The Standard EnvironmentThe 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.Using
stdenvTo build a package with the standard environment, you use the
function stdenv.mkDerivation, instead of the
primitive built-in function derivation, e.g.
stdenv.mkDerivation {
name = "libfoo-1.2.3";
src = fetchurl {
url = http://example.org/libfoo-1.2.3.tar.bz2;
sha256 = "0x2g1jqygyr5wiwg4ma1nd7w4ydpy82z9gkcv8vh2v8dn3y58v5m";
};
}
(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 you need to do. Many
packages have dependencies that are not provided in the standard
environment. It’s usually sufficient to specify those dependencies in
the buildInputs attribute:
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
buildInputs = [libbar perl ncurses];
}
This 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 for
details.)Often 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 .)
For instance, a package that doesn’t supply a makefile but instead has
to be compiled “manually” could be handled like this:
stdenv.mkDerivation {
name = "fnord-4.5";
...
buildPhase = ''
gcc foo.c -o foo
'';
installPhase = ''
mkdir -p $out/bin
cp foo $out/bin
'';
}
(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.)There are many other attributes to customise the build. These
are listed in .While the standard environment provides a generic builder, you
can still supply your own build script:
stdenv.mkDerivation {
name = "libfoo-1.2.3";
...
builder = ./builder.sh;
}
where the builder can do anything it wants, but typically starts with
source $stdenv/setup
to let stdenv set up the environment (e.g., process
the buildInputs). If you want, you can still use
stdenv’s generic builder:
source $stdenv/setup
buildPhase() {
echo "... this is my custom build phase ..."
gcc foo.c -o foo
}
installPhase() {
mkdir -p $out/bin
cp foo $out/bin
}
genericBuild
Tools provided by
stdenvThe standard environment provides the following packages:
The GNU C Compiler, configured with C and C++
support.GNU coreutils (contains a few dozen standard Unix
commands).GNU findutils (contains
find).GNU diffutils (contains diff,
cmp).GNU sed.GNU grep.GNU awk.GNU tar.gzip, bzip2
and xz.GNU Make. It has been patched to provide
nested output that can be fed into the
nix-log2xml command and
log2html stylesheet to create a structured,
readable output of the build steps performed by
Make.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.The patch
command.On Linux, stdenv also includes the
patchelf utility.Specifying dependencies
As 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 for details.
Dependencies 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 for exactly what each platform means.
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.
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.
For now, the run-time/build-time distinction is just a hint for mental clarity, but in the future it perhaps could be enforced.
The 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. which run on the platform where the new derivation will be built.
Currently, that 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 nativeBuildDependencies dependencies would affect the PATH.
For each dependency dep of those dependencies, dep/bin, if present, is added to the PATH environment variable.
The 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.
It is important to note dependencies are not necessary 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 each sort of dependency two integers based one how it's host and target platforms are offset from the depending derivation's platforms.
Those offsets are given are given below in the descriptions of each dependency list attribute.
Algorithmically, we traverse propagated inputs, accumulating every propagated dep's propagated deps and adjusting them to account for the "shift in perspective" described by the current dep'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 deps whose combined offsets go out-of-bounds, which can be viewed as a filter over that transitive closure removing dependencies that are blatantly absurd.
We can define the process precisely with Natural Deduction using the inference rules.
This probably seems a bit obtuse, but so is the bash code that actually implements it!
The findInputs function, currently residing in pkgs/stdenv/generic/setup.sh, implements the propagation logic.
They're confusing in very different ways so...hopefully if something doesn't make sense in one presentation, it does in the other!
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
propagated-dep(h0, t0, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, 1}
-------------------------------------- Transitive property
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)
let mapOffset(h, t, i) = i + (if i <= 0 then h else t - 1)
dep(h0, _, A, B)
propagated-dep(h1, t1, B, C)
h0 + h1 in {-1, 0, 1}
h0 + t1 in {-1, 0, -1}
-------------------------------------- Take immediate deps' propagated deps
propagated-dep(mapOffset(h0, t0, h1),
mapOffset(h0, t0, t1),
A, C)
propagated-dep(h, t, A, B)
-------------------------------------- Propagated deps count as deps
dep(h, t, A, B)
Some 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:
let f(h, t, i) = i + (if i <= 0 then h else t - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else (h + 1) - 1)
let f(h, h + 1, i) = i + (if i <= 0 then h else h)
let f(h, h + 1, i) = i + h
This is where the "sum-like" comes from above:
We can just sum all the host offset to get the host offset of the transitive dependency.
