Ticking away…
The new time change is tomorrow night, and there is quite a bit of discussion about the change being detrimental to transaction-based and time-sensitive systems, mainly in databases.

The main thing to be sure of, though, is that your system itself will update the time correctly.

Mark posted about checking this by using

# zdump -v EST5EDT | grep 2007

The output should look exactly like this:

EST5EDT Sun Mar 11 06:59:59 2007 UTC = Sun Mar 11 01:59:59 2007 EST isdst=0 gmtoff=-18000
EST5EDT Sun Mar 11 07:00:00 2007 UTC = Sun Mar 11 03:00:00 2007 EDT isdst=1 gmtoff=-14400
EST5EDT Sun Nov 4 05:59:59 2007 UTC = Sun Nov 4 01:59:59 2007 EDT isdst=1 gmtoff=-14400
EST5EDT Sun Nov 4 06:00:00 2007 UTC = Sun Nov 4 01:00:00 2007 EST isdst=0 gmtoff=-18000

The zdump is going to open up the binary file where the daylight savings clock changes are kept…. mind you, that the example is checking the one for Eastern time… but if you have done the updates, this will have changed as well, so even if you are in another time zone, checking this one is fine. Piping the contents to the grep command is just for human sanity… we only need the lines that have to do with the year 2007.

The output we get shows the time getting updated in two steps when daylight saving starts, and again in two steps when it ends, first with an offset of -18000 seconds (5 hours) and the second, switching the “is it Daylight Saving Time?” flag to “yes” and issuing an offset of -14400 seconds (4 hours).

But think about your cron jobs… This is from the man page for cron on a linux box:

Note that this means that non-existent times, such as “missing hours” during daylight savings conversion, will never match, causing jobs scheduled during the “missing times” not to be run. Similarly, times that occur more than once (again, during daylight savings conversion) will cause matching jobs to be run twice.

and the same from a Solaris 10 enterprise server:

If some form of daylight savings or summer/winter time is in effect, then jobs scheduled during the switchover period could be executed once, twice, or not at all.

Just more things for you to double check. Ending up with no backup could be bad, but ending up with it done twice isn’t necessarily awful. You will need to check your specific jobs and decide if any changes are needed.