nix-super/doc/manual/release-notes.xml

<article xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="sec-relnotes">

<title>Nix Release Notes</title>



<!--==================================================================-->

<section xml:id="ssec-relnotes-0.11"><title>Release 0.11 (TBA)</title>

<itemizedlist>


  <listitem><para>TODO: multi-user support.  The old setuid method for
  sharing a store between multiple users has been
  removed.</para></listitem>


  <listitem><para>The new command <command>nix-copy-closure</command>
  gives you an easy and efficient way to exchange software between
  machines.  It copies the missing parts of the closure of a set of
  store path to or from a remote machine.</para></listitem>


  <listitem><para><command>nix-prefetch-url</command> now by default
  computes the SHA-256 hash of the file instead of the MD5 hash.  In
  calls to <function>fetchurl</function> you should pass an
  <literal>sha256</literal> attribute instead of
  <literal>md5</literal>.  You can pass either a hexadecimal or a
  base-32 encoding of the hash.</para></listitem>

  
  <listitem><para><command>nix-store</command> has a new operation
  <option>--read-log</option> (<option>-l</option>)
  <parameter>paths</parameter> that shows the build log of the given
  paths.</para></listitem>

  
  <listitem><para>TODO: <varname>allowedReferences</varname> for
  checking the set of references in the output of a
  derivation.</para></listitem>


  <listitem><para>TODO: semantic cleanups of string concatenation
  etc. (mostly in r6740).</para></listitem>


  <listitem><para>TODO: now using Berkeley DB 4.5.</para></listitem>


  <listitem><para>TODO: option <option>--reregister</option> in
  <command>nix-store --register-validity</command>.</para></listitem>


  <listitem><para>TODO: magic <varname>exportReferencesGraph</varname>
  attribute.</para></listitem>


  <listitem><para>TODO: option <option>--max-silent-time</option>,
  configuration setting
  <literal>build-max-silent-time</literal>.</para></listitem>


  <listitem><para>TODO: <command>nix-env</command>
  <option>--set</option>.</para></listitem>
  

  <listitem><para>TODO: <option>--argstr</option>.</para></listitem>


  <listitem><para>TODO: <command>nix-env</command> now maintains meta
  info about installed packages in user environments.  <option>-q
  --xml --meta</option> to show all meta info.</para></listitem>

  
  <listitem><para>TODO: <command>nix-env</command>
  <option>--set-flag</option>.  Specific flags:
  <literal>active</literal>, <literal>priority</literal>,
  <literal>keep</literal>.</para></listitem>

  
  <listitem><para>TODO: <command>nix-env</command> <option>-i</option>
  / <option>-u</option> take package priorities into
  account.</para></listitem>
  

  <listitem><para><command>nix-env -q</command> now has a flag
  <option>--prebuilt-only</option> (<option>-b</option>) that causes
  <command>nix-env</command> to show only those derivations whose
  output is already in the Nix store or that can be substituted (i.e.,
  downloaded from somewhere).  In other words, it shows the packages
  that can be installed “quickly”, i.e., don’t need to be built from
  source.  TODO: flag is also available in nix-env -i /
  -u.</para></listitem>
  

  <listitem><para>TODO: new built-ins
  <function>builtins.attrNames</function>,
  <function>builtins.filterSource</function>,
  <function>builtins.sub</function>,
  <function>builtins.stringLength</function>,
  <function>builtins.substring</function>.</para></listitem>


  <listitem><para>TODO: each subscribed channel is its own attribute
  in the top-level expression generated for the channel, this allows
  disambiguation (<command>nix-env -qaA</command>).</para></listitem>


  <listitem><para>TODO: substitutes table is gone, registering
  substitutes is now much faster.</para></listitem>


  <listitem><para><command>nix-prefetch-url</command> now has a
  limited form of caching.  This is used by
  <command>nix-channel</command> to prevent unnecessary downloads when
  the channel hasn’t changed.</para></listitem>


