diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/manual/Makefile.am | 3 | ||||
| -rw-r--r-- | doc/manual/manual.xml | 6 | ||||
| -rw-r--r-- | doc/manual/overview.xml | 450 | ||||
| -rw-r--r-- | doc/manual/package-management.xml | 229 | ||||
| -rw-r--r-- | doc/manual/quick-start.xml | 3 | ||||
| -rw-r--r-- | doc/manual/writing-nix-expressions.xml | 148 |
6 files changed, 384 insertions, 455 deletions
diff --git a/doc/manual/Makefile.am b/doc/manual/Makefile.am index ef1a4d4a95..28ebb4d155 100644 --- a/doc/manual/Makefile.am +++ b/doc/manual/Makefile.am @@ -10,7 +10,8 @@ man1_MANS = nix-env.1 nix-store.1 nix-instantiate.1 \ nix-collect-garbage.1 nix-push.1 nix-pull.1 \ nix-prefetch-url.1 -SOURCES = manual.xml introduction.xml installation.xml overview.xml \ +SOURCES = manual.xml introduction.xml installation.xml \ + package-management.xml writing-nix-expressions.xml \ $(man1_MANS:.1=.xml) \ troubleshooting.xml bugs.xml opt-common.xml opt-common-syn.xml \ quick-start.xml nix-lang-ref.xml style.css images diff --git a/doc/manual/manual.xml b/doc/manual/manual.xml index 930da3a891..d2f19f0309 100644 --- a/doc/manual/manual.xml +++ b/doc/manual/manual.xml @@ -9,7 +9,8 @@ <!ENTITY introduction SYSTEM "introduction.xml"> <!ENTITY quick-start SYSTEM "quick-start.xml"> <!ENTITY installation SYSTEM "installation.xml"> -<!ENTITY overview SYSTEM "overview.xml"> +<!ENTITY package-management SYSTEM "package-management.xml"> +<!ENTITY writing-nix-expressions SYSTEM "writing-nix-expressions.xml"> <!ENTITY opt-common SYSTEM "opt-common.xml"> <!ENTITY opt-common-syn SYSTEM "opt-common-syn.xml"> <!ENTITY nix-env SYSTEM "nix-env.xml"> @@ -44,7 +45,8 @@ &introduction; &quick-start; &installation; - &overview; + &package-management; + &writing-nix-expressions; <appendix> <title>Command Reference</title> diff --git a/doc/manual/overview.xml b/doc/manual/overview.xml deleted file mode 100644 index d3a7e443bd..0000000000 --- a/doc/manual/overview.xml +++ /dev/null @@ -1,450 +0,0 @@ -<chapter id='chap-overview'> - <title>Overview</title> - - <para> - This chapter provides a guided tour of Nix. - </para> - - - - <!--######################################################################--> - - <sect1> - <title>Basic package management</title> - - <para> - Let's start from the perspective of an end user. Common operations at - this level are to install and remove packages, ask what packages are - installed or available for installation, and so on. These are operations - on the <emphasis>user environment</emphasis>: the set of packages that a - user <quote>sees</quote>. In a command line Unix environment, this means - the set of programs that are available through the <envar>PATH</envar> - environment variable. (In other environments it might mean the set of - programs available on the desktop, through the start menu, and so on.) - </para> - - <para> - The terms <quote>installation</quote> and <quote>uninstallation</quote> - are used in this context to denote the act of adding or removing packages - from the user environment. In Nix, these operations are dissociated from - the physical copying or deleting of files. Installation requires that - the files constituting the package are present, but they may be present - beforehand. Likewise, uninstallation does not actually delete any files; - this is done automatically by running a garbage collector. - </para> - - <para> - User environments are manipulated through the <command>nix-env</command> - command. The query operation can be used to see what packages are - currently installed. - </para> - - <screen> -$ nix-env -q -MozillaFirebird-0.7 -sylpheed-0.9.7 -pan-0.14.2</screen> - - <para> - (<option>-q</option> is actually short for <option>--query - --installed</option>.) The package names are symbolic: they don't have - any particular significance to Nix (as they shouldn't, since they are not - unique—there can be many derivations with the same name). Note that - these packages have many dependencies (e.g., Mozilla uses the - <literal>gtk+</literal> package) but these have not been installed in the - user environment, though they are present on the system. Generally, - there is no need to install such packages; only packages containing - programs should be installed. - </para> - - <para> - To install packages, a <emphasis>Nix expression</emphasis> is required - that tells Nix how to build that package. There is a <ulink - url='https://svn.cs.uu.nl:12443/dist/trace/trace-nixpkgs-trunk.tar.bz2'>set - of standard of Nix expressions</ulink> for many common packages. - Assuming that you have downloaded and unpacked these, you can view the - set of available packages: - </para> - - <screen> -$ nix-env -qaf pkgs/system/i686-linux.nix -gettext-0.12.1 -sylpheed-0.9.7 -aterm-2.0 -gtk+-1.2.10 -apache-httpd-2.0.48 -pan-0.14.2 -...