On Tuesday, 11/29/2016 at 08:56 GMT, Aria Bamdad <a...@bsc.gwu.edu> wrote: > When you say the virtual TOD is on UTC, do you mean that even if I IPL > z/VM using > the local time and timezone, the TOD reported to Linux is in UTC? > Then this means > regardless of what z/VM time is set to, the guests always see UTC as > the TOD time.
Unless you use CP SET VTOD command or the guest issues a SET CLOCK or PERFORM TIMING FACILITY FUNCTION instruction to change the virtual TOD, the virtual TOD will match the LPAR TOD. Further, the LPAR TOD will match the machine TOD. I'm over-simplifying, but it's good enough for our discussion. > Based on the above, I tested setting the correct region, and then > selected 'Hardware > clock set to UTC' in Yast and rebooted. Sure enough, the time in > Linux shows my local > time correctly. > > So does this mean that regardless of what z/VM time is set to, the > Linux guests should > select their time as 'Hardware clock set to UTC'? Before Linux can correctly calculate the time, it needs to know how the (virtual) TOD clock is set. Some people (unwisely) set the TOD clock to the local time instead of UTC by setting local time with offset 0 (gag). But most people set the TOD clock to UTC (ignoring leap seconds). > Is the kernel parameter clocksource=tod needed? I don't think so, but I'm not sure. A long time ago the timer support in Linux was changed to use the TOD rather than depending on a ticking software clock. (Martin?) Alan Altmark Senior Managing z/VM and Linux Consultant Lab Services System z Delivery Practice IBM Systems & Technology Group ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 alan_altm...@us.ibm.com IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
