Cheatsheet
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 | |
|---|---|---|---|---|
| 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 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
Since 17.09pre: users.users.<username>.packages =
with pkgs;[ emacs ];
| |
| 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 | 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 | ||||
| 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 | |
| List package options | ||||
| Global package configuration | Modify configuration file in /etc/ | |||
| Package configuration | ||||
| Find packages | apt-cache search emacs
|
nix-env -qaP '.*emacs.*'
|
nix-env -qaP '.*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 | follow the symlink | |
| Services | ||||
| Start a service | sudo service apache start
|
sudo systemctl start apache
|
||
| Stop a service | sudo service apache stop
|
sudo systemctl stop apache
|
||
| 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.extraUsers.alice =
{ isNormalUser = true;
home = "/home/alice";
description = "Alice Foobar";
extraGroups = [ "wheel" "networkmanager" ];
openssh.authorizedKeys.keys =
[ "ssh-dss AAAAB3Nza... alice@foobar" ];
};
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
|
nixos-version
| |
| Get sources for a package | 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
nox emacs
nix-build '<nixpkgs>' -A emacs.src
nix-shell '<nixpkgs>' -A emacs\
--command 'unpackPhase; patchPhase'
| ||
| Compile & install a package from source | git clone foobar
cat >default.nix <<EOF
with import <nixpkgs> { };
stdenv.lib.overrideDerivation foobar (oldAttrs : {
src = ./foobar;
})
EOF
nix-build
| |||
| Install a binary package | ||||
| Install a .deb | dpkg -i package.deb
|
Install dpkg with Nix, then dpkg -i package.deb
| ||
Working with the nix store
Get the store path for a package
$ nix-repl
nix-repl> :l <nixpkgs>
Added 7486 variables.
nix-repl> "${xorg.libXtst}"
"/nix/store/nlpnx21yjdjx2ii7ln4kcmbm0x1vy7w9-libXtst-1.2.3"
$ nix-build '<nixpkgs>' --no-build-output -A xorg.libXtst
/nix/store/nlpnx21yjdjx2ii7ln4kcmbm0x1vy7w9-libXtst-1.2.3
Adding files to the store
It is sometimes necessary to add files to the store manually. This is particularly the case with packages that cannot be downloaded automatically, for example, proprietary software packages. For most files, it is sufficient to run:
$ nix-store --add-fixed sha256 /path/to/file
Unfortunately, `nix-store` will try to load the entire file into 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:
$ sudo unshare -m bash # open a shell as root in a private mount namespace
$ largefile=/path/to/file
$ hash=$(nix-hash --type sha256 --flat --base32 $largefile) # sha256 hash of the file
$ storepath=$(nix-store --print-fixed-path sha256 $hash $(basename $largefile)) # destination path in the store
$ mount -o remount,rw /nix/store # remount the store in read/write mode (only for this session)
$ cp $largefile $storepath # copy the file
$ printf "$storepath\n\n0\n" | nix-store --register-validity --reregister # register the file in the Nix database
$ exit # exit to the original shell where /nix/store is still mounted read-only
Build nixos from nixpkgs repo
The following snippet will build the system from a git checkout:
$ nixos-rebuild -I nixpkgs=/path/to/nixpkgs switch
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 blog article. It has a couple of advantages over nixpkgs as it allows back-porting of packages/changes to stable versions as well as applying customization.
Use the following command to build directly from a particular branch of a repo in github:
$ nixos-rebuild -I nixpkgs=https://github.com/nixcloud/nixpkgs/archive/release-17.03.tar.gz switch
Building a service as a VM (for testing)
While nixos-rebuild build-vm allows to build a vm out of the current system configuration, there is a more light-weight alternative when only a single service needs to be tested.
