* Rewrite of package management stuff.
This commit is contained in:
Eelco Dolstra
parent
d830b2c1df
commit
692204e0c5
|
|
@ -1,229 +1,190 @@
|
|||
<chapter id='chap-package-management'><title>Package Management</title>
|
||||
|
||||
<para>Let's start from the perspective of an end user. Common
|
||||
operations at this level are to install and remove packages, ask what
|
||||
packages are installed or available for installation, and so on.
|
||||
These are operations on the <emphasis>user environment</emphasis>: the
|
||||
set of packages that a user <quote>sees</quote>. In a command line
|
||||
Unix environment, this means the set of programs that are available
|
||||
through the <envar>PATH</envar> environment variable. (In other
|
||||
environments it might mean the set of programs available on the
|
||||
desktop, through the start menu, and so on.)</para>
|
||||
<para>This chapter discusses how to do package management with Nix,
|
||||
i.e., how to obtain, install, upgrade, and erase components. This is
|
||||
the <quote>user's</quote> perspective of the Nix system — people
|
||||
who want to <emphasis>create</emphasis> components should consult
|
||||
<xref linkend='chap-writing-nix-expressions' />.</para>
|
||||
|
||||
<para>The terms <quote>installation</quote> and
|
||||
<quote>uninstallation</quote> are used in this context to denote the
|
||||
act of adding or removing packages from the user environment. In Nix,
|
||||
these operations are dissociated from the physical copying or deleting
|
||||
of files. Installation requires that the files constituting the
|
||||
package are present, but they may be present beforehand. Likewise,
|
||||
uninstallation does not actually delete any files; this is done
|
||||
automatically by running a garbage collector.</para>
|
||||
|
||||
<para>User environments are manipulated through the
|
||||
<command>nix-env</command> command. The query operation can be used
|
||||
to see what packages are currently installed.</para>
|
||||
<sect1><title>Basic package management</title>
|
||||
|
||||
<para>The main command for package management is
|
||||
<command>nix-env</command>. You can use it to install, upgrade, and
|
||||
erase components, and to query what components are installed or are
|
||||
available for installation.</para>
|
||||
|
||||
<para>In Nix, different users can have different <quote>views</quote>
|
||||
on the set of installed applications. That is, there might be lots of
|
||||
applications present on the system (possibly in many different
|
||||
versions), but users can have a specific selection of those
|
||||
active — where <quote>active</quote> just means that it appears
|
||||
in a directory in the user's <envar>PATH</envar>.</para>
|
||||
|
||||
<para>Such a view on the set of installed applications is called a
|
||||
<emphasis>user environment</emphasis>, which is just a directory tree
|
||||
consisting of symlinks to the files of the active applications. In
|
||||
Nix, operations such as upgrading or removing components never
|
||||
overwrite or remove the files of those components, and they don't even
|
||||
touch the user environments that point to them. Rather, they cause a
|
||||
<emphasis>new</emphasis> user environment to be constructed based on
|
||||
the old one.</para>
|
||||
|
||||
<para>Components are installed from a set of <emphasis>Nix
|
||||
expressions</emphasis> that tell Nix how to build those components,
|
||||
including, if necessary, their dependencies. There is a collection of
|
||||
Nix expressions called the Nix Package collection that contains
|
||||
components ranging from basic development stuff such as GCC and Glibc,
|
||||
to end-user applications like Mozilla Firefox. (Nix is however not
|
||||
tied to the Nix Package collection; you could write your own Nix
|
||||
expression based on that, or completely new.) You can download the
|
||||
latest version from <ulink
|
||||
url='http://catamaran.labs.cs.uu.nl/dist/nix' />. You probably want
|
||||
the latest unstable release; currently the stable releases tend to lag
|
||||
behind quite a bit.</para>
|
||||
|
||||
<para>Assuming that you have downloaded and unpacked a release of Nix
|
||||
Packages, you can view the set of available components in the release:
|
||||
|
||||
<screen>
|
||||
$ nix-env -q
|
||||
MozillaFirebird-0.7
|
||||
sylpheed-0.9.7
|
||||
pan-0.14.2</screen>
|
||||
|
||||
<para>(<option>-q</option> is actually short for <option>--query
|
||||
--installed</option>.) The package names are symbolic: they don't
|
||||
have any particular significance to Nix (as they shouldn't, since they
|
||||
are not unique—there can be many derivations with the same
|
||||
name). Note that these packages have many dependencies (e.g., Mozilla
|
||||
uses the <literal>gtk+</literal> package) but these have not been
|
||||
installed in the user environment, though they are present on the
|
||||
system. Generally, there is no need to install such packages; only
|
||||
packages containing programs should be installed.</para>
|
||||
|
||||
<para>To install packages, a <emphasis>Nix expression</emphasis> is
|
||||
required that tells Nix how to build that package. There is a <ulink
|
||||
url='https://svn.cs.uu.nl:12443/dist/trace/trace-nixpkgs-trunk.tar.bz2'>set
|
||||
of standard of Nix expressions</ulink> for many common packages.
