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126 lines
No EOL
4.8 KiB
Markdown
# Nix/NixOS
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The [Skynet Cluster][nixos_skynet] is (for the most part) running on a Linux variant called NixOS.
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This article aims to introduce you to Nix and Nixos in order to get you up to speed to administer the cluster.
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## What it is
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### Nix
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#### Package Manager
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The word Nix refers to two things: a language and a package manager.
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These are deeply interlinked together with the language being how the package manager is able to do its job.
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Nix grew out of a [PhD by Eelco Dolstra][nix_paper] wherein he proposes a slightly different way to manage dependencies on a system.
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For most Linux systems programs make use of other software installed on the computer, for the most part this works fine.
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Where issue may arise is if one program needs to update one of these dependencies, specially a minor or major patch where backwards compatibility is not guaranteed.
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If another program is using this (system wide) dependency then it may run into interface issues when using it.
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In a sense updating one program can break another on the system.
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The route the Nix package manager takes is it treats each program as a function.
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Using teh Nix language a function for that package is created which states what inputs are required, what is needed to turn those inputs into teh program as well as the name for the output.
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The output is then saved in a read only location in the format of ``/nix/store/$hash-program-name-version``.
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This output can either be used as the input of another program or be used as is by the system/user.
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Using this format means that any change in the inputs or the program itself will result in a different output.
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This means that multiple versions of the program (some even the same version but different commit) can co-exist on the one system.
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An example using different versions of Firefox:
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##### Example
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An example of packaging an application can be found here:
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[Sieve Editor GUI on Nixpkgs][nix_pkgs_sieve]
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This is packaging up a GUI node.js application.
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The application itself allows the user to edit sieve scripts.
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Once you have [downloaded and installed](#download) Nix you will be able to install and run it like so:
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```shell
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nix-shell -p sieve-editor-gui
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sieve-editor-gui .
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```
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#### Language
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There are two partially difficult problems in computer science:
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1. Off by one errors
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2. Caching
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3. Naming things
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Nix falls into this last pitfall.
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The programming language used by teh Nix package manager is called Nix, not Nixlang (as like Erlang) but rather the same name as primary tool that uses it.
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For clarity for teh remainder of this subsection we are only talking about Nix the language.
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Nix is a lazily evaluated functional language which al has REPL (Read, Evaluate, Print, and Loop) capability like what you would see in Python.
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As a whole it takes strong influences from OCaml and other ML derived languages.
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##### Types
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It has most of the normal types that you would expect of a programming language, along with a few extra to deal with the filesystem:
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```nix
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a = 1 # int
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b = 1.001 # float
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c = /path/to/thing # path
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d = "42" # string
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e = true # boolean
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```
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Of these the ``path`` type will be new to most people.
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This can take either an absolute or relative path.
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##### Functions
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If you look at the section below it will seem that these are another type of assignment to a variable.
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That is half right, these are akin to function pointers that you would see in C or C++.
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Functions in Nix do not have types for either parameters or return.
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This is due to it being lazily evaluated, like Python or Javascript.
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As such the ``double`` function will accept any numeric value
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```nix
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double = x: x*2
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mul = a: b: a*b
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double 2
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double 4.2
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mul 7 6
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```
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##### Attribute Sets
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In most languages the way to group data would be either an Object or a Struct.
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Nix has a similar datastructure:
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```nix
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s = { foo = "bar"; biz = "baz"; }
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s.foo # bar
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s.biz # baz
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```
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##### More data
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This is a rough quickstart introduction to Nix.
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For more detailed information I recommend these resources.
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* [Official Guide][nix_guide_official]
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* [Nix Pills][nix_guide_pills]
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### Flakes
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### Nixos
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### Lix
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## Why we use it
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{Details of how the config was ascattered and hard to find}
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{Also embracing devops and reduced manpower}
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## How we use it
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### Requirements
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{add warnign that git and git-lfs should also need to be in teh path}
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### Download
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### Colmena
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#### Local
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##### Building
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##### Repl
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#### Deployment
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[nixos_skynet]: https://forgejo.skynet.ie/Skynet/nixos
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[nix_paper]: https://edolstra.github.io/pubs/nspfssd-lisa2004-final.pdf
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[nix_guide_official]: https://nix.dev/tutorials/first-steps/
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[nix_guide_pills]: https://nixos.org/guides/nix-pills/#
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[nix_pkgs_sieve]: https://github.com/NixOS/nixpkgs/blob/a3c0b3b21515f74fd2665903d4ce6bc4dc81c77c/pkgs/by-name/si/sieve-editor-gui/package.nix |