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<title>Release 0.11 (December 31, 2007)</title>
<para>Nix 0.11 has many improvements over the previous stable release.
The most important improvement is secure multi-user support. It also
features many usability enhancements and language extensions, many of
them prompted by NixOS, the purely functional Linux distribution based
on Nix. Here is an (incomplete) list:</para>
<itemizedlist>
<listitem><para>Secure multi-user support. A single Nix store can
now be shared between multiple (possible untrusted) users. This is
an important feature for NixOS, where it allows non-root users to
install software. The old setuid method for sharing a store between
multiple users has been removed. Details for setting up a
multi-user store can be found in the manual.</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 via
<command>ssh</command>.</para></listitem>
<listitem><para>A new kind of string literal: strings between double
single-quotes (<literal>''</literal>) have indentation
“intelligently” removed. This allows large strings (such as shell
scripts or configuration file fragments in NixOS) to cleanly follow
the indentation of the surrounding expression. It also requires
much less escaping, since <literal>''</literal> is less common in
most languages than <literal>"</literal>.</para></listitem>
<listitem><para><command>nix-env</command> <option>--set</option>
modifies the current generation of a profile so that it contains
exactly the specified derivation, and nothing else. For example,
<literal>nix-env -p /nix/var/nix/profiles/browser --set
firefox</literal> lets the profile named
<filename>browser</filename> contain just Firefox.</para></listitem>
<listitem><para><command>nix-env</command> now maintains
meta-information about installed packages in profiles. The
meta-information is the contents of the <varname>meta</varname>
attribute of derivations, such as <varname>description</varname> or
<varname>homepage</varname>. The command <literal>nix-env -q --xml
--meta</literal> shows all meta-information.</para></listitem>
<listitem><para><command>nix-env</command> now uses the
<varname>meta.priority</varname> attribute of derivations to resolve
filename collisions between packages. Lower priority values denote
a higher priority. For instance, the GCC wrapper package and the
Binutils package in Nixpkgs both have a file
<filename>bin/ld</filename>, so previously if you tried to install
both you would get a collision. Now, on the other hand, the GCC
wrapper declares a higher priority than Binutils, so the former’s
<filename>bin/ld</filename> is symlinked in the user
environment.</para></listitem>
<listitem><para><command>nix-env -i / -u</command>: instead of
breaking package ties by version, break them by priority and version
number. That is, if there are multiple packages with the same name,
then pick the package with the highest priority, and only use the
version if there are multiple packages with the same
priority.</para>
<para>This makes it possible to mark specific versions/variant in
Nixpkgs more or less desirable than others. A typical example would
be a beta version of some package (e.g.,
<literal>gcc-4.2.0rc1</literal>) which should not be installed even
though it is the highest version, except when it is explicitly
selected (e.g., <literal>nix-env -i
gcc-4.2.0rc1</literal>).</para></listitem>
<listitem><para><command>nix-env --set-flag</command> allows meta
attributes of installed packages to be modified. There are several
attributes that can be usefully modified, because they affect the
behaviour of <command>nix-env</command> or the user environment
build script:
<itemizedlist>
<listitem><para><varname>meta.priority</varname> can be changed
to resolve filename clashes (see above).</para></listitem>
<listitem><para><varname>meta.keep</varname> can be set to
<literal>true</literal> to prevent the package from being
upgraded or replaced. Useful if you want to hang on to an older
version of a package.</para></listitem>
<listitem><para><varname>meta.active</varname> can be set to
<literal>false</literal> to “disable” the package. That is, no
symlinks will be generated to the files of the package, but it
remains part of the profile (so it won’t be garbage-collected).