  <listitem><para>TODO: chroot support.</para></listitem>
  

</itemizedlist>

</section>



<!--==================================================================-->

<section><title>Release 0.10.1 (October 11, 2006)</title>

<para>This release fixes two somewhat obscure bugs that occur when
evaluating Nix expressions that are stored inside the Nix store
(<literal>NIX-67</literal>).  These do not affect most users.</para>

</section>



<!--==================================================================-->

<section><title>Release 0.10 (October 6, 2006)</title>

<note><para>This version of Nix uses Berkeley DB 4.4 instead of 4.3.
The database is upgraded automatically, but you should be careful not
to use old versions of Nix that still use Berkeley DB 4.3.  In
particular, if you use a Nix installed through Nix, you should run

<screen>
$ nix-store --clear-substitutes</screen>

first.</para></note>

<warning><para>Also, the database schema has changed slighted to fix a
performance issue (see below).  When you run any Nix 0.10 command for
the first time, the database will be upgraded automatically.  This is
irreversible.</para></warning>

<itemizedlist>

  
  <!-- Usability / features -->

  
  <listitem><para><command>nix-env</command> usability improvements:

    <itemizedlist>

      <listitem><para>An option <option>--compare-versions</option>
      (or <option>-c</option>) has been added to <command>nix-env
      --query</command> to allow you to compare installed versions of
      packages to available versions, or vice versa.  An easy way to
      see if you are up to date with what’s in your subscribed
      channels is <literal>nix-env -qc \*</literal>.</para></listitem>

      <listitem><para><literal>nix-env --query</literal> now takes as
      arguments a list of package names about which to show
      information, just like <option>--install</option>, etc.: for
      example, <literal>nix-env -q gcc</literal>.  Note that to show
      all derivations, you need to specify
      <literal>\*</literal>.</para></listitem>

      <listitem><para><literal>nix-env -i
      <replaceable>pkgname</replaceable></literal> will now install
      the highest available version of
      <replaceable>pkgname</replaceable>, rather than installing all
      available versions (which would probably give collisions)
      (<literal>NIX-31</literal>).</para></listitem>

      <listitem><para><literal>nix-env (-i|-u) --dry-run</literal> now
      shows exactly which missing paths will be built or
      substituted.</para></listitem>

      <listitem><para><literal>nix-env -qa --description</literal>
      shows human-readable descriptions of packages, provided that
      they have a <literal>meta.description</literal> attribute (which
      most packages in Nixpkgs don’t have yet).</para></listitem>

    </itemizedlist>
  
  </para></listitem>
  

  <listitem><para>New language features:

    <itemizedlist>

      <listitem><para>Reference scanning (which happens after each
      build) is much faster and takes a constant amount of
      memory.</para></listitem>

      <listitem><para>String interpolation.  Expressions like

<programlisting>
"--with-freetype2-library=" + freetype + "/lib"</programlisting>

      can now be written as

<programlisting>
"--with-freetype2-library=${freetype}/lib"</programlisting>

      You can write arbitrary expressions within
      <literal>${<replaceable>...</replaceable>}</literal>, not just
      identifiers.</para></listitem>
      
      <listitem><para>Multi-line string literals.</para></listitem>

      <listitem><para>String concatenations can now involve
      derivations, as in the example <code>"--with-freetype2-library="
      + freetype + "/lib"</code>.  This was not previously possible
      because we need to register that a derivation that uses such a
      string is dependent on <literal>freetype</literal>.  The
      evaluator now properly propagates this information.
      Consequently, the subpath operator (<literal>~</literal>) has
      been deprecated.</para></listitem>

      <listitem><para>Default values of function arguments can now
      refer to other function arguments; that is, all arguments are in
      scope in the default values
      (<literal>NIX-45</literal>).</para></listitem>

      <!--
      <listitem><para>TODO: domain checks (r5895).</para></listitem>
      -->

      <listitem><para>Lots of new built-in primitives, such as
      functions for list manipulation and integer arithmetic.  See the
      manual for a complete list.  All primops are now available in
      the set <varname>builtins</varname>, allowing one to test for
      the availability of primop in a backwards-compatible
      way.</para></listitem>

      <listitem><para>Real let-expressions: <literal>let x = ...;
      ... z = ...; in ...</literal>.</para></listitem>

