Ubuntu vs. NixOS

Ubuntu vs. NixOS

The system-wide column is the equivalent of using apt under Ubuntu.

Task	Ubuntu	NixOS (system-wide and root)	NixOS (user) and Nix in general
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 /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.
Package management
Install a package for all users	$ sudo apt-get install emacs	1. Add to /etc/nixos/configuration.nix: environment.systemPackages = with pkgs; [ wget # let's assume wget was already present emacs ]; 2. Run : $ sudo nixos-rebuild switch	$ nix-env -iA nixos.emacs Or with collections, add the package to your ~/.nixpkgs/config.nix and run $ nix-env -iA nixos.all
Install a package for a specific user only	Not possible	1. Add to /etc/nixos/configuration.nix: users.users.alice.packages = with pkgs; [ emacs ]; 2. Run: $ sudo nixos-rebuild switch	1. Add to ~/.nixpkgs/config.nix: users.users.alice.packages = with pkgs;[ emacs ]; 2. Run: $ nix-env -iA nixos.all
Install a service	$ sudo apt install openssh-server	1. Add to /etc/nixos/configuration.nix: services.openssh.enable = true; 2. Run: $ sudo nixos-rebuild switch	Not possible
Uninstall a package	sudo apt-get remove emacs	remove from /etc/nixos/configuration.nix $ sudo nixos-rebuild switch	$ nix-env --uninstall emacs
Uninstall a package removing its configuration	$ sudo apt-get purge emacs	All configuration is in configuration.nix
Update the list of packages	$ sudo apt-get update	$ sudo nix-channel --update	$nix-channel --update
Upgrade packages	$ sudo apt-get upgrade	$ sudo nixos-rebuild switch	$ nix-env -u
Check for broken dependencies	$ sudo apt-get check	$ nix-store --verify --check-contents	unneeded!
List package dependencies	$ apt-cache depends emacs	Show the direct dependencies: $ nix-store --query --requisites /run/current-system or show a nested ASCII tree of dependencies: $ nix-store -q --tree /nix/var/nix/profiles/system (/run/current-system and /nix/var/nix/profiles/system are symbolic links that eventually end up at the same place.)	$ nix-store --query --references\ $(nix-instantiate '<nixpkgs>' -A emacs) For installed packages: $ nix-store --query --references $(which emacs)
List which packages depend on this one (reverse dependencies)	$ apt-cache rdepends emacs		For installed packages (only print reverse dependencies *which are already installed*): $ nix-store --query --referrers $(which emacs)
Verify all installed packages	$ debsums	$ sudo nix-store --verify --check-contents	$ nix-store --verify --check-contents
Fix packages with failed checksums	Reinstall broken packages	$ sudo nix-store --verify --check-contents --repair	$ nix-store --verify --check-contents --repair
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.	$ nix-channel --add\ https://nixos.org/channels/nixpkgs-unstable <name> Add the unstable channel. At that address you will find names for other versions and variants. Name can be any string. $ nix-channel --remove <name> To eliminate a channel. $ nix-channel --list 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 [1]
Install a particular version of a package	$ apt-get install package=version	Although Nix on its own doesn't understand the concept of package versioning, you can install and play with older (or newer!) software via https://nixos.wiki/wiki/FAQ/Pinning_Nixpkgs with https://lazamar.co.uk/nix-versions. For instance, to launch an older version of Vim you could use: $ nix-shell \ -p vim \ -I nixpkgs=\https://github.com/NixOS/nixpkgs/archive/4bba6650a6a5a2009e25bdeed8c1e871601a9bfb.tar.gz
Package configuration
Configure a package	$ sudo dpkg-reconfigure <package>	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	$ apt-cache search emacs	$ nix-env -qaP '.*emacs.*' or $ nix search emacs	$ nix-env -qaP '.*emacs.*' or $ nix search emacs
Show package description	$ apt-cache show emacs	$ nix-env -qa --description '.*emacs.*'	$ nix-env -qa --description '.*emacs.*'
Show files installed by package	$ dpkg -L emacs	$ readlink -f $(which emacs) /nix/store/ji06y4haijly0i0knmr986l2dajffv1p-emacs-24.4/bin/emacs-24.4 then $du -a /nix/store/ji06y4haijly0i0knmr986l2dajffv1p-emacs-24.4
Show package for file	$ dpkg -S /usr/bin/emacs	follow the symlink or nix-locate /bin/emacs (requires nix-index package)	(same)
Services
Start a service	$ sudo systemctl start apache	$ sudo systemctl start apache
Stop a service	$ sudo systemctl stop apache	$ sudo systemctl stop apache
Enable a service	$ sudo systemctl enable apache	In /etc/nixos/configuration.nix, add services.tor.enable = true; , then run $ sudo nixos-rebuild switch
Disable a service	$ sudo systemctl disable apache	In /etc/nixos/configuration.nix, add services.tor.enable = false; , then run $ sudo nixos-rebuild switch
Where your log files live	/var/log/	System-wide packages /var/log/	User packages ~/.nix-profile/var/log/
Adding a user	$ sudo adduser alice	Add users.users.alice = { isNormalUser = true; home = "/home/alice"; description = "Alice Foobar"; extraGroups = [ "wheel" "networkmanager" ]; openssh.authorizedKeys.keys = [ "ssh-dss AAAAB3Nza... alice@foobar" ]; }; to /etc/nixos/configuration.nix and then call nixos-rebuild switch
Misc tasks
List binaries	$ ls /usr/bin/	$ ls /run/current-system/sw/bin &&\ ls /nix/var/nix/profiles/default/bin/	$ ls ~/.nix-profile/bin
Get the current version number	$ cat /etc/debian_version	$ nixos-version
Get sources for a package	$ sudo apt-get source emacs		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: $ nix-env -qaP emacs or $ nox emacs To download the source as specified by the package recipe: nix-build '<nixpkgs>' -A emacs.src The patched source is usually not a derivation itself, but can be produced for most packages with the following command: nix-shell '<nixpkgs>' -A emacs\ --command 'unpackPhase; cd $sourceRoot; patchPhase'
Compile & install a package from source			git clone foobar cat >default.nix <<EOF with import <nixpkgs> { }; lib.overrideDerivation foobar (oldAttrs : { src = ./foobar; }) EOF nix-build
Install a binary package			e.g. via nix-ld
Install a .deb	$ sudo dpkg -i package.deb		Install dpkg with Nix, then dpkg -i package.deb While this is technically possible it will in all likelihood not work.