nixpkgs/nixos/modules/services/networking/ntpd.nix

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{ config, lib, pkgs, ... }:
with lib;
let
inherit (pkgs) ntp;
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cfg = config.services.ntp;
stateDir = "/var/lib/ntp";
ntpUser = "ntp";
configFile = pkgs.writeText "ntp.conf" ''
driftfile ${stateDir}/ntp.drift
restrict default ${toString cfg.restrictDefault}
restrict -6 default ${toString cfg.restrictDefault}
restrict source ${toString cfg.restrictSource}
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restrict 127.0.0.1
restrict -6 ::1
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${toString (map (server: "server " + server + " iburst\n") cfg.servers)}
'';
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ntpFlags = "-c ${configFile} -u ${ntpUser}:nogroup ${toString cfg.extraFlags}";
in
{
###### interface
options = {
services.ntp = {
enable = mkOption {
default = false;
description = ''
Whether to synchronise your machine's time using ntpd, as a peer in
the NTP network.
</para>
<para>
Disables <literal>systemd.timesyncd</literal> if enabled.
'';
};
restrictDefault = mkOption {
type = types.listOf types.str;
description = ''
The restriction flags to be set by default.
</para>
<para>
The default flags prevent external hosts from using ntpd as a DDoS
reflector, setting system time, and querying OS/ntpd version. As
recommended in section 6.5.1.1.3, answer "No" of
http://support.ntp.org/bin/view/Support/AccessRestrictions
'';
default = [ "limited" "kod" "nomodify" "notrap" "noquery" "nopeer" ];
};
restrictSource = mkOption {
type = types.listOf types.str;
description = ''
The restriction flags to be set on source.
</para>
<para>
The default flags allow peers to be added by ntpd from configured
pool(s), but not by other means.
'';
default = [ "limited" "kod" "nomodify" "notrap" "noquery" ];
};
servers = mkOption {
default = config.networking.timeServers;
description = ''
The set of NTP servers from which to synchronise.
'';
};
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extraFlags = mkOption {
type = types.listOf types.str;
description = "Extra flags passed to the ntpd command.";
example = literalExample ''[ "--interface=eth0" ]'';
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default = [];
};
};
};
###### implementation
config = mkIf config.services.ntp.enable {
# Make tools such as ntpq available in the system path.
environment.systemPackages = [ pkgs.ntp ];
services.timesyncd.enable = mkForce false;
systemd.services.systemd-timedated.environment = { SYSTEMD_TIMEDATED_NTP_SERVICES = "ntpd.service"; };
users.users = singleton
{ name = ntpUser;
uid = config.ids.uids.ntp;
description = "NTP daemon user";
home = stateDir;
};
systemd.services.ntpd =
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{ description = "NTP Daemon";
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wantedBy = [ "multi-user.target" ];
wants = [ "time-sync.target" ];
before = [ "time-sync.target" ];
preStart =
''
mkdir -m 0755 -p ${stateDir}
chown ${ntpUser} ${stateDir}
'';
serviceConfig = {
ExecStart = "@${ntp}/bin/ntpd ntpd -g ${ntpFlags}";
Type = "forking";
};
};
};
}