forked from lix-project/lix
449 lines
18 KiB
XML
449 lines
18 KiB
XML
<chapter>
|
|
<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-push</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://losser.st-lab.cs.uu.nl/~eelco/nix-dist/
|
|
obtaining list of Nix archives at http://losser.st-lab.cs.uu.nl/~eelco/nix-dist...
|
|
...</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/links/current/bin</filename>,
|
|
where
|
|
<filename><replaceable>prefix</replaceable>/var/nix/links/current</filename>
|
|
is just a symlink to the current user environment:
|
|
</para>
|
|
|
|
<screen>
|
|
$ ls -l /nix/var/nix/links/
|
|
...
|
|
lrwxrwxrwx 1 eelco ... 15 -> /nix/store/1871...12b0-user-environment
|
|
lrwxrwxrwx 1 eelco ... 16 -> /nix/store/59ba...df6b-user-environment
|
|
lrwxrwxrwx 1 eelco ... current -> /nix/var/nix/links/16</screen>
|
|
|
|
<para>
|
|
That is, <filename>current</filename> in this example is a link to
|
|
<filename>16</filename>, which is the current user environment. Before
|
|
the installation, it pointed to <filename>15</filename>. Note that this
|
|
means that you can atomically roll-back to the previous user environment
|
|
by pointing the symlink <filename>current</filename> at
|
|
<filename>15</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/links/16/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/links/current/bin/svn</filename> =
|
|
<filename>/nix/var/nix/links/16/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>
|