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
$HOSTNAME (without the domain part) that resolves to
127.0.1.1 (!= 127.0.0.1).
- Unknown (could potentially cause other unexpected issues, but special
care was taken).
[0]: Some applications do apparently depend on this behaviour (see
c578924) and this is typically the expected behaviour.
Co-authored-by: Florian Klink <flokli@flokli.de>
The `network-link-${i.name}` units raced with other things trying to
configure the interface, or ran before the interface was available.
Instead of running our own set of shell scripts on boot, and hoping
they're executed at the right time, we can make use of udev to configure
the interface *while they appear*, by providing `.link` files in
/etc/systemd/network/*.link to set MACAddress and MTUBytes.
This doesn't require networkd to be enabled, and is populated properly
on non-networkd systems since
https://github.com/NixOS/nixpkgs/pull/82941.
This continues clean-up work done in
https://github.com/NixOS/nixpkgs/pull/85170 for the scripted networking
stack.
The only leftover part of the `network-link-${i.name}` unit (bringing
the interface up) is moved to the beginning of the
`network-addresses-${i.name}` unit.
Fixes: https://github.com/NixOS/nixpkgs/issues/74471
Closes: https://github.com/NixOS/nixpkgs/pull/87116
I hate the thing too even though I made it, and rather just get rid of
it. But we can't do that yet. In the meantime, this brings us more
inline with autoconf and will make it slightly easier for me to write a
pkg-config wrapper, which we need.
'nix build' is an experimental command so we shouldn't use it
yet. (nixos-rebuild also uses 'nix', but only when using flakes, which
are themselves an experimental feature.)
