nixos-config/modules/nixos/services/borgmatic.nix

# An improved version of the borgmatic module.
{ config, options, lib, pkgs, ... }:

let
  cfg = config.modules.services.borgmatic;

  jobOption = { name, config, ... }: {
    options = {
      startAt = lib.mkOption {
        type = lib.types.str;
        description = ''
          The schedule for the backup. It uses the time format from <literal>systemd.time</literal>.
        '';
        default = "daily";
        example = "04/8:00:00";
      };

      configPath = lib.mkOption {
        type = lib.types.path;
        description = ''
          The path of the configuration file to be used. For a start, you can quickly create a template by running <literal>generate-borgmatic-config</literal>.
        '';
        example = "./personal-drive.yaml";
      };

      doPrune = lib.mkEnableOption "pruning the backup";
    };
  };
in {
  options.modules.services.borgmatic = {
    jobs = lib.mkOption {
      type = with lib.types; attrsOf (submodule jobOption);
      description = "borgmatic jobs with each bearing a configuration file to be used.";
      default = {};
      example = {
        external-hard-drive = {
          startAt = "daily";
          configPath = ./borgmatic.yaml;
        };
      };
    };
  };

  config = {
    systemd.services = (lib.mapAttrs'
      (name: settings:
        lib.nameValuePair
        ("borgmatic-backup-" + name)
        ({
          unitConfig = {
            Description = "Backup with Borgmatic job '${name}'";
            Wants = [ "network-online.target" ];
            After = [ "network-online.target" ];
          };

          startAt = settings.startAt;
          serviceConfig = {
            # Delay start to prevent backups running during boot. Note that systemd-inhibit requires dbus and
            # dbus-user-session to be installed.
            ExecStartPre = "${pkgs.coreutils}/bin/sleep 1m";
            ExecStart = ''
              ${pkgs.systemd}/bin/systemd-inhibit --who="borgmatic" --why="Prevent interrupting scheduled backup" ${pkgs.borgmatic}/bin/borgmatic --verbosity -1 --syslog-verbosity 1 --config ${settings.configPath}
            '';

            # Set security-related stuff.
            LockPersonality = "true";
            ProtectSystem = "full";
            MemoryDenyWriteExecute = "no";
            NoNewPrivileges = "yes";
            PrivateDevices = "yes";
            PrivateTmp = "yes";
            ProtectClock = "yes";
            ProtectControlGroups = "yes";
            ProtectHostname = "yes";
            ProtectKernelLogs = "yes";
            ProtectKernelModules = "yes";
            ProtectKernelTunables = "yes";
            RestrictAddressFamilies = "AF_UNIX AF_INET AF_INET6 AF_NETLINK";
            RestrictNamespaces = "yes";
            RestrictRealtime = "yes";
            RestrictSUIDSGID = "yes";
            SystemCallArchitectures = "native";
            SystemCallFilter = "@system-service";
            SystemCallErrorNumber = "EPERM";
            CapabilityBoundingSet = "CAP_DAC_READ_SEARCH CAP_NET_RAW";

            # Lower CPU and I/O priority.
            Nice = 19;
            CPUSchedulingPolicy = "batch";
            IOSchedulingClass = "best-effort";
            IOSchedulingPriority = 7;
            IOWeight = 100;

            # Prevent rate limiting of borgmatic log events. If you are using an older version of systemd that
            # doesn't support this (pre-240 or so), you may have to remove this option.
            LogRateLimitIntervalSec = "0";
          };
        })) cfg.jobs);
  };
}