<section 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 (2005-04-11)</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>

</section>
