borgmatic: add module

modules/services/borgmatic.nix

@@ -0,0 +1,87 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  serviceConfig = config.services.borgmatic;
+  programConfig = config.programs.borgmatic;
+in {
+  meta.maintainers = [ maintainers.DamienCassou ];
+
+  options = {
+    services.borgmatic = {
+      enable = mkEnableOption "Borgmatic service";
+
+      frequency = mkOption {
+        type = types.str;
+        default = "hourly";
+        description = ''
+          How often to run borgmatic when
+          <code language="nix">services.borgmatic.enable = true</code>.
+          This value is passed to the systemd timer configuration as
+          the onCalendar option. See
+          <citerefentry>
+            <refentrytitle>systemd.time</refentrytitle>
+            <manvolnum>7</manvolnum>
+          </citerefentry>
+          for more information about the format.
+        '';
+      };
+    };
+  };
+
+  config = mkIf serviceConfig.enable {
+    assertions = [
+      (lib.hm.assertions.assertPlatform "services.borgmatic" pkgs
+        lib.platforms.linux)
+    ];
+
+    systemd.user = {
+      services.borgmatic = {
+        Unit = {
+          Description = "borgmatic backup";
+          # Prevent borgmatic from running unless the machine is
+          # plugged into power:
+          ConditionACPower = true;
+        };
+        Service = {
+          Type = "oneshot";
+
+          # Lower CPU and I/O priority:
+          Nice = 19;
+          CPUSchedulingPolicy = "batch";
+          IOSchedulingClass = "best-effort";
+          IOSchedulingPriority = 7;
+          IOWeight = 100;
+
+          Restart = "no";
+          LogRateLimitIntervalSec = 0;
+
+          # Delay start to prevent backups running during boot:
+          ExecStartPre = "sleep 3m";
+
+          ExecStart = ''
+            ${pkgs.systemd}/bin/systemd-inhibit \
+              --who="borgmatic" \
+              --why="Prevent interrupting scheduled backup" \
+              ${programConfig.package}/bin/borgmatic \
+                --stats \
+                --verbosity -1 \
+                --list \
+                --syslog-verbosity 1
+          '';
+        };
+      };
+
+      timers.borgmatic = {
+        Unit.Description = "Run borgmatic backup";
+        Timer = {
+          OnCalendar = serviceConfig.frequency;
+          Persistent = true;
+          RandomizedDelaySec = "10m";
+        };
+        Install.WantedBy = [ "timers.target" ];
+      };
+    };
+  };
+}