[Nix-dev] A few questions from a NixOS newbie.

[Aristid Breitkreuz]

If you want to do a lot of changes or always want to use the newest
versions of things without waiting for them to appear in the channel
(which may take a few days), you probably want to use a checkout
instead of the channel. This can be achieved with an environment
variable:

$ echo $NIX_PATH
nixos=/home/aristid/nixpkgs/nixos:nixpkgs=/home/aristid/nixpkgs:nixos-config=/etc/nixos/configuration.nix

(This will not automatically affect nix-env, though it will affect
nixos-rebuild.)

If you want to get any changes into the official repo, just use a
GitHub pull request on this repo: https://github.com/nixos/nixpkgs

Also, do not use i686-linux, there's no good reason to do so and it
gets far less attention from most developers. And installing
glibc-2.17 with nix-env will NOT cause any other packages to actually
use it, you have to change the package's dependency with { glibc =
pkgs.glibc_2_17 } or so. Please excuse that I only answered some of
your questions.

Cheers,

Aristid

2014-04-21 14:23 GMT+02:00 Mateusz Kowalczyk <fuuzetsu at fuuzetsu.co.uk>:
> Greetings,
>
> I have been planning to move to NixOS for quite a few months now but
> only yesterday I finally clobbered my old /. Like many others, I'm a
> Haskeller looking for a better development environment than we can
> sanely achieve with cabal sandboxes.
>
> Anyway, to the point. I have a few questions and I fear that I've been
> pestering the IRC channel a bit too much. Unfortunately there isn't
> enough information on the web yet for me to solve it, and there are many
> deadlinks and unanswered IRC question which doesn't help my searches.
> For reference, I'm moving from Gentoo. In no particular order:
>
> * How do I get onto a channel that uses nixpkgs? When I file a bug with
> a package, it fortunately tends to get fixed up quite fast but I do not
> know how I'm meant to then receive it. I find various URLs of
> nix-channel --add on the net but things like what's shown on the main
> Getting Nixpkgs page don't work:
>
> [root at lenalee:~]# nix-channel --add
> http://nixos.org/channels/nixpkgs-unstable
>
> [root at lenalee:~]# nix-channel --update
> downloading Nix expressions from
> `http://releases.nixos.org/nixpkgs/nixpkgs-14.04pre42251.552d66c/nixexprs.tar.xz'...
>   % Total    % Received % Xferd  Average Speed   Time    Time     Time
> Current
>                                  Dload  Upload   Total   Spent    Left
> Speed
>   0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--
>     0
> unpacking channels...
>
> [root at lenalee:~]# nixos-rebuild switch --upgrade
> unpacking channels...
> error: unable to find
> `nixpkgs/nixos/modules/installer/tools/nixos-rebuild.sh'
> building Nix...
> error: file `nixpkgs/nixos' was not found in the Nix search path (add it
> using $NIX_PATH or -I)
> error: file `nixpkgs/nixos' was not found in the Nix search path (add it
> using $NIX_PATH or -I)
> error: file `nixpkgs' was not found in the Nix search path (add it using
> $NIX_PATH or -I)
> /tmp/nixos-rebuild.YUCbJ0/nix
> error: unable to find `nixpkgs'
> building the system configuration...
> error: file `nixpkgs/nixos' was not found in the Nix search path (add it
> using $NIX_PATH or -I)
>
>
> Many other pages show a similar invocation but with 'nixos' in the end.
> This 'nixos' is not explained anywhere as far as I can tell! My guess is
> that it simply names the channel locally so that it's easy to refer to,
> is that correct? By the way
>
> nix-channel --add http://nixos.org/channels/nixos-unstable nixos
>
> seems to work but is probably not what I want (getting few-minutes-old
> fixes from nixpkgs git repository).
>
> * The nix packages don't seem to be versioned in any way. On Gentoo, I
> could inspect the software in the tree: I could check the version of the
> software itself, and the version of the e-build. An example use case is
> if the software fetch source dies: we need to update the e-build and
> bump its version but the software version stays the same. Is there an
> equivalent in NixOS?
>
> * What is the proper way to integrate own packages into the tree?
> Yesterday I found it necessary to try and package a (proprietary ;( )
> blob which amongst some other things needs patchelf &c. What I did was
> to fork then clone nixpkgs and written the package in appropriate
