<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="chap-stdenv"> <title>The Standard Environment</title> <para>The 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 <literal>./configure; make; make install</literal> build interface, you don’t need to write a build script at all; the standard environment does everything automatically. If <literal>stdenv</literal> doesn’t do what you need automatically, you can easily customise or override the various build phases.</para> <section xml:id="sec-using-stdenv"><title>Using <literal>stdenv</literal></title> <para>To build a package with the standard environment, you use the function <varname>stdenv.mkDerivation</varname>, instead of the primitive built-in function <varname>derivation</varname>, e.g. <programlisting> stdenv.mkDerivation { name = "libfoo-1.2.3"; src = fetchurl { url = http://example.org/libfoo-1.2.3.tar.bz2; sha256 = "0x2g1jqygyr5wiwg4ma1nd7w4ydpy82z9gkcv8vh2v8dn3y58v5m"; }; }</programlisting> (<varname>stdenv</varname> needs to be in scope, so if you write this in a separate Nix expression from <filename>pkgs/all-packages.nix</filename>, you need to pass it as a function argument.) Specifying a <varname>name</varname> and a <varname>src</varname> 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 <varname>buildInputs</varname> attribute: <programlisting> stdenv.mkDerivation { name = "libfoo-1.2.3"; ... buildInputs = [libbar perl ncurses]; }</programlisting> This attribute ensures that the <filename>bin</filename> subdirectories of these packages appear in the <envar>PATH</envar> environment variable during the build, that their <filename>include</filename> subdirectories are searched by the C compiler, and so on. (See <xref linkend="ssec-setup-hooks"/> for details.)</para> <para>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 <emphasis>phases</emphasis>, 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: <programlisting> stdenv.mkDerivation { name = "fnord-4.5"; ... buildPhase = '' gcc foo.c -o foo ''; installPhase = '' mkdir -p $out/bin cp foo $out/bin ''; }</programlisting> (Note the use of <literal>''</literal>-style string literals, which are very convenient for large multi-line script fragments because they don’t need escaping of <literal>"</literal> and <literal>\</literal>, and because indentation is intelligently removed.)</para> <para>There are many other attributes to customise the build. These are listed in <xref linkend="ssec-stdenv-attributes"/>.</para> <para>While the standard environment provides a generic builder, you can still supply your own build script: <programlisting> stdenv.mkDerivation { name = "libfoo-1.2.3"; ... builder = ./builder.sh; }</programlisting> where the builder can do anything it wants, but typically starts with <programlisting> source $stdenv/setup </programlisting> to let <literal>stdenv</literal> set up the environment (e.g., process the <varname>buildInputs</varname>). If you want, you can still use <literal>stdenv</literal>’s generic builder: <programlisting> 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 </programlisting> </para> </section> <section xml:id="sec-tools-of-stdenv"><title>Tools provided by <literal>stdenv</literal></title> <para>The standard environment provides the following packages: <itemizedlist> <listitem><para>The GNU C Compiler, configured with C and C++ support.</para></listitem> <listitem><para>GNU coreutils (contains a few dozen standard Unix commands).</para></listitem> <listitem><para>GNU findutils (contains <command>find</command>).</para></listitem> <listitem><para>GNU diffutils (contains <command>diff</command>, <command>cmp</command>).</para></listitem> <listitem><para>GNU <command>sed</command>.</para></listitem> <listitem><para>GNU <command>grep</command>.</para></listitem> <listitem><para>GNU <command>awk</command>.</para></listitem> <listitem><para>GNU <command>tar</command>.</para></listitem> <listitem><para><command>gzip</command>, <command>bzip2</command> and <command>xz</command>.</para></listitem> <listitem><para>GNU Make. It has been patched to provide <quote>nested</quote> output that can be fed into the <command>nix-log2xml</command> command and <command>log2html</command> stylesheet to create a structured, readable output of the build steps performed by Make.</para></listitem> <listitem><para>Bash. This is the shell used for all builders in the Nix Packages collection. Not using <command>/bin/sh</command> removes a large source of portability problems.</para></listitem> <listitem><para>The <command>patch</command> command.</para></listitem> </itemizedlist> </para> <para>On Linux, <literal>stdenv</literal> also includes the <command>patchelf</command> utility.</para> </section> <section xml:id="ssec-stdenv-attributes"><title>Attributes</title> <variablelist> <title>Variables affecting <literal>stdenv</literal> initialisation</title> <varlistentry> <term><varname>NIX_DEBUG</varname></term> <listitem><para>If set, <literal>stdenv</literal> will print some debug information during the build. In particular, the <command>gcc</command> and <command>ld</command> wrapper scripts will print out the complete command line passed to the wrapped tools.</para></listitem> </varlistentry> <varlistentry> <term><varname>buildInputs</varname></term> <listitem><para>A list of dependencies used by <literal>stdenv</literal> to set up the environment for the build. For each dependency <replaceable>dir</replaceable>, the directory <filename><replaceable>dir</replaceable>/bin</filename>, if it exists, is added to the <envar>PATH</envar> environment variable. Other environment variables are also set up via a pluggable mechanism. For instance, if <varname>buildInputs</varname> contains Perl, then the <filename>lib/site_perl</filename> subdirectory of each input is added to the <envar>PERL5LIB</envar> environment variable. See <xref linkend="ssec-setup-hooks"/> for details.