-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Monday, 2011-02-21 at 08:31 -0500, Patrick Shanahan wrote:
You really mean ntp docs rather than hwclock's. hwclock maintains a reference but ntp keeps that reference adjusted. And actually that is incorrect, the software clock keeps the reference and ntp keeps that adjusted and hwclock maintains the time when the computer is not running.
I'll write up another view of things :-) There are basically two clocks in a PC. One is mantained by the operating system, somehow (the "somehow" has varied during these years). It can run only while the system runs, obviously. There is another clock, in a cmos chip, that runs from a battery or from the main power, if available - so that it keeps the time while the computer is off. When the PC boots, "something" copies the cmos clock time to the system clock. That "something" can be the program hwclock. On boot it sets the system clock, and on halt it updates the cmos clock - rather, there is a suse script that does that, using hwclock. Then there are adjustements. The cmos clock drifts a constant value, that can be measured; as all quartz clocks, they are very stable, meaning they have an almost constant error. As it is a clock in a computer, the drift can be compensated: this is what the file /etc/adjtime is for. The calculated drift is added to the value read from the cmos clock, so that a corrected time is applied to the system clock. The system clock is different: its speed can be adjusted. The ntp daemon does that: it obtains a very accurate time from internet, then also adjusts the system clock making it go faster or slower till it runs as exact as it can be. But this requires a permanent internet connection (or a local GPS or other very reliable time source). So, another method of adjusting the system clock exists, by more or less manually adjusting its speed - if I recall correctly, by comparing to the cmos clock which has been previously corrected. This last method is what Istvan asked about, I think. - -- Cheers, Carlos E. R. (from 11.2 x86_64 "Emerald" at Telcontar) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.12 (GNU/Linux) iEYEARECAAYFAk1jDOMACgkQtTMYHG2NR9XImwCeI66Pw0xXWbladDhW4/Th2+Hp zNQAniAbuWS9MZmMLvqPRvVaKFkG/j0h =4/TG -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org