nixos/networking: add hostname to /etc/hosts by default, simplify #47241

oxij · 2018-09-23T18:58:59Z

Motivation for this change

#1248 and #36261. This is an alternative simpler implementation of #36261.

Since networking.hosts is properly typed all of that magic /etc/hosts generator does on master can be dropped. People that disagree with the value of networking.hosts can simply mkForce.

Things done

It evaluates.
Tested all my configs to boot.

Do not merge before 2018-09-30.

oxij · 2018-09-23T20:35:28Z

Did you mean ```networking.hosts = lib.mkOptionDefault { ...```

No, this is intended. Any non-default priority will break configs that set `networking.hosts` directly without priority qualifiers. (Which, I expect, most do.) With my version both ``` networking.hosts = { ... }; ``` and ``` networking.hosts = mkForce { ... }; ``` work exactly as before.

I'd order all IPv4 before IPv6 (or IPv6 before IPv4, it does not matter) instead of current alphanumeric string sort. ...

I see, but note that the same issue applies to `master`. This implementation changes nothing in this regard in the most common use case because digits are `<` than ":" in ASCII order, hence this produces the same `/etc/hosts` as before (+ "127.0.1.1" when `hostName` is not empty). This can only be an issue if you explicitly add non-zero prefixed IPv6 addresses to `networking.hosts`.

(It might worth a separate issue/PR...)

In that sense I agree, if that's an actual issue, we can split `cfg.hosts` into IPv4 and IPv6 parts in a separate PR.

danbst · 2018-09-24T07:22:26Z

This can make localhost not in top of /etc/hosts:

10.0.0.1 xxx
127.0.0.1 localhost

Then localhost becomes a bit floating - if you add networking.hosts."4.x.x.x" = "localhost", localhost will resolve to 127.0.0.1, but if you add networking.hosts."10.x.x.x" = "localhost", localhost will resolve to 10.x.x.x

Probably add assert and warning that forbids redefining localhost in networking.hosts? On master both would result to localhost = 127.0.0.1

danbst · 2018-09-24T07:45:06Z

Nah, mkBefore/mkAfter don't work here

{ config, lib, ... }:
let
    inherit (lib) optionalAttrs;
    cfg = config.networking;
    oxijPR = {
        networking.hosts = {
            "127.0.0.1" = [ "localhost" ];
        } // optionalAttrs (cfg.hostName != "") {
            "127.0.1.1" = [ cfg.hostName ];
        } // optionalAttrs cfg.enableIPv6 {
            "::1" = [ "localhost" ];
        };
    };
    correctOrderOverride = {
        networking.hosts = lib.mkBefore {
            "4.0.0.0" = [ "localhost" ];
            "10.0.0.0" = [ "localhost" ];
        };
    };
in {
    imports = [
        oxijPR
        correctOrderOverride
    ];
}

result is

$ nix-instantiate -I nixos-config=$PWD/hosts.nix --eval -E 'with import <nixpkgs/nixos> { }; config.networking.hosts'
{ "10.0.0.0" = <CODE>; "127.0.0.1" = <CODE>; "127.0.1.1" = <CODE>; "4.0.0.0" = <CODE>; "::1" = <CODE>; }

oxij · 2018-09-24T19:05:57Z

localhost can resolve to something other than 127.0.0.1

Right, I didn't think about that.

Probably add assert and warning that forbids redefining localhost in `networking.hosts`?

Right, `assert` seems the best option. Will do.

oxij · 2018-09-30T15:05:19Z

Added the asserts.

danbst · 2018-09-30T20:31:43Z

nixos/modules/config/networking.nix

+      message = ''
+        `networking.hosts` maps a non-loopback address to `localhost`. Generated
+        `/etc/hosts` might make `localhost` resolve to that non-loopback address instead
+        of `127.0.0.1` and `::1` which would break some applications. Please use


This message should be simplified. It is also not very correct, because one may map "127.0.0.2" to localhost and it would be perfectly correct mapping

oxij · 2018-10-01T15:31:52Z

This message should be simplified.

