From 234d95a6fc75208266049fa2f57641d6f4e5bd2a Mon Sep 17 00:00:00 2001 From: Michael Weiss Date: Mon, 23 Dec 2019 15:44:14 +0100 Subject: [PATCH] nixos/networking: Add the FQDN and hostname to /etc/hosts This fixes the output of "hostname --fqdn" (previously the domain name was not appended). Additionally it's now possible to use the FQDN. This works by unconditionally adding two entries to /etc/hosts: 127.0.0.1 localhost ::1 localhost These are the first two entries and therefore gethostbyaddr() will always resolve "127.0.0.1" and "::1" back to "localhost" [0]. This works because nscd (or rather the nss-files module) returns the first matching row from /etc/hosts (and ignores the rest). The FQDN and hostname entries are appended later to /etc/hosts, e.g.: 127.0.0.2 nixos-unstable.test.tld nixos-unstable ::1 nixos-unstable.test.tld nixos-unstable Note: We use 127.0.0.2 here to follow nss-myhostname (systemd) as close as possible. This has the advantage that 127.0.0.2 can be resolved back to the FQDN but also the drawback that applications that only listen to 127.0.0.1 (and not additionally ::1) cannot be reached via the FQDN. If you would like this to work you can use the following configuration: ```nix networking.hosts."127.0.0.1" = [ "${config.networking.hostName}.${config.networking.domain}" config.networking.hostName ]; ``` Therefore gethostbyname() resolves "nixos-unstable" to the FQDN (canonical name): "nixos-unstable.test.tld". Advantages over the previous behaviour: - The FQDN will now also be resolved correctly (the entry was missing). - E.g. the command "hostname --fqdn" will now work as expected. Drawbacks: - Overrides entries form the DNS (an issue if e.g. $FQDN should resolve to the public IP address instead of 127.0.0.1) - Note: This was already partly an issue as there's an entry for $HOSTNAME (without the domain part) that resolves to 127.0.1.1 (!= 127.0.0.1). - Unknown (could potentially cause other unexpected issues, but special care was taken). [0]: Some applications do apparently depend on this behaviour (see c578924) and this is typically the expected behaviour. Co-authored-by: Florian Klink --- nixos/doc/manual/release-notes/rl-2009.xml | 16 +++++++++++ nixos/modules/config/networking.nix | 33 ++++++++++++---------- 2 files changed, 34 insertions(+), 15 deletions(-) diff --git a/nixos/doc/manual/release-notes/rl-2009.xml b/nixos/doc/manual/release-notes/rl-2009.xml index 3bbb7d71d49..3166f98907c 100644 --- a/nixos/doc/manual/release-notes/rl-2009.xml +++ b/nixos/doc/manual/release-notes/rl-2009.xml @@ -415,6 +415,22 @@ systemd.services.nginx.serviceConfig.ReadWritePaths = [ "/var/www" ]; continue to work through Breezy. + + + In addition to the hostname, the fully qualified domain name (FQDN), + which consists of ${cfg.hostName} and + ${cfg.domain} is now added to + /etc/hosts, to allow local FQDN resolution, as used by the + hostname --fqdn command and other applications that + try to determine the FQDN. These new entries take precedence over entries + from the DNS which could cause regressions in some very specific setups. + Additionally the hostname is now resolved to 127.0.0.2 + instead of 127.0.1.1 to be consistent with what + nss-myhostname (from systemd) returns. + The old behaviour can e.g. be restored by using + networking.hosts = lib.mkForce { "127.0.1.1" = [ config.networking.hostName ]; };. + + diff --git a/nixos/modules/config/networking.nix b/nixos/modules/config/networking.nix index 03944de8249..4cb7d81c997 100644 --- a/nixos/modules/config/networking.nix +++ b/nixos/modules/config/networking.nix @@ -8,9 +8,6 @@ let cfg = config.networking; - localhostMapped4 = cfg.hosts ? "127.0.0.1" && elem "localhost" cfg.hosts."127.0.0.1"; - localhostMapped6 = cfg.hosts ? "::1" && elem "localhost" cfg.hosts."::1"; - localhostMultiple = any (elem "localhost") (attrValues (removeAttrs cfg.hosts [ "127.0.0.1" "::1" ])); in @@ -147,12 +144,6 @@ in config = { assertions = [{ - assertion = localhostMapped4; - message = ''`networking.hosts` doesn't map "127.0.0.1" to "localhost"''; - } { - assertion = !cfg.enableIPv6 || localhostMapped6; - message = ''`networking.hosts` doesn't map "::1" to "localhost"''; - } { assertion = !localhostMultiple; message = '' `networking.hosts` maps "localhost" to something other than "127.0.0.1" @@ -161,22 +152,34 @@ in ''; }]; - networking.hosts = { - "127.0.0.1" = [ "localhost" ]; - } // optionalAttrs (cfg.hostName != "") { - "127.0.1.1" = [ cfg.hostName ]; + # These entries are required for "hostname -f" and to resolve both the + # hostname and FQDN correctly: + networking.hosts = let + hostnames = # Note: The FQDN (canonical hostname) has to come first: + optional (cfg.hostName != "" && cfg.domain != null) "${cfg.hostName}.${cfg.domain}" + ++ optional (cfg.hostName != "") cfg.hostName; # Then the hostname (without the domain) + in { + "127.0.0.2" = hostnames; } // optionalAttrs cfg.enableIPv6 { - "::1" = [ "localhost" ]; + "::1" = hostnames; }; networking.hostFiles = let + # Note: localhostHosts has to appear first in /etc/hosts so that 127.0.0.1 + # resolves back to "localhost" (as some applications assume) instead of + # the FQDN! By default "networking.hosts" also contains entries for the + # FQDN so that e.g. "hostname -f" works correctly. + localhostHosts = pkgs.writeText "localhost-hosts" '' + 127.0.0.1 localhost + ${optionalString cfg.enableIPv6 "::1 localhost"} + ''; stringHosts = let oneToString = set: ip: ip + " " + concatStringsSep " " set.${ip} + "\n"; allToString = set: concatMapStrings (oneToString set) (attrNames set); in pkgs.writeText "string-hosts" (allToString (filterAttrs (_: v: v != []) cfg.hosts)); extraHosts = pkgs.writeText "extra-hosts" cfg.extraHosts; - in mkBefore [ stringHosts extraHosts ]; + in mkBefore [ localhostHosts stringHosts extraHosts ]; environment.etc = { # /etc/services: TCP/UDP port assignments.