The target offset is the transitive dep 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.
Because 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 dep 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.
Overall, the unifying theme here is that propagation shouldn't be introducing transitive dependencies involving platforms the needing package is unaware of.
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.
Variables specifying dependenciesdepsBuildBuild
A 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.
They are programs/libraries used at build time that furthermore produce programs/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 nativeBuildInputsinstead.
The most common use for 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.
Since these packages are able to be run at build time, that 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.
nativeBuildInputs
A 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.
They are programs/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 would be called depsBuildHost but for historical continuity.
Since these packages are able to be run at build time, that are added to the PATH, as described above.
But since these packages only are 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.
depsBuildTarget
A 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.
They are programs used at build time that produce code to run at run with code produced by the depending package.
Most commonly, these would tools used to build the runtime or standard library 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 the dependency is unconditional.
This is a somewhat confusing dependency to wrap ones head around, and for good reason.
As the only one where the platform offsets are not adjacent integers, it requires thinking of a bootstrapping stage two away from the current one.
It and it's use-case go hand in hand and are both considered poor form:
try not to need this sort dependency, and try not avoid building standard libraries / 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.
Since these packages are able to be run at build time, that are added to the PATH, as described above.
But since these packages only are 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.
depsHostHost
A list of dependencies whose host and target platforms match the new derivation's host platform.
This means a both 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, that would usually be tools used by compilers for metaprogramming/macro systems, or libraries used by the macros/metaprogramming code itself.
It's always preferable to use a depsBuildBuild dependency in the derivation being built than a depsHostHost on the tool doing the building for this purpose.
buildInputs
A list of dependencies whose host platform and target platform match the new derivation's.
This means a 0 host offset and 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.
These often are programs/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.
depsTargetTarget
A 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.
depsBuildBuildPropagated
The propagated equivalent of depsBuildBuild.
This perhaps never ought to be used, but it is included for consistency [see below for the others].
propagatedNativeBuildInputs
The 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.
depsBuildTargetPropagated
The propagated equivalent of depsBuildTarget.
This is prefixed for the same reason of alerting potential users.
depsHostHostPropagated
The propagated equivalent of depsHostHost.
propagatedBuildInputs
The propagated equivalent of buildInputs.
This would be called depsHostTargetPropagated but for historical continuity.
depsTargetTarget
The propagated equivalent of depsTargetTarget.
This is prefixed for the same reason of alerting potential users.
AttributesVariables affecting stdenv
initialisationNIX_DEBUG
A natural number indicating how much information to log.
If set to 1 or higher, stdenv will print moderate debug 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.
Variables affecting build propertiesenableParallelBuildingIf set to true, stdenv will
pass specific flags to make and other build tools to
enable parallel building with up to build-cores
workers.Unless set to false, some build systems with good
support for parallel building including cmake,
meson, and qmake will set it to
true.preferLocalBuildIf set, specifies that the package is so lightweight
in terms of build operations (e.g. write a text file from a Nix string
to the store) that there's no need to look for it in binary caches --
it's faster to just build it locally. It also tells Hydra and other
facilities that this package doesn't need to be exported in binary
caches (noone would use it, after all).Special variablespassthruThis is an attribute set which can be filled with arbitrary
values. For example:
passthru = {
foo = "bar";
baz = {
value1 = 4;
value2 = 5;
};
}
Values 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.PhasesThe 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.Each 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.
Controlling
phasesThere are a number of variables that control what phases are
executed and in what order:
Variables affecting phase controlphasesSpecifies 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 $preDistPhases
distPhase $postPhases.
Usually, 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.prePhasesAdditional phases executed before any of the default phases.preConfigurePhasesAdditional phases executed just before the configure phase.preBuildPhasesAdditional phases executed just before the build phase.preInstallPhasesAdditional phases executed just before the install phase.preFixupPhasesAdditional phases executed just before the fixup phase.preDistPhasesAdditional phases executed just before the distribution phase.postPhasesAdditional phases executed after any of the default
phases.The unpack phaseThe 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:
Tar filesThese can optionally be compressed using
gzip (.tar.gz,
.tgz or .tar.Z),
bzip2 (.tar.bz2 or
.tbz2) or xz
(.tar.xz or
.tar.lzma).Zip filesZip files are unpacked using
unzip. However, unzip is
not in the standard environment, so you should add it to
buildInputs yourself.Directories in the Nix storeThese 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.