    </itemizedlist>

  </para></listitem>


  <listitem><para>New commands <command>nix-pack-closure</command> and
  <command>nix-unpack-closure</command> than can be used to easily
  transfer a store path with all its dependencies to another machine.
  Very convenient whenever you have some package on your machine and
  you want to copy it somewhere else.</para></listitem>

  
  <listitem><para>XML support:

    <itemizedlist>

      <listitem><para><literal>nix-env -q --xml</literal> prints the
      installed or available packages in an XML representation for
      easy processing by other tools.</para></listitem>

      <listitem><para><literal>nix-instantiate --eval-only
      --xml</literal> prints an XML representation of the resulting
      term.  (The new flag <option>--strict</option> forces ‘deep’
      evaluation of the result, i.e., list elements and attributes are
      evaluated recursively.)</para></listitem>

      <listitem><para>In Nix expressions, the primop
      <function>builtins.toXML</function> converts a term to an XML
      representation.  This is primarily useful for passing structured
      information to builders.</para></listitem>

    </itemizedlist>

  </para></listitem>
  

  <listitem><para>You can now unambigously specify which derivation to
  build or install in <command>nix-env</command>,
  <command>nix-instantiate</command> and <command>nix-build</command>
  using the <option>--attr</option> / <option>-A</option> flags, which
  takes an attribute name as argument.  (Unlike symbolic package names
  such as <literal>subversion-1.4.0</literal>, attribute names in an
  attribute set are unique.)  For instance, a quick way to perform a
  test build of a package in Nixpkgs is <literal>nix-build
  pkgs/top-level/all-packages.nix -A
  <replaceable>foo</replaceable></literal>.  <literal>nix-env -q
  --attr</literal> shows the attribute names corresponding to each
  derivation.</para></listitem>
  

  <listitem><para>If the top-level Nix expression used by
  <command>nix-env</command>, <command>nix-instantiate</command> or
  <command>nix-build</command> evaluates to a function whose arguments
  all have default values, the function will be called automatically.
  Also, the new command-line switch <option>--arg
  <replaceable>name</replaceable>
  <replaceable>value</replaceable></option> can be used to specify
  function arguments on the command line.</para></listitem>

  
  <listitem><para><literal>nix-install-package --url
  <replaceable>URL</replaceable></literal> allows a package to be
  installed directly from the given URL.</para></listitem>


  <listitem><para>Nix now works behind an HTTP proxy server; just set
  the standard environment variables <envar>http_proxy</envar>,
  <envar>https_proxy</envar>, <envar>ftp_proxy</envar> or
  <envar>all_proxy</envar> appropriately.  Functions such as
  <function>fetchurl</function> in Nixpkgs also respect these
  variables.</para></listitem>


  <listitem><para><literal>nix-build -o
  <replaceable>symlink</replaceable></literal> allows the symlink to
  the build result to be named something other than
  <literal>result</literal>.</para></listitem>


  <!-- Stability / performance / etc. -->


  <listitem><para>Platform support:

    <itemizedlist>

      <listitem><para>Support for 64-bit platforms, provided a <link
      xlink:href="http://bugzilla.sen.cwi.nl:8080/show_bug.cgi?id=606">suitably
      patched ATerm library</link> is used.  Also, files larger than 2
      GiB are now supported.</para></listitem>

      <listitem><para>Added support for Cygwin (Windows,
      <literal>i686-cygwin</literal>), Mac OS X on Intel
      (<literal>i686-darwin</literal>) and Linux on PowerPC
      (<literal>powerpc-linux</literal>).</para></listitem>

      <listitem><para>Users of SMP and multicore machines will
      appreciate that the number of builds to be performed in parallel
      can now be specified in the configuration file in the
      <literal>build-max-jobs</literal> setting.</para></listitem>

    </itemizedlist>

  </para></listitem>

  
  <listitem><para>Garbage collector improvements:

    <itemizedlist>

      <listitem><para>Open files (such as running programs) are now
      used as roots of the garbage collector.  This prevents programs
      that have been uninstalled from being garbage collected while
      they are still running.  The script that detects these
      additional runtime roots
      (<filename>find-runtime-roots.pl</filename>) is inherently
      system-specific, but it should work on Linux and on all
      platforms that have the <command>lsof</command>
      utility.</para></listitem>

