DNS not resolving during nixos builds

Help
1

Suddenly my nixos build is no capable of resolving DNS, as the message shows below

trying https://github.com/catppuccin/starship/archive/5906cc369dd8207e063c0e6e2d27bd0c0b567cb8.tar.gz
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
^M 0 0 0 0 0 0 0 0 --:–:-- --:–:-- --:–:-- 0curl: (6) Could not resolve host: github.com
Warning: Problem : timeout. Will retry in 1 second. 3 retries left.
curl: (6) Could not resolve host: github.com
Warning: Problem : timeout. Will retry in 2 seconds. 2 retries left.
curl: (6) Could not resolve host: github.com
Warning: Problem : timeout. Will retry in 4 seconds. 1 retry left.
curl: (6) Could not resolve host: github.com
error checking the existence of https://tarballs.nixos.org//sha256-FLHjbClpTqaK4n2qmepCPkb8rocaAo3qeV4Zp1hia0g=:
curl: (6) Could not resolve host: tarballs.nixos.org
error: cannot download source from any mirror

I’ve trying changing my DNS from Cloudflare to Google to OpenDNS, nothing seems to have work. Using curl -v -L works on both URLs as accessing them by browser.

Things I’ve tried but nothing changed:

  • changed dns providers (using networking.nameservers)
  • Fully disabled ipv6 (when testing with curl, there was a first attempt to resolve IPv6 that always failed)

What worked:

  • Running nixos-rebuild with no sandbox: –-option sandbox false

This happened once, but it felt like a blip in the DNS as I retried a few hours later and it worked, now its constant, I’ve been trying to rebuild this for two days and I get the same error.

2

Can you share the part where you set up your starship prompt, especially the catpuccin theme?

3

Share your DNS settings as well, especially if you’re using systemd-resolved as that has presentations like this on occasion.

4

DNS:
I didn’t had any DNS configuration in my nix files until this issue appeared, was only the router DHCP DNS, this is my current network configuration:

  networking.useDHCP = lib.mkDefault true;

  networking.enableIPv6 = false;
  networking.nameservers = [
    "1.1.1.1"
    "1.0.0.1"
  ];
  networking.networkmanager = {
    enable = true;
    wifi = {
      macAddress = "preserve";
      scanRandMacAddress = false;
      powersave = false;
    };
  };

Starship/Catppuccin (home-manager):

Catppuccin comes from GitHub - catppuccin/nix: ❄️ Soothing pastel theme for Nix.

  programs.starship = {
    enable = true;
    enableZshIntegration = true;
  };

  catppuccin = {
    enable = true;
    flavor = "frappe";
    accent = "sky";
    gtk.icon.enable = true;
    delta.enable = true;
    bat.enable = true;
    ghostty.enable = true;
    btop.enable = true;
    firefox.enable = true;
    fzf.enable = true;
    kitty.enable = true;
    spotify-player.enable = true;
    starship.enable = true;
    zsh-syntax-highlighting.enable = true;
    mangohud.enable = false;
  };

The same issue happens with crates.io, when a rust dependency needs to be installed.

5

Hmmmm.

Looks like you’re using DHCP via network manager. Does the networking.nameservers override that? I don’t know

cat /etc/resolv.conf

[das@l:~]$ nix-shell -p dig
these 2 paths will be fetched (1.35 MiB download, 4.41 MiB unpacked):
  /nix/store/4avybf0fh7bf2cxs2cjvd4h3g4krc9ck-bind-9.20.16-dnsutils
  /nix/store/mhl5gd5ky5rld8djl4hzpxpkj3pdhlpn-bind-9.20.16-lib
copying path '/nix/store/mhl5gd5ky5rld8djl4hzpxpkj3pdhlpn-bind-9.20.16-lib' from 'https://cache.nixos.org'...
copying path '/nix/store/4avybf0fh7bf2cxs2cjvd4h3g4krc9ck-bind-9.20.16-dnsutils' from 'https://cache.nixos.org'...

[nix-shell:~]$ dig github.com

; <<>> DiG 9.20.16 <<>> github.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37790
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;github.com.			IN	A

;; ANSWER SECTION:
github.com.		47	IN	A	140.82.114.3

;; Query time: 0 msec
;; SERVER: 172.16.50.1#53(172.16.50.1) (UDP)
;; WHEN: Thu Dec 18 15:06:22 PST 2025
;; MSG SIZE  rcvd: 55


[nix-shell:~]$
6

My DCHP is also configured to have the dns set to 1.1.1.1 and 1 0.0.1.

Any attempt to resolve dns through terminal (via curl, dig or nslookup) is successful using the expected nameservers (cloudflare).

7

Can you please cat a couple of files?

cat /etc/resolv.conf

cat /etc/nsswitch.conf

Can you try the dig command I showed?

8

dig output:

[nix-shell:~]$ dig github.com

; <<>> DiG 9.20.15 <<>> github.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44757
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;github.com.                    IN      A

;; ANSWER SECTION:
github.com.             17      IN      A       140.82.121.3

;; Query time: 8 msec
;; SERVER: 1.1.1.1#53(1.1.1.1) (UDP)
;; WHEN: Sun Dec 21 00:41:48 CET 2025
;; MSG SIZE  rcvd: 55

/etc/resolv.conf

# Generated by resolvconf
nameserver 1.1.1.1
nameserver 1.0.0.1
options edns0

/etc/nsswitch.conf

passwd:    files systemd
group:     files [success=merge] systemd
shadow:    files systemd
sudoers:   files

hosts:     mymachines mdns4_minimal [NOTFOUND=return] files myhostname dns mdns4
networks:  files

ethers:    files
services:  files
protocols: files
rpc:       files
9

Hmmm. So that looks totally fine to me. And the dig worked and in only 8ms, so that should be ok.

I guess another option would be run a local caching resolver, but this shouldn’t really be required. e.g.