Additional file types can be supported by setting the
unpackCmd variable (see below).Variables controlling the unpack phasesrcs / srcThe list of source files or directories to be
unpacked or copied. One of these must be set.sourceRootAfter 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.setSourceRootAlternatively 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.preUnpackHook executed at the start of the unpack
phase.postUnpackHook executed at the end of the unpack
phase.dontMakeSourcesWritableIf 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.unpackCmdThe unpack phase evaluates the string
$unpackCmd for any unrecognised file. The path
to the current source file is contained in the
curSrc variable.The patch phaseThe patch phase applies the list of patches defined in the
patches variable.Variables controlling the patch phasepatchesThe list of patches. They must be in the format
accepted by the patch command, and may
optionally be compressed using gzip
(.gz), bzip2
(.bz2) or xz
(.xz).patchFlagsFlags to be passed to patch.
If not set, the argument is used, which
causes the leading directory component to be stripped from the
file names in each patch.prePatchHook executed at the start of the patch
phase.postPatchHook executed at the end of the patch
phase.The configure phaseThe configure phase prepares the source tree for building. The
default configurePhase runs
./configure (typically an Autoconf-generated
script) if it exists.Variables controlling the configure phaseconfigureScriptThe name of the configure script. It defaults to
./configure if it exists; otherwise, the
configure phase is skipped. This can actually be a command (like
perl ./Configure.pl).configureFlagsA list of strings passed as additional arguments to the
configure script.configureFlagsArrayA shell array containing additional arguments
passed to the configure script. You must use this instead of
configureFlags if the arguments contain
spaces.dontAddPrefixBy default, the flag
--prefix=$prefix is added to the configure
flags. If this is undesirable, set this variable to
true.prefixThe prefix under which the package must be
installed, passed via the option to the
configure script. It defaults to
.dontAddDisableDepTrackBy 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.dontFixLibtoolBy 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 packagesIt clears the
sys_lib_*search_path
variables in the Libtool script to prevent Libtool from using
libraries in /usr/lib and
such.. If this is undesirable, set this
variable to true.dontDisableStaticBy default, when the configure script has
, the option
is added to the configure flags.If this is undesirable, set this variable to
true.configurePlatforms
By default, when cross compiling, the configure script has and passed.
Packages can instead pass [ "build" "host" "target" ] or a subset to control exactly which platform flags are passed.
Compilers and other tools should use this to also pass the target platform, for example.
Eventually these will be passed when in native builds too, to improve determinism: build-time guessing, as is done today, is a risk of impurity.preConfigureHook executed at the start of the configure
phase.postConfigureHook executed at the end of the configure
phase.The build phaseThe 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.Variables controlling the build phasedontBuildSet to true to skip the build phase.makefileThe file name of the Makefile.makeFlagsA 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).
makeFlags = [ "PREFIX=$(out)" ];
The flags are quoted in bash, but environment variables can
be specified by using the make syntax.makeFlagsArrayA shell array containing additional arguments
passed to make. You must use this instead of
makeFlags if the arguments contain
spaces, e.g.
makeFlagsArray=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar")
Note 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.buildFlags / buildFlagsArrayA list of strings passed as additional flags to
make. Like makeFlags and
makeFlagsArray, but only used by the build
phase.preBuildHook executed at the start of the build
phase.postBuildHook executed at the end of the build
phase.
You can set flags for make through the
makeFlags variable.Before and after running make, the hooks
preBuild and postBuild are
called, respectively.The check phaseThe 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.Variables controlling the check phasedoCheck
Controls 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 doCheck = true; in 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.
checkInputs
A list of dependencies used by the phase. This gets included in buildInputs when doCheck is set.
makeFlags /
makeFlagsArray /
makefileSee the build phase for details.checkTargetThe make target that runs the tests. Defaults to
check.checkFlags / checkFlagsArrayA list of strings passed as additional flags to
make. Like makeFlags and
makeFlagsArray, but only used by the check
phase.preCheckHook executed at the start of the check
phase.postCheckHook executed at the end of the check
phase.The install phaseThe 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.Variables controlling the install phasemakeFlags /
makeFlagsArray /
makefileSee the build phase for details.installTargetsThe make targets that perform the installation.