      <listitem><para><literal>nix-store --gc</literal>
      (a.k.a. <command>nix-collect-garbage</command>) prints out the
      number of bytes freed on standard output.  <literal>nix-store
      --gc --print-dead</literal> shows how many bytes would be freed
      by an actual garbage collection.</para></listitem>

      <listitem><para><literal>nix-collect-garbage -d</literal>
      removes all old generations of <emphasis>all</emphasis> profiles
      before calling the actual garbage collector (<literal>nix-store
      --gc</literal>).  This is an easy way to get rid of all old
      packages in the Nix store.</para></listitem>

      <listitem><para><command>nix-store</command> now has an
      operation <option>--delete</option> to delete specific paths
      from the Nix store.  It won’t delete reachable (non-garbage)
      paths unless <option>--ignore-liveness</option> is
      specified.</para></listitem>
      
    </itemizedlist>

  </para></listitem>

  
  <listitem><para>Berkeley DB 4.4’s process registry feature is used
  to recover from crashed Nix processes.</para></listitem>

  <!--  <listitem><para>TODO: shared stores.</para></listitem> -->

  <listitem><para>A performance issue has been fixed with the
  <literal>referer</literal> table, which stores the inverse of the
  <literal>references</literal> table (i.e., it tells you what store
  paths refer to a given path).  Maintaining this table could take a
  quadratic amount of time, as well as a quadratic amount of Berkeley
  DB log file space (in particular when running the garbage collector)
  (<literal>NIX-23</literal>).</para></listitem>

  <listitem><para>Nix now catches the <literal>TERM</literal> and
  <literal>HUP</literal> signals in addition to the
  <literal>INT</literal> signal.  So you can now do a <literal>killall
  nix-store</literal> without triggering a database
  recovery.</para></listitem>

  <listitem><para><command>bsdiff</command> updated to version
  4.3.</para></listitem>

  <listitem><para>Substantial performance improvements in expression
  evaluation and <literal>nix-env -qa</literal>, all thanks to <link
  xlink:href="http://valgrind.org/">Valgrind</link>.  Memory use has
  been reduced by a factor 8 or so.  Big speedup by memoisation of
  path hashing.</para></listitem>

  <listitem><para>Lots of bug fixes, notably:

    <itemizedlist>

      <listitem><para>Make sure that the garbage collector can run
      succesfully when the disk is full
      (<literal>NIX-18</literal>).</para></listitem>

      <listitem><para><command>nix-env</command> now locks the profile
      to prevent races between concurrent <command>nix-env</command>
      operations on the same profile
      (<literal>NIX-7</literal>).</para></listitem>

      <listitem><para>Removed misleading messages from
      <literal>nix-env -i</literal> (e.g., <literal>installing
      `foo'</literal> followed by <literal>uninstalling
      `foo'</literal>) (<literal>NIX-17</literal>).</para></listitem>

    </itemizedlist>

  </para></listitem>

  <listitem><para>Nix source distributions are a lot smaller now since
  we no longer include a full copy of the Berkeley DB source
  distribution (but only the bits we need).</para></listitem>

  <listitem><para>Header files are now installed so that external
  programs can use the Nix libraries.</para></listitem>

</itemizedlist>

</section>



<!--==================================================================-->

<section><title>Release 0.9.2 (September 21, 2005)</title>

<para>This bug fix release fixes two problems on Mac OS X:

<itemizedlist>

  <listitem><para>If Nix was linked against statically linked versions
  of the ATerm or Berkeley DB library, there would be dynamic link
  errors at runtime.</para></listitem>

  <listitem><para><command>nix-pull</command> and
  <command>nix-push</command> intermittently failed due to race
  conditions involving pipes and child processes with error messages
  such as <literal>open2: open(GLOB(0x180b2e4), >&amp;=9) failed: Bad
  file descriptor at /nix/bin/nix-pull line 77</literal> (issue
  <literal>NIX-14</literal>).</para></listitem>

