592 lines
23 KiB
XML
592 lines
23 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id='chap-package-management'>
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<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 packages. This is
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the “user’s” perspective of the Nix system — people
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who want to <emphasis>create</emphasis> packages should consult
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<xref linkend='chap-writing-nix-expressions' />.</para>
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<section><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 an 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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</section>
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<section xml:id="sec-profiles"><title>Profiles</title>
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<para>Profiles and user environments are Nix’s mechanism for
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implementing the ability to allow different users to have different
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configurations, and to do atomic upgrades and rollbacks. To
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understand how they work, it’s useful to know a bit about how Nix
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works. In Nix, packages are stored in unique locations in the
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<emphasis>Nix store</emphasis> (typically,
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<filename>/nix/store</filename>). For instance, a particular version
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of the Subversion package might be stored in a directory
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<filename>/nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3/</filename>,
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while another version might be stored in
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<filename>/nix/store/5mq2jcn36ldlmh93yj1n8s9c95pj7c5s-subversion-1.1.2</filename>.
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The long strings prefixed to the directory names are cryptographic
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hashes<footnote><para>160-bit truncations of SHA-256 hashes encoded in
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a base-32 notation, to be precise.</para></footnote> of
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<emphasis>all</emphasis> inputs involved in building the package —
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sources, dependencies, compiler flags, and so on. So if two
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packages differ in any way, they end up in different locations in
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the file system, so they don’t interfere with each other. <xref
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linkend='fig-user-environments' /> shows a part of a typical Nix
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store.</para>
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<figure xml:id='fig-user-environments'><title>User environments</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref='figures/user-environments.png' format='PNG' />
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</imageobject>
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</mediaobject>
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</figure>
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<para>Of course, you wouldn’t want to type
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<screen>
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$ /nix/store/dpmvp969yhdq...-subversion-1.1.3/bin/svn</screen>
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every time you want to run Subversion. Of course we could set up the
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<envar>PATH</envar> environment variable to include the
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<filename>bin</filename> directory of every package we want to use,
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but this is not very convenient since changing <envar>PATH</envar>
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doesn’t take effect for already existing processes. The solution Nix
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uses is to create directory trees of symlinks to
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<emphasis>activated</emphasis> packages. These are called
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<emphasis>user environments</emphasis> and they are packages
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themselves (though automatically generated by
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<command>nix-env</command>), so they too reside in the Nix store. For
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instance, in <xref linkend='fig-user-environments' /> the user
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environment <filename>/nix/store/5mq2jcn36ldl...-user-env</filename>
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contains a symlink to just Subversion 1.1.2 (arrows in the figure
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indicate symlinks). This would be what we would obtain if we had done
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<screen>
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$ nix-env -i subversion</screen>
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on a set of Nix expressions that contained Subversion 1.1.2.</para>
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<para>This doesn’t in itself solve the problem, of course; you
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wouldn’t want to type
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<filename>/nix/store/0c1p5z4kda11...-user-env/bin/svn</filename>
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either. That’s why there are symlinks outside of the store that point
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to the user environments in the store; for instance, the symlinks
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<filename>default-42-link</filename> and
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<filename>default-43-link</filename> in the example. These are called
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<emphasis>generations</emphasis> since every time you perform a
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<command>nix-env</command> operation, a new user environment is
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generated based on the current one. For instance, generation 43 was
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created from generation 42 when we did
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<screen>
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$ nix-env -i subversion mozilla</screen>
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on a set of Nix expressions that contained Mozilla and a new version
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of Subversion.</para>
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<para>Generations are grouped together into
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<emphasis>profiles</emphasis> so that different users don’t interfere
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with each other if they don’t want to. For example:
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<screen>
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$ ls -l /nix/var/nix/profiles/
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...