</screen> - - <para> - The Nix expression in the file <filename>i686-linux.nix</filename> yields - the set of packages for a Linux system running on x86 hardware. For - other platforms, copy and modify this file for your platform as - appropriate. [TODO: improve this] - </para> - - <para> - It is also possible to see the <emphasis>status</emphasis> of available - packages, i.e., whether they are installed into the user environment - and/or present in the system: - </para> - - <screen> -$ nix-env -qasf pkgs/system/i686-linux.nix --P gettext-0.12.1 -IP sylpheed-0.9.7 --- aterm-2.0 --P gtk+-1.2.10</screen> - - <para> - This reveals that the <literal>sylpheed</literal> package is already - installed, or more precisely, that exactly the same instantiation of - <literal>sylpheed</literal> is installed. This guarantees that the - available package is exactly the same as the installed package with - regard to sources, dependencies, build flags, and so on. Similarly, we - see that the <literal>gettext</literal> and <literal>gtk+</literal> - packages are present but not installed in the user environment, while the - <literal>aterm</literal> package is not installed or present at all (so, - if we were to install it, it would have to be built or downloaded first). - </para> - - <para> - The install operation is used install available packages from a Nix - environment. To install the <literal>pan</literal> package (a - newsreader), you would do: - </para> - - <screen> -$ nix-env -if pkgs/system/i686-linux.nix pan</screen> - - <para> - Since installation may take a long time, depending on whether any - packages need to be built or downloaded, it's a good idea to make - <command>nix-env</command> run verbosely by using the <option>-v</option> - (<option>--verbose</option>) option. This option may be repeated to - increase the level of verbosity. A good value is 3 - (<option>-vvv</option>). - </para> - - <para> - In fact, if you run this command verbosely you will observe that Nix - starts to build many packages, including large and fundamental ones such - as <literal>glibc</literal> and <literal>gcc</literal>. I.e., you are - performing a source installation. This is generally undesirable, since - installation from sources may require large amounts of disk and CPU - resources. Therefore a <quote>binary</quote> installation is generally - preferable. - </para> - - <para> - Rather than provide different mechanisms to create and perform - the installation of binary packages, Nix supports binary deployment - <emphasis>transparently</emphasis> through a generic mechanism of - <emphasis>substitute expressions</emphasis>. If an request is made to - build some Nix expression, Nix will first try to build any substitutes - for that expression. These substitutes presumably perform an identical - build operation with respect to the result, but require less resources. - For instance, a substitute that downloads a pre-built package from the - network requires less CPU and disk resources, and possibly less time. - </para> - - <para> - Nix's use of cryptographic hashes makes this entirely safe. It is not - possible, for instance, to accidentally substitute a build of some - package for a Solaris or Windows system for a build on a SuSE/x86 system. - </para> - - <para> - While the substitute mechanism is a generic mechanism, Nix provides two - standard tools called <command>nix-pull</command> and - <command>nix-push</command> that maintain and use a shared cache of - prebuilt derivations on some network site (reachable through HTTP). If - you attempt to install some package that someone else has previously - built and <quote>pushed</quote> into the cache, and you have done a - <quote>pull</quote> to register substitutes that download these prebuilt - packages, then the installation will automatically use these. - </para> - - <para> - For example, to pull from our <ulink - url='http://losser.st-lab.cs.uu.nl/~eelco/nix-dist/'>cache</ulink> of - prebuilt packages (at the time of writing, for SuSE Linux/x86), use the - following command: - </para> - - <screen> -$ nix-pull http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST -obtaining list of Nix archives at http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST... -...