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* Update the user environments figure to show multiple profiles and

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users.
* Change to base-32 hashes.
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Eelco Dolstra 2005-03-16 14:40:48 +00:00
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@ -5,8 +5,8 @@
<para>The easiest way to obtain Nix is to download a <ulink
url='http://www.cs.uu.nl/groups/ST/Trace/Nix'>source
distribution</ulink>. RPMs for Red Hat 9 are also available. These
distributions are generated automatically.</para>
distribution</ulink>. RPMs for Red Hat, SuSE, and Fedore Core are
also available.</para>
<para>Alternatively, the most recent sources of Nix can be obtained
from its <ulink

101
doc/manual/package-management.xml
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@ -2,7 +2,7 @@
<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
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>
@ -19,7 +19,7 @@ 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>. Such a view on the set of
in the user’s <envar>PATH</envar>. 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. </para>
@ -52,7 +52,7 @@ bzip2-1.0.2
...</screen>
where <literal>nixpkgs-<replaceable>version</replaceable></literal> is
where you've unpacked the release.</para>
where you’ve unpacked the release.</para>
<para>It is also possible to see the <emphasis>status</emphasis> of
available components, i.e., whether they are installed into the user
@ -72,7 +72,7 @@ component is installed in your current user environment. The second
(in which case installing it into your user environment would be a
very quick operation). 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
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>
@ -98,7 +98,7 @@ 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
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:
@ -111,7 +111,7 @@ 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 DSL line it's on the order of a few minutes.</para>
such as an DSL line it’s on the order of a few minutes.</para>
<para>Naturally, packages can also be uninstalled:
@ -129,7 +129,7 @@ $ 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 arbitrary rules regarding ordering of version
numbers (which generally do what you'd expect of them). To just
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
@ -143,7 +143,7 @@ $ nix-env -f nixpkgs-<replaceable>version</replaceable> -u '*'</screen>
</para>
<para>Sometimes it's useful to be able to ask what
<para>Sometimes it’s useful to be able to ask what
<command>nix-env</command> would do, without actually doing it. For
instance, to find out what packages would be upgraded by
<literal>nix-env -u '*'</literal>, you can do
@ -177,28 +177,26 @@ set.</para></footnote></para>
<sect1><title>Profiles</title>
<para>Profiles and user environments are Nix's mechanism for
<para>Profiles and user environments are Nix’s mechanism for
implementing the ability to allow differens users to have different
configurations, and to do atomic upgrades and rollbacks. To
understand how they work, it's useful to know a bit about how Nix
understand how they work, it’s useful to know a bit about how Nix
works. In Nix, components are stored in unique locations in the
<emphasis>Nix store</emphasis> (typically,
<filename>/nix/store</filename>). For instance, a particular version
of the Subversion component might be stored in a directory
<filename>/nix/store/eeeeaf42e56b...-subversion-0.32.1/</filename>,
<filename>/nix/store/dpmvp969yhdqs7lm2r1a3gng7pyq6vy4-subversion-1.1.3/</filename>,
while another version might be stored in
<filename>/nix/store/58823d558a6a...-subversion-0.34/</filename>. The
long hexadecimal numbers prefixed to the directory names are
cryptographic hashes<footnote><para>160-bit truncations of SHA-256
hashes, to be precise.</para></footnote> of <emphasis>all</emphasis>
inputs involved in building the component — sources, dependencies,
compiler flags, and so on. So if two components differ in any way,
they end up in different locations in the file system, so they don't
interfere with each other. <xref linkend='fig-user-environments'
/><footnote><para>TODO: the figure isn't entirely up to date. It
should show multiple profiles and
<filename>~/.nix-profile</filename>.</para></footnote> shows a part of
a typical Nix store.</para>
<filename>/nix/store/5mq2jcn36ldlmh93yj1n8s9c95pj7c5s-subversion-1.1.2</filename>.
The long strings prefixed to the directory names are cryptographic
hashes<footnote><para>160-bit truncations of SHA-256 hashes encoded in
a base-32 notation, to be precise.</para></footnote> of
<emphasis>all</emphasis> inputs involved in building the component —
sources, dependencies, compiler flags, and so on. So if two
components differ in any way, they end up in different locations in
the file system, so they don’t interfere with each other. <xref
linkend='fig-user-environments' /> shows a part of a typical Nix
store.</para>
<figure id='fig-user-environments'><title>User environments</title>
<mediaobject>
@ -208,41 +206,42 @@ a typical Nix store.</para>
</mediaobject>
</figure>
<para>Of course, you wouldn't want to type
<para>Of course, you wouldn’t want to type
<screen>
$ /nix/store/eeeeaf42e56b...-subversion-0.32.1/bin/svn</screen>
$ /nix/store/dpmvp969yhdq...-subversion-1.1.3/bin/svn</screen>
every time you want to run Subversion. Of course we could set up the
<envar>PATH</envar> environment variable to include the
<filename>bin</filename> directory of every component we want to use,
but this is not very convenient since changing <envar>PATH</envar>
doesn't take effect for already existing processes. The solution Nix
doesn’t take effect for already existing processes. The solution Nix
uses is to create directory trees of symlinks to
<emphasis>activated</emphasis> components. These are called
<emphasis>user environments</emphasis> and they are components
themselves (though automatically generated by
<command>nix-env</command>), so they too reside in the Nix store. For
instance, in <xref linkend='fig-user-environments' /> the user
environment <filename>/nix/store/068150f63831...-user-env</filename>
contains a symlink to just Subversion 0.32.1 (arrows in the figure
environment <filename>/nix/store/5mq2jcn36ldl...-user-env</filename>
contains a symlink to just Subversion 1.1.2 (arrows in the figure
indicate symlinks). This would be what we would obtain if we had done
<screen>
$ nix-env -i subversion</screen>
on a set of Nix expressions that contained Subversion 0.32.1.</para>
on a set of Nix expressions that contained Subversion 1.1.2.</para>
<para>This doesn't in itself solve the problem, of course; you
wouldn't want to type
<filename>/nix/store/068150f63831...-user-env/bin/svn</filename>
either. Therefore there are symlinks outside of the store that point
<para>This doesn’t in itself solve the problem, of course; you
wouldn’t want to type
<filename>/nix/store/0c1p5z4kda11...-user-env/bin/svn</filename>
either. That’s why there are symlinks outside of the store that point
to the user environments in the store; for instance, the symlinks
<filename>42</filename> and <filename>43</filename> in the example.