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lrwxrwxrwx 1 eelco ... default-42-link -> /nix/store/0c1p5z4kda11...-user-env
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lrwxrwxrwx 1 eelco ... default-43-link -> /nix/store/3aw2pdyx2jfc...-user-env
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lrwxrwxrwx 1 eelco ... default -> default-43-link</screen>
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This shows a profile called <filename>default</filename>. The file
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<filename>default</filename> itself is actually a symlink that points
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to the current generation. When we do a <command>nix-env</command>
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operation, a new user environment and generation link are created
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based on the current one, and finally the <filename>default</filename>
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symlink is made to point at the new generation. This last step is
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atomic on Unix, which explains how we can do atomic upgrades. (Note
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that the building/installing of new packages doesn’t interfere in
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any way with old packages, since they are stored in different
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locations in the Nix store.)</para>
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<para>If you find that you want to undo a <command>nix-env</command>
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operation, you can just do
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<screen>
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$ nix-env --rollback</screen>
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which will just make the current generation link point at the previous
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link. E.g., <filename>default</filename> would be made to point at
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<filename>default-42-link</filename>. You can also switch to a
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specific generation:
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<screen>
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$ nix-env --switch-generation 43</screen>
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which in this example would roll forward to generation 43 again. You
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can also see all available generations:
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<screen>
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$ nix-env --list-generations</screen></para>
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<para>Actually, there is another level of indirection not shown in the
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figure above. You generally wouldn’t have
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<filename>/nix/var/nix/profiles/<replaceable>some-profile</replaceable>/bin</filename>
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in your <envar>PATH</envar>. Rather, there is a symlink
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<filename>~/.nix-profile</filename> that points to your current
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profile. This means that you should put
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<filename>~/.nix-profile/bin</filename> in your <envar>PATH</envar>
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(and indeed, that’s what the initialisation script
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<filename>/nix/etc/profile.d/nix.sh</filename> does). This makes it
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easier to switch to a different profile. You can do that using the
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command <command>nix-env --switch-profile</command>:
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<screen>
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$ nix-env --switch-profile /nix/var/nix/profiles/my-profile
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$ nix-env --switch-profile /nix/var/nix/profiles/default</screen>
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These commands switch to the <filename>my-profile</filename> and
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default profile, respectively. If the profile doesn’t exist, it will
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be created automatically. You should be careful about storing a
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profile in another location than the <filename>profiles</filename>
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directory, since otherwise it might not be used as a root of the
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garbage collector (see <xref linkend='sec-garbage-collection'
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/>).</para>
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<para>All <command>nix-env</command> operations work on the profile
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pointed to by <command>~/.nix-profile</command>, but you can override
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this using the <option>--profile</option> option (abbreviation
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<option>-p</option>):
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<screen>
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$ nix-env -p /nix/var/nix/profiles/other-profile -i subversion</screen>
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This will <emphasis>not</emphasis> change the
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<command>~/.nix-profile</command> symlink.</para>
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</section>
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<section xml:id='sec-garbage-collection'><title>Garbage collection</title>
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<para><command>nix-env</command> operations such as upgrades
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(<option>-u</option>) and uninstall (<option>-e</option>) never
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actually delete packages from the system. All they do (as shown
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above) is to create a new user environment that no longer contains
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symlinks to the “deleted” packages.</para>
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<para>Of course, since disk space is not infinite, unused packages
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should be removed at some point. You can do this by running the Nix
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garbage collector. It will remove from the Nix store any package
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not used (directly or indirectly) by any generation of any
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profile.</para>
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<para>Note however that as long as old generations reference a
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package, it will not be deleted. After all, we wouldn’t be able to
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do a rollback otherwise. So in order for garbage collection to be
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effective, you should also delete (some) old generations. Of course,
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this should only be done if you are certain that you will not need to
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roll back.</para>
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<para>To delete all old (non-current) generations of your current
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profile:
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<screen>
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$ nix-env --delete-generations old</screen>
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Instead of <literal>old</literal> you can also specify a list of
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generations, e.g.,
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<screen>
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$ nix-env --delete-generations 10 11 14</screen>
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</para>
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<para>After removing appropriate old generations you can run the
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garbage collector as follows:
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<screen>
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$ nix-store --gc</screen>
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If you are feeling uncertain, you can also first view what files would
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be deleted:
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<screen>
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$ nix-store --gc --print-dead</screen>
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Likewise, the option <option>--print-live</option> will show the paths
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that <emphasis>won’t</emphasis> be deleted.</para>
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<para>There is also a convenient little utility
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<command>nix-collect-garbage</command>, which when invoked with the
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<option>-d</option> (<option>--delete-old</option>) switch deletes all
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old generations of all profiles in
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<filename>/nix/var/nix/profiles</filename>. So
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<screen>
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$ nix-collect-garbage -d</screen>
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is a quick and easy way to clean up your system.</para>
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<section xml:id="ssec-gc-roots"><title>Garbage collector roots</title>
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<para>The roots of the garbage collector are all store paths to which
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there are symlinks in the directory
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<filename><replaceable>prefix</replaceable>/nix/var/nix/gcroots</filename>.