</screen> - - <para> - If <command>nix-pull</command> is run without any arguments, it will pull - from the URLs specified in the file - <filename><replaceable>prefix</replaceable>/etc/nix/prebuilts.conf</filename>. - </para> - - <para> - Assuming that the <literal>pan</literal> installation produced no errors, - it can be used immediately, that is, it now appears in a directory in the - <envar>PATH</envar> environment variable. Specifically, - <envar>PATH</envar> includes the entry - <filename><replaceable>prefix</replaceable>/var/nix/profiles/default/bin</filename>, - where - <filename><replaceable>prefix</replaceable>/var/nix/profiles/default</filename> - is just a symlink to the current user environment: - </para> - - <screen> -$ ls -l /nix/var/nix/profiles/ -... -lrwxrwxrwx 1 eelco ... default-15-link -> /nix/store/1871...12b0-user-environment -lrwxrwxrwx 1 eelco ... default-16-link -> /nix/store/59ba...df6b-user-environment -lrwxrwxrwx 1 eelco ... default -> default-16-link</screen> - - <para> - That is, <filename>default</filename> in this example is a link - to <filename>default-16-link</filename>, which is the current - user environment. Before the installation, it pointed to - <filename>default-15-link</filename>. Note that this means that - you can atomically roll-back to the previous user environment by - pointing the symlink <filename>default</filename> at - <filename>default-15-link</filename> again. This also shows - that operations such as installation are atomic in the Nix - system: any arbitrarily complex set of installation, - uninstallation, or upgrade actions eventually boil down to the - single operation of pointing a symlink somewhere else (which can - be implemented atomically in Unix). - </para> - - <para> - What's in a user environment? It's just a set of symlinks to the files - that constitute the installed packages. For instance: - </para> - - <screen> -$ ls -l /nix/var/nix/profiles/default-16-link/bin -lrwxrwxrwx 1 eelco ... MozillaFirebird -> /nix/store/35f8...4ae6-MozillaFirebird-0.7/bin/MozillaFirebird -lrwxrwxrwx 1 eelco ... svn -> /nix/store/3829...fb5d-subversion-0.32.1/bin/svn -...</screen> - - <para> - Note that, e.g., <filename>svn</filename> = - <filename>/nix/var/nix/profiles/default/bin/svn</filename> = - <filename>/nix/var/nix/profiles/default-16-link/bin/svn</filename> = - <filename>/nix/store/59ba...df6b-user-environment/bin/svn</filename> = - <filename>/nix/store/3829...fb5d-subversion-0.32.1/bin/svn</filename>. - </para> - - <para> - Naturally, packages can also be uninstalled: - </para> - - <screen> -$ nix-env -e pan</screen> - - <para> - This means that the package is removed from the user - environment. It is <emphasis>not</emphasis> yet removed from - the system. When a package is uninstalled from a user - environment, it may still be used by other packages, or may - still be present in other user environments. Deleting it under - such conditions would break those other packages or user - environments. To prevent this, packages are only - <quote>physically</quote> deleted by running the Nix garbage - collector, which searches for all packages in the Nix store that - are no longer <quote>reachable</quote> from outside the store. - Thus, uninstalling a package is always safe: it cannot break - other packages. - </para> - - <para> - Upgrading packages is easy. Given a Nix expression that - contains newer versions of installed packages (that is, packages - with the same package name, but a higher version number), - <command>nix-env -u</command> will replace the installed package - in the user environment with the newer package. For example, - - <screen> -$ nix-env -uf pkgs/system/i686-linux.nix pan</screen> - - looks for a newer version of Pan, and installs it if found. - Also useful is the ability to upgrade <emphasis>all</emphasis> - packages: - - <screen> -$ nix-env -uf pkgs/system/i686-linux.nix '*'</screen> - - The asterisk matches all installed packages<footnote><para>No, - we don't support arbitrary regular - expressions</para></footnote>. Note that <literal>*</literal> - must be quoted to prevent shell globbing. - </para> - - </sect1> - - - - <!