View source for Ubuntu vs. NixOS

<!-- TODO''': Provide well-commented sample configuration.nix and ~/.nixpkgs/config.nix files with examples of common tasks. -->

<div class="table-responsive">
{| class="wikitable"
!|Task
!|Ubuntu
!|NixOS (system-wide and root)
!|NixOS (user) and Nix in general
|-
| colspan="5" style="text-align:center"| '''Basic concepts'''
|-
|
|
|This column will let you do everything you can with Ubuntu and more.
|This column just isn't possible in Ubuntu.
|-
|Who can install packages and who can run them?
|All packages are always system-wide and only root can install packages.
|Packages root installs are system-wide. It does so through /etc/nixos/configuration.nix. If root installs packages the same way users do, through ~/.nixpkgs/config.nix, they are also global. Root's default profile is the system-wide default profile.
|Users can install their own packages and have their own profiles (environments) through ~/.nixpkgs/config.nix
|-
|Package manager
|apt which is really running on top of dpkg, sometimes wrapped by UIs like aptitude.
|nix, but many system-wide operations are provided by nixos packages.
|Just nix without the involvement of nixos.
|-
|How do you select your official sources and major releases
|These are baked into the distribution (e.g. Ubuntu version X). Upgrades are hard and permanent.
|At any time you select from a collection of channels. They're system-wide when set by root. You can roll back changes or switch channels with ease.
|Channels are per-user if they're not set by root.
|-
|Where are packages installed?
|apt installs globally into /bin/, /usr/, etc.
|System-wide packages are in /run/current-system/sw/ (these are installed because of /etc/nixos/configuration.nix) and /nix/var/nix/profiles/default/bin/ (this is the profile managed by root). Note that the files are just symlinks to the real packages managed by nix in /nix/store/.
|User packages are in ~/.nix-profile/. Note that the files are just symlinks to the real packages managed by nix in /nix/store/.
|-
|When changes take effect
|As soon as the command runs. Commands are not atomic and can leave your machine in a bad state.
|Most of the time you modify the configuration file and apply changes with nixos-rebuild switch
'''TODO''': How does one get nixos to do all the work for a switch and separate out the actual switching from fetching/building?
|Most of the time you apply changes with nix-env -i all
'''TODO''': How does one get nix to do all the work for a switch and separate out the actual switching from fetching/building?
|-
|Packages
|Uniformly referred to as packages
|Technically called "derivations" but everyone calls them packages.
|Technically called "derivations" but everyone calls them packages.
|-
| colspan="5" style="text-align:center"| '''Package management'''
|-
|-
|Install a package for all users
|<syntaxhighlight lang="console">$ sudo apt-get install emacs</syntaxhighlight>
|
1. Add to /etc/nixos/configuration.nix:
<syntaxhighlight lang="nix">
environment.systemPackages = with pkgs; [
  wget # let's assume wget was already present
  emacs
];</syntaxhighlight>
2. Run :
<syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -iA nixos.emacs</syntaxhighlight>
Or with collections, add the package to your ~/.nixpkgs/config.nix and run
<syntaxhighlight lang="console">$ nix-env -iA nixos.all</syntaxhighlight>
|-
|Install a package for a specific user only
|Not possible
|
1. Add to /etc/nixos/configuration.nix:
<syntaxhighlight lang="nix">
users.users.alice.packages = with pkgs; [ emacs ];</syntaxhighlight>
2. Run:
<syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|
1. Add to ~/.nixpkgs/config.nix:
<syntaxhighlight lang="nix">users.users.alice.packages = with pkgs;[ emacs ];</syntaxhighlight>
2. Run:
<syntaxhighlight lang="console">$ nix-env -iA nixos.all</syntaxhighlight>
|-
|Install a service
|<syntaxhighlight lang="console">$ sudo apt install openssh-server</syntaxhighlight>
|
1. Add to /etc/nixos/configuration.nix:
<syntaxhighlight lang="nix">services.openssh.enable = true;</syntaxhighlight>
2. Run: <syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|Not possible
|-
|Uninstall a package
|<syntaxhighlight lang="bash">sudo apt-get remove emacs</syntaxhighlight>
|remove from /etc/nixos/configuration.nix
<syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|
<syntaxhighlight lang="console">$ nix-env --uninstall emacs</syntaxhighlight>
|-
|Uninstall a package removing its configuration
|<syntaxhighlight lang="console">$ sudo apt-get purge emacs</syntaxhighlight>
|All configuration is in configuration.nix
|
|-
|Update the list of packages
|<syntaxhighlight lang="console">$ sudo apt-get update</syntaxhighlight>
|<syntaxhighlight lang="console">$ sudo nix-channel --update</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-channel --update</syntaxhighlight>
|-
|Upgrade packages
|<syntaxhighlight lang="console">$ sudo apt-get upgrade</syntaxhighlight>
|<syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -u</syntaxhighlight>
|-
|Check for broken dependencies
|<syntaxhighlight lang="console">$ sudo apt-get check</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-store --verify --check-contents</syntaxhighlight>
|unneeded!
|-
|List package dependencies
|<syntaxhighlight lang="console">$ apt-cache depends emacs</syntaxhighlight>
|Show the direct dependencies:
<syntaxhighlight lang="console">$ nix-store --query --requisites /run/current-system</syntaxhighlight>
or show a nested ASCII tree of dependencies:
<syntaxhighlight lang="console">$ nix-store -q --tree /nix/var/nix/profiles/system</syntaxhighlight>
(/run/current-system and /nix/var/nix/profiles/system are symbolic links that eventually end up at the same place.)
|<syntaxhighlight lang="console">$ nix-store --query --references\
  $(nix-instantiate '<nixpkgs>' -A emacs)</syntaxhighlight>
For installed packages:
<syntaxhighlight lang="console">$ nix-store --query --references $(which emacs)</syntaxhighlight>
|-
|List which packages depend on this one (reverse dependencies)
|<syntaxhighlight lang="console">$ apt-cache rdepends emacs</syntaxhighlight>
|
|For installed packages (only print reverse dependencies *which are already installed*):
<syntaxhighlight lang="console">$ nix-store --query --referrers $(which emacs)</syntaxhighlight>
|-
|Verify all installed packages
|<syntaxhighlight lang="console">$ debsums</syntaxhighlight>
|<syntaxhighlight lang="console">$ sudo nix-store --verify --check-contents</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-store --verify --check-contents</syntaxhighlight>
|-
|Fix packages with failed checksums
|Reinstall broken packages
|<syntaxhighlight lang="console">$ sudo nix-store --verify --check-contents --repair</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-store --verify --check-contents --repair</syntaxhighlight>
|-
|Select major version and stable/unstable
|Change sources.list and apt-get dist-upgrade. A an extremely infrequent and destructive operation. The nix variants are safe and easy to use.
|<syntaxhighlight lang="console">$ nix-channel --add\
   https://nixos.org/channels/nixpkgs-unstable <name></syntaxhighlight>
Add the unstable channel. At that address you will find names for other versions and variants. Name can be any string.
<syntaxhighlight lang="console">$ nix-channel --remove <name></syntaxhighlight>
To eliminate a channel.
<syntaxhighlight lang="console">$ nix-channel --list</syntaxhighlight>
To show all installed channel.
|When run by a user channels work locally, when run by root they're used as the system-wide channels.
|-
|Private package repository
|PPA
|Define your package tree as in the general column, and include it in configuration.nix, then list your packages in systemPackages to make them available system wide
|See [https://sandervanderburg.blogspot.de/2014/07/managing-private-nix-packages-outside.html]
|-
|Install a particular version of a package
|<syntaxhighlight lang="console">$ apt-get install package=version</syntaxhighlight>
|Although Nix on its own doesn't understand the concept of package versioning, you can install and play with older (or newer!) software via [[FAQ/Pinning Nixpkgs]] with https://lazamar.co.uk/nix-versions.


