mirror of
https://github.com/NixOS/nix-pills
synced 2024-09-19 04:00:13 -04:00
342 lines
12 KiB
XML
342 lines
12 KiB
XML
<chapter 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="install-on-your-running-system">
|
|
|
|
<title>Install on Your Running System</title>
|
|
|
|
<para>
|
|
Welcome to the second Nix pill. In the <link
|
|
linkend="why-you-should-give-it-a-try">first</link> pill we
|
|
briefly described Nix.
|
|
</para>
|
|
|
|
<para>
|
|
Now we'll install Nix on our running system and understand what
|
|
changed in our system after the installation.
|
|
<emphasis role="bold">If you're using NixOS, Nix is already installed;
|
|
you can skip to the <link
|
|
linkend="enter-environment">next</link> pill.</emphasis>
|
|
</para>
|
|
|
|
<para>
|
|
For installation instructions, please refer to the Nix Reference Manual on
|
|
<link xlink:href="https://nixos.org/manual/nix/stable/installation/installation.html">
|
|
Installing Nix</link>.
|
|
</para>
|
|
|
|
<section>
|
|
<title>Installation</title>
|
|
|
|
<para>
|
|
These articles are not a tutorial on <emphasis>using</emphasis> Nix.
|
|
Instead, we're going to walk through the Nix system to understand the fundamentals.
|
|
</para>
|
|
|
|
<para>
|
|
The first thing to note: derivations in the Nix store refer to other
|
|
derivations which are themselves in the Nix store. They don't use <literal>libc</literal>
|
|
from our system or anywhere else. It's a self-contained store of all the software we need to bootstrap up
|
|
to any particular package.
|
|
</para>
|
|
|
|
<note><para>
|
|
In a multi-user installation, such as the one used in NixOS,
|
|
the store is owned by root and multiple users can install and build
|
|
software through a Nix daemon. You can read more about multi-user
|
|
installations here: <link
|
|
xlink:href="https://nixos.org/manual/nix/stable/installation/installing-binary.html#multi-user-installation">https://nixos.org/manual/nix/stable/installation/installing-binary.html#multi-user-installation</link>.
|
|
</para></note>
|
|
</section>
|
|
|
|
<section>
|
|
<title>The beginnings of the Nix store</title>
|
|
|
|
<para>
|
|
Start looking at the output of the install command:
|
|
</para>
|
|
|
|
<screen>copying Nix to /nix/store..........................</screen>
|
|
|
|
<para>
|
|
That's the <filename>/nix/store</filename> we
|
|
were talking about in the first article. We're copying in the
|
|
necessary software to bootstrap a Nix system. You can see bash,
|
|
coreutils, the C compiler toolchain, perl libraries, sqlite and Nix itself
|
|
with its own tools and libnix.
|
|
</para>
|
|
|
|
<para>
|
|
You may have noticed that <filename>/nix/store</filename> can contain
|
|
not only directories, but also files, still always in the form
|
|
<replaceable>hash-name</replaceable>.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>The Nix database</title>
|
|
|
|
<para>
|
|
Right after copying the store, the installation process
|
|
initializes a database:
|
|
</para>
|
|
|
|
<screen>initialising Nix database...</screen>
|
|
|
|
<para>
|
|
Yes, Nix also has a database. It's stored under
|
|
<filename>/nix/var/nix/db</filename>. It is a sqlite database
|
|
that keeps track of the dependencies between derivations.
|
|
</para>
|
|
|
|
<para>
|
|
The schema is very simple: there's a table of valid paths,
|
|
mapping from an auto increment integer to a store path.
|
|
</para>
|
|
|
|
<para>
|
|
Then there's a dependency relation from path to paths upon which they depend.
|
|
</para>
|
|
|
|
<para>
|
|
You can inspect the database by installing sqlite
|
|
(<command>nix-env -iA sqlite -f '<nixpkgs>'</command>) and then running
|
|
<command>sqlite3 /nix/var/nix/db/db.sqlite</command>.
|
|
</para>
|
|
|
|
<note><para>If this is the first time you're using Nix after the
|
|
initial installation, remember you must close and open your
|
|
terminals first, so that your shell environment will be updated.</para></note>
|
|
|
|
<important><para>
|
|
Never change <filename>/nix/store</filename> manually. If you do, then it will
|
|
no longer be in sync with the sqlite db, unless you <emphasis>really</emphasis>
|
|
know what you are doing.