--######################################################################--> - - <sect1> - <title>Writing Nix expressions</title> - - <sect2> - <title>A simple Nix expression</title> - - <para> - This section shows how to write simple Nix expressions—the things - that describe how to build a package. - </para> - - <example id='ex-hello-nix'> - <title>Nix expression for GNU Hello</title> - <programlisting> -{stdenv, fetchurl, perl}: <co id='ex-hello-nix-co-1' /> - -derivation { <co id='ex-hello-nix-co-2' /> - name = "hello-2.1.1"; <co id='ex-hello-nix-co-3' /> - system = stdenv.system; <co id='ex-hello-nix-co-4' /> - builder = ./builder.sh; <co id='ex-hello-nix-co-5' /> - src = fetchurl { <co id='ex-hello-nix-co-6' /> - url = ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz; - md5 = "70c9ccf9fac07f762c24f2df2290784d"; - }; - stdenv = stdenv; <co id='ex-hello-nix-co-7' /> - perl = perl; -}</programlisting> - </example> - - <para> - A simple Nix expression is shown in <xref linkend='ex-hello-nix' />. It - describes how to the build the <ulink - url='http://www.gnu.org/directory/GNU/hello.html'>GNU Hello - package</ulink>. This package has several dependencies. First, it - requires a number of other packages, such as a C compiler, standard - Unix shell tools, and Perl. Rather than have this Nix expression refer - to and use specific versions of these packages, it should be generic; - that is, it should be a <emphasis>function</emphasis> that takes the - required packages as inputs and yield a build of the GNU Hello package - as a result. This Nix expression defines a function with three - arguments <xref linkend='ex-hello-nix-co-1' />, namely: - <orderedlist> - <listitem><para><varname>stdenv</varname>, which should be a - <emphasis>standard environment package</emphasis>. The standard - environment is a set of tools and other components that would be - expected in a fairly minimal Unix-like environment: a C compiler - and linker, Unix shell tools, and so on.</para> - </listitem> - <listitem><para><varname>fetchurl</varname>, which should be a - function that given parameters <varname>url</varname> and - <varname>md5</varname>, will fetch a file from the specified - location and check that this file has the given MD5 hash code. - The hash is required because build operations must be - <emphasis>pure</emphasis>: given the same inputs they should - always yield the same output. Since network resources can change - at any time, we must in some way guarantee what the result will - be.</para> - </listitem> - <listitem><para><varname>perl</varname>, which should be a Perl - interpreter.</para> - </listitem> - </orderedlist> - </para> - - <para> - The remainder of the file is the body of the function, which happens to - be a <emphasis>derivation</emphasis> <xref - linkend='ex-hello-nix-co-2' />, which is the built-in function - <varname>derivation</varname> applied to a set of attributes that - encode all the necessary information for building the GNU Hello - package. - </para> - - <example> - <title>Build script (<filename>builder.sh</filename>) for GNU - Hello</title> - <programlisting> -#! /bin/sh - -buildinputs="$perl" -. $stdenv/setup || exit 1 - -tar xvfz $src || exit 1 -cd hello-* || exit 1 -./configure --prefix=$out || exit 1 -make || exit 1 -make install || exit 1</programlisting> - </example> - - </sect2> - - <sect2> - <title>A more complex Nix expression</title> - - <example id='ex-svn-nix'> - <title>Nix expression for Subversion</title> - <programlisting> -{ localServer ? false <co id='ex-svn-nix-co-1' /> -, httpServer ? false -, sslSupport ? false -, swigBindings ? false -, stdenv, fetchurl -, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null -}: - -assert !isNull expat; <co id='ex-svn-nix-co-2' /> -assert localServer -> !isNull db4; -assert httpServer -> !isNull httpd && httpd.expat == expat; <co id='ex-svn-nix-co-3' /> -assert sslSupport -> !isNull openssl && (httpServer -> httpd.openssl == openssl); -assert swigBindings -> !isNull swig; - -derivation { - name = "subversion-0.32.1"; - system = stdenv.system; - - builder = ./builder.sh; - src = fetchurl { - url = http://svn.collab.net/tarballs/subversion-0.32.1.tar.gz; - md5 = "b06717a8ef50db4b5c4d380af00bd901"; - }; - - localServer = localServer; - httpServer = httpServer; - sslSupport = sslSupport; - swigBindings = swigBindings; - - stdenv = stdenv; - openssl = if sslSupport then openssl else null; <co id='ex-svn-nix-co-4' /> - httpd = if httpServer then httpd else null; - expat = expat; - db4 = if localServer then db4 else null; - swig = if swigBindings then swig else null; -}</programlisting> - </example> - - <para> - This example shows several features. Default parameters <xref - linkend='ex-svn-nix-co-1'/> can be used to simplify call sites: if an - argument that has a default is