For instance, to launch an older version of Vim you could use:
<syntaxhighlight lang="console">
$ nix-shell \
    -p vim \
    -I nixpkgs=\https://github.com/NixOS/nixpkgs/archive/4bba6650a6a5a2009e25bdeed8c1e871601a9bfb.tar.gz
</syntaxhighlight>
|
|-
| colspan="5" style="text-align:center"| '''Package configuration'''
|-
|Configure a package
|<syntaxhighlight lang="console">$ sudo dpkg-reconfigure <package></syntaxhighlight>
|Edit /etc/nixos/configuration.nix
|Edit ~/.nixpkgs/config.nix; '''TODO''': More details about how to edit
|-
|Global package configuration
|Modify configuration file in /etc/
|Edit /etc/nixos/configuration.nix
|
|-
|Find packages
|<syntaxhighlight lang="console">$ apt-cache search emacs</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -qaP '.*emacs.*'</syntaxhighlight> or <syntaxhighlight lang="console">$ nix search nixpkgs emacs</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -qaP '.*emacs.*'</syntaxhighlight> or <syntaxhighlight lang="console">$ nix search nixpkgs emacs</syntaxhighlight>
|-
|Show package description
|<syntaxhighlight lang="console">$ apt-cache show emacs</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -qa --description '.*emacs.*'</syntaxhighlight>
|<syntaxhighlight lang="console">$ nix-env -qa --description '.*emacs.*'</syntaxhighlight>
|-
|Show files installed by package
|<syntaxhighlight lang="console">$ dpkg -L emacs</syntaxhighlight>
|<syntaxhighlight lang="console">$ readlink -f $(which emacs)
 /nix/store/ji06y4haijly0i0knmr986l2dajffv1p-emacs-24.4/bin/emacs-24.4</syntaxhighlight>
then
<syntaxhighlight lang="console">$du -a /nix/store/ji06y4haijly0i0knmr986l2dajffv1p-emacs-24.4</syntaxhighlight>
|<syntaxhighlight lang="console"></syntaxhighlight>
|-
|Show package for file
|<syntaxhighlight lang="console">$ dpkg -S /usr/bin/emacs</syntaxhighlight>
|follow the symlink or <syntaxhighlight lang="console">nix-locate /bin/emacs</syntaxhighlight> (requires <syntaxhighlight lang="console">nix-index</syntaxhighlight> package)
|(same)
|-
| colspan="5" style="text-align:center"| '''Services'''
|-
|Start a service
|<syntaxhighlight lang="console">$ sudo systemctl start apache</syntaxhighlight>
|<syntaxhighlight lang="console">$ sudo systemctl start apache</syntaxhighlight>
|
|-
|Stop a service
|<syntaxhighlight lang="console">$ sudo systemctl stop apache</syntaxhighlight>
|<syntaxhighlight lang="console">$ sudo systemctl stop apache</syntaxhighlight>
|
|-
| Enable a service
| <syntaxhighlight lang="console">$ sudo systemctl enable apache</syntaxhighlight>
| In /etc/nixos/configuration.nix, add <syntaxhighlight lang="console">services.tor.enable = true;</syntaxhighlight>, then run <syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|-
| Disable a service
| <syntaxhighlight lang="console">$ sudo systemctl disable apache</syntaxhighlight>
| In /etc/nixos/configuration.nix, add <syntaxhighlight lang="console">services.tor.enable = false;</syntaxhighlight>, then run <syntaxhighlight lang="console">$ sudo nixos-rebuild switch</syntaxhighlight>
|-
|Where your log files live
|/var/log/
|System-wide packages /var/log/
|User packages ~/.nix-profile/var/log/
|-
|Adding a user
|<syntaxhighlight lang="console">$ sudo adduser alice</syntaxhighlight>
|Add <syntaxhighlight lang="nix">users.users.alice =
 { isNormalUser = true;
   home = "/home/alice";
   description = "Alice Foobar";
   extraGroups = [ "wheel" "networkmanager" ];
   openssh.authorizedKeys.keys =
      [ "ssh-dss AAAAB3Nza... alice@foobar" ];
 };</syntaxhighlight> to /etc/nixos/configuration.nix and then call <syntaxhighlight lang="nix">nixos-rebuild switch</syntaxhighlight>
|
|-
| colspan="5" style="text-align:center"| '''Misc tasks'''
|-
|List binaries
|<syntaxhighlight lang="console">$ ls /usr/bin/</syntaxhighlight>
|<syntaxhighlight lang="console">$ ls /run/current-system/sw/bin &&\
ls /nix/var/nix/profiles/default/bin/</syntaxhighlight>
|<syntaxhighlight lang="console">$ ls ~/.nix-profile/bin</syntaxhighlight>
|-
|Get the current version number
|<syntaxhighlight lang="console">$ cat /etc/debian_version</syntaxhighlight>
|<syntaxhighlight lang="console">$ nixos-version</syntaxhighlight>
|
|-
|Get sources for a package
|<syntaxhighlight lang="bash">$ sudo apt-get source emacs</syntaxhighlight>
|
|In Debian, apt-get source gets both the patched upstream source and the recipe for the package. Those need two steps in Nix.

