nixos/nixos-generate-config: use networking.useDHCP by default

Currently we're still using scripted networking by default. A problem
with scripted networking is that having `useDHCP` on potentially
non-existing interfaces (e.g. an ethernet interface for USB tethering)
can cause the boot to hang.

Closes #107908

1 files changed, 7 insertions, 5 deletions

diff --git a/nixos/modules/installer/tools/nixos-generate-config.pl b/nixos/modules/installer/tools/nixos-generate-config.pl
index fb5d3ba47325..6d32d727501e 100644
--- a/nixos/modules/installer/tools/nixos-generate-config.pl
+++ b/nixos/modules/installer/tools/nixos-generate-config.pl
@@ -581,17 +581,19 @@ ${\join "", (map { "  $_\n" } (uniq @attrs))}}
 EOF
 
 sub generateNetworkingDhcpConfig {
+    # FIXME disable networking.useDHCP by default when switching to networkd.
     my $config = <<EOF;
-  # The global useDHCP flag is deprecated, therefore explicitly set to false here.
-  # Per-interface useDHCP will be mandatory in the future, so this generated config
-  # replicates the default behaviour.
-  networking.useDHCP = lib.mkDefault false;
+  # Enables DHCP on each ethernet and wireless interface. In case of scripted networking
+  # (the default) this is the recommended approach. When using systemd-networkd it's
+  # still possible to use this option, but it's recommended to explicitly set it
+  # per-interface using `networking.interfaces.<interface>.useDHCP`.
+  networking.useDHCP = lib.mkDefault true;
 EOF
 
     foreach my $path (glob "/sys/class/net/*") {
         my $dev = basename($path);
         if ($dev ne "lo") {
-            $config .= "  networking.interfaces.$dev.useDHCP = lib.mkDefault true;\n";
+            $config .= "  # networking.interfaces.$dev.useDHCP = lib.mkDefault true;\n";
         }
     }