|
||||
Assuming that you have downloaded and unpacked these, you can view the
|
||||
set of available packages:</para>
|
||||
|
||||
<screen>
|
||||
$ nix-env -qaf pkgs/system/i686-linux.nix
|
||||
gettext-0.12.1
|
||||
sylpheed-0.9.7
|
||||
aterm-2.0
|
||||
gtk+-1.2.10
|
||||
apache-httpd-2.0.48
|
||||
pan-0.14.2
|
||||
$ nix-env -qaf nixpkgs-<replaceable>version</replaceable>
|
||||
ant-blackdown-1.4.2
|
||||
aterm-2.2
|
||||
bash-3.0
|
||||
binutils-2.15
|
||||
bison-1.875d
|
||||
blackdown-1.4.2
|
||||
bzip2-1.0.2
|
||||
...</screen>
|
||||
|
||||
<para>The Nix expression in the file
|
||||
<filename>i686-linux.nix</filename> yields the set of packages for a
|
||||
Linux system running on x86 hardware. For other platforms, copy and
|
||||
modify this file for your platform as appropriate. [TODO: improve
|
||||
this]</para>
|
||||
where <literal>nixpkgs-<replaceable>version</replaceable></literal> is
|
||||
where you've unpacked the release.</para>
|
||||
|
||||
<para>It is also possible to see the <emphasis>status</emphasis> of
|
||||
available packages, i.e., whether they are installed into the user
|
||||
environment and/or present in the system:</para>
|
||||
available component, i.e., whether they are installed into the user
|
||||
environment and/or present in the system:
|
||||
|
||||
<screen>
|
||||
$ nix-env -qasf pkgs/system/i686-linux.nix
|
||||
-P gettext-0.12.1
|
||||
IP sylpheed-0.9.7
|
||||
-- aterm-2.0
|
||||
-P gtk+-1.2.10</screen>
|
||||
|
||||
<para>This reveals that the <literal>sylpheed</literal> package is
|
||||
already installed, or more precisely, that exactly the same
|
||||
instantiation of <literal>sylpheed</literal> is installed. This
|
||||
guarantees that the available package is exactly the same as the
|
||||
installed package with regard to sources, dependencies, build flags,
|
||||
and so on. Similarly, we see that the <literal>gettext</literal> and
|
||||
<literal>gtk+</literal> packages are present but not installed in the
|
||||
user environment, while the <literal>aterm</literal> package is not
|
||||
installed or present at all (so, if we were to install it, it would
|
||||
have to be built or downloaded first).</para>
|
||||
|
||||
<para>The install operation is used install available packages from a
|
||||
Nix environment. To install the <literal>pan</literal> package (a
|
||||
newsreader), you would do:</para>
|
||||
|
||||
<screen>
|
||||
$ nix-env -if pkgs/system/i686-linux.nix pan</screen>
|
||||
|
||||
<para>Since installation may take a long time, depending on whether
|
||||
any packages need to be built or downloaded, it's a good idea to make
|
||||
<command>nix-env</command> run verbosely by using the
|
||||
<option>-v</option> (<option>--verbose</option>) option. This option
|
||||
may be repeated to increase the level of verbosity. A good value is 3
|
||||
(<option>-vvv</option>).</para>
|
||||
|
||||
<para>In fact, if you run this command verbosely you will observe that
|
||||
Nix starts to build many packages, including large and fundamental
|
||||
ones such as <literal>glibc</literal> and <literal>gcc</literal>.
