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The hosts synchronize the time with both NTP and PTP. This is done by the timemaster service during the network configuration section. (see see Network section section).
Three tools are used:

• chrony synchronize the system clock with NTP. The NTP server can be configured to be on the local network or on the internet.

• ptp4l synchronize the hardware clock (PHC) with PTP.

• phc2sys synchronize hardware and system clocks.

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• Load the kernel module ptp_kvm, either automatically at boot or manually.
  This will create the a ptp device in /dev/ptp0 device, which is the PTP clock. To determine which device is the one created by ptp_kvm, simply check that the file /sys/class/ptp/ptp*/clock_name does indeed say "KVM virtual PTP". 
  In this example, our ptp_kvm device is ptp0.

• Synchronize the system clock with the PTP clock.

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