrapped multiple times. As this is a property of the wrapper itself, the multiple wrappings are needed whether or not the same underlying binaries can target multiple platforms.