omitted, its default value is used. - </para> - - <para> - You can use <emphasis>assertions</emphasis> to test whether arguments - satisfy certain constraints. The simple assertion <xref - linkend='ex-svn-nix-co-2'/> tests whether the - <varname>expat</varname> argument is not a null value. The more - complex assertion <xref linkend='ex-svn-nix-co-3'/> says that if - Subversion is built with Apache support, then <varname>httpd</varname> - (the Apache package) must not be null and it must have been built using - the same instance of the <varname>expat</varname> library as was passed - to the Subversion expression. This is since the Subversion code is - dynamically linked against the Apache code and they both use Expat, - they must be linked against the same instance—otherwise a - conflict might occur. - </para> - - </sect2> - - </sect1> - - -</chapter> diff --git a/doc/manual/package-management.xml b/doc/manual/package-management.xml new file mode 100644 index 0000000000..90f8f95b65 --- /dev/null +++ b/doc/manual/package-management.xml @@ -0,0 +1,229 @@ +<chapter id='chap-package-management'><title>Package Management</title> + +<para>Let's start from the perspective of an end user. Common +operations at this level are to install and remove packages, ask what +packages are installed or available for installation, and so on. +These are operations on the <emphasis>user environment</emphasis>: the +set of packages that a user <quote>sees</quote>. In a command line +Unix environment, this means the set of programs that are available +through the <envar>PATH</envar> environment variable. (In other +environments it might mean the set of programs available on the +desktop, through the start menu, and so on.)</para> + +<para>The terms <quote>installation</quote> and +<quote>uninstallation</quote> are used in this context to denote the +act of adding or removing packages from the user environment. In Nix, +these operations are dissociated from the physical copying or deleting +of files. Installation requires that the files constituting the +package are present, but they may be present beforehand. Likewise, +uninstallation does not actually delete any files; this is done +automatically by running a garbage collector.</para> + +<para>User environments are manipulated through the +<command>nix-env</command> command. The query operation can be used +to see what packages are currently installed.</para> + +<screen> +$ nix-env -q +MozillaFirebird-0.7 +sylpheed-0.9.7 +pan-0.14.2</screen> + +<para>(<option>-q</option> is actually short for <option>--query +--installed</option>.) The package names are symbolic: they don't +have any particular significance to Nix (as they shouldn't, since they +are not unique—there can be many derivations with the same +name). Note that these packages have many dependencies (e.g., Mozilla +uses the <literal>gtk+</literal> package) but these have not been +installed in the user environment, though they are present on the +system. Generally, there is no need to install such packages; only +packages containing programs should be installed.</para> + +<para>To install packages, a <emphasis>Nix expression</emphasis> is +required that tells Nix how to build that package. There is a <ulink +url='https://svn.cs.uu.nl:12443/dist/trace/trace-nixpkgs-trunk.tar.bz2'>set +of standard of Nix expressions</ulink> for many common packages. +Assuming that you have downloaded and unpacked these, you can view the +set of available packages:</para> + +<screen> +$ nix-env -qaf pkgs/system/i686-linux.nix +gettext-0.12.1 +sylpheed-0.9.7 +aterm-2.0 +gtk+-1.2.10 +apache-httpd-2.0.48 +pan-0.14.2 +...</screen> + +<para>The Nix expression in the file +<filename>i686-linux.nix</filename> yields the set of packages for a +Linux system running on x86 hardware. For other platforms, copy and +modify this file for your platform as appropriate. [TODO: improve +this]</para> + +<para>It is also possible to see the <emphasis>status</emphasis> of +available packages, i.e., whether they are installed into the user +environment and/or present in the system:</para> + +<screen> +$ nix-env -qasf pkgs/system/i686-linux.nix +-P gettext-0.12.1 +IP sylpheed-0.9.7 +-- aterm-2.0 +-P gtk+-1.2.10</screen> + +<para>This reveals that the <literal>sylpheed</literal> package is +already installed, or more precisely, that exactly the same +instantiation of <literal>sylpheed</literal> is installed. This +guarantees that the available package is exactly the same as the +installed package with regard to sources, dependencies, build flags, +and so on. Similarly, we see that the <literal>gettext</literal> and +<literal>gtk+</literal> packages are present but not installed in the +user environment, while the <literal>aterm</literal> package is not +installed or present at all (so, if we were to install it, it would +have to be built or downloaded first).