A cheat sheet and rough mapping between Ubuntu and NixOS

This is meant to give you basic ideas and get you unstuck. NixOS being very different from most distributions, a deeper understanding will be necessary sooner or later! Follow the links to the manual pages and browse the wiki to find real NixOS tutorials.

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

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

Task	Ubuntu	NixOS (system-wide and root)	NixOS (user) and Nix in general	Relevant section of the manual
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 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 management
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	sudo apt-get install emacs	In /etc/nixos/configuration.nix: If it's a program add to systemPackages: systemPackages = with pkgs; [ <other packages...> emacs ]; If it's a service add: services.openssh.enable = true;	nix-env -i emacs Or with collections, add the package to your ~/.nixpkgs/config.nix and run nix-env -i all
Uninstall a package	sudo apt-get remove emacs	remove from /etc/nixos/configuration.nix sudo nixos-rebuild switch
Uninstall a package removing its configuration	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	nix-store --query --requisites $(readlink -f /run/current-system) nix-store -q --tree /nix/var/nix/profiles/system	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