Defaults to install. Example:
installTargets = "install-bin install-doc";installFlags / installFlagsArrayA list of strings passed as additional flags to
make. Like makeFlags and
makeFlagsArray, but only used by the install
phase.preInstallHook executed at the start of the install
phase.postInstallHook executed at the end of the install
phase.The fixup phaseThe 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:
It moves the man/,
doc/ and info/
subdirectories of $out to
share/.It strips libraries and executables of debug
information.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.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.Variables controlling the fixup phasedontStripIf set, libraries and executables are not
stripped. By default, they are.dontStripHost
Like dontStripHost, but only affects the strip command targetting the package's host platform.
Useful when supporting cross compilation, but otherwise feel free to ignore.
dontStripTarget
Like dontStripHost, but only affects the strip command targetting the packages' target platform.
Useful when supporting cross compilation, but otherwise feel free to ignore.
dontMoveSbinIf set, files in $out/sbin are not moved
to $out/bin. By default, they are.stripAllListList 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.stripAllFlagsFlags passed to the strip
command applied to the files in the directories listed in
stripAllList. Defaults to
(i.e. ).stripDebugListList of directories to search for libraries and
executables from which only debugging-related symbols should be
stripped. It defaults to lib bin
sbin.stripDebugFlagsFlags passed to the strip
command applied to the files in the directories listed in
stripDebugList. Defaults to
(i.e. ).dontPatchELFIf set, the patchelf command is
not used to remove unnecessary RPATH entries.
Only applies to Linux.dontPatchShebangsIf set, scripts starting with
#! do not have their interpreter paths
rewritten to paths in the Nix store.forceShareThe list of directories that must be moved from
$out to $out/share.
Defaults to man doc info.setupHookA package can export a setup hook 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.preFixupHook executed at the start of the fixup
phase.postFixupHook executed at the end of the fixup
phase.separateDebugInfoIf 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.For example, with GDB, you can add
set debug-file-directory ~/.nix-profile/lib/debug
to ~/.gdbinit. GDB will then be able to find
debug information installed via nix-env
-i.The installCheck phaseThe installCheck phase checks whether the package was installed
correctly by running its test suite against the installed directories.
The default installCheck calls make
installcheck.Variables controlling the installCheck phasedoInstallCheck
Controls 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 doInstallCheck = true; in 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.
installCheckInputs
A list of dependencies used by the phase. This gets included in buildInputs when doInstallCheck is set.
preInstallCheckHook executed at the start of the installCheck
phase.postInstallCheckHook executed at the end of the installCheck
phase.The distribution
phaseThe 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.Variables controlling the distribution phasedistTargetThe make target that produces the distribution.
Defaults to dist.distFlags / distFlagsArrayAdditional flags passed to
make.tarballsThe names of the source distribution files to be
copied to $out/tarballs/. It can contain
shell wildcards. The default is
*.tar.gz.dontCopyDistIf set, no files are copied to
$out/tarballs/.preDistHook executed at the start of the distribution
phase.postDistHook executed at the end of the distribution
phase.Shell functionsThe standard environment provides a number of useful
functions.makeWrapperexecutablewrapperfileargsConstructs a wrapper for a program with various
possible arguments. For example:
# adds `FOOBAR=baz` to `$out/bin/foo`’s environment
makeWrapper $out/bin/foo $wrapperfile --set FOOBAR baz
# prefixes the binary paths of `hello` and `git`
# Be advised that paths often should be patched in directly
# (via string replacements or in `configurePhase`).
makeWrapper $out/bin/foo $wrapperfile --prefix PATH : ${lib.makeBinPath [ hello git ]}
There’s many more kinds of arguments, they are documented in
nixpkgs/pkgs/build-support/setup-hooks/make-wrapper.sh.wrapProgram is a convenience function you probably
want to use most of the time.substituteinfileoutfilesubsPerforms string substitution on the contents of
infile, writing the result to
outfile. The substitutions in
subs are of the following form:
s1s2Replace every occurrence of the string
s1 by
s2.varNameReplace 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.varNamesReplace every occurrence of
@varName@ by
the string s.Example:
substitute ./foo.in ./foo.out \
--replace /usr/bin/bar $bar/bin/bar \
--replace "a string containing spaces" "some other text" \
--subst-var someVar
substitute is implemented using the
replace
command. Unlike with the sed command, you
don’t have to worry about escaping special characters. It
supports performing substitutions on binary files (such as
executables), though there you’ll probably want to make sure
that the replacement string is as long as the replaced
string.substituteInPlacefilesubsLike substitute, but performs
the substitutions in place on the file
file.substituteAllinfileoutfileReplaces every occurrence of
@varName@, where
varName is any environment variable, in
infile, writing the result to
outfile. For instance, if
infile has the contents
#! @bash@/bin/sh
PATH=@coreutils@/bin
echo @foo@
and the environment contains
bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39
and
coreutils=/nix/store/68afga4khv0w...-coreutils-6.12,
but does not contain the variable foo, then the
output will be
#! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh
PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin
echo @foo@
That is, no substitution is performed for undefined variables.Environment variables that start with an uppercase letter or an
underscore are filtered out,
to prevent global variables (like HOME) or private
variables (like __ETC_PROFILE_DONE) from accidentally
getting substituted.
The variables also have to be valid bash “names”, as
defined in the bash manpage (alphanumeric or _,
must not start with a number).substituteAllInPlacefileLike substituteAll, but performs
the substitutions in place on the file
file.stripHashpathStrips the directory and hash part of a store
path, outputting the name part to stdout.
For example:
# prints coreutils-8.24
stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
If you wish to store the result in another variable, then the
following idiom may be useful:
name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24"
someVar=$(stripHash $name)
wrapProgramexecutablemakeWrapperArgsConvenience function for makeWrapper
that automatically creates a sane wrapper file
It takes all the same arguments as makeWrapper,
except for --argv0.It cannot be applied multiple times, since it will overwrite the wrapper
file.Package setup hooks
Nix itself considers a build-time dependency 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 it's 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.
In 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.
The 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 adding 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.
The 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 libaries 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).
Packages 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 it 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 it's 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
addEnvHooks "$hostOffset" myBashFunction
The existence of setups hooks has long been documented and packages inside Nixpkgs are free to use these 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.
Here are some packages that provide a setup hook.
Since the mechanism is modular, this probably isn't an exhaustive list.
Then again, since the mechanism is only to be used as a last resort, it might be.
Bintools Wrapper
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 Bintools Wrapper.
Packages typically depend on CC Wrapper, which in turn (at run time) depends on Bintools Wrapper.
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 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.
Bintools Wrapper's setup hook causes any lib and lib64 subdirectories to be added to NIX_LDFLAGS.
Since CC Wrapper and Bintools Wrapper use the same strategy, most of the Bintools Wrapper code is sparsely commented and refers to CC Wrapper.
But CC Wrapper's code, by contrast, has quite lengthy comments.
Bintools Wrapper merely cites those, rather than repeating them, to avoid falling out of sync.
A final task of the setup hook is defining a number of standard environment variables to tell build systems which executables full-fill which purpose.
They are defined to just be the base name of the tools, under the assumption that 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.
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.
BUILD_- and TARGET_-prefixed versions of the normal environment variable are defined for the additional Bintools Wrappers, properly disambiguating them.
A problem with this final task is that 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=$CC".
CC Wrapper
CC Wrapper wraps a C toolchain for a bunch of miscellaneous purposes.
Specifically, a C compiler (GCC or Clang), wrapped binary tools, and a C standard library (glibc or Darwin's libSystem, just for the dynamic loader) are all fed in, and dependency finding, hardening (see below), and purity checks for each are handled by CC Wrapper.
Packages typically depend on CC Wrapper, which in turn (at run time) depends on Bintools Wrapper.
Dependency finding is undoubtedly the main task of CC Wrapper.
This works just like Bintools Wrapper, except that any include subdirectory of any relevant dependency is added to NIX_CFLAGS_COMPILE.
The setup hook itself contains some lengthy comments describing the exact convoluted mechanism by which this is accomplished.
CC Wrapper also like Bintools Wrapper defines standard environment variables with the names of the tools it wraps, for the same reasons described above.
Importantly, while it includes a cc symlink to the c compiler for portability, the CC will be defined using the compiler's "real name" (i.e. gcc or clang).
This helps lousy build systems that inspect on the name of the compiler rather than run it.