Set it back to <literal>true</literal> to re-enable the
package.</para></listitem>
</itemizedlist>
</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. The <option>-b</option> flag is also available in
<command>nix-env -i</command> and <command>nix-env -u</command> to
filter out derivations for which no pre-built binary is
available.</para></listitem>
<listitem><para>The new option <option>--argstr</option> (in
<command>nix-env</command>, <command>nix-instantiate</command> and
<command>nix-build</command>) is like <option>--arg</option>, except
that the value is a string. For example, <literal>--argstr system
i686-linux</literal> is equivalent to <literal>--arg system
\"i686-linux\"</literal> (note that <option>--argstr</option>
prevents annoying quoting around shell arguments).</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: semantic cleanups of string concatenation
etc. (mostly in r6740).</para></listitem>
-->
<listitem><para>Nix now uses Berkeley DB 4.5. The database is
upgraded automatically, but you should be careful not to use old
versions of Nix that still use Berkeley DB 4.4.</para></listitem>
<!-- foo
<listitem><para>TODO: option <option>- -reregister</option> in
<command>nix-store - -register-validity</command>.</para></listitem>
-->
<listitem><para>The option <option>--max-silent-time</option>
(corresponding to the configuration setting
<literal>build-max-silent-time</literal>) allows you to set a
timeout on builds — if a build produces no output on
<literal>stdout</literal> or <literal>stderr</literal> for the given
number of seconds, it is terminated. This is useful for recovering
automatically from builds that are stuck in an infinite
loop.</para></listitem>
<listitem><para><command>nix-channel</command>: each subscribed
channel is its own attribute in the top-level expression generated
for the channel. This allows disambiguation (e.g. <literal>nix-env
-i -A nixpkgs_unstable.firefox</literal>).</para></listitem>
<listitem><para>The substitutes table has been removed from the
database. This makes operations such as <command>nix-pull</command>
and <command>nix-channel --update</command> much, much
faster.</para></listitem>
<listitem><para><command>nix-pull</command> now supports
bzip2-compressed manifests. This speeds up
channels.</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><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 the
<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>Nix can now perform builds in an automatically
generated “chroot”. This prevents a builder from accessing stuff
outside of the Nix store, and thus helps ensure purity. This is an
experimental feature.</para></listitem>
<listitem><para>The new command <command>nix-store
--optimise</command> reduces Nix store disk space usage by finding
identical files in the store and hard-linking them to each other.
It typically reduces the size of the store by something like
25-35%.</para></listitem>
<listitem><para><filename>~/.nix-defexpr</filename> can now be a
directory, in which case the Nix expressions in that directory are
combined into an attribute set, with the file names used as the
names of the attributes. The command <command>nix-env
--import</command> (which set the
<filename>~/.nix-defexpr</filename> symlink) is
removed.</para></listitem>
<listitem><para>Derivations can specify the new special attribute
<varname>allowedReferences</varname> to enforce that the references
in the output of a derivation are a subset of a declared set of
paths. For example, if <varname>allowedReferences</varname> is an
empty list, then the output must not have any references. This is
used in NixOS to check that generated files such as initial ramdisks
for booting Linux don’t have any dependencies.</para></listitem>
<listitem><para>The new attribute
<varname>exportReferencesGraph</varname> allows builders access to
the references graph of their inputs. This is used in NixOS for
tasks such as generating ISO-9660 images that contain a Nix store
populated with the closure of certain paths.</para></listitem>
<listitem><para>Fixed-output derivations (like
<function>fetchurl</function>) can define the attribute
<varname>impureEnvVars</varname> to allow external environment
variables to be passed to builders. This is used in Nixpkgs to
support proxy configuration, among other things.</para></listitem>
<listitem><para>Several new built-in functions:
<function>builtins.attrNames</function>,
<function>builtins.filterSource</function>,
<function>builtins.isAttrs</function>,
<function>builtins.isFunction</function>,
<function>builtins.listToAttrs</function>,
<function>builtins.stringLength</function>,
<function>builtins.sub</function>,
<function>builtins.substring</function>,
<function>throw</function>,
<function>builtins.trace</function>,
<function>builtins.readFile</function>.</para></listitem>
</itemizedlist>
</chapter>
