[ntp:questions] Re: NTP, Unix and the 34-year itch

Darren Dunham ddunham at redwood.taos.com
Mon Jan 26 16:47:10 UTC 2004


Thomas A. Horsley <tom.horsley at att.net> wrote:
>>I just learned that big time offsets can come in places least
>>expected. Twice over the last three weeks an otherwise well-behaved Sun
>>Netra X1 with Solaris 8 experienced a sudden change of its sytem time to
>>exactly 100 years into the past, to January 1904 (while it was running).

> The exactly 100 years part sounds suspiciously like some program
> somewhere is treating a tm_year field as though it is the year
> modulo 100 rather than the year - 1900 (of course, all the manic
> y2k code reviews were supposed to have fixed things like that :-).

I have seen two Sun/SPARC machines that eventually failed completely
(motherboard swap required) that had clock issues presage the total
failure.

Their clocks could not keep the correct time, but usually with some
integral year offset.  This led me to assume that something on the
motherboard held the time in a format other than UTC.  This is from
memory, but one of the bad machines acted something like this..

# date 1115142000 ; while [ 1 ] ; do date ; done
Wed Nov 15 14:20:00 PST 2000
Wed Nov 15 14:20:00 PST 2000
Wed Nov 15 14:20:00 PST 2000
Sun Nov 15 14:20:01 PST 1998
Sun Nov 15 14:20:01 PST 1998
Sun Nov 15 14:20:01 PST 1998
Sun Nov 15 14:20:01 PST 1998
Sun Nov 15 14:20:01 PST 1998
Sun Nov 15 14:20:02 PST 1998
Sun Nov 15 14:20:02 PST 1998
^C

The date would always "set", but one second later it would be bad.  I
recall this particular machine only had certain years that it couldn't
hold.  If I set it ahead to 2004, it held, but dates between 2000 and
2003 did not.

The next day it didn't boot, the MB was swapped, and the clock was
fixed.  I wonder if the time on the MB is kept in some sort of BCD
format that a one bit error could cause a 100 year slew...

-- 
Darren Dunham                                           ddunham at taos.com
Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
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