* component -> package.
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@ -6,9 +6,9 @@
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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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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> components should consult
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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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@ -16,8 +16,8 @@ who want to <emphasis>create</emphasis> components should consult
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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 components, and to query what
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components are installed or are available for installation.</para>
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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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@ -30,10 +30,10 @@ 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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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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components ranging from basic development stuff such as GCC and Glibc,
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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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@ -41,7 +41,7 @@ the latest version from <link
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xlink:href='http://nix.cs.uu.nl/dist/nix' />.</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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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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@ -74,7 +74,7 @@ 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 components, i.e., whether they are installed into the user
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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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@ -86,24 +86,24 @@ 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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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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component, 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 component from
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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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components contained in them. This is done using <literal>nix-env
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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 component called <literal>subversion</literal> (which
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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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@ -112,7 +112,7 @@ management system</link>).</para>
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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 components are
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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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@ -153,7 +153,7 @@ 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 components for which there are newer
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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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@ -199,19 +199,19 @@ set.</para></footnote></para>
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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, components are stored in unique locations in the
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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 component might be stored in a directory
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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 component —
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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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components differ in any way, they end up in different locations in
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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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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 component we want to use,
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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> components. These are called
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<emphasis>user environments</emphasis> and they are components
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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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@ -285,8 +285,8 @@ 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 components doesn’t interfere in
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any way with old components, since they are stored in different
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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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@ -352,18 +352,18 @@ This will <emphasis>not</emphasis> change the
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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 components from the system. All they do (as shown
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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” components.</para>
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symlinks to the “deleted” packages.</para>
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<para>Of course, since disk space is not infinite, unused components
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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 component
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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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component, it will not be deleted. After all, we wouldn’t be able to
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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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@ -486,7 +486,7 @@ makes the union of each channel’s Nix expressions the default for
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<screen>
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$ nix-env -u '*'</screen>
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to upgrade all components in your profile to the latest versions
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to upgrade all packages in your profile to the latest versions
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available in the subscribed channels.</para>
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</section>
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