diff options
Diffstat (limited to 'third_party/nix/doc/manual/introduction/about-nix.xml')
| -rw-r--r-- | third_party/nix/doc/manual/introduction/about-nix.xml | 268 |
1 files changed, 0 insertions, 268 deletions
diff --git a/third_party/nix/doc/manual/introduction/about-nix.xml b/third_party/nix/doc/manual/introduction/about-nix.xml deleted file mode 100644 index c21ed34ddc..0000000000 --- a/third_party/nix/doc/manual/introduction/about-nix.xml +++ /dev/null @@ -1,268 +0,0 @@ -<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="ch-about-nix"> - -<title>About Nix</title> - -<para>Nix is a <emphasis>purely functional package manager</emphasis>. -This means that it treats packages like values in purely functional -programming languages such as Haskell — they are built by functions -that don’t have side-effects, and they never change after they have -been built. Nix stores packages in the <emphasis>Nix -store</emphasis>, usually the directory -<filename>/nix/store</filename>, where each package has its own unique -subdirectory such as - -<programlisting> -/nix/store/b6gvzjyb2pg0kjfwrjmg1vfhh54ad73z-firefox-33.1/ -</programlisting> - -where <literal>b6gvzjyb2pg0…</literal> is a unique identifier for the -package that captures all its dependencies (it’s a cryptographic hash -of the package’s build dependency graph). This enables many powerful -features.</para> - - -<simplesect><title>Multiple versions</title> - -<para>You can have multiple versions or variants of a package -installed at the same time. This is especially important when -different applications have dependencies on different versions of the -same package — it prevents the “DLL hell”. Because of the hashing -scheme, different versions of a package end up in different paths in -the Nix store, so they don’t interfere with each other.</para> - -<para>An important consequence is that operations like upgrading or -uninstalling an application cannot break other applications, since -these operations never “destructively” update or delete files that are -used by other packages.</para> - -</simplesect> - - -<simplesect><title>Complete dependencies</title> - -<para>Nix helps you make sure that package dependency specifications -are complete. In general, when you’re making a package for a package -management system like RPM, you have to specify for each package what -its dependencies are, but there are no guarantees that this -specification is complete. If you forget a dependency, then the -package will build and work correctly on <emphasis>your</emphasis> -machine if you have the dependency installed, but not on the end -user's machine if it's not there.</para> - -<para>Since Nix on the other hand doesn’t install packages in “global” -locations like <filename>/usr/bin</filename> but in package-specific -directories, the risk of incomplete dependencies is greatly reduced. -This is because tools such as compilers don’t search in per-packages -directories such as -<filename>/nix/store/5lbfaxb722zp…-openssl-0.9.8d/include</filename>, -so if a package builds correctly on your system, this is because you -specified the dependency explicitly. This takes care of the build-time -dependencies.</para> - -<para>Once a package is built, runtime dependencies are found by -scanning binaries for the hash parts of Nix store paths (such as -<literal>r8vvq9kq…</literal>). This sounds risky, but it works -extremely well.</para> - -</simplesect> - - -<simplesect><title>Multi-user support</title> - -<para>Nix has multi-user support. This means that non-privileged -users can securely install software. Each user can have a different -<emphasis>profile</emphasis>, a set of packages in the Nix store that -appear in the user’s <envar>PATH</envar>. If a user installs a -package that another user has already installed previously, the -package won’t be built or downloaded a second time. At the same time, -it is not possible for one user to inject a Trojan horse into a -package that might be used by another user.</para> - -</simplesect> - - -<simplesect><title>Atomic upgrades and rollbacks</title> - -<para>Since package management operations never overwrite packages in -the Nix store but just add new versions in different paths, they are -<emphasis>atomic</emphasis>. So during a package upgrade, there is no -time window in which the package has some files from the old version -and some files from the new version — which would be bad because a -program might well crash if it’s started during that period.</para> - -<para>And since packages aren’t overwritten, the old versions are still -there after an upgrade. This means that you can <emphasis>roll -back</emphasis> to the old version:</para> - -<screen> -$ nix-env --upgrade <replaceable>some-packages</replaceable> -$ nix-env --rollback -</screen> - -</simplesect> - - -<simplesect><title>Garbage collection</title> - -<para>When you uninstall a package like this… - -<screen> -$ nix-env --uninstall firefox -</screen> - -the package isn’t deleted from the system right away (after all, you -might want to do a rollback, or it might be in the profiles of other -users). Instead, unused packages can be deleted safely by running the -<emphasis>garbage collector</emphasis>: - -<screen> -$ nix-collect-garbage -</screen> - -This deletes all packages that aren’t in use by any user profile or by -a currently running program.