Please suggest a better one. This is the best I managed.

It is also not very correct, because one may map "127.0.0.2" to localhost and it would be perfectly correct mapping

But I expect some applications to break with that too.

danbst · 2018-10-01T17:23:19Z

Maybe

You are trying to map "localhost" to address 127.0.0.2, but "localhost" must resolve
to 127.0.0.1 or ::1 only. Override environment.etc."hosts" and use /etc/hosts format if
you really want to do this.

Since `networking.hosts` is properly typed all of that magic `/etc/hosts` generator does can be dropped. People that disagree with the value of `networking.hosts` can simply `mkForce`.

We use `127.0.1.1` instead of `127.0.0.1` because some applications will fail if `127.0.0.1` resolves to something other than `localhost`. Debian does the same. See NixOS#1248 and NixOS#36261.

oxij · 2018-10-03T00:00:11Z

Done.

oxij · 2018-10-12T20:18:16Z

ping!

oxij · 2018-10-19T17:03:05Z

@GrahamcOfBorg eval

oxij · 2018-10-26T18:09:37Z

Can we merge this yet?

/cc @xeji @Mic92

costrouc · 2019-01-30T15:03:59Z

So by no means a problem with this PR but I wanted to note that this broke my dnsmasq configuration. The server that had dnsmasq running would return its ip address along with 127.0.1.1. which would cause that when I would try to ssh into the dnsmasq server it would instead ssh into localhost. This was my fault for using /etc/hosts in the addn-hosts option. Hope this may help someone in the future if they run into this issue. I instead created another /etc/dnsmasq.hosts file with environment.etc = { "dnsmasq.hosts".text = ''..........''};

oxij mentioned this pull request Sep 23, 2018

nixos/networking: add hostname to /etc/hosts by default #36261

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8 tasks

GrahamcOfBorg added 6.topic: nixos 8.has: module (update) 10.rebuild-darwin: 0 10.rebuild-linux: 0 labels Sep 23, 2018

oxij force-pushed the pull/36261-fix-local-hostname-alternative branch from 2434e18 to f3362dc Compare September 30, 2018 14:43

danbst reviewed Sep 30, 2018

View reviewed changes

oxij added 2 commits October 2, 2018 23:58

nixos/networking: simplify /etc/hosts generation, add asserts

1ece504

Since `networking.hosts` is properly typed all of that magic `/etc/hosts` generator does can be dropped. People that disagree with the value of `networking.hosts` can simply `mkForce`.

nixos/networking: add hostname to /etc/hosts by default

c578924

We use `127.0.1.1` instead of `127.0.0.1` because some applications will fail if `127.0.0.1` resolves to something other than `localhost`. Debian does the same. See NixOS#1248 and NixOS#36261.

oxij force-pushed the pull/36261-fix-local-hostname-alternative branch from f3362dc to c578924 Compare October 2, 2018 23:59

oxij mentioned this pull request Oct 12, 2018

Firefox takes 30+ seconds to start if networking.hostName is not in DNS resolution #45671

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danbst approved these changes Oct 19, 2018

View reviewed changes

xeji merged commit 6419bda into NixOS:master Oct 27, 2018

oxij deleted the pull/36261-fix-local-hostname-alternative branch November 18, 2018 08:57

adamtulinius mentioned this pull request Mar 13, 2019

ZooKeeper clustering broken on 19.03 due to /etc/hosts change #57566

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nixos/networking: add hostname to /etc/hosts by default, simplify #47241

nixos/networking: add hostname to /etc/hosts by default, simplify #47241

oxij commented Sep 23, 2018

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costrouc commented Jan 30, 2019

nixos/networking: add hostname to /etc/hosts by default, simplify #47241

nixos/networking: add hostname to /etc/hosts by default, simplify #47241

Conversation

oxij commented Sep 23, 2018

Motivation for this change

Things done

oxij commented Sep 23, 2018 via email

danbst commented Sep 24, 2018

danbst commented Sep 24, 2018

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