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 Forum index » House Training » Bugs ( Submit bugs )
Slacko not setting time right at summer's end
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Joined: 28 Dec 2009
Posts: 858

PostPosted: Tue 27 Nov 2012, 13:05    Post_subject:  

These show that my machine is set correctly to Europe/London ie GMT.
So it does not explain the discrepancy I reported initially.

It's good to know that your Puppy is back on the correct time.

Here's one possible explanation.

Your hardware clock ("rtc") is keeping local time. You probably have it set this way because you sometimes boot another operating system (such as Windows) that expects the hardware clock to give local time.

When Summer Time begins or ends, Linux will immediately adjust the clock displayed on your desktop and any other clocks based upon the software clock, but does not adjust the hardware clock. (The software clock is the clock that is used for everything except, obviously, setting itself at boot time, which is what the hardware clock is for.) So if you leave the PC powered-on during the night that the time shift occurs, it will display the new correct time when you awake the next day. It will continue to display the correct time until you shut it down or reboot.

If you or your other O.S. does not adjust the hardware clock before you next boot Puppy, when you eventually boot your Puppy and it sets the software clock based upon what it reads from the hardware clock, the time will be incorrect because the hardware clock is still incorrect.

When you next boot your other O.S., it checks to see when it was last run, sees that it hasn't been run since the time shift, and so it adjusts the hardware clock.

Then, when you next boot your Puppy, the hardware clock will be correct, and so the software clock will be set correctly.

So why doesn't Puppy adjust the hardware clock?

Have you ever risen the morning after a time shift, adjusted all of your various wall, floor, and shelf clocks, and sat down to a good breakfast, happy in the knowledge that your prompt actions have brought your household up to date again -- happy, that is, until you arrive at church an hour late and realize that your spouse was even more prompt that you, and reset all of the clocks before going to bed? That's why Puppy doesn't adjust the hardware clock. If it did, your other O.S. would adjust it a second time the next time it booted. (The same problem would likely happen if you booted two different installations of Windows -- one would have no way of knowing that the other had already reset the clock.)

Remember, keeping the hardware clock on local time is just for the convenience of the other operating system. A pure Linux PC has no need for this twice-yearly dance. Like other Unix-like systems, it can keep the hardware clock set to UTC year-round. (Getting the local time to display on your desktop and the timestamps for your files is, of course, a simple matter of mathematics for the PC -- I hear computers are good at that.) So if you ever retire your other O.S., you can set your hardware clock to UTC, tell all your Puppies that you did that, and not have to deal with that again.

Until you retire your other O.S., the best way to keep both it and Linux happy is probably to boot your other O.S. the morning after a time shift. That way the hardware clock gets reset, and your other O.S. knows that it has been reset, so won't try to set it again.

Some people use their other O.S. so rarely, that they set the hardware clock to UTC anyway, and get used to the fact that the other O.S. will then display the time and timestamps in UTC. This, of course, will only work if you can tell the other O.S. that it is using UTC, so that it won't keep trying to adjust the hardware clock for Summer Time. (I've heard rumors that newer versions of one O.S., Windows, can be told to keep the hardware clock in UTC and display the time and timestamps in local time (just like Linux always could). I've also heard rumors that that option is a bit buggy.)

On a side issue, I could not get the complete string of commands to run all at once; I had to enter them separately as above.

I don't know what would cause that. I just copied and pasted the line into a urxvt window and it ran OK on my Puppy (Slacko 5.3.3). I don't know what might be different on your system to prevent it from running. But, no matter; entering the commands individually achieved satisfactory results.
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Joined: 27 Oct 2011
Posts: 94
Location: Wales

PostPosted: Wed 28 Nov 2012, 05:46    Post_subject: (solved)Slacko not setting right time at Summer's end
Sub_title: OK now

Thanks npierce for your comprehensive explanation of factors affecting the correct setting of local and hardware clocks in Linux, Windows etc. Everything seems to be OK now. Many thanks.
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Joined: 28 Dec 2009
Posts: 858

PostPosted: Wed 28 Nov 2012, 08:34    Post_subject:  

You're welcome.
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