------------ Original Message ------------
> Date: Monday, March 30, 2015 20:04:56 +0100
> From: Lester Caine <lester@xxxxxxxxxxx>
>
> On 30/03/15 16:41, Larry Martell wrote:
>>>> The use case is that I have a server uptime reporting script
>>>> and it
>>>> >> uses a database of times that the server was able to be
>>>> >> pinged. If there is no entry for a period it indicated the
>>>> >> server was down. So on March 29, running in London, it found
>>>> >> no entries from 1am to 2am and it reported the server was
>>>> >> down for an hour, when in fact the period from 1am to 2am
>>>> >> did not exist because of the switch to summer time.
>>> >
>>> > If you are logging ANYTHING other than UTC then your reporting
>>> > system is the problem. You DISPLAY times using the local time,
>>> > and log everything using a clean UTC time.
>> I 100% agree with you, but this client does not do that. I have
>> told them they should, but they did not want to change.
>
> As Ryan says ... convert to UTC to do the check, but personally
> I'd be looking at why 1amGMT and 2amBST is reporting 2 hours
> rather than 1 hour. I've been through this many years ago now with
> clients who simply recorded the 'time'. Railway timetables never
> used to run over night at that time, but when they started,
> timetables got interesting ;) When the underlying process was
> switched to UTC and all of the hacks to get the correct running
> times were removed the objections were also removed.
>
> I presume that all you get from the database is '1am' or '2am', so
> you just need to add the missing offset information from the
> calendar. So you have 1amGMT and 2amBST to compare.
>
You can get the information you're after with "zdump -v" of the
zoneinfo file for a timezone, e.g.,
zdump -v GB | grep 2015
GB Sun Mar 29 00:59:59 2015 UTC = Sun Mar 29 00:59:59 2015 GMT
isdst=0 gmtoff=0
GB Sun Mar 29 01:00:00 2015 UTC = Sun Mar 29 02:00:00 2015 BST
isdst=1 gmtoff=3600
GB Sun Oct 25 00:59:59 2015 UTC = Sun Oct 25 01:59:59 2015 BST
isdst=1 gmtoff=3600
GB Sun Oct 25 01:00:00 2015 UTC = Sun Oct 25 01:00:00 2015 GMT
isdst=0 gmtoff=0
how you deal with it from there is up to you -- there are many
options I would think, including loading it into a DB that you
check. The system TZ files do change from time to time, as the local
rules change, so you'd need to manage for that.
- Richard
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