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NTP configuration with Elemental​

Overview​

The default OS channel shipped with Elemental provides NTP support via systemd-timesyncd.

This page covers configuring systemd-timesyncd with the provided SLE Micro images, which is pre-configured with some default (fallback) NTP servers: ([0-3].suse.pool.ntp.org).

The easiest way to configure a specific NTP server, is to drop a configuration file in the /etc/systemd/timesyncd.conf.d directory. The directory and the configuration file should be accessible by the systemd-timesync user.

Configure a static NTP server​

The NTP configuration can be provided via a cloud-config snippet added to the MachineRegistration configuration.

We will need to:

  • ensure the timesyncd.conf.d directory can be read by the systemd-timesync user
  • write the custom config file in the timesyncd.conf.d directory
  • restart the systemd-timesyncd service to use the new configuration

As an example, let's see how to configure ntp.ripe.net as the primary NTP server (lines 6-14):

config:
  cloud-config:
    users:
      - name: root
        passwd: root
    write_files:
      - content: |
          [Time]
          NTP=ntp.ripe.net
        path: /etc/systemd/timesyncd.conf.d/custom-ntp.conf
        permissions: 644
    runcmd:
      - chmod 755 /etc/systemd/timesyncd.conf.d
      - systemctl restart systemd-timesyncd
  elemental:
    install:
      device: /dev/vda
      reboot: true
machineInventoryLabels:
  element: fire

Configure NTP from DHCP​

In order to get the NTP server from the network via the NTP DHCP option, we need a NetworkManager dispatcher script to reconfigure dynamically the systemd-timesync service when needed.

We will have both to:

  • provide the dispatcher script which creates and deletes the systemd-timesyncd config files
  • enable the NetworkManager-dispatcher service

See lines 6-34 in the following MachineRegistration configuration example:

config:
  cloud-config:
    users:
      - name: root
        passwd: root
    write_files:
      - content: |
          #! /usr/bin/bash

          [ -n "$CONNECTION_UUID" ] || exit

          INTERFACE=$1
          ACTION=$2

          case $ACTION in
              up | dhcp4-change | dhcp6-change)
                  [ -n "$DHCP4_NTP_SERVERS" ] || exit
                  mkdir -p /etc/systemd/timesyncd.conf.d/
                  cat<<EOF > /etc/systemd/timesyncd.conf.d/$CONNECTION_UUID.conf
          [Time]
          NTP=$DHCP4_NTP_SERVERS
          RootDistanceMaxSec=15
          EOF
                  systemctl restart systemd-timesyncd
                  ;;
              down)
                  rm -f /etc/systemd/timesyncd.conf.d/$CONNECTION_UUID.conf
                  systemctl restart systemd-timesyncd
                  ;;
          esac
        path: /etc/NetworkManager/dispatcher.d/10-update-timesyncd
        permissions: 700
    runcmd:
      - systemctl enable NetworkManager-dispatcher
  elemental:
    install:
      device: /dev/vda
      reboot: true
machineInventoryLabels:
  element: fire