[asterisk-dev] CDR and daylight savings time

[Hans Petter Selasky]

On Monday 01 January 2007 16:08, Tilghman Lesher wrote:
> On Monday 01 January 2007 06:17, Hans Petter Selasky wrote:
> > On Monday 01 January 2007 04:07, Kevin P. Fleming wrote:
> > > Hans Petter Selasky wrote:
> > > > From examining the code, this seems to be the case:
> > > >
> > > >                 gettimeofday(&cdr->start, NULL);
> > > >                 gettimeofday(&cdr->answer, NULL);
> > > >                 gettimeofday(&cdr->end, NULL);
> > >
> > > If you had read the man page for gettimeofday(), you would not have
> > > asked this question :-)
> > >
> > > gettimeofday(), when passed NULL as the second parameter (which we
> > > always do and is recommended practice) returns the number of
> > > seconds/microseconds since the Unix 'epoch' (January 1, 1970). It does
> > > not care about timezones at all, and is not affected by timezones or
> > > time shifts. In other words, it returns absolute time, not local time.
>
> <snip>
>
> > Here you clearly see that gettimeofday() is directly connected with the
> > local time on the computer. On the other hand, CLOCK_MONOTONIC is not.
> > That is what you want to use. Or am I wrong ?
>
> The manpage for gettimeofday(2) returns this nugget, which is probably
> explains the problem on your system:
>
>        Under Linux there is some peculiar 'warp clock' semantics associated
> to the settimeofday system call if on the very first call (after  booting)
> that  has  a  non-NULL  tz  argument,  the  tv argument is NULL and the
> tz_minuteswest field is non-zero. In such a case it is assumed that the
> CMOS  clock is on local time, and that it has to be incremented by this
> amount to get UTC system time.  No doubt it is a bad idea to  use  this
> feature.
>
> No doubt when you set up your system, you opted to have the clock set to
> local time instead of UTC.  Systems which are set to dual boot with Windows
> typically have their clocks set to local time (because that's what Windows
> uses), while servers (which need not this weirdness) should have their
> hardware clocks set to UTC.

Your right. My system was not set to UTC. After a short trip into "sysinstall" 
the "Time Zone" is now set to UTC. Now I also see that "date" adjusts 
automatically on the 25th of March 2007, while "time()" does not increment by 
an hour. Thanks.

>
> It is further instructive that if you read the libc source to *BSD, you
> will find that time(3) is defined by calling gettimeofday(2) with a NULL
> second argument.

Ok.

--HPS