</para></listitem> </varlistentry> <varlistentry> <term><varname>propagatedBuildInputs</varname></term> <listitem><para>Like <varname>buildInputs</varname>, but these dependencies are <emphasis>propagated</emphasis>: that is, the dependencies listed here are added to the <varname>buildInputs</varname> of any package that uses <emphasis>this</emphasis> package as a dependency. So if package Y has <literal>propagatedBuildInputs = [X]</literal>, and package Z has <literal>buildInputs = [Y]</literal>, then package X will appear in Z’s build environment automatically.</para></listitem> </varlistentry> </variablelist> <variablelist> <title>Variables affecting build properties</title> <varlistentry> <term><varname>enableParallelBuilding</varname></term> <listitem><para>If set, <literal>stdenv</literal> will pass specific flags to <literal>make</literal> and other build tools to enable parallel building with up to <literal>build-cores</literal> workers.</para></listitem> </varlistentry> <varlistentry> <term><varname>preferLocalBuild</varname></term> <listitem><para>If 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).</para></listitem> </varlistentry> </variablelist> <variablelist> <title>Special variables</title> <varlistentry> <term><varname>passthru</varname></term> <listitem><para>This is an attribute set which can be filled with arbitrary values. For example: <programlisting> passthru = { foo = "bar"; baz = { value1 = 4; value2 = 5; }; } </programlisting> </para> <para>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. <literal>hello.baz.value1</literal>. We don't specify any usage or schema of <literal>passthru</literal> - 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.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="sec-stdenv-phases"><title>Phases</title> <para>The generic builder has a number of <emphasis>phases</emphasis>. 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.</para> <para>Each phase can be overridden in its entirety either by setting the environment variable <varname><replaceable>name</replaceable>Phase</varname> to a string containing some shell commands to be executed, or by redefining the shell function <varname><replaceable>name</replaceable>Phase</varname>. The former is convenient to override a phase from the derivation, while the latter is convenient from a build script.</para> <section xml:id="ssec-controlling-phases"><title>Controlling phases</title> <para>There are a number of variables that control what phases are executed and in what order: <variablelist> <title>Variables affecting phase control</title> <varlistentry> <term><varname>phases</varname></term> <listitem> <para>Specifies 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 <literal>$prePhases unpackPhase patchPhase $preConfigurePhases configurePhase $preBuildPhases buildPhase checkPhase $preInstallPhases installPhase fixupPhase $preDistPhases distPhase $postPhases</literal>. </para> <para>Usually, if you just want to add a few phases, it’s more convenient to set one of the variables below (such as <varname>preInstallPhases</varname>), as you then don’t specify all the normal phases.</para> </listitem> </varlistentry> <varlistentry> <term><varname>prePhases</varname></term> <listitem> <para>Additional phases executed before any of the default phases.</para> </listitem> </varlistentry> <varlistentry> <term><varname>preConfigurePhases</varname></term> <listitem> <para>Additional phases executed just before the configure phase.</para> </listitem> </varlistentry> <varlistentry> <term><varname>preBuildPhases</varname></term> <listitem> <para>Additional phases executed just before the build phase.</para> </listitem> </varlistentry> <varlistentry> <term><varname>preInstallPhases</varname></term> <listitem> <para>Additional phases executed just before the install phase.</para> </listitem> </varlistentry> <varlistentry> <term><varname>preFixupPhases</varname></term> <listitem> <para>Additional phases executed just before the fixup phase.</para> </listitem> </varlistentry> <varlistentry> <term><varname>preDistPhases</varname></term> <listitem> <para>Additional phases executed just before the distribution phase.</para> </listitem> </varlistentry> <varlistentry> <term><varname>postPhases</varname></term> <listitem> <para>Additional phases executed after any of the default phases.</para> </listitem> </varlistentry> </variablelist> </para> </section> <section xml:id="ssec-unpack-phase"><title>The unpack phase</title> <para>The unpack phase is responsible for unpacking the source code of the package. The default implementation of <function>unpackPhase</function> unpacks the source files listed in the <envar>src</envar> environment variable to the current directory. It supports the following files by default: <variablelist> <varlistentry> <term>Tar files</term> <listitem><para>These can optionally be compressed using <command>gzip</command> (<filename>.tar.gz</filename>, <filename>.tgz</filename> or <filename>.tar.Z</filename>), <command>bzip2</command> (<filename>.tar.bz2</filename> or <filename>.tbz2</filename>) or <command>xz</command> (<filename>.tar.xz</filename> or <filename>.tar.lzma</filename>).</para></listitem> </varlistentry> <varlistentry> <term>Zip files</term> <listitem><para>Zip files are unpacked using <command>unzip</command>. However, <command>unzip</command> is not in the standard environment, so you should add it to <varname>buildInputs</varname> yourself.</para></listitem> </varlistentry> <varlistentry> <term>Directories in the Nix store</term> <listitem><para>These are simply copied to the current directory. The hash part of the file name is stripped, e.g. <filename>/nix/store/1wydxgby13cz...