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

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{ config, lib, pkgs, ... }:
with lib;
let
inherit (pkgs) chrony;
stateDir = "/var/lib/chrony";
keyFile = "/etc/chrony.keys";
cfg = config.services.chrony;
in
{
###### interface
options = {
services.chrony = {
enable = mkOption {
default = false;
description = ''
Whether to synchronise your machine's time using chrony.
Make sure you disable NTP if you enable this service.
'';
};
servers = mkOption {
default = config.services.ntp.servers;
description = ''
The set of NTP servers from which to synchronise.
'';
};
initstepslew = mkOption {
default = {
enabled = true;
threshold = 1000; # by default, same threshold as 'ntpd -g' (1000s)
servers = cfg.servers;
};
description = ''
Allow chronyd to make a rapid measurement of the system clock error at
boot time, and to correct the system clock by stepping before normal
operation begins.
'';
};
extraConfig = mkOption {
default = "";
description = ''
Extra configuration directives that should be added to
<literal>chrony.conf</literal>
'';
};
};
};
###### implementation
config = mkIf cfg.enable {
# Make chronyc available in the system path
environment.systemPackages = [ pkgs.chrony ];
environment.etc."chrony.conf".text =
''
${concatMapStringsSep "\n" (server: "server " + server) cfg.servers}
${optionalString
cfg.initstepslew.enabled
"initstepslew ${toString cfg.initstepslew.threshold} ${concatStringsSep " " cfg.initstepslew.servers}"
}
driftfile ${stateDir}/chrony.drift
keyfile ${keyFile}
generatecommandkey
${optionalString (!config.time.hardwareClockInLocalTime) "rtconutc"}
${cfg.extraConfig}
'';
users.extraGroups = singleton
{ name = "chrony";
gid = config.ids.gids.chrony;
};
users.extraUsers = singleton
{ name = "chrony";
uid = config.ids.uids.chrony;
group = "chrony";
description = "chrony daemon user";
home = stateDir;
};
systemd.services.ntpd.enable = mkForce false;
systemd.services.chronyd =
{ description = "chrony NTP daemon";
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wantedBy = [ "multi-user.target" ];
wants = [ "time-sync.target" ];
before = [ "time-sync.target" ];
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after = [ "network.target" ];
conflicts = [ "ntpd.service" "systemd-timesyncd.service" ];
path = [ pkgs.chrony ];
preStart =
''
mkdir -m 0755 -p ${stateDir}
touch ${keyFile}
chmod 0640 ${keyFile}
chown chrony:chrony ${stateDir} ${keyFile}
'';
serviceConfig =
{ ExecStart = "${pkgs.chrony}/bin/chronyd -n -m -u chrony";
};
};
};
}