These are called <emphasis>generations</emphasis> since every time you
perform a <command>nix-env</command> operation, a new user environment
is generated based on the current one. For instance, generation 43
was created from generation 42 when we did
<filename>default-42-link</filename> and
<filename>default-43-link</filename> in the example. These are called
<emphasis>generations</emphasis> since every time you perform a
<command>nix-env</command> operation, a new user environment is
generated based on the current one. For instance, generation 43 was
created from generation 42 when we did
<screen>
$ nix-env -i subversion mozilla</screen>
@ -251,14 +250,14 @@ on a set of Nix expressions that contained Mozilla and a new version
of Subversion.</para>
<para>Generations are grouped together into
<emphasis>profiles</emphasis> so that different users don't interfere
with each other if they don't want to. For example:
<emphasis>profiles</emphasis> so that different users don’t interfere
with each other if they don’t want to. For example:
<screen>
$ ls -l /nix/var/nix/profiles/
...
lrwxrwxrwx 1 eelco ... default-42-link -> /nix/store/068150f63831...-user-env
lrwxrwxrwx 1 eelco ... default-43-link -> /nix/store/84c85f89ddbf...-user-env
lrwxrwxrwx 1 eelco ... default-42-link -> /nix/store/0c1p5z4kda11...-user-env
lrwxrwxrwx 1 eelco ... default-43-link -> /nix/store/3aw2pdyx2jfc...-user-env
lrwxrwxrwx 1 eelco ... default -> default-43-link</screen>
This shows a profile called <filename>default</filename>. The file
@ -268,7 +267,7 @@ operation, a new user environment and generation link are created
based on the current one, and finally the <filename>default</filename>
symlink is made to point at the new generation. This last step is
atomic on Unix, which explains how we can do atomic upgrades. (Note
that the building/installing of new components doesn't interfere in
that the building/installing of new components doesn’t interfere in
any way with old components, since they are stored in different
locations in the Nix store.)</para>
@ -293,13 +292,13 @@ can also see all available generations:
$ nix-env --list-generations</screen></para>
<para>Actually, there is another level of indirection not shown in the
figure above. You generally wouldn't have
figure above. You generally wouldn’t have
<filename>/nix/var/nix/profiles/<replaceable>some-profile</replaceable>/bin</filename>
in your <envar>PATH</envar>. Rather, there is a symlink
<filename>~/.nix-profile</filename> that points to your current
profile. This means that you should put
<filename>~/.nix-profile/bin</filename> in your <envar>PATH</envar>
(and indeed, that's what the initialisation script
(and indeed, that’s what the initialisation script
<filename>/nix/etc/profile.d/nix.sh</filename> does). This makes it
easier to switch to a different profile. You can do that using the
command <command>nix-env --switch-profile</command>:
@ -310,7 +309,7 @@ $ nix-env --switch-profile /nix/var/nix/profiles/my-profile
$ nix-env --switch-profile /nix/var/nix/profiles/default</screen>
These commands switch to the <filename>my-profile</filename> and
default profile, respectively. If the profile doesn't exist, it will
default profile, respectively. If the profile doesn’t exist, it will
be created automatically. You should be careful about storing a
profile in another location than the <filename>profiles</filename>
directory, since otherwise it might not be used as a root of the
@ -346,7 +345,7 @@ not used (directly or indirectly) by any generation of any
profile.</para>
<para>Note however that as long as old generations reference a
component, it will not be deleted. After all, we wouldn't be able to
component, it will not be deleted. After all, we wouldn’t be able to
do a rollback otherwise. So in order for garbage collection to be
effective, you should also delete (some) old generations. Of course,
this should only be done if you are certain that you will not need to
@ -378,7 +377,7 @@ You can alo first view what files would be deleted:
$ nix-collect-garbage --print-dead</screen>
Likewise, the option <option>--print-live</option> will show the paths
that <emphasis>won't</emphasis> be deleted.</para>
that <emphasis>won’t</emphasis> be deleted.</para>
<sect2><title>Garbage collector roots</title>
@ -402,11 +401,11 @@ so all generations of all profiles are also roots of the collector.</para>
<sect1><title>Channels</title>
<para>If you want to stay up to date with a set of packages, it's not
<para>If you want to stay up to date with a set of packages, it’s not
very convenient to manually download the latest set of Nix expressions
for those packages, use <command>nix-pull</command> to register
pre-built binaries (if available), and upgrade using
<command>nix-env</command>. Fortunately, there's a better way:
<command>nix-env</command>. Fortunately, there’s a better way:
<emphasis>Nix channels</emphasis>.</para>
<para>A Nix channel is just a URL that points to a place that contains
@ -440,7 +439,7 @@ This downloads the Nix expressions in every channel (downloaded from
and registers any available pre-built binaries in every channel
(by <command>nix-pull</command>ing
<literal><replaceable>url</replaceable>/MANIFEST</literal>). It also
makes the union of each channel's Nix expressions the default for
makes the union of each channel’s Nix expressions the default for
<command>nix-env</command> operations. Consequently, you can then say
<screen>