> directory. I now don't know how to work with this repository so that the
> rest of the system sees it. What I did was cd to the repository and then
> use nix-env -f . -i mypackage but I fear that as soon as I go back to
> using nix-env -i outside of that repository, nix will be confused: it
> had newer packages a second ago and now it's back to old!
>
> * In my aforementioned package, there's a binary that I expected to be
> able to run after nix-env -i. That's however not the case. Is there a
> section that's necessary in the .nix file that tells nix which files
> should be made visible? I looked at some other packages briefly but
> didn't see much.
>
> * I started off with a 64-bit version of NixOS, installed from the .iso
> but I quickly found myself needing to run 32-bit software. It quickly
> became apparent that NixOS does not offer anything like ia32-lib
> (Ubuntu) on multilib (Arch). What is the procedure for running 32-bit
> software? After a longer time searching, I figured out how to install
> some 32-bit versions of software, mainly using nix-env -iA and referring
> to the package explicitly. Namely, something like nix-env -iA
> nixos.pkgs.pkgsi686Linux.mesa. This doesn't work for every package in
> tree however: to get 32-bit libX11, a different invocation was necessary
> and only after painful amount of time spent on Google, I managed to came
> up with nixpkgs.xorg.libX11.i686-linux (if I'm remembering correctly).
> How do I just list properties of the packages? For example I'd like to
> see all incantations needed to get packages of different architectures.
>
> * The versioning displayed seems to be a bit weird:
>
> ✗ 1 lenalee shana % nix-env -qa | grep xmonad
> haskell-xmonad-contrib-ghc7.6.3-0.11.2
> haskell-xmonad-contrib-ghc7.6.3-0.11.2
> haskell-xmonad-contrib-ghc7.6.3-0.11.2-profiling
> haskell-xmonad-extras-ghc7.6.3-0.12
> haskell-xmonad-extras-ghc7.6.3-0.12
> haskell-xmonad-extras-ghc7.6.3-0.12-profiling
> haskell-xmonad-ghc7.6.3-0.11
> haskell-xmonad-ghc7.6.3-0.11
> haskell-xmonad-ghc7.6.3-0.11-profiling
>
> Here we have multiple packages which display the same version (why?) and
> some -profiling packages. What is the naming scheme followed? Does the
> version start at the last `-%d'? How do I check the difference between
> the packages that display in the same fashion?
>
> * How can I find out more about packages? For example, I'd like to query
> a package of a license, or to see its .nix file. Someone told me on IRC
> how to do the second one but it involved grepping all-packages.nix,
> getting the path from there and then opening that. Is there no mechanism
> in place which can tell me more about a package? I'd expect at least the
> information given by the `eix' tool on Gentoo: installed and available
> versions, short description, homepage and license. It seems to me like
> fairly basic and useful information.
>
> * Sometimes when I nixos-rebuild switch --upgrade, I get messages about
> clashing packages. Unfortunately I don't have the messages on hand
> because it doesn't always happens (only seems to happen when there are
> things to actually update). How did I get myself into this mess and how
> do I fix it? I am guessing it's either one of the two: running nix-env
> -f . -i ... in the nixpkgs git checkout while being on a channel that's
> less up-to-date *or* the fact that I switched architectures from 64-bit
> to 32-bit and now nix is confused about the packages from each both
> being present.
>
> * Regarding switching architectures, I was very pleased to hear that I
> could simply put `nixpkgs.system = "i686-linux"' in my configuration
> file and then rebuild. I was a bit less pleased to see that all my old,
> 64-bit packages did not go away and the 32-bit packages wouldn't install
> on top of them automatically. For now I ran nix-env -e and then nix-env
> -i for the packages that nix-env -qs showed me but I imagine this would
> be very unsatisfactory if the system was more than a day old. What is
> the proper way to switch between architectures, including rebuilding the
> packages so that the architecture is correct?
>
> * Yesterday I ran nix-env -i while I already had a build running. This
> caused both the invocations to crash (sorry, again, I don't have the
> error for you, I did not think much of it when it happened). I was
> assured on IRC that this should not happen so I will be on the lookout
