It looks like I also missed to send this to the list... I wanted to double check how this works, so I made sure to verify this before it actually happens (thanks for SET VTOD)
I used SET VTOD to set the virtual machine offset to the system clock. In fact, I got it wrong several times because the VM system runs in another timezone than my Linux guest (the VM timezone is relevant because that is used to interpret the SET VTOD command). And I was waiting for something to happen at 02:00 until I realized it is at 03:00 that the clock is set back. :-) Here we go: CP Q TIMEZONE Zone Direction Offset Status UTC ---- 00.00.00 Inactive GMT ---- 00.00.00 Inactive EDT West 04.00.00 Active EST West 05.00.00 Inactive CP Q VTOD System TOD: 2004-10-29 10:09:45 (BC0A6E52443BB528) User TOD: 2004-10-30 19:45:30 (BC0C30E0855B657E) Delta: 0001C28E411FB056 On Linux, my /etc/localtime is a copy of /usr/share/zoneinfo/Europe/Amsterdam linux10:~ # for i in 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16; do date ; sleep 60 ; done Sun Oct 31 02:57:46 CEST 2004 Sun Oct 31 02:58:46 CEST 2004 Sun Oct 31 02:59:46 CEST 2004 Sun Oct 31 02:00:46 CET 2004 Sun Oct 31 02:01:46 CET 2004 Even the system logger knows how to deal with this: Oct 31 02:50:23 linux10 kernel: eth0: no IPv6 routers present Oct 31 02:50:23 linux10 sshd�606�: Accepted publickey for root from ::f Oct 31 02:59:01 linux10 /USR/SBIN/CRON�641�: (root) CMD ( rm -f /var/sp Oct 31 02:00:00 linux10 syslogd 1.4.1: restart. So the bottom line is: 1. The hardware TOD should run on UTC and does not need change with DST 2. The z/VM timezone defines the offset to UTC to obtain local time. Selecting a different timezone on z/VM is done by hand or through magic in the system configuration file 3. CP commands and some CMS things use local time from CP. Many services on z/VM don't care about the sudden time shift. 4. Linux uses STCK and gets the LPAR TOD clock which is not affected by the timezone on z/VM. It does not make a difference whether you IPL Linux or not. 5. Linux computes local time from the TOD using /etc/localtime and knows when to switch time zone. Many applications on Linux handle the sudden jump in local time nicely (either because it does not matter or because they record in UTC where it does matter). Too bad my presentation "Teaching Penguins to Tell Time" in Miami Beach is *after* the weekend of the time change :-) Rob PS It does not help you at all if you know how this works, you need to educate people too. I just got a note saying: "All [...] z/VM systems will be IPLed Monday morning between 6:00am and 8:00am EST for the time change." -- Rob van der Heij rvdheij @ gmail.com ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
