Move all of NixOS to nixos/ in preparation of the repository merge

nixos/modules/services/backup/postgresql-backup.nix

@@ -0,0 +1,66 @@
+{ config, pkgs, ... }:
+
+with pkgs.lib;
+
+let
+  inherit (pkgs) postgresql gzip;
+
+  location = config.services.postgresqlBackup.location ;
+
+  postgresqlBackupCron = db:
+    ''
+      ${config.services.postgresqlBackup.period} root ${postgresql}/bin/pg_dump ${db} | ${gzip}/bin/gzip -c > ${location}/${db}.gz
+    '';
+
+in
+
+{
+
+  options = {
+
+    services.postgresqlBackup = {
+
+      enable = mkOption {
+        default = false;
+        description = ''
+          Whether to enable PostgreSQL dumps.
+        '';
+      };
+
+      period = mkOption {
+        default = "15 01 * * *";
+        description = ''
+          This option defines (in the format used by cron) when the
+          databases should be dumped.
+          The default is to update at 01:15 (at night) every day.
+        '';
+      };
+
+      databases = mkOption {
+        default = [];
+        description = ''
+          List of database names to dump.
+        '';
+      };
+
+      location = mkOption {
+        default = "/var/backup/postgresql";
+        description = ''
+          Location to put the gzipped PostgreSQL database dumps.
+        '';
+      };
+    };
+
+  };
+
+  config = mkIf config.services.postgresqlBackup.enable {
+    services.cron.systemCronJobs = map postgresqlBackupCron config.services.postgresqlBackup.databases;
+
+    system.activationScripts.postgresqlBackup = stringAfter [ "stdio" "users" ]
+      ''
+        mkdir -m 0700 -p ${config.services.postgresqlBackup.location}
+        chown root ${config.services.postgresqlBackup.location}
+      '';
+  };
+
+}