-my-sources</filename> would be copied to <filename>my-sources</filename>.</para></listitem> </varlistentry> </variablelist> Additional file types can be supported by setting the <varname>unpackCmd</varname> variable (see below).</para> <para></para> <variablelist> <title>Variables controlling the unpack phase</title> <varlistentry> <term><varname>srcs</varname> / <varname>src</varname></term> <listitem><para>The list of source files or directories to be unpacked or copied. One of these must be set.</para></listitem> </varlistentry> <varlistentry> <term><varname>sourceRoot</varname></term> <listitem><para>After running <function>unpackPhase</function>, the generic builder changes the current directory to the directory created by unpacking the sources. If there are multiple source directories, you should set <varname>sourceRoot</varname> to the name of the intended directory.</para></listitem> </varlistentry> <varlistentry> <term><varname>setSourceRoot</varname></term> <listitem><para>Alternatively to setting <varname>sourceRoot</varname>, you can set <varname>setSourceRoot</varname> to a shell command to be evaluated by the unpack phase after the sources have been unpacked. This command must set <varname>sourceRoot</varname>.</para></listitem> </varlistentry> <varlistentry> <term><varname>preUnpack</varname></term> <listitem><para>Hook executed at the start of the unpack phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postUnpack</varname></term> <listitem><para>Hook executed at the end of the unpack phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontMakeSourcesWritable</varname></term> <listitem><para>If set to <literal>1</literal>, the unpacked sources are <emphasis>not</emphasis> 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.</para></listitem> </varlistentry> <varlistentry> <term><varname>unpackCmd</varname></term> <listitem><para>The unpack phase evaluates the string <literal>$unpackCmd</literal> for any unrecognised file. The path to the current source file is contained in the <varname>curSrc</varname> variable.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-patch-phase"><title>The patch phase</title> <para>The patch phase applies the list of patches defined in the <varname>patches</varname> variable.</para> <variablelist> <title>Variables controlling the patch phase</title> <varlistentry> <term><varname>patches</varname></term> <listitem><para>The list of patches. They must be in the format accepted by the <command>patch</command> command, and may optionally be compressed using <command>gzip</command> (<filename>.gz</filename>), <command>bzip2</command> (<filename>.bz2</filename>) or <command>xz</command> (<filename>.xz</filename>).</para></listitem> </varlistentry> <varlistentry> <term><varname>patchFlags</varname></term> <listitem><para>Flags to be passed to <command>patch</command>. If not set, the argument <option>-p1</option> is used, which causes the leading directory component to be stripped from the file names in each patch.</para></listitem> </varlistentry> <varlistentry> <term><varname>prePatch</varname></term> <listitem><para>Hook executed at the start of the patch phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postPatch</varname></term> <listitem><para>Hook executed at the end of the patch phase.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-configure-phase"><title>The configure phase</title> <para>The configure phase prepares the source tree for building. The default <function>configurePhase</function> runs <filename>./configure</filename> (typically an Autoconf-generated script) if it exists.</para> <variablelist> <title>Variables controlling the configure phase</title> <varlistentry> <term><varname>configureScript</varname></term> <listitem><para>The name of the configure script. It defaults to <filename>./configure</filename> if it exists; otherwise, the configure phase is skipped. This can actually be a command (like <literal>perl ./Configure.pl</literal>).</para></listitem> </varlistentry> <varlistentry> <term><varname>configureFlags</varname></term> <listitem><para>A list of strings passed as additional arguments to the configure script.</para></listitem> </varlistentry> <varlistentry> <term><varname>configureFlagsArray</varname></term> <listitem><para>A shell array containing additional arguments passed to the configure script. You must use this instead of <varname>configureFlags</varname> if the arguments contain spaces.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontAddPrefix</varname></term> <listitem><para>By default, the flag <literal>--prefix=$prefix</literal> is added to the configure flags. If this is undesirable, set this variable to true.</para></listitem> </varlistentry> <varlistentry> <term><varname>prefix</varname></term> <listitem><para>The prefix under which the package must be installed, passed via the <option>--prefix</option> option to the configure script. It defaults to <option>$out</option>.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontAddDisableDepTrack</varname></term> <listitem><para>By default, the flag <literal>--disable-dependency-tracking</literal> is added to the configure flags to speed up Automake-based builds. If this is undesirable, set this variable to true.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontFixLibtool</varname></term> <listitem><para>By default, the configure phase applies some special hackery to all files called <filename>ltmain.sh</filename> before running the configure script in order to improve the purity of Libtool-based packages<footnote><para>It clears the <varname>sys_lib_<replaceable>*</replaceable>search_path</varname> variables in the Libtool script to prevent Libtool from using libraries in <filename>/usr/lib</filename> and such.