Cheatsheet: Difference between revisions

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VisualWikitext

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 == Get the store path for a package ==
-<source lang="javascript">
+<source lang="nix">
 $ nix-repl
 nix-repl> :l <nixpkgs>
@@ Line 269: / Line 269: @@
 $ nix-build '<nixpkgs>' --no-build-output -A xorg.libXtst
 /nix/store/nlpnx21yjdjx2ii7ln4kcmbm0x1vy7w9-libXtst-1.2.3
+</source>
+### 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:
+<source lang="bash">
+$ nix-store --add-fixed sha256 /path/to/file
+</source>
+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:
+<source lang="bash">
+$ 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
+</source>
+== Build nixos from nixpkgs repo ==
+The following snippet will build the system from a git checkout:
+<source lang="bash">
+$ nixos-rebuild -I nixpkgs=/path/to/nixpkgs switch
+</source>
+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](http://anderspapitto.com/posts/2015-11-01-nixos-with-local-nixpkgs-checkout.html).
+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:
+<source lang="bash">
+$ nixos-rebuild -I nixpkgs=https://github.com/nixcloud/nixpkgs/archive/release-17.03.tar.gz switch
+</source>
+## 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:
+<source lang="nix">
+# vm.nix
+{ lib, config, ... }:
+{
+  services.tor.enable = true;
+  users.users.root.initialPassword = "root";
+}
+</source>
+a vm can be build using the following command:
+<source lang="bash">
+$ nixos-rebuild -I nixpkgs=/path/to/nixpkgs -I nixos-config=./vm.nix build-vm
+</source>
+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:
+<source lang="bash">
+nix-build '<nixpkgs/nixos>' -A vm -k -I nixos-config=./vm.nix
+</source>
+== 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:
+<source lang="bash">
+$ git clone https://github.com/iovisor/bcc.git
+$ cd bcc
+</source>
+Add the following `default.nix` to the project:
+<source lang="nix">
+with import <nixpkgs> {};
+linuxPackages.bcc.overrideDerivation (old: {
+  # overrideDerivation allows it to specify additional dependencies
+  buildInputs = [ bashInteractive ninja ] ++ old.buildInputs;
+})
+</source>
+To initiate the build environment run `nix-shell` in the project root directory
+<source lang="bash">
+# this will download add development dependencies and set up the environment so build tools will find them.
+$ nix-shell
+</source>
+The following is specific to bcc or cmake in general:
+(so you need to adapt the workflow depending on the project, you hack on)
+<source lang="bash">
+$ mkdir build
+$ cd build
+# cmakeFlags is also defined in the bcc package. autotools based projects might defined $configureFlags
+$ eval cmake $cmakeFlags ..
+$ make
+</source>
+== 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:
+<source lang="nix">
+$ sudo nix-channel --list
+nixos https://nixos.org/channels/nixos-17.03
+nixos-unstable https://nixos.org/channels/nixos-unstable
+</source>
+and the following in `configuration.nix`:
+<source lang="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;
+    };
+  };
+};
+</source>
+which allows you to switch particular packages to the unstable channel:
+<source lang="nix">
+environment = {
+  systemPackages = with pkgs; [
+    ddate
+    devilspie2
+    evince
+    unstable.google-chrome
+    # ...
+    zsh
+  ];
+};
+</source>
+== Building statically linked packages ==
+<source lang="bash">
+$ nix-build -E 'with (import ./. {}); (curl.override { stdenv = makeStaticLibraries stdenv;}).out'
+</source>
+== Rebuild a package with debug symbols ==
+<source lang="bash">
+$ 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
 </source>