WTF with my computer clock?

You might also dig a little deeper into the support site for your machine and see if there isn't a workaround or update.

My machine is switched off when not in use. The prog which synchronises the machine time to the network runs at boot. It also tells you what it's done. And perhaps a couple of times a week it adjusts the time by a few seconds. So the internal clock is near as accurate as an ordinary quartz battery one. I'm not quite sure just when it would matter if the internal clock was a few seconds out anyway.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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This thread reminds me of an old Columbo movie. As I recall, the murderer had reset his PC clock so that certain data would be erroneously timestamped while his PC was used during his absence -- thus providing his alibi later. I don't recall how Columbo realized this bit of trickery had taken place, but, being Columbo, he did. Nowadays, the culprit would need to remember to also keep the machine from syncing with online time servers!

Not particularly helpful to the OP, just throwing it out there as an amusing tangent.

More on point, I have an old W2K machine -- Abit KT-7 RAID mobo that I had to recap -- that loses about 10mins every couple weeks. It isn't a "mission-critical" machine and isn't online often, but I don't mind occasionally resetting its clock.

Once a week I run a cron program that streamrips a radio program. I want to get the start of the program [prairie home companion]. At 20 minutes a day time loss, I have to sync the time just before I want to start recording. So far I have set two additional cron jobs, one at the start of the particular day, then one 15 minutes before the program begins. It is like using a sledge hammer for everything I do.

Plenty of goop to read regarding speific linux kernel modules flubbing up real time clock updates. Should have mentioned an OS in the first place.

Me too. Have a look at man hwclock.

Maybe running hwclock -r to resync the system time to the CMOS (RTC) clock every so often as a cron job would suffice. hwclock does tweaking to counter long-term drift in the RTC. Not as spiffy as syncing with a time server, but no internet connection needed.

Bryce

Beatnik internet clock

JR

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That just jams the clock to the correct time once in a while. In between those times the clock still runs at the same rate it always did, which is not correct.

What the NTP process does is essentially to monitor the local clock compared to a reference to understand just what its errors are, and synthesize a "perfect" clock from it. The synthesized clock can remain within a few microseconds (or better) of a reference timekeeper all the time.

Isaac

If you're just an ordinary user, it probably doesn't. If you are the telephone company, or a television broadcaster, though, things really do work a lot better when the digital signals carried by your network all are at precisely the same bitrate, no matter where they come from.

A GPS receiver feeding a UNIX box running NTP can give you a local timebase accurate to about one part in ten (American) billions.

Isaac

Indeed.

Right. At one time TV stations etc had their own accurate pulse generator referenced to the national standard. Here in the UK it was IIRC from the National Physics Laboratory.

But I suppose things move on. ;-)

Trouble is for most is just how accurate is the NTP time from your ISP?

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Maybe that works if you leave the computer on all the time. I started the ntpd daemon early in the morning and by late afternoon the time was, once again, way the hell off. Since I only care one time, one day a week what the time is I have set up crontab entries to do the job.

On 8/13/2009 4:58 AM root spake thus:

I see the problem, that seems to have been missed by those suggesting a software kluge that periodically stuffs the clock with the right value.

Here's an idea I haven't seen in this thread yet: If you're really interested in getting to the bottom of this problem, how about trying to determine whether it's the actual clock (RTCC hardware) that's off, or whether the OS is missing interrupts or there's some other software problem?

How about booting the computah under some other OS, say Windoze or even DOS, and running a utility that checks the RTCC for accuracy? (Don't know of any, but I'm ass-uming that there are lots of such utilities out there. Maybe there's even one for Linux.) That way you could know whether the clock needs to be tweaked (new crystal as suggested by others), or whether it's an OS problem.

Just an idea.

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I suggested booting Hiren's a few days ago. Also the OP could just boot into the CMOS setup and watch the clock there. Haven't needed to test any RTC hardware here seeing how SNTP has been around since the mid 80's and is among one of the oldest network protocols. Personal computer clocks are notoriously inaccurate, always have been. SNTP was developed for the needs of networked servers where precision time keeping was desired. SNTP daemons have been built into Windows OS for nearly a decade.

I reckon that TV companies must now use these laptops with very rough RTCs ! Have you noticed that now programme material is not networked from one region into some or all of the others, and adverts are no longer 'local', there is not any need for accurate cueing points around the network, so advertised starting times are not even nodded at ? I checked the starting times of about half a dozen programmes tonight, using the teletext clock, which I believe to be accurate, and not a single one started within 1 minute of the correct time, and a couple of them were off by several minutes. Just another manifestation of declining standards throughout the civilised world ... :-\\

Arfa

At least some of that starting-time error seems to be a deliberate policy by the stations/networks. By de-synchronizing a network's start times from those of its competitors, the network can make channel-surfing less attractive to the viewer... by the time you finish watching a show on that network, the shows on the other networks have already started and you'd miss something by surfing away.

It's a frightful bother who use DVRs and VCRs to time-shift programs... losing the first or last minute of a show is quite common.

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It doesn't come "from" my ISP; more like "through" it. And if I have a decent NTP client setup, my computer's clock (not the hardware, but the software one the OS provides to applications) will run at *precisely* the correct rate in the long term (the longer the term, the greater the precision), and will provide the proper epoch within a couple of microseconds or so -- maybe better. The rate be very, very close for shorter intervals. The place where it will not do so well is with very short measures because the jitter may be a bit high compared to, say, a rubidium clock.

Isaac

That's not the place where television needs precise time; it involves the generation and dissemination of NTSC or PAL in the past, or MPEG multiplexes in the present, not the *content* carried by those signals.

There's pretty good reason to suspect that broadcasters purposely offset the starting times of their programs precisely to make it less desirable for you to change channels during the interval -- if you can never watch both the end of one program and the beginning of another, you're less likely to do it. Note that a lot of contemporary shows start directly with some dialog and action, while the title and intro follow on a bit later. You miss the first few seconds, you lose. Same with the ends of shows.

Isaac

And that is exactly what NTP expects/needs.

It's also necessary to have a means to couple the output of the disciplined clock to other apps that do things like run the clock on the screen. Honestly, I'm not familiar with that; I've only used NTP to synchronize things on embedded systems where we had control of all the processes.

I do know that it can take quite a while (few dozen hours??) of continuous operation before ntpd gets things figured out, and if the host goes offline or sleeps it's necessary to start all over again. If you read the man page, I think you'll see that there are ways to force a faster, less precise, synch.

For more than you (probably) ever wanted to know about it, google up RFC

1305 and RFC 1128b.

ISaac

As I said earlier, if the local clock (crystal, whatever) is free-running (not synced to a standard reference using e.g. ntpd), it

*will not* stay accurate because it *cannot* be running at precisely the proper rate all the time. No matter how often you set it. No matter how often you tweak that little capacitor (which is very likely *not there* to tweak in the first place. You can *never* get it "right on". The question is not whether it is ever "correct", but only how fast it diverges from "correct" whenever you stop messing with it. The brilliance and elegance of NTP is that it can take that crappy, imprecise, piece of temperature-sensitive quartz, and from it synthesize an amazingly precise timekeeper.

Isaac