Added basic support for borgbackup

default.nix

@@ -477,10 +477,139 @@ in
         description = ''
           The configuration used for monitoring via monit.
           Use a mail address that you actively check and set it via 'set alert ...'.
-          '';
-          };
+        '';
+      };
+    };
+
+    borgbackup = {
+      enable = mkEnableOption "backup via borgbackup";
+
+      repoLocation = mkOption {
+        type = types.string;
+        default = "/var/borgbackup";
+        description = ''
+          The location where borg saves the backups.
+          This can be a local path or a remote location such as user@host:/path/to/repo.
+          It is exported and thus available as an environment variable to cmdPreexec and cmdPostexec.
+        '';
+      };
+
+      startAt = mkOption {
+        type = types.string;
+        default = "hourly";
+        description = "When or how often the backup should run. Must be in the format described in systemd.time 7.";
+      };
+
+      user = mkOption {
+        type = types.string;
+        default = "virtualMail";
+        description = "The user borg and its launch script is run as.";
+      };
+
+      group = mkOption {
+        type = types.string;
+        default = "virtualMail";
+        description = "The group borg and its launch script is run as.";
+      };
+
+      compression = {
+        method = mkOption {
+          type = types.nullOr (types.enum ["none" "lz4" "zstd" "zlib" "lzma"]);
+          default = null;
+          description = "Leaving this unset allows borg to choose. The default for borg 1.1.4 is lz4.";
         };
 
+        level = mkOption {
+          type = types.nullOr types.int;
+          default = null;
+          description = ''
+            Denotes the level of compression used by borg.
+            Most methods accept levels from 0 to 9 but zstd which accepts values from 1 to 22.
+            If null the decision is left up to borg.
+          '';
+        };
+        
+        auto = mkOption {
+          type = types.bool;
+          default = false;
+          description = "Leaves it to borg to determine whether an individual file should be compressed.";
+        };
+      };
+
+      encryption = {
+        method = mkOption {
+          type = types.enum [
+            "none"
+            "authenticated"
+            "authenticated-blake2"
+            "repokey"
+            "keyfile"
+            "repokey-blake2"
+            "keyfile-blake2"
+          ];
+          default = "none";
+          description = ''
+            The backup can be encrypted by choosing any other value than 'none'.
+            When using encryption the password / passphrase must be provided in passphraseFile.
+          '';
+        };
+        
+        passphraseFile = mkOption {
+          type = types.nullOr types.path;
+          default = null;
+        };
+      };
+
+      name = mkOption {
+        type = types.string;
+        default = "{hostname}-{user}-{now}";
+        description = ''
+          The name of the individual backups as used by borg.
+          Certain placeholders will be replaced by borg.
+        '';
+      };
+
+      locations = mkOption {
+        type = types.listOf types.path;
+        default = [cfg.mailDirectory];
+        description = "The locations that are to be backed up by borg.";
+      };
+
+      extraArgumentsForInit = mkOption {
+        type = types.listOf types.string;
+        default = ["--critical"];
+        description = "Additional arguments to add to the borg init command line.";
+      };
+
+      extraArgumentsForCreate = mkOption {
+        type = types.listOf types.string;
+        default = [ ];
+        description = "Additional arguments to add to the borg create command line e.g. '--stats'.";
+      };
+
+      cmdPreexec = mkOption {
+        type = types.nullOr types.string;
+        default = null;
+        description = ''
+          The command to be executed before each backup operation.
+          This is called prior to borg init in the same script that runs borg init and create and cmdPostexec.
+          Example:
+            export BORG_RSH="ssh -i /path/to/private/key"
+        '';
+      };
+
+      cmdPostexec = mkOption {
+        type = types.nullOr types.string;
+        default = null;
+        description = ''
+          The command to be executed after each backup operation.
+          This is called after borg create completed successfully and in the same script that runs
+          cmdPreexec, borg init and create.
+        '';
+      };
+
+    };
+
     backup = {
       enable = mkEnableOption "backup via rsnapshot";
 
@@ -542,6 +671,7 @@ in
   };
 
   imports = [
+    ./mail-server/borgbackup.nix
     ./mail-server/rsnapshot.nix
     ./mail-server/clamav.nix
     ./mail-server/monit.nix