NixOS on unstable – How to fix a broken nixos-rebuild
From time to time it can happen that
nixos-rebuild fails due to a package
Here is how to fix this.
nixos-rebuild tells you something like this:
(hashes removed for readability)
building the system configuration...
these derivations will be built:
building path(s) ‘/nix/store/<hash>-libvterm-v2015-02-23-src’
builder for ‘/nix/store/<hash>-libvterm-v2015-02-23-src.drv’ failed with exit code 1
cannot build derivation ‘/nix/store/<hash>-neovim-libvterm-2015-02-23.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-neovim-0.1.0.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-neovim-0.1.0-configured.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-system-path.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-dbus-conf.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-unit-polkit.service.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-unit-dbus.service.drv’: 1 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-system-units.drv’: 2 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-etc.drv’: 2 dependencies couldn't be built
cannot build derivation ‘/nix/store/<hash>-nixos-system-yuu-16.03pre71289.7ae05ed.drv’: 2 dependencies couldn't be built
error: build of ‘/nix/store/<hash>-nixos-system-yuu-16.03pre71289.7ae05ed.drv’ failed
And you don't know what to do? Well, there's a solution to that, and the solution is rather simple, actually.
Step 1: Find the broken package
If the break happens due to an error in your
configuration.nix, you should fix
this error. Then you don't need to go on reading here.
If the build fails due to an error in the nixpkgs, as above, you should continue reading.
So we have to find the broken package. From the backtrace
us, we can find out that the break happens due to an error in the
package. This is clearly an error in the nixpkgs and we can fix this error only
with the nixpkgs available, so...
Step 2: Get nixpkgs
If you havn't already cloned the nixpkgs repository, you need to do this first.
You also need to fetch the unstable channel commit, which is provided by the
git clone https://github.com/nixos/nixpkgs && cd nixpkgs
git remote add channels https://github.com/nixos/nixpkgs-channels
Step 3: Check out the commit of your system
Now you should have a commit which shows the current unstable channel. You can check this like so:
nixos-version # 16.03.git.ab0a7e9 (Emu)
git show nixos-unstable # commit ab0a7e9
If the commit is the same as the hash which is shown from calling
nixos-version you have found the channel commit your system is build from.
You can now check this commit out and create a new branch in the nixpkgs from
git checkout ab0a7e9
git checkout -b nixos-unstable-fixes
Step 4: Search for fixes.
Sometimes there are already fixes available in the master branch of nixpkgs, but are not in unstable yet. You can simply do something like this:
- Find out where the broken package lives
- Get the log from the current unstable channel commit to master
- Apply these fixes in your
- Rebuild the system with the local nixpkgs
If there are no fixes available, you have to fix the build yourself and I cannot help you with that, because the build problems are often very package-specific.
We already know that libvterm is the problem here.
grep -rnil libvterm pkgs/
# or 'ag -l libvterm pkgs', which is much faster
This gives us four possible locations:
We also know (from the backtrace) that it has something to do with neovim. So we check the changes of this one first:
git log --oneline nixos-unstable..master -- pkgs/applications/editors/neovim/default.nix
2617919 neovim: fix wrong ad30764d68a
Well, we found a fix. Let's apply it!
git checkout nixos-unstable-fixes # just to be sure
git cherry-pick 2617919
Now we can rebuild our system with this patch applied:
sudo nixos-rebuild switch -I nixpkgs=/home/user/nixpkgs/
... and our system is updated.
Now you can try to update packages the same way using the diff from
master and apply the appropriate patches onto your
After a channel update you can simply rebase the
-fixes branch onto the new
channel commit. If rebase fails due to conflicts (which shouldn't happen that
often) you can just hard-reset your
-fixes branch onto the unstable channel
commit and re-apply patches as needed.