</para></footnote>. If this is undesirable, set this variable to true.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontDisableStatic</varname></term> <listitem><para>By default, when the configure script has <option>--enable-static</option>, the option <option>--disable-static</option> is added to the configure flags.</para> <para>If this is undesirable, set this variable to true.</para></listitem> </varlistentry> <varlistentry> <term><varname>preConfigure</varname></term> <listitem><para>Hook executed at the start of the configure phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postConfigure</varname></term> <listitem><para>Hook executed at the end of the configure phase.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="build-phase"><title>The build phase</title> <para>The build phase is responsible for actually building the package (e.g. compiling it). The default <function>buildPhase</function> simply calls <command>make</command> if a file named <filename>Makefile</filename>, <filename>makefile</filename> or <filename>GNUmakefile</filename> exists in the current directory (or the <varname>makefile</varname> is explicitly set); otherwise it does nothing.</para> <variablelist> <title>Variables controlling the build phase</title> <varlistentry> <term><varname>dontBuild</varname></term> <listitem><para>Set to true to skip the build phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>makefile</varname></term> <listitem><para>The file name of the Makefile.</para></listitem> </varlistentry> <varlistentry> <term><varname>makeFlags</varname></term> <listitem><para>A list of strings passed as additional flags to <command>make</command>. These flags are also used by the default install and check phase. For setting make flags specific to the build phase, use <varname>buildFlags</varname> (see below).</para></listitem> </varlistentry> <varlistentry> <term><varname>makeFlagsArray</varname></term> <listitem><para>A shell array containing additional arguments passed to <command>make</command>. You must use this instead of <varname>makeFlags</varname> if the arguments contain spaces, e.g. <programlisting> makeFlagsArray=(CFLAGS="-O0 -g" LDFLAGS="-lfoo -lbar") </programlisting> Note that shell arrays cannot be passed through environment variables, so you cannot set <varname>makeFlagsArray</varname> in a derivation attribute (because those are passed through environment variables): you have to define them in shell code.</para></listitem> </varlistentry> <varlistentry> <term><varname>buildFlags</varname> / <varname>buildFlagsArray</varname></term> <listitem><para>A list of strings passed as additional flags to <command>make</command>. Like <varname>makeFlags</varname> and <varname>makeFlagsArray</varname>, but only used by the build phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>preBuild</varname></term> <listitem><para>Hook executed at the start of the build phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postBuild</varname></term> <listitem><para>Hook executed at the end of the build phase.</para></listitem> </varlistentry> </variablelist> <para> You can set flags for <command>make</command> through the <varname>makeFlags</varname> variable.</para> <para>Before and after running <command>make</command>, the hooks <varname>preBuild</varname> and <varname>postBuild</varname> are called, respectively.</para> </section> <section xml:id="ssec-check-phase"><title>The check phase</title> <para>The check phase checks whether the package was built correctly by running its test suite. The default <function>checkPhase</function> calls <command>make check</command>, but only if the <varname>doCheck</varname> variable is enabled.</para> <variablelist> <title>Variables controlling the check phase</title> <varlistentry> <term><varname>doCheck</varname></term> <listitem><para>If set to a non-empty string, the check phase is executed, otherwise it is skipped (default). Thus you should set <programlisting> doCheck = true;</programlisting> in the derivation to enable checks.</para></listitem> </varlistentry> <varlistentry> <term><varname>makeFlags</varname> / <varname>makeFlagsArray</varname> / <varname>makefile</varname></term> <listitem><para>See the build phase for details.</para></listitem> </varlistentry> <varlistentry> <term><varname>checkTarget</varname></term> <listitem><para>The make target that runs the tests. Defaults to <literal>check</literal>.</para></listitem> </varlistentry> <varlistentry> <term><varname>checkFlags</varname> / <varname>checkFlagsArray</varname></term> <listitem><para>A list of strings passed as additional flags to <command>make</command>. Like <varname>makeFlags</varname> and <varname>makeFlagsArray</varname>, but only used by the check phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>preCheck</varname></term> <listitem><para>Hook executed at the start of the check phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postCheck</varname></term> <listitem><para>Hook executed at the end of the check phase.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-install-phase"><title>The install phase</title> <para>The install phase is responsible for installing the package in the Nix store under <envar>out</envar>. The default <function>installPhase</function> creates the directory <literal>$out</literal> and calls <command>make install</command>.</para> <variablelist> <title>Variables controlling the install phase</title> <varlistentry> <term><varname>makeFlags</varname> / <varname>makeFlagsArray</varname> / <varname>makefile</varname></term> <listitem><para>See the build phase for details.