</para> + +<para>The install operation is used install available packages from a +Nix environment. To install the <literal>pan</literal> package (a +newsreader), you would do:</para> + +<screen> +$ nix-env -if pkgs/system/i686-linux.nix pan</screen> + +<para>Since installation may take a long time, depending on whether +any packages need to be built or downloaded, it's a good idea to make +<command>nix-env</command> run verbosely by using the +<option>-v</option> (<option>--verbose</option>) option. This option +may be repeated to increase the level of verbosity. A good value is 3 +(<option>-vvv</option>).</para> + +<para>In fact, if you run this command verbosely you will observe that +Nix starts to build many packages, including large and fundamental +ones such as <literal>glibc</literal> and <literal>gcc</literal>. +I.e., you are performing a source installation. This is generally +undesirable, since installation from sources may require large amounts +of disk and CPU resources. Therefore a <quote>binary</quote> +installation is generally preferable.</para> + +<para>Rather than provide different mechanisms to create and perform +the installation of binary packages, Nix supports binary deployment +<emphasis>transparently</emphasis> through a generic mechanism of +<emphasis>substitute expressions</emphasis>. If an request is made to +build some Nix expression, Nix will first try to build any substitutes +for that expression. These substitutes presumably perform an +identical build operation with respect to the result, but require less +resources. For instance, a substitute that downloads a pre-built +package from the network requires less CPU and disk resources, and +possibly less time.</para> + +<para>Nix's use of cryptographic hashes makes this entirely safe. It +is not possible, for instance, to accidentally substitute a build of +some package for a Solaris or Windows system for a build on a SuSE/x86 +system.</para> + +<para>While the substitute mechanism is a generic mechanism, Nix +provides two standard tools called <command>nix-pull</command> and +<command>nix-push</command> that maintain and use a shared cache of +prebuilt derivations on some network site (reachable through HTTP). +If you attempt to install some package that someone else has +previously built and <quote>pushed</quote> into the cache, and you +have done a <quote>pull</quote> to register substitutes that download +these prebuilt packages, then the installation will automatically use +these.</para> + +<para>For example, to pull from our <ulink +url='http://losser.st-lab.cs.uu.nl/~eelco/nix-dist/'>cache</ulink> of +prebuilt packages (at the time of writing, for SuSE Linux/x86), use +the following command:</para> + +<screen> +$ nix-pull http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST +obtaining list of Nix archives at http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST... +...</screen> + +<para>If <command>nix-pull</command> is run without any arguments, it +will pull from the URLs specified in the file +<filename><replaceable>prefix</replaceable>/etc/nix/prebuilts.conf</filename>.</para> + +<para>Assuming that the <literal>pan</literal> installation produced +no errors, it can be used immediately, that is, it now appears in a +directory in the <envar>PATH</envar> environment variable. +Specifically, <envar>PATH</envar> includes the entry +<filename><replaceable>prefix</replaceable>/var/nix/profiles/default/bin</filename>, +where +<filename><replaceable>prefix</replaceable>/var/nix/profiles/default</filename> +is just a symlink to the current user environment:</para> + +<screen> +$ ls -l /nix/var/nix/profiles/ +... +lrwxrwxrwx 1 eelco ... default-15-link -> /nix/store/1871...12b0-user-environment +lrwxrwxrwx 1 eelco ... default-16-link -> /nix/store/59ba...df6b-user-environment +lrwxrwxrwx 1 eelco ... default -> default-16-link</screen> + +<para>That is, <filename>default</filename> in this example is a link +to <filename>default-16-link</filename>, which is the current user +environment. Before the installation, it pointed to +<filename>default-15-link</filename>. Note that this means that you +can atomically roll-back to the previous user environment by pointing +the symlink <filename>default</filename> at +<filename>default-15-link</filename> again. This also shows that +operations such as installation are atomic in the Nix system: any +arbitrarily complex set of installation, uninstallation, or upgrade +actions eventually boil down to the single operation of pointing a +symlink somewhere else (which can be implemented atomically in Unix).