|
||||
I.e., you are performing a source installation. This is generally
|
||||
undesirable, since installation from sources may require large amounts
|
||||
of disk and CPU resources. Therefore a <quote>binary</quote>
|
||||
installation is generally preferable.</para>
|
||||
|
||||
<para>Rather than provide different mechanisms to create and perform
|
||||
the installation of binary packages, Nix supports binary deployment
|
||||
<emphasis>transparently</emphasis> through a generic mechanism of
|
||||
<emphasis>substitute expressions</emphasis>. If an request is made to
|
||||
build some Nix expression, Nix will first try to build any substitutes
|
||||
for that expression. These substitutes presumably perform an
|
||||
identical build operation with respect to the result, but require less
|
||||
resources. For instance, a substitute that downloads a pre-built
|
||||
package from the network requires less CPU and disk resources, and
|
||||
possibly less time.</para>
|
||||
|
||||
<para>Nix's use of cryptographic hashes makes this entirely safe. It
|
||||
is not possible, for instance, to accidentally substitute a build of
|
||||
some package for a Solaris or Windows system for a build on a SuSE/x86
|
||||
system.</para>
|
||||
|
||||
<para>While the substitute mechanism is a generic mechanism, Nix
|
||||
provides two standard tools called <command>nix-pull</command> and
|
||||
<command>nix-push</command> that maintain and use a shared cache of
|
||||
prebuilt derivations on some network site (reachable through HTTP).
|
||||
If you attempt to install some package that someone else has
|
||||
previously built and <quote>pushed</quote> into the cache, and you
|
||||
have done a <quote>pull</quote> to register substitutes that download
|
||||
these prebuilt packages, then the installation will automatically use
|
||||
these.</para>
|
||||
|
||||
<para>For example, to pull from our <ulink
|
||||
url='http://losser.st-lab.cs.uu.nl/~eelco/nix-dist/'>cache</ulink> of
|
||||
prebuilt packages (at the time of writing, for SuSE Linux/x86), use
|
||||
the following command:</para>
|
||||
|
||||
<screen>
|
||||
$ nix-pull http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST
|
||||
obtaining list of Nix archives at http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-<replaceable>version</replaceable>/MANIFEST...
|
||||
...</screen>
|
||||
|
||||
<para>If <command>nix-pull</command> is run without any arguments, it
|
||||
will pull from the URLs specified in the file
|
||||
<filename><replaceable>prefix</replaceable>/etc/nix/prebuilts.conf</filename>.</para>
|
||||
|
||||
<para>Assuming that the <literal>pan</literal> installation produced
|
||||
no errors, it can be used immediately, that is, it now appears in a
|
||||
directory in the <envar>PATH</envar> environment variable.
|
||||
Specifically, <envar>PATH</envar> includes the entry
|
||||
<filename><replaceable>prefix</replaceable>/var/nix/profiles/default/bin</filename>,
|
||||
where
|
||||
<filename><replaceable>prefix</replaceable>/var/nix/profiles/default</filename>
|
||||
is just a symlink to the current user environment:</para>
|
||||
|
||||
<screen>
|
||||
$ ls -l /nix/var/nix/profiles/
|
||||
$ nix-env -qasf nixpkgs-<replaceable>version</replaceable>
|
||||
...
