Messages in this thread | | | Date | Thu, 17 Nov 2005 08:52:14 +1100 | From | Eyal Lebedinsky <> | Subject | Re: hware clock left bad after a system failure |
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linux-os (Dick Johnson) wrote: > On Wed, 16 Nov 2005, Eyal Lebedinsky wrote: > > >>I recently had two cases where my machine locked up and needed >>a hard reset. The last time magic SysRq did not respond at all. >> >>In these cases I found that the hware clock was set incorrectly >>and the machine comes up with a bad date. It seems that the clock >>is ahead by as much as my TZ (+10 in my case). I may be able >>to understand if it was set 10h behind (kernel set it to UTC) >>but this is the other way. The machine comes up with UTC+20. >> >>Now this is just trouble. The machine comes up and spends 15m >>fscking. I then reset the clock and reboot and it does the whole >>fsck again because it thinks the fs was not checked for eons. It >>does not understand time in the future. >> >>So the points are >> >>- why is the clock mangled in this way? > > > I am assuming that you have an ix86 kind of machine. > > It's probably mangled because you had a hardware-crash. > > If you have a driver that accesses the RTC, it needs to leave > the index register at offset 0 so that a hardware crash can > only upset the seconds. Otherwise, even the RTC checksum > can get screwed up, forcing manual reconfiguration of the > BIOS. > > During a hardware-crash, the chip enables may go TRUE. This > means that an RTC write can occur with junk that's on the > data-bus. > > Now, you need to find out why you had a hardware-crash which > is quite unlike a software-crash. A hardware crash occurs when > you turn OFF the power or the power-good line from the > power-supply goes FALSE. You do not get a hardware-crash from > hitting the reset button. You may have induced the RTC failure > if you hit the power switch instead of the reset button.
I hit the reset. In one case I managed to reboot using magic SysRq.
The crashes are related to disk problems. In one case the hda/b controller went down (last message said DMA disabled on both) and in another case the system was doing a proper shutdown when it failed to complete and a reset was necessary. I suspect a problem with the SATA card which I know has some driver issues (promise SATA II 150 TX4).
The point of the post was the fact that the clock was not randomly set but clearly at +20h after the reboot. This was the case in the last two crashes. This is too coincidental and I suspect that some logic does play with the RTC and if a proper shutdown does not complete it may not be restored correctly.
-- Eyal Lebedinsky (eyal@eyal.emu.id.au) <http://samba.org/eyal/> attach .zip as .dat - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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