</itemizedlist>

</para>

</section>



<!--==================================================================-->

<section><title>Release 0.9.1 (September 20, 2005)</title>

<para>This bug fix release addresses a problem with the ATerm library
when the <option>--with-aterm</option> flag in
<command>configure</command> was <emphasis>not</emphasis> used.</para>

</section>



<!--==================================================================-->

<section><title>Release 0.9 (September 16, 2005)</title>

<para>NOTE: this version of Nix uses Berkeley DB 4.3 instead of 4.2.
The database is upgraded automatically, but you should be careful not
to use old versions of Nix that still use Berkeley DB 4.2.  In
particular, if you use a Nix installed through Nix, you should run

<screen>
$ nix-store --clear-substitutes</screen>

first.</para>


<itemizedlist>

  <listitem><para>Unpacking of patch sequences is much faster now
  since we no longer do redundant unpacking and repacking of
  intermediate paths.</para></listitem>

  <listitem><para>Nix now uses Berkeley DB 4.3.</para></listitem>

  <listitem><para>The <function>derivation</function> primitive is
  lazier.  Attributes of dependent derivations can mutually refer to
  each other (as long as there are no data dependencies on the
  <varname>outPath</varname> and <varname>drvPath</varname> attributes
  computed by <function>derivation</function>).</para>

  <para>For example, the expression <literal>derivation
  attrs</literal> now evaluates to (essentially)

  <programlisting>
attrs // {
  type = "derivation";
  outPath = derivation! attrs;
  drvPath = derivation! attrs;
}</programlisting>

  where <function>derivation!</function> is a primop that does the
  actual derivation instantiation (i.e., it does what
  <function>derivation</function> used to do).  The advantage is that
  it allows commands such as <command>nix-env -qa</command> and
  <command>nix-env -i</command> to be much faster since they no longer
  need to instantiate all derivations, just the
  <varname>name</varname> attribute.</para>

  <para>Also, it allows derivations to cyclically reference each
  other, for example,

  <programlisting>
webServer = derivation {
  ...
  hostName = "svn.cs.uu.nl";
  services = [svnService];
};
&#x20;
svnService = derivation {
  ...
  hostName = webServer.hostName;
};</programlisting>

  Previously, this would yield a black hole (infinite recursion).</para>
  
  </listitem>

  <listitem><para><command>nix-build</command> now defaults to using
  <filename>./default.nix</filename> if no Nix expression is
  specified.</para></listitem>

  <listitem><para><command>nix-instantiate</command>, when applied to
  a Nix expression that evaluates to a function, will call the
  function automatically if all its arguments have
  defaults.</para></listitem>

  <listitem><para>Nix now uses libtool to build dynamic libraries.
  This reduces the size of executables.</para></listitem>

  <listitem><para>A new list concatenation operator
  <literal>++</literal>.  For example, <literal>[1 2 3] ++ [4 5
  6]</literal> evaluates to <literal>[1 2 3 4 5
  6]</literal>.</para></listitem>

  <listitem><para>Some currently undocumented primops to support
  low-level build management using Nix (i.e., using Nix as a Make
  replacement).  See the commit messages for <literal>r3578</literal>
  and <literal>r3580</literal>.</para></listitem>

  <listitem><para>Various bug fixes and performance
  improvements.</para></listitem>

</itemizedlist>

</section>



<!--==================================================================-->

<section><title>Release 0.8.1 (April 13, 2005)</title>

<para>This is a bug fix release.</para>

<itemizedlist>

  <listitem><para>Patch downloading was broken.</para></listitem>

  <listitem><para>The garbage collector would not delete paths that
  had references from invalid (but substitutable)
  paths.</para></listitem>

</itemizedlist>

</section>



<!--==================================================================-->

<section><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 succesful 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>



<!--==================================================================-->

<section><title>Release 0.7 (January 12, 2005)</title>

<itemizedlist>

  <listitem><para>Binary patching.  When upgrading components using
  pre-built binaries (through nix-pull / nix-channel), Nix can
  automatically download and apply binary patches to already installed
  components instead of full downloads.  Patching is “smart”: if there
  is a <emphasis>sequence</emphasis> of patches to an installed
  component, Nix will use it.  Patches are currently generated
  automatically between Nixpkgs (pre-)releases.</para></listitem>

