NixOS Install Options

Posted on November 13, 2014 by Daniel

Nix can be overwhelming because it has so many different ways to install software. I’m going to muse aloud about 5 ways to install packages.

System Wide

System wide install is the closest to how other Linux distros handle packages. It’s only available in NixOS, not if you’re running Nix on top of some other distribution. You can download the latest package list and upgrade with nixos-rebuild switch --upgrade. The complete package list is stored in the file /etc/nixos/configuration.nix.

I think this is great — other distros I’ve used over the years haven’t made it easy to see all the packages I’ve requested, without the clutter of all their dependencies. It’s also easy to version control. Finally, NixOS adds options to the boot menu to boot into previous configurations. I haven’t broken my system badly enough to need this yet.

User Profiles

User profiles are the first step into limiting which installed software is available in a given context.

When you switch user profiles, it affects all running shells and other programs. This is good and bad. Sometimes I like the simplicity, and other times I want to be working on two different projects in two windows — say, when one is taking an hour to compile. In general, I’m moving away from multiple Nix profiles.

The fact that user profiles are upgraded independantly is also good and bad. Upgrading everything takes more commands. But sometimes I like the fine-grained control. I can roll back a buggy version, and keep it back while upgrading other programs.

nix-shell

nix-shell looks for a file in the current directory (shell.nix or default.nix), and makes the specified packages available only in that shell. With the --pure option, only these packages are available, not anything else installed system-wide or in your Nix profile. These features are great for software development. We can check the .nix files into the git repo, and everyone can always build in the same environment. The downsides are multiple .nix files if you want the same packages for multiple projects, and that nix-shell always uses the newest version it knows of, which may not be the same version you know worked yesterday.

buildEnv

buildEnv environments are simply a way to group packages which are installed in one of the ways above. I have a group for half a dozen programs I use for photography, which I install in my user environment, and upgrade all together. I also like that this keeps my list of programs in a file which I can version control & sync between computers.

myEnvFun

myEnvFun environments have shell scope and upgrade only when you ask, not on every use. That is, like buildEnv, you can specify a group of packages and assign them a name. You install the resulting group with nix-env -i, and upgrade it the same way. This provides a single command, load-env-someName, which launches a subshell with the specified packages available, much like nix-shell. This is convenient for sharing the same environment across several projects, but it’s less convenient to check the environment definition into version control with the projects, and I have to assume that multiple developers won’t be running the same versions, since they will update their install on different schedules.

What I do

I find myself mostly using nix-shell for software development (Haskell, mostly, but I may move my JavaScript development in that direction), and a single Nix user environment, with a bunch of buildEnv groups, for most userspace programs.