|
||||
lrwxrwxrwx 1 eelco ... default-15-link -> /nix/store/1871...12b0-user-environment
|
||||
lrwxrwxrwx 1 eelco ... default-16-link -> /nix/store/59ba...df6b-user-environment
|
||||
lrwxrwxrwx 1 eelco ... default -> default-16-link</screen>
|
||||
|
||||
<para>That is, <filename>default</filename> in this example is a link
|
||||
to <filename>default-16-link</filename>, which is the current user
|
||||
environment. Before the installation, it pointed to
|
||||
<filename>default-15-link</filename>. Note that this means that you
|
||||
can atomically roll-back to the previous user environment by pointing
|
||||
the symlink <filename>default</filename> at
|
||||
<filename>default-15-link</filename> again. This also shows that
|
||||
operations such as installation are atomic in the Nix system: any
|
||||
arbitrarily complex set of installation, uninstallation, or upgrade
|
||||
actions eventually boil down to the single operation of pointing a
|
||||
symlink somewhere else (which can be implemented atomically in Unix).</para>
|
||||
|
||||
<para>What's in a user environment? It's just a set of symlinks to the
|
||||
files that constitute the installed packages. For instance:</para>
|
||||
|
||||
<screen>
|
||||
$ ls -l /nix/var/nix/profiles/default-16-link/bin
|
||||
lrwxrwxrwx 1 eelco ... MozillaFirebird -> /nix/store/35f8...4ae6-MozillaFirebird-0.7/bin/MozillaFirebird
|
||||
lrwxrwxrwx 1 eelco ... svn -> /nix/store/3829...fb5d-subversion-0.32.1/bin/svn
|
||||
-PS bash-3.0
|
||||
--S binutils-2.15
|
||||
IPS bison-1.875d
|
||||
...</screen>
|
||||
|
||||
<para>Note that, e.g., <filename>svn</filename> =
|
||||
<filename>/nix/var/nix/profiles/default/bin/svn</filename> =
|
||||
<filename>/nix/var/nix/profiles/default-16-link/bin/svn</filename> =
|
||||
<filename>/nix/store/59ba...df6b-user-environment/bin/svn</filename> =
|
||||
<filename>/nix/store/3829...fb5d-subversion-0.32.1/bin/svn</filename>.</para>
|
||||
The first character (<literal>I</literal>) indicates whether the
|
||||
component is installed in your current user environment. The second
|
||||
(<literal>P</literal>) indicates whether it is present on your system
|
||||
(in which case installing it into your user environment would be very
|
||||
quick). The last one (<literal>S</literal>) indicates whether there
|
||||
is a so-called <emphasis>substitute</emphasis> for the component,
|
||||
which is Nix's mechanism for doing binary deployment. It just means
|
||||
that Nix know that it can fetch a pre-built component from somewhere
|
||||
(typically a network server) instead of building it locally.</para>
|
||||
|
||||
<para>Naturally, packages can also be uninstalled:</para>
|
||||
<para>So now that we have a set of Nix expressions we can build the
|
||||
components contained in them. This is done using <literal>nix-env
|
||||
-i</literal>. For instance,
|
||||
|
||||
<screen>
|
||||
$ nix-env -e pan</screen>
|
||||
$ nix-env -f nixpkgs-<replaceable>version</replaceable> -i subversion</screen>
|
||||
|
||||
<para>This means that the package is removed from the user
|
||||
environment. It is <emphasis>not</emphasis> yet removed from the
|
||||
system. When a package is uninstalled from a user environment, it may
|
||||
still be used by other packages, or may still be present in other user
|
||||
environments. Deleting it under such conditions would break those
|
||||
other packages or user environments. To prevent this, packages are
|
||||
only <quote>physically</quote> deleted by running the Nix garbage
|
||||
collector, which searches for all packages in the Nix store that are
|
||||
no longer <quote>reachable</quote> from outside the store. Thus,
|
||||
uninstalling a package is always safe: it cannot break other
|
||||
packages.</para>
|
||||
will install the component called <literal>subversion</literal> (which
|
||||
is, of course, the <ulink
|
||||
url='http://subversion.tigris.org/'>Subversion version management
|
||||
system</ulink>).</para>
|
||||
|
||||
<para>When you do this for the first time, Nix will start building
|
||||
Subversion and all its dependencies. This will take quite a while
|
||||
— typically an hour or two on modern machines. Fortunately,
|
||||
there is a faster way (so just do a Ctrl-C on that install
|
||||