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For instance, the following command makes the path
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<filename>/nix/store/d718ef...-foo</filename> a root of the collector:
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<screen>
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$ ln -s /nix/store/d718ef...-foo /nix/var/nix/gcroots/bar</screen>
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That is, after this command, the garbage collector will not remove
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<filename>/nix/store/d718ef...-foo</filename> or any of its
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dependencies.</para>
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<para>Subdirectories of
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<filename><replaceable>prefix</replaceable>/nix/var/nix/gcroots</filename>
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are also searched for symlinks. Symlinks to non-store paths are
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followed and searched for roots, but symlinks to non-store paths
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<emphasis>inside</emphasis> the paths reached in that way are not
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followed to prevent infinite recursion.</para>
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</section>
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</section>
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<section xml:id="sec-channels"><title>Channels</title>
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<para>If you want to stay up to date with a set of packages, it’s not
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very convenient to manually download the latest set of Nix expressions
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for those packages, use <command>nix-pull</command> to register
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pre-built binaries (if available), and upgrade using
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<command>nix-env</command>. Fortunately, there’s a better way:
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<emphasis>Nix channels</emphasis>.</para>
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<para>A Nix channel is just a URL that points to a place that contains
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a set of Nix expressions and a manifest. Using the command <link
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linkend="sec-nix-channel"><command>nix-channel</command></link> you
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can automatically stay up to date with whatever is available at that
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URL.</para>
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<para>You can “subscribe” to a channel using
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<command>nix-channel --add</command>, e.g.,
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<screen>
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$ nix-channel --add http://nixos.org/channels/nixpkgs-unstable</screen>
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subscribes you to a channel that always contains that latest version
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of the Nix Packages collection. (Instead of
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<literal>nixpkgs-unstable</literal> you could also subscribe to
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<literal>nixpkgs-stable</literal>, which should have a higher level of
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stability, but right now is just outdated.) Subscribing really just
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means that the URL is added to the file
|
||
<filename>~/.nix-channels</filename>. Right now there is no command
|
||
to “unsubscribe”; you should just edit that file manually
|
||
and delete the offending URL.</para>
|
||
|
||
<para>To obtain the latest Nix expressions available in a channel, do
|
||
|
||
<screen>
|
||
$ nix-channel --update</screen>
|
||
|
||
This downloads the Nix expressions in every channel (downloaded from
|
||
<literal><replaceable>url</replaceable>/nixexprs.tar.bz2</literal>)
|
||
and registers any available pre-built binaries in every channel
|
||
(by <command>nix-pull</command>ing
|
||
<literal><replaceable>url</replaceable>/MANIFEST</literal>). It also
|
||
makes the union of each channel’s Nix expressions the default for
|
||
<command>nix-env</command> operations. Consequently, you can then say
|
||
|
||
<screen>
|
||
$ nix-env -u '*'</screen>
|
||
|
||
to upgrade all packages in your profile to the latest versions
|
||
available in the subscribed channels.</para>
|
||
|
||
</section>
|
||
|
||
|
||
<section xml:id="sec-one-click"><title>One-click installs</title>
|
||
|
||
<para>Often, when you want to install a specific package (e.g., from
|
||
the <link
|
||
xlink:href="http://nixos.org/nixpkgs/">Nix
|
||
Packages collection</link>), subscribing to a channel is a bit
|
||
cumbersome. And channels don’t help you at all if you want to install
|
||
an older version of a package than the one provided by the current
|
||
contents of the channel, or a package that has been removed from the
|
||
channel. That’s when <emphasis>one-click installs</emphasis> come in
|
||
handy: you can just go to the web page that contains the package,
|
||
click on it, and it will be installed with all the necessary
|
||
dependencies.</para>
|
||
|
||
<para>For instance, you can go to <link
|
||
xlink:href="http://hydra.nixos.org/jobset/nixpkgs/trunk/channel/latest"
|
||
/> and click on any link for the individual packages for your
|
||
platform. The first time you do this, your browser will ask what to
|
||
do with <literal>application/nix-package</literal> files. You should
|
||
open them with <filename>/nix/bin/nix-install-package</filename>.