</para> + +<para>What's in a user environment? It's just a set of symlinks to the +files that constitute the installed packages. For instance:</para> + +<screen> +$ ls -l /nix/var/nix/profiles/default-16-link/bin +lrwxrwxrwx 1 eelco ... MozillaFirebird -> /nix/store/35f8...4ae6-MozillaFirebird-0.7/bin/MozillaFirebird +lrwxrwxrwx 1 eelco ... svn -> /nix/store/3829...fb5d-subversion-0.32.1/bin/svn +...</screen> + +<para>Note that, e.g., <filename>svn</filename> = +<filename>/nix/var/nix/profiles/default/bin/svn</filename> = +<filename>/nix/var/nix/profiles/default-16-link/bin/svn</filename> = +<filename>/nix/store/59ba...df6b-user-environment/bin/svn</filename> = +<filename>/nix/store/3829...fb5d-subversion-0.32.1/bin/svn</filename>.</para> + +<para>Naturally, packages can also be uninstalled:</para> + +<screen> +$ nix-env -e pan</screen> + +<para>This means that the package is removed from the user +environment. It is <emphasis>not</emphasis> yet removed from the +system. When a package is uninstalled from a user environment, it may +still be used by other packages, or may still be present in other user +environments. Deleting it under such conditions would break those +other packages or user environments. To prevent this, packages are +only <quote>physically</quote> deleted by running the Nix garbage +collector, which searches for all packages in the Nix store that are +no longer <quote>reachable</quote> from outside the store. Thus, +uninstalling a package is always safe: it cannot break other +packages.</para> + +<para>Upgrading packages is easy. Given a Nix expression that +contains newer versions of installed packages (that is, packages with +the same package name, but a higher version number), <command>nix-env +-u</command> will replace the installed package in the user +environment with the newer package. For example, + +<screen> +$ nix-env -uf pkgs/system/i686-linux.nix pan</screen> + +looks for a newer version of Pan, and installs it if found. Also +useful is the ability to upgrade <emphasis>all</emphasis> packages: + +<screen> +$ nix-env -uf pkgs/system/i686-linux.nix '*'</screen> + +The asterisk matches all installed packages<footnote><para>No, we +don't support arbitrary regular expressions</para></footnote>. Note +that <literal>*</literal> must be quoted to prevent shell +globbing.</para> + +</chapter> \ No newline at end of file diff --git a/doc/manual/quick-start.xml b/doc/manual/quick-start.xml index a6ec25514e..2350aed34b 100644 --- a/doc/manual/quick-start.xml +++ b/doc/manual/quick-start.xml @@ -2,8 +2,7 @@ <para>This chapter is for impatient people who don't like reading documentation. For more in-depth information you are kindly referred -to <xref linkend='chap-installation' /> and <xref -linkend='chap-overview' />.</para> +to the following chapters.</para> <orderedlist> diff --git a/doc/manual/writing-nix-expressions.xml b/doc/manual/writing-nix-expressions.xml new file mode 100644 index 0000000000..c4ea5d1f39 --- /dev/null +++ b/doc/manual/writing-nix-expressions.xml @@ -0,0 +1,148 @@ +<chapter id='chap-writing-nix-expressions'><title>Writing Nix Expressions</title> + +<sect1><title>A simple Nix expression</title> + +<para>This section shows how to write simple Nix expressions—the +things that describe how to build a package.</para> + +<example id='ex-hello-nix'><title>Nix expression for GNU Hello</title> +<programlisting> +{stdenv, fetchurl, perl}: <co id='ex-hello-nix-co-1' /> + +derivation { <co id='ex-hello-nix-co-2' /> + name = "hello-2.1.1"; <co id='ex-hello-nix-co-3' /> + system = stdenv.system; <co id='ex-hello-nix-co-4' /> + builder = ./builder.sh; <co id='ex-hello-nix-co-5' /> + src = fetchurl { <co id='ex-hello-nix-co-6' /> + url = ftp://ftp.nluug.nl/pub/gnu/hello/hello-2.1.1.tar.gz; + md5 = "70c9ccf9fac07f762c24f2df2290784d"; + }; + stdenv = stdenv; <co id='ex-hello-nix-co-7' /> + perl = perl; +}</programlisting> +</example> + +<para>A simple Nix expression is shown in <xref linkend='ex-hello-nix' +/>. It describes how to the build the <ulink +url='http://www.gnu.org/directory/GNU/hello.html'>GNU