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+<chapter xmlns="http://docbook.org/ns/docbook"
+      xmlns:xlink="http://www.w3.org/1999/xlink"
+      xmlns:xi="http://www.w3.org/2001/XInclude"
+      version="5.0"
+      xml:id="ch-relnotes-0.8">
+
+<title>Release 0.8 (April 11, 2005)</title>
+
+<para>NOTE: the hashing scheme in Nix 0.8 changed (as detailed below).
+As a result, <command>nix-pull</command> manifests and channels built
+for Nix 0.7 and below will now work anymore.  However, the Nix
+expression language has not changed, so you can still build from
+source.  Also, existing user environments continue to work.  Nix 0.8
+will automatically upgrade the database schema of previous
+installations when it is first run.</para>
+
+<para>If you get the error message
+
+<screen>
+you have an old-style manifest `/nix/var/nix/manifests/[...]'; please
+delete it</screen>
+
+you should delete previously downloaded manifests:
+
+<screen>
+$ rm /nix/var/nix/manifests/*</screen>
+
+If <command>nix-channel</command> gives the error message
+
+<screen>
+manifest `http://catamaran.labs.cs.uu.nl/dist/nix/channels/[channel]/MANIFEST'
+is too old (i.e., for Nix &lt;= 0.7)</screen>
+
+then you should unsubscribe from the offending channel
+(<command>nix-channel --remove
+<replaceable>URL</replaceable></command>; leave out
+<literal>/MANIFEST</literal>), and subscribe to the same URL, with
+<literal>channels</literal> replaced by <literal>channels-v3</literal>
+(e.g., <link
+xlink:href='http://catamaran.labs.cs.uu.nl/dist/nix/channels-v3/nixpkgs-unstable'
+/>).</para>
+
+<para>Nix 0.8 has the following improvements:
+
+<itemizedlist>
+
+  <listitem><para>The cryptographic hashes used in store paths are now
+  160 bits long, but encoded in base-32 so that they are still only 32
+  characters long (e.g.,
+  <filename>/nix/store/csw87wag8bqlqk7ipllbwypb14xainap-atk-1.9.0</filename>).
+  (This is actually a 160 bit truncation of a SHA-256
+  hash.)</para></listitem>
+
+  <listitem><para>Big cleanups and simplifications of the basic store
+  semantics.  The notion of “closure store expressions” is gone (and
+  so is the notion of “successors”); the file system references of a
+  store path are now just stored in the database.</para>
+
+  <para>For instance, given any store path, you can query its closure:
+
+  <screen>
+$ nix-store -qR $(which firefox)
+... lots of paths ...</screen>
+
+  Also, Nix now remembers for each store path the derivation that
+  built it (the “deriver”):
+
+  <screen>
+$ nix-store -qR $(which firefox)
+/nix/store/4b0jx7vq80l9aqcnkszxhymsf1ffa5jd-firefox-1.0.1.drv</screen>
+
+  So to see the build-time dependencies, you can do
+
+  <screen>
+$ nix-store -qR $(nix-store -qd $(which firefox))</screen>
+
+  or, in a nicer format:
+
+  <screen>
+$ nix-store -q --tree $(nix-store -qd $(which firefox))</screen>
+
+  </para>
+
+  <para>File system references are also stored in reverse.  For
+  instance, you can query all paths that directly or indirectly use a
+  certain Glibc:
+
+  <screen>
+$ nix-store -q --referrers-closure \
+    /nix/store/8lz9yc6zgmc0vlqmn2ipcpkjlmbi51vv-glibc-2.3.4</screen>
+
+  </para>
+
+  </listitem>
+
+  <listitem><para>The concept of fixed-output derivations has been
+  formalised.  Previously, functions such as
+  <function>fetchurl</function> in Nixpkgs used a hack (namely,
+  explicitly specifying a store path hash) to prevent changes to, say,
+  the URL of the file from propagating upwards through the dependency
+  graph, causing rebuilds of everything.  This can now be done cleanly
+  by specifying the <varname>outputHash</varname> and
+  <varname>outputHashAlgo</varname> attributes.  Nix itself checks
+  that the content of the output has the specified hash.  (This is
+  important for maintaining certain invariants necessary for future
+  work on secure shared stores.)</para></listitem>
+
+  <listitem><para>One-click installation :-) It is now possible to
+  install any top-level component in Nixpkgs directly, through the web
+  — see, e.g., <link
+  xlink:href='http://catamaran.labs.cs.uu.nl/dist/nixpkgs-0.8/' />.