operation!): you just need to tell Nix that pre-built binaries of all
|
||||
those components are available somewhere. This is done using the
|
||||
<command>nix-pull</command> command, which must be supplied with a URL
|
||||
containing a <emphasis>manifest</emphasis> describing what binaries
|
||||
are available. This URL should correspond to the Nix Packages release
|
||||
that you're using. For instance, if you obtained a release from
|
||||
<ulink
|
||||
url='http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-0.6pre1554/' />,
|
||||
then you should do:
|
||||
|
||||
<para>Upgrading packages is easy. Given a Nix expression that
|
||||
contains newer versions of installed packages (that is, packages with
|
||||
the same package name, but a higher version number), <command>nix-env
|
||||
-u</command> will replace the installed package in the user
|
||||
environment with the newer package. For example,
|
||||
|
||||
<screen>
|
||||
$ nix-env -uf pkgs/system/i686-linux.nix pan</screen>
|
||||
$ nix-pull http://catamaran.labs.cs.uu.nl/dist/nix/nixpkgs-0.6pre1554/MANIFEST</screen>
|
||||
|
||||
If you then issue the installation command, it should start
|
||||
downloading binaries from <systemitem
|
||||
class='fqdomainname'>catamaran.labs.cs.uu.nl</systemitem>, instead of
|
||||
building them from source. This might still take a while since all
|
||||
dependencies must be downloaded, but on a reasonably fast connection
|
||||
such as an ADSL line it's on the order of a few minutes.</para>
|
||||
|
||||
<para>Naturally, packages can also be uninstalled:
|
||||
|
||||
looks for a newer version of Pan, and installs it if found. Also
|
||||
useful is the ability to upgrade <emphasis>all</emphasis> packages:
|
||||
|
||||
<screen>
|
||||
$ nix-env -uf pkgs/system/i686-linux.nix '*'</screen>
|
||||
$ nix-env -e subversion</screen>
|
||||
|
||||
</para>
|
||||
|
||||
<para>Upgrading to a new version is just as easy. If you have a new
|
||||
release of Nix Packages, you can do:
|
||||
|
||||
<screen>
|
||||
$ nix-env -f nixpkgs-<replaceable>version</replaceable> -u subversion</screen>
|
||||
|
||||
This will <emphasis>only</emphasis> upgrade Subversion if there is a
|
||||
<quote>newer</quote> version in the new set of Nix expressions, as
|
||||
defined by some pretty much arbitrary rules regarding ordering of
|
||||
version numbers (which generally do what you'd expect of them). To
|
||||
just unconditionally replace Subversion with whatever version is in
|
||||
the Nix expressions, use <parameter>-i</parameter> instead of
|
||||
<parameter>-u</parameter> — <parameter>-i</parameter> will
|
||||
remove whatever version is already installed.</para>
|
||||
|
||||
<para>You can also upgrade all components for which there are newer
|
||||
versions:
|
||||
|
||||
<screen>
|
||||
$ nix-env -f nixpkgs-<replaceable>version</replaceable> -u '*'</screen>
|
||||
|
||||
</para>
|
||||
|
||||
<para>If you grow tired of specifying the Nix expressions using
|
||||
<parameter>-f</parameter> all the time, you can set a default
|
||||
location:
|
||||
|
||||
<screen>
|
||||
$ nix-env -I nixpkgs-<replaceable>version</replaceable></screen>
|
||||
|
||||
After this you can just say, for instance, <literal>nix-env -u
|
||||
'*'</literal>.<footnote><para>Setting a default using
|
||||
<parameter>-I</parameter> currently clashes with using Nix channels,
|
||||
since <literal>nix-channel --update</literal> calls <literal>nix-env
|
||||
-I</literal> to set the default to the Nix expressions it downloaded
|
||||
from the channel, replacing whatever default you had
|
||||
set.</para></footnote></para>
|
||||
|
||||
</sect1>
|
||||
|
||||
|
||||
<sect1><title>Profiles</title>
|
||||
|
||||
<para>Bla</para>
|
||||
|
||||
</sect1>
|
||||
|
||||
|
||||
<sect1><title>Garbage collection</title>
|
||||
|
||||
<para>Bla</para>
|
||||
|
||||
</sect1>
|
||||
|
||||
|
||||
<sect1><title>Channels</title>
|
||||
|
||||
<para>Bla</para>
|
||||
|
||||
</sect1>
|
||||
|
||||
The asterisk matches all installed packages<footnote><para>No, we
|
||||
don't support arbitrary regular expressions</para></footnote>. Note
|
||||
that <literal>*</literal> must be quoted to prevent shell
|
||||
globbing.</para>
|
||||
|
||||
</chapter>
|
||||
Loading…
Reference in New Issue