</para></listitem> </varlistentry> <varlistentry> <term><varname>installTargets</varname></term> <listitem><para>The make targets that perform the installation. Defaults to <literal>install</literal>. Example: <programlisting> installTargets = "install-bin install-doc";</programlisting> </para></listitem> </varlistentry> <varlistentry> <term><varname>installFlags</varname> / <varname>installFlagsArray</varname></term> <listitem><para>A list of strings passed as additional flags to <command>make</command>. Like <varname>makeFlags</varname> and <varname>makeFlagsArray</varname>, but only used by the install phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>preInstall</varname></term> <listitem><para>Hook executed at the start of the install phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postInstall</varname></term> <listitem><para>Hook executed at the end of the install phase.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-fixup-phase"><title>The fixup phase</title> <para>The fixup phase performs some (Nix-specific) post-processing actions on the files installed under <filename>$out</filename> by the install phase. The default <function>fixupPhase</function> does the following: <itemizedlist> <listitem><para>It moves the <filename>man/</filename>, <filename>doc/</filename> and <filename>info/</filename> subdirectories of <envar>$out</envar> to <filename>share/</filename>.</para></listitem> <listitem><para>It strips libraries and executables of debug information.</para></listitem> <listitem><para>On Linux, it applies the <command>patchelf</command> command to ELF executables and libraries to remove unused directories from the <literal>RPATH</literal> in order to prevent unnecessary runtime dependencies.</para></listitem> <listitem><para>It rewrites the interpreter paths of shell scripts to paths found in <envar>PATH</envar>. E.g., <filename>/usr/bin/perl</filename> will be rewritten to <filename>/nix/store/<replaceable>some-perl</replaceable>/bin/perl</filename> found in <envar>PATH</envar>.</para></listitem> </itemizedlist> </para> <variablelist> <title>Variables controlling the fixup phase</title> <varlistentry> <term><varname>dontStrip</varname></term> <listitem><para>If set, libraries and executables are not stripped. By default, they are.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontMoveSbin</varname></term> <listitem><para>If set, files in <filename>$out/sbin</filename> are not moved to <filename>$out/bin</filename>. By default, they are.</para></listitem> </varlistentry> <varlistentry> <term><varname>stripAllList</varname></term> <listitem><para>List of directories to search for libraries and executables from which <emphasis>all</emphasis> 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.</para></listitem> </varlistentry> <varlistentry> <term><varname>stripAllFlags</varname></term> <listitem><para>Flags passed to the <command>strip</command> command applied to the files in the directories listed in <varname>stripAllList</varname>. Defaults to <option>-s</option> (i.e. <option>--strip-all</option>).</para></listitem> </varlistentry> <varlistentry> <term><varname>stripDebugList</varname></term> <listitem><para>List of directories to search for libraries and executables from which only debugging-related symbols should be stripped. It defaults to <literal>lib bin sbin</literal>.</para></listitem> </varlistentry> <varlistentry> <term><varname>stripDebugFlags</varname></term> <listitem><para>Flags passed to the <command>strip</command> command applied to the files in the directories listed in <varname>stripDebugList</varname>. Defaults to <option>-S</option> (i.e. <option>--strip-debug</option>).</para></listitem> </varlistentry> <varlistentry> <term><varname>dontPatchELF</varname></term> <listitem><para>If set, the <command>patchelf</command> command is not used to remove unnecessary <literal>RPATH</literal> entries. Only applies to Linux.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontPatchShebangs</varname></term> <listitem><para>If set, scripts starting with <literal>#!</literal> do not have their interpreter paths rewritten to paths in the Nix store.</para></listitem> </varlistentry> <varlistentry> <term><varname>forceShare</varname></term> <listitem><para>The list of directories that must be moved from <filename>$out</filename> to <filename>$out/share</filename>. Defaults to <literal>man doc info</literal>.</para></listitem> </varlistentry> <varlistentry> <term><varname>setupHook</varname></term> <listitem><para>A package can export a <link linkend="ssec-setup-hooks">setup hook</link> by setting this variable. The setup hook, if defined, is copied to <filename>$out/nix-support/setup-hook</filename>. Environment variables are then substituted in it using <function linkend="fun-substituteAll">substituteAll</function>.</para></listitem> </varlistentry> <varlistentry> <term><varname>preFixup</varname></term> <listitem><para>Hook executed at the start of the fixup phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postFixup</varname></term> <listitem><para>Hook executed at the end of the fixup phase.</para></listitem> </varlistentry> <varlistentry xml:id="stdenv-separateDebugInfo"> <term><varname>separateDebugInfo</varname></term> <listitem><para>If set to <literal>true</literal>, 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 <literal>debug</literal>. (This output is enabled automatically; you don’t need to set the <varname>outputs</varname> attribute explicitly.) To be precise, the debug information is stored in <filename><replaceable>debug</replaceable>/lib/debug/.build-id/<replaceable>XX</replaceable>/<replaceable>YYYY…</replaceable></filename>, where <replaceable>XXYYYY…</replaceable> is the <replaceable>build ID</replaceable> 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.</para> <para>For example, with GDB, you can add <programlisting> set debug-file-directory ~/.nix-profile/lib/debug </programlisting> to <filename>~/.gdbinit</filename>. GDB will then be able to find debug information installed via <literal>nix-env -i</literal>.