Given the following configuration:
# vm.nix
{ lib, config, ... }:
{
services.tor.enable = true;
users.users.root.initialPassword = "root";
}
a vm can be build using the following command:
$ nixos-rebuild -I nixpkgs=/path/to/nixpkgs -I nixos-config=./vm.nix build-vm
where -I nixpkgs=/path/to/nixpkgs 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:
$ nix-build '<nixpkgs/nixos>' -A vm -k -I nixos-config=./vm.nix
By default the resulting vm will require X11 to create a virtual display.
By specifying additional arguments via the environment variables QEMU_OPTSand QEMU_KERNEL_PARAMS it is possible to reuse the current running terminal as serial console for the vm:
$ export QEMU_OPTS="-nographic -serial mon:stdio" QEMU_KERNEL_PARAMS=console=ttyS0
$ /nix/store/lshw31yfbb6izs2s594jd89ma4wf8zw6-nixos-vm/bin/run-nixos-vm
To be able to log in you will need a getty started on a serial console as well in your nixos configuration:
{...}: {
# ..
systemd.services."serial-getty@ttyS0".enable = true;
}
To forward a port you can set export QEMU_NET_OPTS. In the following example port 2222 on the host is forwarded to port 22 in the vm:
$ export QEMU_NET_OPTS="hostfwd=tcp::2222-:22"
Don't forget that by default nixos comes with a firewall enabled:
{...}: {
networking.firewall.enable = false;
}
Reuse a package as a build environment
As packages already contains all build dependencies, they can be reused to a build environment quickly. In the following a setup for the cmake-based project [bcc](https://github.com/iovisor/bcc) is shown. After obtaining the source:
$ git clone https://github.com/iovisor/bcc.git
$ cd bcc
Add the following default.nix to the project:
with import <nixpkgs> {};
linuxPackages.bcc.overrideDerivation (old: {
# overrideDerivation allows it to specify additional dependencies
buildInputs = [ bashInteractive ninja ] ++ old.buildInputs;
})
To initiate the build environment run `nix-shell` in the project root directory
# this will download add development dependencies and set up the environment so build tools will find them.
$ nix-shell
The following is specific to bcc or cmake in general: (so you need to adapt the workflow depending on the project, you hack on)
$ mkdir build
$ cd build
# cmakeFlags is also defined in the bcc package. autotools based projects might defined $configureFlags
$ eval cmake $cmakeFlags ..
$ make
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).
$ nix-build '<nixpkgs>' --arg crossSystem '(import <nixpkgs> {}).lib.systems.examples.aarch64-multiplatform' -A tinc
You can add your own specifications, or look at existing ones, in nixpkgs/lib/systems/examples.nix.
Customizing Packages
Upgrading individual packages to a different channel
One can track multiple channels on NixOS simultaneously, and then declaratively change packages from the default channel to another one.
For example one can have both the unstable and stable channels on system root:
$ sudo nix-channel --list
nixos https://nixos.org/channels/nixos-17.03
nixos-unstable https://nixos.org/channels/nixos-unstable
and the following in `configuration.nix`:
nixpkgs.config = {
# Allow proprietary packages
allowUnfree = true;
# Create an alias for the unstable channel
packageOverrides = pkgs: {
unstable = import <nixos-unstable> {
# pass the nixpkgs config to the unstable alias
# to ensure `allowUnfree = true;` is propagated:
config = config.nixpkgs.config;
};
};
};
which allows you to switch particular packages to the unstable channel:
environment = {
systemPackages = with pkgs; [
ddate
devilspie2
evince
unstable.google-chrome
# ...
zsh
];
};
Building statically linked packages
$ nix-build -E 'with (import ./. {}); (curl.override { stdenv = makeStaticLibraries stdenv;}).out'
Rebuild a package with debug symbols
$ nix-build -E 'with import <nixpkgs> {}; enableDebugging st'
$ file result/bin/st
result/bin/st: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /nix/store/f111ij1fc83965m48bf2zqgiaq88fqv5-glibc-2.25/lib/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, not stripped, with debug_info