> for this in the future, but are there any known bugs to do with this?
>
> * Regarding having to report packages, are there no runtime checks done?
> For example, I reported the `uzbl' yesterday. While it compiled fine,
> none of the binaries it provides would as much as even run, they all
> errored straight away. What's done in terms of testing that the packages
> actually work? I know that on Gentoo the packagers at least run the
> package's test-suite and the user can even ask to run it themselves by
> setting the `test' USE flag.
>
> * Regarding USE, I quite liked the functionality. For those unaware, USE
> flags let you toggle some options to do with the package. As Gentoo is
> source-based, this pretty much always simply changed the compilation
> flags. This provided great flexibility: one can choose whether they want
> ALSA or Gnome or KDE or taglib or test or whatever support for each
> package and the dependencies would be pulled in (or left out)
> accordingly. As far as I know, there is no such system in place for nix.
> Say I wanted to install emacs but didn't want a graphical environment:
> it's a perfectly valid use case to want to run emacs on your headless
> VPS. Yet, if I were to just nix-env -i emacs, I would be prompted to
> install gtk3, Xorg and who knows what else (I have not actually tried
> but this is simply for demonstration purposes). In Gentoo I can simply
> set the -gtk3 and -X flags and any software that allows me to switch
> those off will do so. How do I achieve this on NixOS? As far as I can
> tell, one has to effectively make their own emacs package that removes
> all the things we don't want along with their dependencies and then
> install that. This is of course a problem: a lot of hassle, anything
> depending on emacs doesn't see that we now have it, even if we convince
> things depending on emacs that we do now have it, they might actually
> depend on emacs with gtk3 and so on and so on. What's the way this
> problem is solved on NixOS? If I wanted to use NixOS on any of my
> servers, just this stops it from me doing so.
>
> * I found myself needing older glibc yesterday. Namely, I wanted glibc
> 2.17. Normally I would be very wary of changing my glibc version but I
> thought nix can make this easy for me and if something breaks I can just
> use an older configuration anyway, right? To my surprise, I only found
> glibc 2.19 in nix-env -qa! How do I access older packages? I honestly
> don't think that only glibc 2.19 was every packaged which means the
> older version was there somewhere. Does -qa hide it from me? Was it
> removed from the tree and if yes, why? If `it would make -qa' messy is
> the answer, maybe the way looking for packages works should be
> rethought. I honestly hope I'm not expected to package glibc 2.17 myself
> after about a day of usage...
>
> * Assuming I managed to get glibc 2.17 in the tree, how do I use 2.17
> for some packages but 2.19 for the rest? For example, I could make the
> packages that require 2.17 depend on it, but then when I try to install
> them, nix will either refuse me because it would break everything
> depending on 2.19 or it would install it and break everything. I suppose
> I'm asking about how to sandbox packages. I hear nix-shell is something
> that might be applicable here but I'm unsure.
>
> * Unfortunately about half of the software that I used in the past seems
> to be missing and I assure you I didn't use much software at all. While
> I'm not blaming anyone and realise I'll most likely have to package it
> all myself, what is the procedure of getting your packages back into the
> official channels? With Gentoo, one would file a request to include
> software in the tree on the bug tracker and then wait. We'd provide an
> e-build if we wanted to speed things up a bit but after that, it's the
> packagers that take ownership of it. How is the situation in NixOS? I
> write the package then what? I imagine I send a pull request to nixpkgs
> on GitHub. If it gets merged, am I now responsible for it? Does anyone
> else take the blame when it's not up-to-date or broken?
>
> I think this about covers all my initial questions. Hopefully I can get
> answers to most of them and this can then serve anyone else trying to
> Google like mad for these.
>
> Thanks!
> --
> Mateusz K.
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