</para> </listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-installCheck-phase"><title>The installCheck phase</title> <para>The installCheck phase checks whether the package was installed correctly by running its test suite against the installed directories. The default <function>installCheck</function> calls <command>make installcheck</command>.</para> <variablelist> <title>Variables controlling the installCheck phase</title> <varlistentry> <term><varname>doInstallCheck</varname></term> <listitem><para>If set to a non-empty string, the installCheck phase is executed, otherwise it is skipped (default). Thus you should set <programlisting>doInstallCheck = true;</programlisting> in the derivation to enable install checks.</para></listitem> </varlistentry> <varlistentry> <term><varname>preInstallCheck</varname></term> <listitem><para>Hook executed at the start of the installCheck phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postInstallCheck</varname></term> <listitem><para>Hook executed at the end of the installCheck phase.</para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-distribution-phase"><title>The distribution phase</title> <para>The distribution phase is intended to produce a source distribution of the package. The default <function>distPhase</function> first calls <command>make dist</command>, then it copies the resulting source tarballs to <filename>$out/tarballs/</filename>. This phase is only executed if the attribute <varname>doDist</varname> is set.</para> <variablelist> <title>Variables controlling the distribution phase</title> <varlistentry> <term><varname>distTarget</varname></term> <listitem><para>The make target that produces the distribution. Defaults to <literal>dist</literal>.</para></listitem> </varlistentry> <varlistentry> <term><varname>distFlags</varname> / <varname>distFlagsArray</varname></term> <listitem><para>Additional flags passed to <command>make</command>.</para></listitem> </varlistentry> <varlistentry> <term><varname>tarballs</varname></term> <listitem><para>The names of the source distribution files to be copied to <filename>$out/tarballs/</filename>. It can contain shell wildcards. The default is <filename>*.tar.gz</filename>.</para></listitem> </varlistentry> <varlistentry> <term><varname>dontCopyDist</varname></term> <listitem><para>If set, no files are copied to <filename>$out/tarballs/</filename>.</para></listitem> </varlistentry> <varlistentry> <term><varname>preDist</varname></term> <listitem><para>Hook executed at the start of the distribution phase.</para></listitem> </varlistentry> <varlistentry> <term><varname>postDist</varname></term> <listitem><para>Hook executed at the end of the distribution phase.</para></listitem> </varlistentry> </variablelist> </section> </section> <section xml:id="ssec-stdenv-functions"><title>Shell functions</title> <para>The standard environment provides a number of useful functions.</para> <variablelist> <varlistentry xml:id='fun-substitute'> <term><function>substitute</function> <replaceable>infile</replaceable> <replaceable>outfile</replaceable> <replaceable>subs</replaceable></term> <listitem> <para>Performs string substitution on the contents of <replaceable>infile</replaceable>, writing the result to <replaceable>outfile</replaceable>. The substitutions in <replaceable>subs</replaceable> are of the following form: <variablelist> <varlistentry> <term><option>--replace</option> <replaceable>s1</replaceable> <replaceable>s2</replaceable></term> <listitem><para>Replace every occurence of the string <replaceable>s1</replaceable> by <replaceable>s2</replaceable>.</para></listitem> </varlistentry> <varlistentry> <term><option>--subst-var</option> <replaceable>varName</replaceable></term> <listitem><para>Replace every occurence of <literal>@<replaceable>varName</replaceable>@</literal> by the contents of the environment variable <replaceable>varName</replaceable>. This is useful for generating files from templates, using <literal>@<replaceable>...</replaceable>@</literal> in the template as placeholders.</para></listitem> </varlistentry> <varlistentry> <term><option>--subst-var-by</option> <replaceable>varName</replaceable> <replaceable>s</replaceable></term> <listitem><para>Replace every occurence of <literal>@<replaceable>varName</replaceable>@</literal> by the string <replaceable>s</replaceable>.</para></listitem> </varlistentry> </variablelist> </para> <para>Example: <programlisting> substitute ./foo.in ./foo.out \ --replace /usr/bin/bar $bar/bin/bar \ --replace "a string containing spaces" "some other text" \ --subst-var someVar </programlisting> </para> <para><function>substitute</function> is implemented using the <command xlink:href="http://replace.richardlloyd.org.uk/">replace</command> command. Unlike with the <command>sed</command> 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.</para> </listitem> </varlistentry> <varlistentry xml:id='fun-substituteInPlace'> <term><function>substituteInPlace</function> <replaceable>file</replaceable> <replaceable>subs</replaceable></term> <listitem><para>Like <function>substitute</function>, but performs the substitutions in place on the file <replaceable>file</replaceable>.</para></listitem> </varlistentry> <varlistentry xml:id='fun-substituteAll'> <term><function>substituteAll</function> <replaceable>infile</replaceable> <replaceable>outfile</replaceable></term> <listitem><para>Replaces every occurence of <literal>@<replaceable>varName</replaceable>@</literal>, where <replaceable>varName</replaceable> is any environment variable, in <replaceable>infile</replaceable>, writing the result to <replaceable>outfile</replaceable>. For instance, if <replaceable>infile</replaceable> has the contents <programlisting> #! @bash@/bin/sh PATH=@coreutils@/bin echo @foo@ </programlisting> and the environment contains <literal>bash=/nix/store/bmwp0q28cf21...