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== A NixOS cheat sheet and comparison to Ubuntu ==
{{Merge|Nix (command line utilities)}}
[[Ubuntu_vs._NixOS|Ubuntu vs. NixOS]] provides a table mapping of common administrative tasks and their commands in Ubuntu to similar capabilities in NixOS.
 
This cheatsheet is a collection of handy snippets for working with a NixOS system.


== Working with the nix store ==
== Working with the nix store ==
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==== Adding files to the store ====
==== Get store path for a package from the Flake input ====
When packages are managed using [[Flakes]], store paths to them can be retrieved using <code>nix eval --inputs-from</code>, like this:<syntaxhighlight lang="shell">
$ nix eval --inputs-from "$flake_path" --raw "$input#$package"
</syntaxhighlight>For instance, when packages are managed using [[Home Manager]] using standard configuration, store path to the [[Git]] package can be retrieved using this command:<syntaxhighlight lang="shell">
$ nix eval --inputs-from ~/.config/home-manager --raw nixpkgs#git
</syntaxhighlight>


=== Add files to the store ===
{{Warning|Editing the Nix Store manually may cause undefined behaviour to occur in Nix's database. Avoid making manual changes to the store unless you are absolutely sure you know what you're doing.}}
It is sometimes necessary to add files to the store manually.
It is sometimes necessary to add files to the store manually.
This is particularly the case with packages that cannot be downloaded automatically,
This is particularly the case with packages that cannot be downloaded automatically,
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Unfortunately, `nix-store` will try to load the entire file into memory,
Unfortunately, <code>nix-store</code> will try to load the entire file into memory,
which will fail if the file size exceeds available memory.
which will fail if the file size exceeds available memory.
If we have root access, we can copy the file to the store ourselves:
If we have root access, we can copy the file to the store ourselves:
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=== Build nixos from nixpkgs repo ===
=== Build NixOS from nixpkgs repo ===


The following snippet will build the system from a git checkout:
The following snippet will build the system from a git checkout:
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This method can be used when testing nixos services for a pull request to nixpkgs.
This method can be used when testing NixOS services for a pull request to nixpkgs.


Building nixos from a git is an alternative to using nix channels and set up permanent following this [https://web.archive.org/web/20160327190212/http://anderspapitto.com/posts/2015-11-01-nixos-with-local-nixpkgs-checkout.html blog article].
Building NixOS from a git is an alternative to using nix channels and set up permanent following this [https://web.archive.org/web/20160327190212/http://anderspapitto.com/posts/2015-11-01-nixos-with-local-nixpkgs-checkout.html blog article].
It has a couple of advantages over nixpkgs as it allows back-porting of packages/changes to stable versions
It has a couple of advantages over nixpkgs as it allows back-porting of packages/changes to stable versions
as well as applying customization.
as well as applying customization.
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=== Evaluate a NixOS configuration without building ===
=== Evaluate a NixOS configuration without building ===


If you only want to evaluate `configuration.nix` without building (e.g. to syntax-check or see if you are using module options correctly), you can use:
If you only want to evaluate <code>configuration.nix</code> without building (e.g. to syntax-check or see if you are using module options correctly), you can use:


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This creates the `.drv` file that `nixos-rebuild build` would build.
This creates the <code>.drv</code> file that <code>nixos-rebuild build</code> would build.
 
=== Explore a NixOS configuration in the REPL ===
If you want to see what ''value'' a NixOS option takes without building, as opposed to merely checking that all options work, you can run:
<syntaxhighlight lang="console">
$ nix repl --file '<nixpkgs/nixos>'
Welcome to Nix 2.18.2. Type :? for help.
 
Loading installable ''...
Added 6 variables.
nix-repl> config.environment.shells  # for example
[ "/run/current-system/sw/bin/zsh" ... ]
 
# Equivalently, if starting from an existing REPL:
nix-repl> :l <nixpkgs/nixos>
Added 6 variables.
 
nix-repl> config.environment.shells
</syntaxhighlight>
 
This can be helpful if your configuration is spread across multiple modules, or if you import modules from external sources, or if NixOS has defaults and you want to know whether a default is being used or extended in your configuration, or a variety of other cases in which you might want the computer to tell you what the end result of all your Nixing is going to be before you switch to it.
 
You can do this with configuration files other than the one installed in <code>/etc/nixos</code>, too:
 
<pre>
nix-repl> :a import <nixpkgs/nixos> { configuration = /path/to/config.nix; }
</pre>


=== Manually switching a NixOS system to a certain version of system closure ===
=== Manually switching a NixOS system to a certain version of system closure ===
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where <code>-I nixpkgs=/path/to/nixpkgs</code> is optionally depending whether the vm should be build from git checkout or a channel.
where <code>-I nixpkgs=/path/to/nixpkgs</code> is optionally depending whether the vm should be build from git checkout or a channel.


On non-nixos (linux) systems the following command can be used instead:
On non-NixOS (linux) systems the following command can be used instead:


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Don't forget that by default nixos comes with a firewall enabled:
Don't forget that by default NixOS comes with a firewall enabled:


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To initiate the build environment run `nix-shell` in the project root directory
To initiate the build environment run <code>nix-shell</code> in the project root directory


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=== Evaluate packages for a different platform ===
=== Evaluate packages for a different platform ===


Sometimes you want to check whether a change to a package (such as adding a new dependency) would evaluate even on a different type of system. For example, you may want to check on `x86_64-linux` whether a package evaluates for `x86_64-darwin` or `aarch64-linux`.
Sometimes you want to check whether a change to a package (such as adding a new dependency) would evaluate even on a different type of system. For example, you may want to check on <code>x86_64-linux</code> whether a package evaluates for <code>x86_64-darwin</code> or <code>aarch64-linux</code>.


Use the `system` argument:
Use the <code>system</code> argument:


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=== Cross-compile packages ===
=== Cross-compile packages ===


The following command will cross compile the tinc package for the aarch64 CPU architecture from a different architecture (e.g. x86_64).
The following command will cross compile the <code>tinc</code> package for the aarch64 CPU architecture from the current system architecture (e.g. x86_64 if you are running a x86_64 system).


<syntaxHighlight lang="console">
<syntaxhighlight lang="console">
$ nix-build '<nixpkgs>' --arg crossSystem '(import <nixpkgs> {}).lib.systems.examples.aarch64-multiplatform' -A tinc
$ nix-build '<nixpkgs>' -A pkgsCross.aarch64-multiplatform.tinc
</syntaxHighlight>
</syntaxhighlight>


You can add your own specifications, or look at existing ones, in nixpkgs/lib/systems/examples.nix.
There are alternative ways to specify and build cross compiled packages, see [[Cross Compiling]].


=== Customizing Packages ===
=== Customizing Packages ===
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and the following in `configuration.nix`:
and the following in <code>configuration.nix</code>:


<syntaxHighlight lang="nix">
<syntaxHighlight lang="nix">
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== See also ==
== See also ==


- [[Garbage Collection]]
* [[Garbage Collection]]
- [[NFS#Nix_store_on_NFS|Nix store on NFS]]
* [[NFS#Nix_store_on_NFS|Nix store on NFS]]


[[Category:Cookbook]]
[[Category:Cookbook]]
[[Category:Software]]
[[Category:Software]]
Retrieved from "https://wiki.nixos.org/wiki/Cheatsheet"