  <listitem><para>Simplifications to the substitute
  mechanism.</para></listitem>

  <listitem><para>Nix-pull now stores downloaded manifests in
  <filename>/nix/var/nix/manifests</filename>.</para></listitem>

  <listitem><para>Metadata on files in the Nix store is canonicalised
  after builds: the last-modified timestamp is set to 0 (00:00:00
  1/1/1970), the mode is set to 0444 or 0555 (readable and possibly
  executable by all; setuid/setgid bits are dropped), and the group is
  set to the default.  This ensures that the result of a build and an
  installation through a substitute is the same; and that timestamp
  dependencies are revealed.</para></listitem>

</itemizedlist>

</section>



<!--==================================================================-->

<section><title>Release 0.6 (November 14, 2004)</title>

<itemizedlist>

  <listitem>
    <para>Rewrite of the normalisation engine.

    <itemizedlist>

      <listitem><para>Multiple builds can now be performed in parallel
      (option <option>-j</option>).</para></listitem>

      <listitem><para>Distributed builds.  Nix can now call a shell
      script to forward builds to Nix installations on remote
      machines, which may or may not be of the same platform
      type.</para></listitem>

      <listitem><para>Option <option>--fallback</option> allows
      recovery from broken substitutes.</para></listitem>

      <listitem><para>Option <option>--keep-going</option> causes
      building of other (unaffected) derivations to continue if one
      failed.</para></listitem>

    </itemizedlist>

    </para>

  </listitem>

  <listitem><para>Improvements to the garbage collector (i.e., it
  should actually work now).</para></listitem>

  <listitem><para>Setuid Nix installations allow a Nix store to be
  shared among multiple users.</para></listitem>

  <listitem><para>Substitute registration is much faster
  now.</para></listitem>

  <listitem><para>A utility <command>nix-build</command> to build a
  Nix expression and create a symlink to the result int the current
  directory; useful for testing Nix derivations.</para></listitem>

  <listitem><para>Manual updates.</para></listitem>

  <listitem>

    <para><command>nix-env</command> changes:

    <itemizedlist>

      <listitem><para>Derivations for other platforms are filtered out
      (which can be overriden using
      <option>--system-filter</option>).</para></listitem>

      <listitem><para><option>--install</option> by default now
      uninstall previous derivations with the same
      name.</para></listitem>

      <listitem><para><option>--upgrade</option> allows upgrading to a
      specific version.</para></listitem>

      <listitem><para>New operation
      <option>--delete-generations</option> to remove profile
      generations (necessary for effective garbage
      collection).</para></listitem>

      <listitem><para>Nicer output (sorted,
      columnised).</para></listitem>

    </itemizedlist>
    
    </para>

  </listitem>

  <listitem><para>More sensible verbosity levels all around (builder
  output is now shown always, unless <option>-Q</option> is
  given).</para></listitem>

  <listitem>

    <para>Nix expression language changes:

    <itemizedlist>
      
      <listitem><para>New language construct: <literal>with
      <replaceable>E1</replaceable>;
      <replaceable>E2</replaceable></literal> brings all attributes
      defined in the attribute set <replaceable>E1</replaceable> in
      scope in <replaceable>E2</replaceable>.</para></listitem>

      <listitem><para>Added a <function>map</function>
      function.</para></listitem>

      <listitem><para>Various new operators (e.g., string
      concatenation).</para></listitem>

    </itemizedlist>

    </para>

  </listitem>

  <listitem><para>Expression evaluation is much
  faster.</para></listitem>

  <listitem><para>An Emacs mode for editing Nix expressions (with
  syntax highlighting and indentation) has been
  added.</para></listitem>

  <listitem><para>Many bug fixes.</para></listitem>

</itemizedlist>

</section>



<!--==================================================================-->

<section><title>Release 0.5 and earlier</title>

<para>Please refer to the Subversion commit log messages.</para>

</section>



</article>