No info found about `ethtool -T` output?

Question

Nowhere I can find such info, to interpret the following number:

PTP Hardware Clock: 1

Most documentation I can find (e.g. from RedHat it shows 0). What does it mean?

Answer 1

-T --show-time-stamping

Show the device's time stamping capabilities and associated PTP hardware clock.

https://linux.die.net/man/8/ethtool

PTP stands for Precision Time Protocol that allows sub-microsecond synchronization to a network master clock.

Answer 2

This is normally output via running ethtool -T <ifname> and indicates the index of the PTP clock. If there are multiple hardware clocks in the system you will see increasing values for this. For example, if there are two suitable NICs in a server one can show:

PTP Hardware Clock: 2

and the other:

PTP Hardware Clock: 3

In my example I have two interfaces on the first NIC and if I run ethtool -T ... on either of them I will see the same index reported.

This index can also be used when browsing sysfs under /sys/class/ptp/ptp<index>. This will contain various files and directories that may be of use. If you're unsure what a PTP clock is you may wish to use the index to search:

strings /sys/class/ptp/ptp<index>/device/vpd

This will output various bits of information from the device's VPD such as the product name, e.g. "Broadcom NetXtreme Gigabit Ethernet" for a Broadcom network card.

Answer 3

PTP - Precision Time Protocol is a protocol used to synchronise clocks throughout a computer network. On a local area network, it achieves clock accuracy in the sub-microsecond range, making it suitable for measurement and control systems.

For a system to use PTP for clock synchronisation it requires a NIC that supports time stamping in the physical hardware.

As already answered that ethtool flag can be used to show if a NIC provides that required support:

-T --show-time-stamping

Show the device's time stamping capabilities and associated PTP hardware clock.