======Raspberry Pi NTP Server======
This article shows how to use a Raspberry Pi on Ubuntu Mate with a real time clock to create a NTP server.

https://thepihut.com/products/adafruit-pirtc-pcf8523-real-time-clock-for-raspberry-pi

=====Configure Clock=====
  - Power Off Raspberry Pi
  - Install PFC8523 on I/O Pins and install the battery
  - Power Up Raspberry Pi
  - After login run ''sudo raspi-config'' and enable i2c interface
  - Edit ''/boot/config.txt'' and add the following to the end of the file''dtoverlay=i2c-rtc,pcf8523''
  - After updating the ''/boot/config.txt'', reboot the Raspberry Pi
  - Manually set the data/time on the Raspberry Pi, then use <code>hwclock --systohc</code> to set the time on the pfc8523
  - Confirm the pfc8523 is working correctly by using <code>hwclock --show</code>


=====Configure Sync=====
In order to get the Raspberry Pi to read the RTC and keep the pfc8523 correctly synchronised follow the instructions below

Edit the file ''/etc/systemd/timesyncd.conf'' with the following entries:
<code>[Time]
  NTP=0.europe.pool.ntp.org 1.europe.pool.ntp.org 2.europe.pool.ntp.org 3.europe.pool.ntp.org
  FallbackNTP=0.europe.pool.ntp.org 1.europe.pool.ntp.org 2.europe.pool.ntp.org 3.europe.pool.ntp.org</code>
Update the file ''/etc/rc.local'' by adding the following lines:
<code>[ ! -e /var/lib/systemd/clock -a "`systemctl is-active systemd-timesyncd | grep -i active`" ] && timedatectl set-ntp 1 > /dev/null 2>&1</code>
Create a file ''/etc/systemd/system/hwclock-sync.service'' with the following contents:
<code>[Unit]
  Description=Time Synchronisation from RTC Source
  After=systemd-modules-load.service
  RequiresMountsFor=/dev/rtc
  Conflicts=shutdown.target
  [Service]
  Type=oneshot
  ExecStart=/sbin/hwclock -s
  TimeoutSec=0
  [Install]
  WantedBy=time-sync.target</code>
Now we need to shutdown and disable services for ''ntp'' and ''fake-hwclock'' and remove the corresponding packages that come by default with the OS by executing the following set of commands on the "root" shell prompt:
<code>systemctl stop fake-hwclock</code>
<code>systemctl disable fake-hwclock prefer-timesyncd.service systemd-timedated.service</code>
<code>apt-get -y remove fake-hwclock</code>
To finally enable the automatic start-up of the RTC synchonrisation during bootup using the ''systemd-timesyncd'' service, execute the following commands on the shell prompt:
<code>systemctl enable hwclock-sync systemd-timesyncd</code>
<code>systemctl start hwclock-sync systemd-timesyncd</code>

=====Install NTP=====
<code>apt-get install ntp</code>
Edit ''/etc/ntp.conf''
<code>server 0.europe.pool.ntp.org
  server 1.europe.pool.ntp.org
  server 2.europe.pool.ntp.org
  server 3.europe.pool.ntp.org</code>
Run the following commands to activate ntp
<code>sudo systemctl enable ntp</code>
<code>sudo systemctl start ntp</code>
After five minutes, run ''ntpq'' and use the command peers to show the clocks ntp is synchronised with
<code>ntpq> peers</code>
<code>ntpq> exit</code>
Now verify correct operation by using the <code>timedatectl</code> command to obtain results similar to below
<code>Local time: Sun 2017-10-15 12:13:55 BST
  Universal time: Sun 2017-10-15 11:13:55 UTC
  RTC time: Sun 2017-10-15 11:13:55
  Time zone: Europe/London (BST, +0100)
  Network time on: yes
  NTP synchronized: yes
  RTC in local TZ: no</code>