One thing to be aware of is that in Linux, the HW clock runs independently of the SW clock. The idea is that you are using a good time synch tool (like NTPD) which constantly updates the SW clock frequency keeping it in sync with the time server. This makes the SW clock a MUCH better time source than the HW clock of a typical PC since after settling down it will rarely drift more than a few milliseconds before being resynchronized.
The HW clock is SET from the SW clock at shutdown, and is used to set the initial value of the SW clock at bootup. The HW clock is used only as a cache for a reasonable approximation of the time, and after booting NTPD is expected to adjust for any HW clock drift while the OS was not running. The only way the two ever sync during normal operation (i.e. not in the context of a shutdown or bootup) is via the hwclock(8) command. So, unless you intervene manually the SW clock should not jump around between reboots, regardless of what the HW clock does. That's sort of a fundamental assumption in the kernel -- time is smooth. If you see timestamp jumps at reboots, the culprit is almost surely the NVRAM battery on the motherboard. Just a few days ago I saw this on a 5-year old system. I got a BIOS warning during a reboot and, curiously, the clock had reset itself to 00:00:00 *without changing the date* (i.e. the date was still correct). Let's say something similar happened to you. Your system wakes up and sets the (wrong) time from HW clock, then NTPD queries the servers and gets an offset that's too big. You should see a message in your system log about NTPD refusing to reset the clock. The other possibility is that the time server you are syncing to had a glitch and was sending out the wrong time. That's highly unlikely though, and assuming you query at least 3 servers, NTPD is smart enough to discard the outlier. You do have at least 3 servers in your NTPD config, right? Now, if you're seeing random time jumps without a reboot then something else is seriously broken. -- Jim Garrison ([email protected]) PGP Keys at http://www.jhmg.net RSA 0x04B73B7F DH 0x70738D88 _______________________________________________ PLUG mailing list [email protected] http://lists.pdxlinux.org/mailman/listinfo/plug