To find the package's attribute path: <syntaxhighlight lang="console">$ nix-env -qaP emacs</syntaxhighlight> or <syntaxhighlight lang="console">$ nox emacs</syntaxhighlight>
To download the source as specified by the package recipe: <syntaxhighlight lang="bash">nix-build '<nixpkgs>' -A emacs.src</syntaxhighlight>
The patched source is usually not a derivation itself, but can be produced for most packages with the following command: <syntaxhighlight lang="bash">nix-shell '<nixpkgs>' -A emacs\
 --command 'unpackPhase; cd $sourceRoot; patchPhase'</syntaxhighlight>
|-
|Compile & install a package from source
|
|
|<syntaxhighlight lang="console">git clone foobar
cat >default.nix <<EOF
with import <nixpkgs> { };
lib.overrideDerivation foobar (oldAttrs : {
src = ./foobar;
})
EOF
nix-build</syntaxhighlight>
|-
|Install a binary package
|
| 
|e.g. via [https://github.com/Mic92/nix-ld#nix-ld nix-ld] 
|-
|Install a .deb
|<syntaxhighlight lang="console">$ sudo dpkg -i package.deb</syntaxhighlight>
|
|Install dpkg with Nix, then <syntaxhighlight lang="bash">dpkg -i package.deb</syntaxhighlight> While this is technically possible it will in all likelihood not work.
|}
</div>

== See also ==

* [[Cheatsheet]]
* https://nixcademy.com/cheatsheet/
** https://nixcademy.com/downloads/cheatsheet.pdf

[[Category:Cookbook]]