170 lines
6.6 KiB
XML
170 lines
6.6 KiB
XML
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<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="ch-basic-package-mgmt">
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<title>Basic Package Management</title>
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<para>The main command for package management is <link
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linkend="sec-nix-env"><command>nix-env</command></link>. You can use
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it to install, upgrade, and erase packages, and to query what
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packages are installed or are available for installation.</para>
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<para>In Nix, different users can have different “views”
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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 “active” 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 packages,
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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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packages 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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expressions based on it, or completely new ones.) You can download
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the latest version from <link
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xlink:href='http://nixos.org/nixpkgs/download.html' />.</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 packages 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. The flag <option>-q</option>
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specifies a query operation; <option>-a</option> means that you want
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to show the “available” (i.e., installable) packages, as opposed to
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the installed packages; and <option>-f</option>
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<filename>nixpkgs-<replaceable>version</replaceable></filename>
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specifies the source of the packages. The argument
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<literal>'*'</literal> shows all installable packages. (The quotes are
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necessary to prevent shell expansion.) You can also select specific
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packages by name:
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<screen>
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$ nix-env -qaf nixpkgs-<replaceable>version</replaceable> gcc
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gcc-3.4.6
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gcc-4.0.3
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gcc-4.1.1</screen>
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</para>
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<para>It is also possible to see the <emphasis>status</emphasis> of
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available packages, 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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package 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 a
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very quick operation). The last one (<literal>S</literal>) indicates
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whether there is a so-called <emphasis>substitute</emphasis> for the
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package, which is Nix’s mechanism for doing binary deployment. It
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just means that Nix knows that it can fetch a pre-built package from
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somewhere (typically a network server) instead of building it
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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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packages 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 package called <literal>subversion</literal> (which
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is, of course, the <link
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xlink:href='http://subversion.tigris.org/'>Subversion version
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management system</link>).</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 do a Ctrl-C on that install operation!): you just need
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to tell Nix that pre-built binaries of all those packages 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 <link
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xlink:href='http://nixos.org/releases/nixpkgs/nixpkgs-0.12pre11712-4lrp7j8x'
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/>, then you should do:
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<screen>
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$ nix-pull http://nixos.org/releases/nixpkgs/nixpkgs-0.12pre11712-4lrp7j8x/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'>nixos.org</systemitem>, instead of building
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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 a DSL 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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“newer” version in the new set of Nix expressions, as
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defined by some pretty arbitrary rules regarding ordering of version
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numbers (which generally do what you’d expect of them). To just
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unconditionally replace Subversion with whatever version is in the Nix
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expressions, use <parameter>-i</parameter> instead of
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<parameter>-u</parameter>; <parameter>-i</parameter> will remove
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whatever version is already installed.</para>
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<para>You can also upgrade all packages 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>Sometimes it’s useful to be able to ask what
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<command>nix-env</command> would do, without actually doing it. For
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instance, to find out what packages would be upgraded by
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<literal>nix-env -u '*'</literal>, you can do
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<screen>
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$ nix-env ... -u '*' --dry-run
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(dry run; not doing anything)
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upgrading `libxslt-1.1.0' to `libxslt-1.1.10'
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upgrading `graphviz-1.10' to `graphviz-1.12'
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upgrading `coreutils-5.0' to `coreutils-5.2.1'</screen>
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</para>
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</chapter>
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