forked from lix-project/lix
37d7abd694
The expression `with E1; E2' evaluates to E2 with all bindings in
the attribute set E1 substituted. E.g.,
with {x = 123;}; x
evaluates to 123. That is, the attribute set E1 is in scope in E2.
This is particularly useful when importing files containing lots
definitions. E.g., instead of
let {
inherit (import ./foo.nix) a b c d e f;
body = ... a ... f ...;
}
we can now say
with import ./foo.nix;
... a ... f ...
I.e., we don't have to say what variables should be brought into scope.
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7.2 KiB
XML
198 lines
No EOL
7.2 KiB
XML
<chapter id='chap-package-management'><title>Package Management</title>
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<para>This chapter discusses how to do package management with Nix,
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i.e., how to obtain, install, upgrade, and erase components. This is
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the <quote>user's</quote> perspective of the Nix system — people
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who want to <emphasis>create</emphasis> components should consult
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<xref linkend='chap-writing-nix-expressions' />.</para>
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<sect1><title>Basic package management</title>
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<para>The main command for package management is
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<command>nix-env</command>. You can use it to install, upgrade, and
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erase components, and to query what components are installed or are
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available for installation.</para>
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<para>In Nix, different users can have different <quote>views</quote>
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on the set of installed applications. That is, there might be lots of
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applications present on the system (possibly in many different
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versions), but users can have a specific selection of those active —
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where <quote>active</quote> just means that it appears in a directory
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in the user's <envar>PATH</envar>. Such a view on the set of
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installed applications is called a <emphasis>user
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environment</emphasis>, which is just a directory tree consisting of
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symlinks to the files of the active applications. </para>
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<para>Components are installed from a set of <emphasis>Nix
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expressions</emphasis> that tell Nix how to build those components,
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including, if necessary, their dependencies. There is a collection of
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Nix expressions called the Nix Package collection that contains
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components ranging from basic development stuff such as GCC and Glibc,
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to end-user applications like Mozilla Firefox. (Nix is however not
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tied to the Nix Package collection; you could write your own Nix
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expression based on that, or completely new.) You can download the
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latest version from <ulink
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url='http://catamaran.labs.cs.uu.nl/dist/nix' />. You probably want
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the latest unstable release; currently the stable releases tend to lag
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behind quite a bit.</para>
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<para>Assuming that you have downloaded and unpacked a release of Nix
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Packages, you can view the set of available components in the release:
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<screen>
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$ nix-env -qaf nixpkgs-<replaceable>version</replaceable>
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ant-blackdown-1.4.2
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aterm-2.2
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bash-3.0
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binutils-2.15
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bison-1.875d
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blackdown-1.4.2
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bzip2-1.0.2
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...</screen>
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where <literal>nixpkgs-<replaceable>version</replaceable></literal> is
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where you've unpacked the release.</para>
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<para>It is also possible to see the <emphasis>status</emphasis> of
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available component, i.e., whether they are installed into the user
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environment and/or present in the system:
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<screen>
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$ nix-env -qasf nixpkgs-<replaceable>version</replaceable>
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...
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-PS bash-3.0
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--S binutils-2.15
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IPS bison-1.875d
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...</screen>
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The first character (<literal>I</literal>) indicates whether the
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component is installed in your current user environment. The second
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(<literal>P</literal>) indicates whether it is present on your system
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(in which case installing it into your user environment would be very
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quick). The last one (<literal>S</literal>) indicates whether there
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is a so-called <emphasis>substitute</emphasis> for the component,
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which is Nix's mechanism for doing binary deployment. It just means
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that Nix know that it can fetch a pre-built component from somewhere
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(typically a network server) instead of building it locally.</para>
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<para>So now that we have a set of Nix expressions we can build the
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components contained in them. This is done using <literal>nix-env
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-i</literal>. For instance,
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<screen>
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$ nix-env -f nixpkgs-<replaceable>version</replaceable> -i subversion</screen>
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will install the component called <literal>subversion</literal> (which
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is, of course, the <ulink
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url='http://subversion.tigris.org/'>Subversion version management
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system</ulink>).</para>
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<para>When you do this for the first time, Nix will start building
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Subversion and all its dependencies. This will take quite a while —
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typically an hour or two on modern machines. Fortunately, there is a
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faster way (so just do a Ctrl-C on that install operation!): you just
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need to tell Nix that pre-built binaries of all those components are
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available somewhere. This is done using the
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<command>nix-pull</command> command, which must be supplied with a URL
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containing a <emphasis>manifest</emphasis> describing what binaries
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are available. This URL should correspond to the Nix Packages release
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that you're using. For instance, if you obtained a release from
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<ulink
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url='http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-0.6pre1554/' />,
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then you should do:
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<screen>
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$ nix-pull http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-0.6pre1554/MANIFEST</screen>
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If you then issue the installation command, it should start
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downloading binaries from <systemitem
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class='fqdomainname'>catamaran.labs.cs.uu.nl</systemitem>, instead of
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building them from source. This might still take a while since all
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dependencies must be downloaded, but on a reasonably fast connection
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such as an ADSL line it's on the order of a few minutes.</para>
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<para>Naturally, packages can also be uninstalled:
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<screen>
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$ nix-env -e subversion</screen>
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</para>
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<para>Upgrading to a new version is just as easy. If you have a new
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release of Nix Packages, you can do:
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<screen>
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$ nix-env -f nixpkgs-<replaceable>version</replaceable> -u subversion</screen>
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This will <emphasis>only</emphasis> upgrade Subversion if there is a
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<quote>newer</quote> version in the new set of Nix expressions, as
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defined by some pretty much arbitrary rules regarding ordering of
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version numbers (which generally do what you'd expect of them). To
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just unconditionally replace Subversion with whatever version is in
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the Nix expressions, use <parameter>-i</parameter> instead of
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<parameter>-u</parameter> — <parameter>-i</parameter> will
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remove whatever version is already installed.</para>
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<para>You can also upgrade all components for which there are newer
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versions:
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<screen>
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$ nix-env -f nixpkgs-<replaceable>version</replaceable> -u '*'</screen>
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</para>
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<para>If you grow tired of specifying the Nix expressions using
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<parameter>-f</parameter> all the time, you can set a default
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location:
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<screen>
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$ nix-env -I nixpkgs-<replaceable>version</replaceable></screen>
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After this you can just say, for instance, <literal>nix-env -u
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'*'</literal>.<footnote><para>Setting a default using
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<parameter>-I</parameter> currently clashes with using Nix channels,
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since <literal>nix-channel --update</literal> calls <literal>nix-env
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-I</literal> to set the default to the Nix expressions it downloaded
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from the channel, replacing whatever default you had
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set.</para></footnote></para>
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</sect1>
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<sect1><title>Profiles</title>
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<para>In Nix, operations such as upgrading or removing components
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never overwrite or remove the files of those components, and they
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don't even touch the user environments that point to them. Rather,
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they cause a <emphasis>new</emphasis> user environment to be
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constructed based on the old one. This is illustrated in Figure
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bla.</para>
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<figure><title>User environments</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref='figures/userenv-frame3.png' format='PNG' />
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</imageobject>
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</mediaobject>
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</figure>
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</sect1>
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<sect1><title>Garbage collection</title>
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<para>Bla</para>
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</sect1>
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<sect1><title>Channels</title>
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<para>Bla</para>
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</sect1>
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</chapter> |