[FreeBSD-Announce] Upcoming change in Daylight Savings Time

Ken Smith kensmith at cse.Buffalo.EDU
Sun Feb 25 06:01:25 UTC 2007

This message, hopfully, summarizes all the questions people may have
about the change affecting when Daylight Savings Time begins and ends
for various time zones which takes effect this year.

NOTE: Before you decide this message does not effect you please bear in
mind that the most critical file involved in all of this
is /etc/localtime.  That is the zoneinfo file your system will be using
to convert the native system time to the format appropriate for your
local time zone.  Typically that file gets installed at the point you
initially install your system and then never changed unless you change
it manually (typically using tzsetup(8)).  So if you have an older
system that you have been updating using the normal mechanism of
cvsup-ing to update /usr/src and then rebuilding the system from that
you will still have the /etc/localtime file that was put in place during
the initial install of the machine, not an updated one.  If you are in a
time zone that is effected by the new Daylight Savings Time rules and
you did not do an initial install from a release that had the correct
zoneinfo files in it you should probably re-run tzsetup(8) to
update /etc/localtime.

Of the branches that are currently being supported by the Security Team
RELENG_6_2 and RELENG_5_5 both have the correct zoneinfo files so they
are not effected.  RELENG_6_1 has the correct zoneinfo files for time
zones in the United States but incorrect zoneinfo files for some of the
other countries effected (e.g. Canada).  An Errata Notice to update the
zoneinfo files in RELENG_6_1 will be coming shortly.  The HEAD,
RELENG_6, and RELENG_5 development branches all have the correct
zoneinfo files.

If you are running a system that is not among the supported branches you
can still update your zoneinfo files by installing the misc/zoneinfo
port, and then running tzsetup(8).  This works just fine on, for
example, FreeBSD 4.11 systems.

Since it is such a frequently asked question...  Using an NTP server
will NOT automatically handle the change in Daylight Savings Time rules
for you.  You still need to worry about getting the zoneinfo files (in
particular /etc/localtime) updated.  NTP servers provide the exact same
value (based on UTC) no matter what time zone they're in, and the
FreeBSD kernel stores time internally based on UTC.  The zoneinfo files
get used to convert that internal format to what is appropriate for your
local time zone.  Incorrect (outdated) zoneinfo files will result in
that conversion done incorrectly.

                                                Ken Smith
- From there to here, from here to      |       kensmith at cse.buffalo.edu
  there, funny things are everywhere.   |
                      - Theodore Geisel |

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