I use Redhat system , I found that when the system is reboot , the system will sync the bios time to system time , I just would like to ask if this is a system default setting ? is it good practice to disable this function ? if yes , how to do disable it ?

thx

Yes, it is the default setting and really not a good idea to disable the function. Without the hardware clock the system clock would initialize to 00:00:00 01 Jan 1970 at boot up. Assuming you are running NTP it still takes several minutes to sync so your log files will have time jumps which may or may not be a big deal but is necessary if your using any sort of authentication requests. It will mess up file timestamps which again may or may not be a big deal.

So why do you want to disable it?

thanks your explaination,

the reason for I want to disable it is the hardware clock is always incorrect , it always run faster than normal , I tried contact the hardware vendor , but they can not provide the solution unless replace the hardware . as your explaination , you said it will changed to 00:00 after reboot , how can I disable it so that the server keep current time rather than changed to 00:00 ?

thanks.

Is the hardware clock off by hours and how much does it drift? BIOS hardware clocks tends to drift for various reasons and is normal. If it drifts a lot it could be due to the BIOS battery needing to be replaced or as suggested bad hardware.

Running NTP will keep the hardware clock synched to the system clock and will attempt to compensate for its drift rate. Typically if the hardware clock is incorrect by hours the OS is configured to think it is set at UTC rather then local time. At stated without the hardware clock the system clock will start at 00:00 1 Jan 1970 by default when the computer is first turned on. When NTP synches if running it will force the system clock to the current time but as stated will mess up the log files which may or may not be an issue. The only thing that would keep the current time when the computer is off would be a replacement PCI hardware clock card.

thanks for reply ,

If I just what to disable the sync time process , that mean the OS ( redhat ) do not sync the hardware time when reboot , is it good way to fix it ? if yes , how to do it ?

Thanks

You might want to check if the BIOS button battery needs replacing.

BIOS button battery ?? the auto sync is not set by redhat ? it is releted to the battery?

thanks.

sync hardware code is default setting of redhat server ? is it practical ? thx

Yes, on most computer motherboards the BIOS clock etc. are maintained by a small round watch-battery which is usually quite easily spotted.

NTP can handle "clock drift" and can periodically readjust the clock, but significant drift is abnormal and often indicates that the battery's running out of juice.

thanks reply,

As my previous question , is it good to disable the function of sync hardware clock to OS ? if yes , an advise how to do it ?

Thanks.

From post #2 in this thread:
So again..NO, it is not a good idea to do it. Again, check the battery on your motherboard. You can also use hwclock...read the man page for it.

thanks reply ,

I just would like to ask why it is not good to disable the function ? why not let the server use its own time clock ? As your recommendation , I think it is not related to battery , the hardware clock is correct , my current problem is the hardware clock is GMT , but my system is BST , the time is different , so I want to disable the sync function

Therefore , I want to disable the function.

Thanks.

Because hardware clocks are inaccurate and drift badly, that's why. If you don't believe us here, go look it up.
So do what you want...why bother asking if it's a good idea or not, when you've clearly decided what you want to do?

AGAIN, look at the hwclock function, which sets the hardware clock to NTP (and NTP *IS* accurate). Or, amazingly, you can go into BIOS and pick whatever time zone you want. Read the man pages on hwclock, do some research on WHY this is a bad idea (since you don't believe us), and if you want to do it anyway, go right ahead.

You need to tell the OS that the hardware clock is set to UTC. Modify or add a line UTC=true to the /etc/sysconfig/clock file.

As stated the system clock will start at 00:00:00 01 Jan 1970 until the ntp daemon starts and sets it. So what ever process starts before ntp its logs will be the wrong date and time. You could get fsck errors of mount time in the future which might cause some problems.

As stated go ahead and disable the system clock from being synched and see what happens. Look in the start up scripts for hwclock --hctosys and comment out the line.

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