Perl
Adds the lib/site_perl subdirectory of each build input to the PERL5LIB environment variable.
For instance, if buildInputs contains Perl, then the lib/site_perl subdirectory of each input is added to the PERL5LIB environment variable.
PythonAdds the
lib/${python.libPrefix}/site-packages subdirectory of
each build input to the PYTHONPATH environment
variable.pkg-configAdds the lib/pkgconfig and
share/pkgconfig subdirectories of each
build input to the PKG_CONFIG_PATH environment
variable.AutomakeAdds the share/aclocal
subdirectory of each build input to the ACLOCAL_PATH
environment variable.AutoconfThe autoreconfHook derivation adds
autoreconfPhase, which runs autoreconf, libtoolize and
automake, essentially preparing the configure script in autotools-based
builds.libxml2Adds 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.teTeX / TeX LiveAdds the share/texmf-nix
subdirectory of each build input to the TEXINPUTS
environment variable.Qt 4Sets the QTDIR environment variable
to Qt’s path.gdk-pixbufExports GDK_PIXBUF_MODULE_FILE
environment variable the the builder. Add librsvg package
to buildInputs to get svg support.GHCCreates a temporary package database and registers
every Haskell build input in it (TODO: how?).GStreamerAdds the
GStreamer plugins subdirectory of
each build input to the GST_PLUGIN_SYSTEM_PATH_1_0 or
GST_PLUGIN_SYSTEM_PATH environment variable.paxctlDefines the paxmark helper for
setting per-executable PaX flags on Linux (where it is available by
default; on all other platforms, paxmark is a no-op).
For example, to disable secure memory protections on the executable
foo:
postFixup = ''
paxmark m $out/bin/foo
'';
The m flag is the most common flag and is typically
required for applications that employ JIT compilation or otherwise need to
execute code generated at run-time. Disabling PaX protections should be
considered a last resort: if possible, problematic features should be
disabled or patched to work with PaX.autoPatchelfHookThis 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. All packages within the
runtimeDependencies environment variable are unconditionally
added to executables, which is useful for programs that use
dlopen3
to load libraries at runtime.Purity in Nixpkgs[measures taken to prevent dependencies on packages outside the
store, and what you can do to prevent them]GCC doesn't search in locations such as
/usr/include. In fact, attempts to add such
directories through the 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.Hardening in NixpkgsThere are flags available to harden packages at compile or link-time.
These can be toggled using the stdenv.mkDerivation parameters
hardeningDisable and hardeningEnable.
Both 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.
The following flags are enabled by default and might require disabling with
hardeningDisable if the program to package is incompatible.
formatAdds the 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.This needs to be turned off or fixed for errors similar to:
/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]
printf(help_message);
^
cc1plus: some warnings being treated as errors
stackprotectorAdds the
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).This needs to be turned off or fixed for errors similar to:
bin/blib.a(bios_console.o): In function `bios_handle_cup':
/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'
fortifyAdds the 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.
Additionally, some warnings are enabled which might trigger build
failures if compiler warnings are treated as errors in the package build.
In this case, set to
.This needs to be turned off or fixed for errors similar to:
malloc.c:404:15: error: return type is an incomplete type
malloc.c:410:19: error: storage size of 'ms' isn't known
strdup.h:22:1: error: expected identifier or '(' before '__extension__'
strsep.c:65:23: error: register name not specified for 'delim'
installwatch.c:3751:5: error: conflicting types for '__open_2'
fcntl2.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
picAdds the compiler options. This options adds
support for position independent code in shared libraries and thus making
ASLR possible.Most 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.
This needs to be turned off or fixed for assembler errors similar to:
ccbLfRgg.s: Assembler messages:
ccbLfRgg.s:33: Error: missing or invalid displacement expression `private_key_len@GOTOFF'
strictoverflowSigned 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
makes gcc behave as if signed
integer overflows were defined.
This flag should not trigger any build or runtime errors.relroAdds the 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.
This 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.bindnowAdds the 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.
This 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:
intel_drv.so: undefined symbol: vgaHWFreeHWRec
The following flags are disabled by default and should be enabled
with hardeningEnable for packages that take untrusted
input like network services.
pieAdds the compiler and
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.
For more in-depth information on these hardening flags and hardening in
general, refer to the
Debian Wiki,
Ubuntu Wiki,
Gentoo Wiki,
and the
Arch Wiki.