-bash-3.2-p39</literal> and <literal>coreutils=/nix/store/68afga4khv0w...-coreutils-6.12</literal>, but does not contain the variable <varname>foo</varname>, then the output will be <programlisting> #! /nix/store/bmwp0q28cf21...-bash-3.2-p39/bin/sh PATH=/nix/store/68afga4khv0w...-coreutils-6.12/bin echo @foo@ </programlisting> That is, no substitution is performed for undefined variables.</para> <para>Environment variables that start with an uppercase letter or an underscore are filtered out, to prevent global variables (like <literal>HOME</literal>) or private variables (like <literal>__ETC_PROFILE_DONE</literal>) from accidentally getting substituted. The variables also have to be valid bash “names”, as defined in the bash manpage (alphanumeric or <literal>_</literal>, must not start with a number).</para> </listitem> </varlistentry> <varlistentry xml:id='fun-substituteAllInPlace'> <term><function>substituteAllInPlace</function> <replaceable>file</replaceable></term> <listitem><para>Like <function>substituteAll</function>, but performs the substitutions in place on the file <replaceable>file</replaceable>.</para></listitem> </varlistentry> <varlistentry xml:id='fun-stripHash'> <term><function>stripHash</function> <replaceable>path</replaceable></term> <listitem><para>Strips the directory and hash part of a store path, outputting the name part to <literal>stdout</literal>. For example: <programlisting> # prints coreutils-8.24 stripHash "/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24" </programlisting> If you wish to store the result in another variable, then the following idiom may be useful: <programlisting> name="/nix/store/9s9r019176g7cvn2nvcw41gsp862y6b4-coreutils-8.24" someVar=$(stripHash $name) </programlisting> </para></listitem> </varlistentry> </variablelist> </section> <section xml:id="ssec-setup-hooks"><title>Package setup hooks</title> <para>The following packages provide a setup hook: <variablelist> <varlistentry> <term>GCC wrapper</term> <listitem><para>Adds the <filename>include</filename> subdirectory of each build input to the <envar>NIX_CFLAGS_COMPILE</envar> environment variable, and the <filename>lib</filename> and <filename>lib64</filename> subdirectories to <envar>NIX_LDFLAGS</envar>.</para></listitem> </varlistentry> <varlistentry> <term>Perl</term> <listitem><para>Adds the <filename>lib/site_perl</filename> subdirectory of each build input to the <envar>PERL5LIB</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>Python</term> <listitem><para>Adds the <filename>lib/${python.libPrefix}/site-packages</filename> subdirectory of each build input to the <envar>PYTHONPATH</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>pkg-config</term> <listitem><para>Adds the <filename>lib/pkgconfig</filename> and <filename>share/pkgconfig</filename> subdirectories of each build input to the <envar>PKG_CONFIG_PATH</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>Automake</term> <listitem><para>Adds the <filename>share/aclocal</filename> subdirectory of each build input to the <envar>ACLOCAL_PATH</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>Autoconf</term> <listitem><para>The <varname>autoreconfHook</varname> derivation adds <varname>autoreconfPhase</varname>, which runs autoreconf, libtoolize and automake, essentially preparing the configure script in autotools-based builds.</para></listitem> </varlistentry> <varlistentry> <term>libxml2</term> <listitem><para>Adds every file named <filename>catalog.xml</filename> found under the <filename>xml/dtd</filename> and <filename>xml/xsl</filename> subdirectories of each build input to the <envar>XML_CATALOG_FILES</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>teTeX / TeX Live</term> <listitem><para>Adds the <filename>share/texmf-nix</filename> subdirectory of each build input to the <envar>TEXINPUTS</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>Qt 4</term> <listitem><para>Sets the <envar>QTDIR</envar> environment variable to Qt’s path.</para></listitem> </varlistentry> <varlistentry> <term>gdk-pixbuf</term> <listitem><para>Exports <envar>GDK_PIXBUF_MODULE_FILE</envar> environment variable the the builder. Add librsvg package to <varname>buildInputs</varname> to get svg support.</para></listitem> </varlistentry> <varlistentry> <term>GHC</term> <listitem><para>Creates a temporary package database and registers every Haskell build input in it (TODO: how?).</para></listitem> </varlistentry> <varlistentry> <term>GStreamer</term> <listitem><para>Adds the GStreamer plugins subdirectory of each build input to the <envar>GST_PLUGIN_SYSTEM_PATH_1_0</envar> or <envar>GST_PLUGIN_SYSTEM_PATH</envar> environment variable.</para></listitem> </varlistentry> <varlistentry> <term>paxctl</term> <listitem><para>Defines the <varname>paxmark</varname> helper for setting per-executable PaX flags on Linux (where it is available by default; on all other platforms, <varname>paxmark</varname> is a no-op). For example, to disable secure memory protections on the executable <replaceable>foo</replaceable>: <programlisting> postFixup = '' paxmark m $out/bin/<replaceable>foo</replaceable> ''; </programlisting> The <literal>m</literal> 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.</para></listitem> </varlistentry> </variablelist> </para> </section> <section xml:id="sec-purity-in-nixpkgs"><title>Purity in Nixpkgs</title> <para>[measures taken to prevent dependencies on packages outside the store, and what you can do to prevent them]</para> <para>GCC doesn't search in locations such as <filename>/usr/include</filename>. In fact, attempts to add such directories through the <option>-I</option> flag are filtered out. Likewise, the linker (from GNU binutils) doesn't search in standard locations such as <filename>/usr/lib</filename>. Programs built on Linux are linked against a GNU C Library that likewise doesn't search in the default system locations.