(nixos-install & nixos-enter) Chroot cannot resolve dns names

[nlvw]

Issue description

After installing NixOS then using nixos-enter to chroot into the installation dns does not work. I am trying to clone down a repository but it fails because it cannot resolve github.com.

Here is a picture of the of some commands run inside the chrooted installation

Bootstrap.sh being run to install and call the chrooted commands.
Configuration.nix being used

Steps to reproduce

1. Boot a vm using one of the 18.03.132155.b50443b5c4a isos (UEFI Mode).
2. Clone this repo and tree
3. run bootstrap.sh
4. select "test" machine (option 4) when prompted (this is setup for hyper-v so you may need to fix the hardware-configuration.nix back to the default one generated).
5. Observer error after installation finishes

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

[lheckemann]

I'm guessing this is because nixos-enter doesn't create a resolv.conf. I think the appropriate solution would be to bind-mount that in from the host system.

As a workaround, you should be able to make it work by running cp /etc/resolv.conf /mnt/etc/.

[nlvw]

This leaves me a bit confused. I'm using the nixos-enter after nixos-install has completed. Does resolv.conf not get generated during the build?

I noticed that I did not have networkmanager specifically enabled in my configuration. I'll test that and report back.

[nlvw]

So specifically enabling networkmanager didn't fix anything. Copying resolv.conf into the chroot didn't fix the issue either. It turns out that nixos-enter regenerates the resolv.conf every time it's called

edit: I retested the commands from the pics above with an external network adapter instead of a natted one. Same result.

[lheckemann]

And everything works fine outside nixos-enter?

[nlvw]

Yep no issues in the regular environment. DNS resolution works fine, as well, once rebooted into the fresh installation.

It is just in the nixos-enter environment right after installation, before reboot, that DNS doesn't want to work.

[johnae]

I have a similar problem during install where an overlay does a curl as part of make install - fails because it can't resolve dns (in this case github.com).

[johnae]

Skipping the install of that overlay and then trying nixos-enter:

nixos-enter -c "curl https://github.com"
setting up /etc...
curl: (6) Could not resolve host: github.com

[johnae]

Trying the below does work (so clearly something isn't right about the generated resolv.conf):

nixos-enter -c "echo nameserver 8.8.8.8 > /etc/resolv.conf; curl https://github.com"
... lots of html output as expected ...

[johnae]

Finally, bind mounting the host resolv.conf readonly does allow me to to run nixos-enter:

mount -o bind,ro /etc/resolv.conf /mnt/etc/resolv.conf
nixos-enter -c "curl https://github.com" | head
setting up /etc...
/nix/store/zm1cn7di1zcapka1jlr9w4p714sl3jxq-openresolv-3.9.0/libexec/resolvconf/libc: line 230: /etc/resolv.conf: Read-only file system
... lots of expected html output ...

So now nixos-enter fails to generate the resolv.conf (and a working bind mounted one gets used) as it's readonly. Unfortunately the same doesn't seem to be true for nixos-install strangely enough (the overlay still fails to install), not sure why.

I could however do:

nixos-enter -c "bash"
... enable the overlay again ...
mkdir /tmp
nixos-rebuild switch

I get some errors from the above but it does install the overlay package. In general there seems to be a dns resolution problem during nixos-install (if dns is required by the build, like doing a curl from the Makefile) and also when doing nixos-enter. In my case I was using the unstable image: nixos-minimal-18.09pre140958.696c6bed4e8-x86_64-linux.iso.

[johnae]

So my host resolv.conf looks like this:

# Generated by resolvconf
nameserver 10.0.2.3
options edns0

The generated resolv.conf under /mnt/etc (when not bind mounting) looks like this:

# Generated by resolvconf
options edns0

So it's missing the nameserver(s).

[johnae]

Hmm. As I am a nixos newbie it may just be that I don't fully understand the notion of fixedOutput packages. Looking through the sources for the package manager it seems the build environment will only allow networking when the output is a fixedOutputHash one. However, that does seem like it would mean the package cannot be built everywhere as the binary won't have the same hash...

[johnae]

Ok so I think I get it now. I was installing packages in an impure way I suppose as they were downloading things "behind the scene", sorry I'm a newbie still. So nixos-install is doing what it should do I think.

Still, I don't understand why nixos-enter generates an unusable resolv.conf as detailed above and I think that's what this issue really is about.

[nlvw]

The issue becomes more severe when you take into account that even if you create a correct resolv.conf it will get replaced every time nixos-enter is called. So if you are using nixos-enter in a script it becomes a blocking issue.

[jluttine]

I have the same problem. I'm running a live USB NixOS but I have already installed NixOS on my computer. I'd like to just chroot to my already installed NixOS system and run nixos-install there but it doesn't work because network fails.

[nlvw]

@jluttine After you mount the installation you can just run "nixos-install --no-root-passwd" again. It will pull the configuration from whatever is already installed in the /mnt folder and just update it.

The core root of the problem for this ticket/issue is resolve.conf being generated incorrectly. Just waiting for nixos-enter to be fixed in this regard for the ticket to be closed.