ETR- and STP-based clock synchronization

Your Linux instance might be part of an extended remote copy (XRC) setup that requires synchronization of the Linux time-of-day (TOD) clock with a timing network.

SUSE Linux Enterprise Server 12 SP4 for IBM Z supports external time reference (ETR) and system time protocol (STP) based TOD synchronization. ETR and STP work independently of one another. If both ETR and STP are enabled, Linux might use either to synchronize the clock.

For information about STP, see

www.ibm.com/systems/z/advantages/pso/stp.html

ETR requires at least one ETR unit that is connected to an external time source. For availability reasons, many installations use a second ETR unit. The ETR units correspond to two ETR ports on Linux. Always set both ports online if two ETR units are available.

Attention: Be sure that a reliable timing signal is available before enabling clock synchronization. With enabled clock synchronization, Linux expects regular timing signals and might stop indefinitely to wait for such signals if it does not receive them.