unit-status-mail for backups

configuration.nix

@@ -386,7 +386,8 @@ in {
       options = "--delete-older-than 14d";
   };
 
-  systemd.services."make-snapshot-dirs" = let
+  systemd.services = {
+    "make-snapshot-dirs" = let
       vals = builtins.attrValues backup_paths;
       mountpoints = builtins.catAttrs "mountpoint" vals;
       unique_mountpoints = lib.unique mountpoints;
@@ -400,6 +401,39 @@ in {
       };
     };
 
+    # https://northernlightlabs.se/2014-07-05/systemd-status-mail-on-unit-failure.html
+    "unit-status-mail@" = {
+      description = "Send an email on unit failure";
+      serviceConfig = {
+        Type = "simple";
+        ExecStart = pkgs.writeShellScript "unit-status-mail" ''
+          MAILTO="motiejus+alerts@jakstys.lt"
+          UNIT=$1
+          EXTRA=""
+          for e in "''${@:2}"; do
+            EXTRA+="$e"$'\n'
+          done
+          UNITSTATUS=$(${pkgs.systemd}/bin/systemctl status $UNIT)
+          ${pkgs.postfix}/bin/sendmail $MAILTO <<EOF
+          Subject:Status mail for unit: $UNIT
+
+          Status report for unit: $UNIT
+          $EXTRA
+
+          $UNITSTATUS
+          EOF
+
+          echo -e "Status mail sent to: $MAILTO for unit: $UNIT"
+          '';
+      };
+    };
+  } // lib.mapAttrs' (name: value: {
+      name = "borgbackup-job-${name}";
+      value = {
+        serviceConfig.OnFailure = "unit-status-mail@${name}.service";
+      };
+    }) backup_paths;
+
   # Do not change
   system.stateVersion = "22.11";
 }