Hello +package</ulink>. This package has several dependencies. First, it +requires a number of other packages, such as a C compiler, standard +Unix shell tools, and Perl. Rather than have this Nix expression +refer to and use specific versions of these packages, it should be +generic; that is, it should be a <emphasis>function</emphasis> that +takes the required packages as inputs and yield a build of the GNU +Hello package as a result. This Nix expression defines a function +with three arguments <xref linkend='ex-hello-nix-co-1' />, namely: + + <orderedlist> + <listitem><para><varname>stdenv</varname>, which should be a + <emphasis>standard environment package</emphasis>. The standard + environment is a set of tools and other components that would be + expected in a fairly minimal Unix-like environment: a C compiler + and linker, Unix shell tools, and so on.</para></listitem> + + <listitem><para><varname>fetchurl</varname>, which should be a + function that given parameters <varname>url</varname> and + <varname>md5</varname>, will fetch a file from the specified + location and check that this file has the given MD5 hash code. + The hash is required because build operations must be + <emphasis>pure</emphasis>: given the same inputs they should + always yield the same output. Since network resources can change + at any time, we must in some way guarantee what the result will + be.</para></listitem> + + <listitem><para><varname>perl</varname>, which should be a Perl + interpreter.</para></listitem> + + </orderedlist> +</para> + +<para>The remainder of the file is the body of the function, which +happens to be a <emphasis>derivation</emphasis> <xref +linkend='ex-hello-nix-co-2' />, which is the built-in function +<varname>derivation</varname> applied to a set of attributes that +encode all the necessary information for building the GNU Hello +package.</para> + +<example><title>Build script (<filename>builder.sh</filename>) for GNU +Hello</title> +<programlisting> +#! /bin/sh + +buildinputs="$perl" +. $stdenv/setup || exit 1 + +tar xvfz $src || exit 1 +cd hello-* || exit 1 +./configure --prefix=$out || exit 1 +make || exit 1 +make install || exit 1</programlisting> +</example> + +</sect1> + + +<sect1><title>A more complex Nix expression</title> + +<example id='ex-svn-nix'><title>Nix expression for Subversion</title> +<programlisting> +{ localServer ? false <co id='ex-svn-nix-co-1' /> +, httpServer ? false +, sslSupport ? false +, swigBindings ? false +, stdenv, fetchurl +, openssl ? null, httpd ? null, db4 ? null, expat, swig ? null +}: + +assert !isNull expat; <co id='ex-svn-nix-co-2' /> +assert localServer -> !isNull db4; +assert httpServer -> !isNull httpd && httpd.expat == expat; <co id='ex-svn-nix-co-3' /> +assert sslSupport -> !isNull openssl && (httpServer -> httpd.openssl == openssl); +assert swigBindings -> !isNull swig; + +derivation { + name = "subversion-0.32.1"; + system = stdenv.system; + + builder = ./builder.sh; + src = fetchurl { + url = http://svn.collab.net/tarballs/subversion-0.32.1.tar.gz; + md5 = "b06717a8ef50db4b5c4d380af00bd901"; + }; + + localServer = localServer; + httpServer = httpServer; + sslSupport = sslSupport; + swigBindings = swigBindings; + + stdenv = stdenv; + openssl = if sslSupport then openssl else null; <co id='ex-svn-nix-co-4' /> + httpd = if httpServer then httpd else null; + expat = expat; + db4 = if localServer then db4 else null; + swig = if swigBindings then swig else null; +}</programlisting> +</example> + +<para>This example shows several features. Default parameters <xref +linkend='ex-svn-nix-co-1'/> can be used to simplify call sites: if an +argument that has a default is omitted, its default value is +used.</para> + +<para>You can use <emphasis>assertions</emphasis> to test whether +arguments satisfy certain constraints. The simple assertion <xref +linkend='ex-svn-nix-co-2'/> tests whether the <varname>expat</varname> +argument is not a null value. The more complex assertion <xref +linkend='ex-svn-nix-co-3'/> says that if Subversion is built with +Apache support, then <varname>httpd</varname> (the Apache package) +must not be null and it must have been built using the same instance +of the <varname>expat</varname> library as was passed to the +Subversion expression. This is since the Subversion code is +dynamically linked against the Apache code and they both use Expat, +they must be linked against the same instance—otherwise a +conflict might occur.</para> + +</sect1> + + +</chapter> |