+  All you have to do is associate
+  <filename>/nix/bin/nix-install-package</filename> with the MIME type
+  <literal>application/nix-package</literal> (or the extension
+  <filename>.nixpkg</filename>), and clicking on a package link will
+  cause it to be installed, with all appropriate dependencies.  If you
+  just want to install some specific application, this is easier than
+  subscribing to a channel.</para></listitem>
+
+  <listitem><para><command>nix-store -r
+  <replaceable>PATHS</replaceable></command> now builds all the
+  derivations PATHS in parallel.  Previously it did them sequentially
+  (though exploiting possible parallelism between subderivations).
+  This is nice for build farms.</para></listitem>
+
+  <listitem><para><command>nix-channel</command> has new operations
+  <option>--list</option> and
+  <option>--remove</option>.</para></listitem>
+
+  <listitem><para>New ways of installing components into user
+  environments:
+
+  <itemizedlist>
+
+    <listitem><para>Copy from another user environment:
+
+    <screen>
+$ nix-env -i --from-profile .../other-profile firefox</screen>
+
+    </para></listitem>
+
+    <listitem><para>Install a store derivation directly (bypassing the
+    Nix expression language entirely):
+
+    <screen>
+$ nix-env -i /nix/store/z58v41v21xd3...-aterm-2.3.1.drv</screen>
+
+    (This is used to implement <command>nix-install-package</command>,
+    which is therefore immune to evolution in the Nix expression
+    language.)</para></listitem>
+
+    <listitem><para>Install an already built store path directly:
+
+    <screen>
+$ nix-env -i /nix/store/hsyj5pbn0d9i...-aterm-2.3.1</screen>
+
+    </para></listitem>
+
+    <listitem><para>Install the result of a Nix expression specified
+    as a command-line argument:
+
+    <screen>
+$ nix-env -f .../i686-linux.nix -i -E 'x: x.firefoxWrapper'</screen>
+
+    The difference with the normal installation mode is that
+    <option>-E</option> does not use the <varname>name</varname>
+    attributes of derivations.  Therefore, this can be used to
+    disambiguate multiple derivations with the same
+    name.</para></listitem>
+
+  </itemizedlist></para></listitem>
+
+  <listitem><para>A hash of the contents of a store path is now stored
+  in the database after a successful build.  This allows you to check
+  whether store paths have been tampered with: <command>nix-store
+  --verify --check-contents</command>.</para></listitem>
+
+  <listitem>
+
+    <para>Implemented a concurrent garbage collector.  It is now
+    always safe to run the garbage collector, even if other Nix
+    operations are happening simultaneously.</para>
+
+    <para>However, there can still be GC races if you use
+    <command>nix-instantiate</command> and <command>nix-store
+    --realise</command> directly to build things.  To prevent races,
+    use the <option>--add-root</option> flag of those commands.</para>
+
+  </listitem>
+
+  <listitem><para>The garbage collector now finally deletes paths in
+  the right order (i.e., topologically sorted under the “references”
+  relation), thus making it safe to interrupt the collector without
+  risking a store that violates the closure
+  invariant.</para></listitem>
+
+  <listitem><para>Likewise, the substitute mechanism now downloads
+  files in the right order, thus preserving the closure invariant at
+  all times.</para></listitem>
+
+  <listitem><para>The result of <command>nix-build</command> is now
+  registered as a root of the garbage collector.  If the
+  <filename>./result</filename> link is deleted, the GC root
+  disappears automatically.</para></listitem>
+
+  <listitem>
+
+    <para>The behaviour of the garbage collector can be changed
+    globally by setting options in
+    <filename>/nix/etc/nix/nix.conf</filename>.
+
+    <itemizedlist>
+
+      <listitem><para><literal>gc-keep-derivations</literal> specifies
+      whether deriver links should be followed when searching for live
+      paths.</para></listitem>
+
+      <listitem><para><literal>gc-keep-outputs</literal> specifies
+      whether outputs of derivations should be followed when searching
+      for live paths.</para></listitem>
+
+      <listitem><para><literal>env-keep-derivations</literal>
+      specifies whether user environments should store the paths of
+      derivations when they are added (thus keeping the derivations
+      alive).</para></listitem>
+
+    </itemizedlist>
+
+  </para></listitem>
+
+  <listitem><para>New <command>nix-env</command> query flags
+  <option>--drv-path</option> and
+  <option>--out-path</option>.</para></listitem>
+
+  <listitem><para><command>fetchurl</command> allows SHA-1 and SHA-256
+  in addition to MD5.  Just specify the attribute
+  <varname>sha1</varname> or <varname>sha256</varname> instead of
+  <varname>md5</varname>.</para></listitem>
+
+  <listitem><para>Manual updates.</para></listitem>
+
+</itemizedlist>
+
+</para>
+
+</chapter>
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