On Monday, 11/03/2003 at 09:27 EST, Eric Sammons <[EMAIL PROTECTED]> wrote: > I have started looking at standards, processes, and procedures for our to > be built z/Linux environment. I am currently interested in how folks are > performing time synchronization updates? Do the guests get their time > from VM / thus the system hardware, or is their clock some how managed at > a software level. I suppose the time is obtained from the LPAR of which > z/VM resides. If this is the case I would assume that z/VM is performing > time sync operations with a reliable source. And finally, if the time is > managed in this fashion are the linux guests continuously updated with the > correct time or is this a once at boot thing?
In general, on a single machine, all LPARs and virtual machines have clocks that are synchronized with the real hardware time-of-day (TOD) clock. If you are using a Sysplex Timer, it is capable of adjusting the real h/w TOD. If the adjustments are sufficiently small, the logical (LPAR) and virtual TOD are transparently "nudged" to the correct value. For large jumps, the clocks are not "driven," but an operating system can register to receive notification of a large change in the clock. z/OS does that. z/VM and Linux do not. (The correct time is picked up the next time the LPAR is deactivated/reactivated.) On z/VM there is a CP SET TOD that can adjust an individual guest's TOD, but there is no command to change CP's perception of time (except to change timezones). Alan Altmark Sr. Software Engineer IBM z/VM Development