</para> </section> <section xml:id="sec-hardening-in-nixpkgs"><title>Hardening in Nixpkgs</title> <para>There are flags available to harden packages at compile or link-time. These can be toggled using the <varname>stdenv.mkDerivation</varname> parameters <varname>hardeningDisable</varname> and <varname>hardeningEnable</varname>. </para> <para>The following flags are enabled by default and might require disabling if the program to package is incompatible. </para> <variablelist> <varlistentry> <term><varname>format</varname></term> <listitem><para>Adds the <option>-Wformat -Wformat-security -Werror=format-security</option> compiler options. At present, this warns about calls to <varname>printf</varname> and <varname>scanf</varname> functions where the format string is not a string literal and there are no format arguments, as in <literal>printf(foo);</literal>. This may be a security hole if the format string came from untrusted input and contains <literal>%n</literal>.</para> <para>This needs to be turned off or fixed for errors similar to:</para> <programlisting> /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 </programlisting></listitem> </varlistentry> <varlistentry> <term><varname>stackprotector</varname></term> <listitem> <para>Adds the <option>-fstack-protector-strong --param ssp-buffer-size=4</option> 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).</para> <para>This needs to be turned off or fixed for errors similar to:</para> <programlisting> 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' </programlisting></listitem> </varlistentry> <varlistentry> <term><varname>fortify</varname></term> <listitem> <para>Adds the <option>-O2 -D_FORTIFY_SOURCE=2</option> 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. </para> <para>Addtionally, some warnings are enabled which might trigger build failures if compiler warnings are treated as errors in the package build. In this case, set <option>NIX_CFLAGS_COMPILE</option> to <option>-Wno-error=warning-type</option>.</para> <para>This needs to be turned off or fixed for errors similar to:</para> <programlisting> malloc.c:404:15: error: return type is an incomplete type malloc.c:410:19: error: storage size of 'ms' isn't known </programlisting> <programlisting> strdup.h:22:1: error: expected identifier or '(' before '__extension__' </programlisting> <programlisting> strsep.c:65:23: error: register name not specified for 'delim' </programlisting> <programlisting> installwatch.c:3751:5: error: conflicting types for '__open_2' </programlisting> <programlisting> 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 </programlisting> </listitem> </varlistentry> <varlistentry> <term><varname>pic</varname></term> <listitem> <para>Adds the <option>-fPIC</option> compiler options. This options adds support for position independant code in shared libraries and thus making ASLR possible.</para> <para>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. </para> <para>This needs to be turned off or fixed for assembler errors similar to:</para> <programlisting> ccbLfRgg.s: Assembler messages: ccbLfRgg.s:33: Error: missing or invalid displacement expression `private_key_len@GOTOFF' </programlisting> </listitem> </varlistentry> <varlistentry> <term><varname>strictoverflow</varname></term> <listitem> <para>Signed 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 <option>-fno-strict-overflow</option> makes gcc behave as if signed integer overflows were defined. </para> <para>This flag should not trigger any build or runtime errors.</para> </listitem> </varlistentry> <varlistentry> <term><varname>relro</varname></term> <listitem> <para>Adds the <option>-z relro</option> 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. </para> <para>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 <varname>bindnow</varname> flag must also be disabled and incompatible programs typically fail with similar errors at runtime.</para> </listitem> </varlistentry> <varlistentry> <term><varname>bindnow</varname></term> <listitem> <para>Adds the <option>-z bindnow</option> linker option. During program load, all dynamic symbols are resolved, allowing for the complete GOT to be marked read-only (due to <varname>relro</varname>). 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. </para> <para>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:</para> <programlisting> intel_drv.so: undefined symbol: vgaHWFreeHWRec </programlisting> </listitem> </varlistentry> </variablelist> <para>The following flags are disabled by default and should be enabled for packages that take untrusted input, like network services. </para> <variablelist> <varlistentry> <term><varname>pie</varname></term> <listitem> <para>Adds the <option>-fPIE</option> compiler and <option>-pie</option> 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 <varname>pic</varname> flag, so they gain ASLR automatically, but binary .text regions need to be build with <varname>pie</varname> 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. </para> </listitem> </varlistentry> </variablelist> <para>For more in-depth information on these hardening flags and hardening in general, refer to the <link xlink:href="https://wiki.debian.org/Hardening">Debian Wiki</link>, <link xlink:href="https://wiki.ubuntu.com/Security/Features">Ubuntu Wiki</link>, <link xlink:href="https://wiki.gentoo.org/wiki/Project:Hardened">Gentoo Wiki</link>, and the <link xlink:href="https://wiki.archlinux.org/index.php/DeveloperWiki:Security"> Arch Wiki</link>. </para> </section> </chapter>