My default nix configuration on NixOS. This configuration is more for building/debugging stuff and caching with nix-serve. Usually my package version is locked since different versions of nix can have some effects.
nix Copy { config, … }: { nix = { package = (import ../versions.nix).nix_2_12 { inherit config; }; settings = { log-lines = 25; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-log-lines"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-log-lines"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-log-lines</a> fallback = true; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-fallback"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-fallback"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-fallback</a> tarball-ttl = 0; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-tarball-ttl"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-tarball-ttl"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-tarball-ttl</a> show-trace = true; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-show-trace"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-show-trace"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-show-trace</a> connect-timeout = 5; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-connect-timeout"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-connect-timeout"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-connect-timeout</a> auto-optimise-store = true; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-auto-optimise-store"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-auto-optimise-store"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-auto-optimise-store</a> narinfo-cache-negative-ttl = 0; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-negative-ttl"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-negative-ttl"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-negative-ttl</a> narinfo-cache-positive-ttl = 0; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-positive-ttl"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-positive-ttl"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-narinfo-cache-positive-ttl</a> builders-use-substitutes = true; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-builders-use-substitutes"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-builders-use-substitutes"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-builders-use-substitutes</a> min-free = 268435456; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-min-free"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-min-free"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-min-free</a> (256 MB in Bytes) max-free = 1073741824; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-max-free"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-max-free"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-max-free</a> (1 GB in Bytes) allowed-users = [ "root" "@wheel" ]; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-allowed-users"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-allowed-users"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-allowed-users</a> trusted-users = [ "root" "@wheel" ]; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-trusted-users"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-trusted-users"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-trusted-users</a> experimental-features = "nix-command flakes"; # <a
  rel="noopener no-referrer"
  href="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-experimental-features"
  title="https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-experimental-features"
  >https://nixos.org/manual/nix/unstable/command-ref/conf-file.html#conf-experimental-features</a> }; }; } My nix-configuration.nix on version 22.11