Determining daylight savings changes on BSD

[Jerry McAllister]

On Fri, Feb 02, 2007 at 01:18:14PM -0600, Dan Nelson wrote:

> In the last episode (Feb 02), Jerry McAllister said:
> > On Fri, Feb 02, 2007 at 10:36:37AM -0600, Dan Nelson wrote:
> > > In the last episode (Feb 02), Robert Fitzpatrick said:
> > 
 <some deleted>

> > I don't know how to read this.  There was another command I saw a while
> > back that gave similar looking information, but actually put out something
> > for 2007.   But, I can't find that mesage at the moment.
> > 
> > > That means you need to update your zoneinfo tables.  You can also use
> > > the date command to see if you need updating:
> > > 
> > > date -r 1173679260
> > > 
> > > If that prints "Mon Mar 12 02:01:00 EST 2007" you know you need to
> > > update.
> > 
> > Are you sure?   I see the EST where mine says EDT, but mine gives the
> > exact same date/time information as you show above outside of the EST.
> > 
> > If I subtract out exactly one day (86400 seconds) I get:
> >   Sun Mar 11 01:01:00 EST 2007    which is just 59 minutes before
> > the changeover.
> > 
> > Then, if I add an hour (3600 seconds) I get:
> >   Sun Mar 11 03:01:00 EDT 2007
> 
> So you're saying that for dates on March 11 after 2AM, you get EDT, but
> on March 12 it's back to EST?  That doesn't make sense :)  I get:

No.  For March 12 I get what I expect - EDT.

> 
> $ TZ=America/New_York ; export TZ
> $ date -r 1173592860
> Sun Mar 11 01:01:00 EST 2007
> $ date -r 1173596460
> Sun Mar 11 03:01:00 EDT 2007
> $ date -r 1173679260
> Mon Mar 12 02:01:00 EDT 2007
> $ 

Yes, that is exactly what I get and that seems right to me.
I was just questioning the one first posted above that was:
  date -r 1173679260            resulting in:
  Mon Mar 12 02:01:00 EST 2007
That would be the EDT figures, except it is labeled EST
But, if it was really EST (and thus need the zonefile updated)
I thought it would say:
  Mon Mar 12 01:01:00 EST 2007
> 
> > So, I would expect the non-updated system to give:
> >   Mon Mar 12 01:01:00 EST 2007
> 
> Yes, that's what a system without the updated zoneinfo should print, I
> think.

OK.   So the earlier post must have been a typo.

////jerry

>  
> > Or is something else really messed up?
> > My system seems to be giving the correct current date/time.
> 
> -- 
> 	Dan Nelson
> 	dnelson at allantgroup.com