</para> - -</simplesect> - - -<simplesect><title>Functional package language</title> - -<para>Packages are built from <emphasis>Nix expressions</emphasis>, -which is a simple functional language. A Nix expression describes -everything that goes into a package build action (a “derivation”): -other packages, sources, the build script, environment variables for -the build script, etc. Nix tries very hard to ensure that Nix -expressions are <emphasis>deterministic</emphasis>: building a Nix -expression twice should yield the same result.</para> - -<para>Because it’s a functional language, it’s easy to support -building variants of a package: turn the Nix expression into a -function and call it any number of times with the appropriate -arguments. Due to the hashing scheme, variants don’t conflict with -each other in the Nix store.</para> - -</simplesect> - - -<simplesect><title>Transparent source/binary deployment</title> - -<para>Nix expressions generally describe how to build a package from -source, so an installation action like - -<screen> -$ nix-env --install firefox -</screen> - -<emphasis>could</emphasis> cause quite a bit of build activity, as not -only Firefox but also all its dependencies (all the way up to the C -library and the compiler) would have to built, at least if they are -not already in the Nix store. This is a <emphasis>source deployment -model</emphasis>. For most users, building from source is not very -pleasant as it takes far too long. However, Nix can automatically -skip building from source and instead use a <emphasis>binary -cache</emphasis>, a web server that provides pre-built binaries. For -instance, when asked to build -<literal>/nix/store/b6gvzjyb2pg0…-firefox-33.1</literal> from source, -Nix would first check if the file -<uri>https://cache.nixos.org/b6gvzjyb2pg0….narinfo</uri> exists, and -if so, fetch the pre-built binary referenced from there; otherwise, it -would fall back to building from source.</para> - -</simplesect> - - -<!-- -<simplesect><title>Binary patching</title> - -<para>In addition to downloading binaries automatically if they’re -available, Nix can download binary deltas that patch an existing -package in the Nix store into a new version. This speeds up -upgrades.</para> - -</simplesect> ---> - - -<simplesect><title>Nix Packages collection</title> - -<para>We provide a large set of Nix expressions containing hundreds of -existing Unix packages, the <emphasis>Nix Packages -collection</emphasis> (Nixpkgs).</para> - -</simplesect> - - -<simplesect><title>Managing build environments</title> - -<para>Nix is extremely useful for developers as it makes it easy to -automatically set up the build environment for a package. Given a -Nix expression that describes the dependencies of your package, the -command <command>nix-shell</command> will build or download those -dependencies if they’re not already in your Nix store, and then start -a Bash shell in which all necessary environment variables (such as -compiler search paths) are set.</para> - -<para>For example, the following command gets all dependencies of the -Pan newsreader, as described by <link -xlink:href="https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/newsreaders/pan/default.nix">its -Nix expression</link>:</para> - -<screen> -$ nix-shell '<nixpkgs>' -A pan -</screen> - -<para>You’re then dropped into a shell where you can edit, build and test -the package:</para> - -<screen> -[nix-shell]$ tar xf $src -[nix-shell]$ cd pan-* -[nix-shell]$ ./configure -[nix-shell]$ make -[nix-shell]$ ./pan/gui/pan -</screen> - -<!-- -<para>Since Nix packages are reproducible and have complete dependency -specifications, Nix makes an excellent basis for <a -href="[%root%]hydra">a continuous build system</a>.</para> ---> - -</simplesect> - - -<simplesect><title>Portability</title> - -<para>Nix runs on Linux and macOS.</para> - -</simplesect> - - -<simplesect><title>NixOS</title> - -<para>NixOS is a Linux distribution based on Nix. It uses Nix not -just for package management but also to manage the system -configuration (e.g., to build configuration files in -<filename>/etc</filename>). This means, among other things, that it -is easy to roll back the entire configuration of the system to an -earlier state. Also, users can install software without root -privileges. For more information and downloads, see the <link -xlink:href="http://nixos.org/">NixOS homepage</link>.</para> - -</simplesect> - - -<simplesect><title>License</title> - -<para>Nix is released under the terms of the <link -xlink:href="http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html">GNU -LGPLv2.1 or (at your option) any later version</link>.</para> - -</simplesect> - - -</chapter> |