|
|
</para></important>
|
|
</section>
|
|
|
|
<section>
|
|
<title>The first profile</title>
|
|
|
|
<para>
|
|
Next in the installation, we encounter the concept of the <link
|
|
xlink:href="https://nixos.org/manual/nix/stable/package-management/profiles.html">profile</link>:
|
|
</para>
|
|
|
|
<screen>creating /home/nix/.nix-profile
|
|
installing 'nix-2.1.3'
|
|
building path(s) `/nix/store/a7p1w3z2h8pl00ywvw6icr3g5l9vm5r7-<emphasis role="strong">user-environment</emphasis>'
|
|
created 7 symlinks in user environment</screen>
|
|
|
|
|
|
<para>
|
|
A profile in Nix is a general and convenient concept for
|
|
realizing rollbacks. Profiles are used to compose
|
|
components that are spread among multiple paths under a new
|
|
unified path. Not only that, but profiles are made up of multiple
|
|
"generations": they are versioned. Whenever you change a profile,
|
|
a new generation is created.
|
|
</para>
|
|
|
|
<para>
|
|
Generations can be switched and rolled back atomically, which makes
|
|
them convenient for managing changes to your system.
|
|
</para>
|
|
|
|
<para>
|
|
Let's take a closer look at our profile:
|
|
</para>
|
|
|
|
<screen>$ ls -l ~/.nix-profile/
|
|
bin -> /nix/store/ig31y9gfpp8pf3szdd7d4sf29zr7igbr-<emphasis role="strong">nix-2.1.3</emphasis>/bin
|
|
[...]
|
|
manifest.nix -> /nix/store/q8b5238akq07lj9gfb3qb5ycq4dxxiwm-<emphasis role="strong">env-manifest.nix</emphasis>
|
|
[...]
|
|
share -> /nix/store/ig31y9gfpp8pf3szdd7d4sf29zr7igbr-<emphasis role="strong">nix-2.1.3</emphasis>/share</screen>
|
|
|
|
<para>
|
|
That <package>nix-2.1.3</package> derivation in the Nix store is
|
|
Nix itself, with binaries and libraries. The process of "installing"
|
|
the derivation in the profile basically reproduces the hierarchy of the
|
|
<package>nix-2.1.3</package> store derivation in the profile by means of
|
|
symbolic links.
|
|
</para>
|
|
<para>
|
|
The contents of this profile are special, because only one
|
|
program has been installed in our profile, therefore e.g. the
|
|
<filename>bin</filename> directory points to the only program
|
|
which has been installed (Nix itself).
|
|
</para>
|
|
<para>
|
|
But that's only the contents of the latest generation of our
|
|
profile. In fact, <filename>~/.nix-profile</filename> itself is a
|
|
symbolic link to
|
|
<filename>/nix/var/nix/profiles/default</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
In turn, that's a symlink to <filename>default-1-link</filename>
|
|
in the same directory. Yes, that means it's the first generation of
|
|
the <literal>default</literal> profile.
|
|
</para>
|
|
|
|
<para>
|
|
Finally, <filename>default-1-link</filename> is a symlink to the nix
|
|
store "user-environment" derivation that you saw printed during the installation process.
|
|
</para>
|
|
|
|
<para>
|
|
We'll talk about <filename>manifest.nix</filename> more in the next article.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Nixpkgs expressions</title>
|
|
|
|
<para>
|
|
More output from the installer:
|
|
</para>
|
|
|
|
<screen>downloading Nix expressions from `http://releases.nixos.org/nixpkgs/nixpkgs-14.10pre46060.a1a2851/nixexprs.tar.xz'...
|
|
unpacking channels...
|
|
created 2 symlinks in user environment
|
|
modifying /home/nix/.profile...
|
|
</screen>
|
|
|
|
<para>
|
|
Nix expressions are written in the <link
|
|
xlink:href="https://nix.dev/tutorials/nix-language">Nix language</link> and used to
|
|
describe packages and how to build them. <link
|
|
xlink:href="https://nixos.org/nixpkgs/">Nixpkgs</link> is the
|
|
repository containing all of the expressions: <link
|
|
xlink:href="https://github.com/NixOS/nixpkgs">https://github.com/NixOS/nixpkgs</link>.