|
||
This will open a window that asks you to confirm that you want to
|
||
install the package. When you answer <literal>Y</literal>, the
|
||
package and all its dependencies will be installed. This is a binary
|
||
deployment mechanism — you get packages pre-compiled for the selected
|
||
platform type.</para>
|
||
|
||
<para>You can also install <literal>application/nix-package</literal>
|
||
files from the command line directly. See <xref
|
||
linkend='sec-nix-install-package' /> for details.</para>
|
||
|
||
</section>
|
||
|
||
|
||
<section xml:id="sec-sharing-packages"><title>Sharing packages between machines</title>
|
||
|
||
<para>Sometimes you want to copy a package from one machine to
|
||
another. Or, you want to install some packages and you know that
|
||
another machine already has some or all of those packages or their
|
||
dependencies. In that case there are mechanisms to quickly copy
|
||
packages between machines.</para>
|
||
|
||
<para>The command <command
|
||
linkend="sec-nix-copy-closure">nix-copy-closure</command> copies a Nix
|
||
store path along with all its dependencies to or from another machine
|
||
via the SSH protocol. It doesn’t copy store paths that are already
|
||
present on the target machine. For example, the following command
|
||
copies Firefox with all its dependencies:
|
||
|
||
<screen>
|
||
$ nix-copy-closure --to alice@itchy.example.org $(type -p firefox)</screen>
|
||
|
||
See <xref linkend='sec-nix-copy-closure' /> for details.</para>
|
||
|
||
<para>With <command linkend='refsec-nix-store-export'>nix-store
|
||
--export</command> and <command
|
||
linkend='refsec-nix-store-import'>nix-store --import</command> you can
|
||
write the closure of a store path (that is, the path and all its
|
||
dependencies) to a file, and then unpack that file into another Nix
|
||
store. For example,
|
||
|
||
<screen>
|
||
$ nix-store --export $(type -p firefox) > firefox.closure</screen>
|
||
|
||
writes the closure of Firefox to a file. You can then copy this file
|
||
to another machine and install the closure:
|
||
|
||
<screen>
|
||
$ nix-store --import < firefox.closure</screen>
|
||
|
||
Any store paths in the closure that are already present in the target
|
||
store are ignored. It is also possible to pipe the export into
|
||
another command, e.g. to copy and install a closure directly to/on
|
||
another machine:
|
||
|
||
<screen>
|
||
$ nix-store --export $(type -p firefox) | bzip2 | \
|
||
ssh alice@itchy.example.org "bunzip2 | nix-store --import"</screen>
|
||
|
||
But note that <command>nix-copy-closure</command> is generally more
|
||
efficient in this example because it only copies paths that are not
|
||
already present in the target Nix store.</para>
|
||
|
||
<para>Finally, if you can mount the Nix store of a remote machine in
|
||
your local filesystem, Nix can copy paths from the remote Nix store to
|
||
the local Nix store <emphasis>on demand</emphasis>. For instance,
|
||
suppose that you mount a remote machine containing a Nix store via
|
||
<command
|
||
xlink:href="http://fuse.sourceforge.net/sshfs.html">sshfs</command>:
|
||
|
||
<screen>
|
||
$ sshfs alice@itchy.example.org:/ /mnt</screen>
|
||
|
||
You should then set the <envar>NIX_OTHER_STORES</envar> environment
|
||
variable to tell Nix about this remote Nix store:
|
||
|
||
<screen>
|
||
$ export NIX_OTHER_STORES=/mnt/nix</screen>
|
||
|
||
Then if you do any Nix operation, e.g.
|
||
|
||
<screen>
|
||
$ nix-env -i firefox</screen>
|
||
|
||
and Nix has to build a path that it sees is already present in
|
||
<filename>/mnt/nix</filename>, then it will just copy from there
|
||
instead of building it from source.</para>
|
||
|
||
|
||
</section>
|
||
|
||
|
||
</chapter>
|