|
|
</para>
|
|
|
|
<para>
|
|
The installer downloaded the package descriptions from commit
|
|
<literal>a1a2851</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
The second profile we discover is the channels profile.
|
|
<filename>~/.nix-defexpr/channels</filename> points to
|
|
<filename>/nix/var/nix/profiles/per-user/nix/channels</filename>
|
|
which points to <literal>channels-1-link</literal> which points
|
|
to a Nix store directory containing the downloaded Nix
|
|
expressions.
|
|
</para>
|
|
|
|
<para>
|
|
Channels are a set of packages and expressions available for
|
|
download. Similar to Debian stable and unstable, there's a
|
|
stable and unstable channel. In this installation, we're
|
|
tracking <literal>nixpkgs-unstable</literal>.
|
|
</para>
|
|
|
|
<para>
|
|
Don't worry about Nix expressions yet, we'll get to them later.
|
|
</para>
|
|
|
|
<para>
|
|
Finally, for your convenience, the installer modified
|
|
<filename>~/.profile</filename> to automatically enter the Nix
|
|
environment. What
|
|
<filename>~/.nix-profile/etc/profile.d/nix.sh</filename> really
|
|
does is simply to add <filename>~/.nix-profile/bin</filename> to
|
|
<varname>PATH</varname> and
|
|
<filename>~/.nix-defexpr/channels/nixpkgs</filename> to
|
|
<varname>NIX_PATH</varname>. We'll discuss
|
|
<varname>NIX_PATH</varname> later.
|
|
</para>
|
|
|
|
<para>
|
|
Read <filename>nix.sh</filename>, it's short.
|
|
</para>
|
|
|
|
</section>
|
|
|
|
<section>
|
|
<title>FAQ: Can I change /nix to something else?</title>
|
|
|
|
<para>
|
|
You can, but there's a good reason to keep using
|
|
<filename>/nix</filename> instead of a different directory. All
|
|
the derivations depend on other derivations by using absolute paths. We
|
|
saw in the first article that bash referenced a
|
|
<package>glibc</package> under a specific absolute path in <filename>/nix/store</filename>.
|
|
</para>
|
|
|
|
<para>
|
|
You can see for yourself, don't worry if you see multiple
|
|
bash derivations:
|
|
</para>
|
|
|
|
|
|
<screen>
|
|
$ ldd /nix/store/*bash*/bin/bash
|
|
[...]
|
|
</screen>
|
|
|
|
<para>
|
|
Keeping the store in <filename>/nix</filename> means we can grab
|
|
the binary cache from nixos.org (just like you grab packages
|
|
from debian mirrors) otherwise:
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<package>glibc</package> would be installed under <filename>/foo/store</filename>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Thus bash would need to point to <package>glibc</package> under <filename>/foo/store</filename>,
|
|
instead of under <filename>/nix/store</filename>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
So the binary cache can't help, because we need a <emphasis>different</emphasis> bash,
|
|
and so we'd have to recompile everything ourselves.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
After all <filename>/nix</filename> is a sensible place for the store.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Conclusion</title>
|
|
<para>
|
|
We've installed Nix on our system, fully isolated and owned by
|
|
the <literal>nix</literal> user as we're still coming to terms with
|
|
this new system.
|
|
</para>
|
|
<para>
|
|
We learned some new concepts like profiles and channels. In
|
|
particular, with profiles we're able to manage multiple
|
|
generations of a composition of packages, while with channels
|
|
we're able to download binaries from <literal>nixos.org</literal>.
|
|
</para>
|
|
<para>
|
|
The installation put everything under <filename>/nix</filename>,
|
|
and some symlinks in the Nix user home. That's because every
|
|
user is able to install and use software in her own environment.
|
|
</para>
|
|
<para>
|
|
I hope I left nothing uncovered so that you think there's
|
|
some kind of magic going on behind the scenes. It's all
|
|
about putting components in the store and symlinking
|
|
these components together.
|
|
</para>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Next pill...</title>
|
|
|
|
<para>
|
|
...we will enter the Nix environment and learn how to interact
|
|
with the store.
|
|
</para>
|
|
</section>
|
|
|
|
</chapter>
|