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Timezone issues -- Daylight savings

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Operating Systems AIX Timezone issues -- Daylight savings
# 1  
Old 12-19-2016
Timezone issues -- Daylight savings


I like to set the CDT timezone, but it shows CST still even after I activated the DayLight Time

 cat /etc/environment | grep TZ

Now looking at date:

Tue Dec 20 05:34:45 CST 2016

How can I make it from CST to CDT ?

# 2  
Old 12-19-2016
a little bit waiting (till summer 2017) would help, I think ;-)

Daylight saving time - Wikipedia
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# 3  
Old 12-19-2016
thanks agent.kgb,

but i need to change it to CDT for some testing with oracle EM, any help will be appreciated
# 4  
Old 12-19-2016
You would need to change the date of the server for this to be effective. Setting the system clock to April 2017 would do the trick, but that might have unwanted impact. Additionally you would need to check if an NTP sync is run at any point (usually boot, but potentially elsewhere) as that could set the system clock back the real time (let's not get into the philosophical debate about whether time is real though Smilie)

Would this help? If not, can you explain why this would be a problem?

Kind regards,
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# 5  
Old 12-20-2016
There is a difference in timezone setting in AIX 5.3 vs AIX 6.1

For AIX 5.3, if you are using timezone with daylight savings then you would need to enable it, and also you need to apply the apar for it
There are two methods to make the AIX Unix operating system change to Daylight Savings Time on the new dates. The patches change the default dates, and the TZ variable, if set, overrides whatever the default dates are. You may use either method by itself. and doing both will not cause a conflict.
Apply correcting APARs from IBM for the latest supported versions
Modify the TZ variable in the /etc/environment file.
Either method requires a system reboot prior to March 11, 2007 to take effect.
Note that all of the patches mentioned in this section can be applied at once to AIX by updating to level 5300-05-05.

The TZ variable method might be preferable where you do not want to change or update anything else; you just want to fix the Daylight Time change dates. Setting the TZ environment variable should be regarded as a temporary measure until more permanent patches can be installed. Both methods are described on these IBM web pages:

AIX O/S updated to support 2007 Daylight Saving Time change
IBM AIX: Managing the Time Zone Variable
AIX also contains time zone information in directory /usr/share/lib/zoneinfo which is used only by the zdump command. This information is not used by any other parts of the system itself, though it is used by the MySQL database system, and possibly other application programs. The following IBM APARs address these Unix Zoneinfo data files to insure that the zdump command will return correct output:

APAR IY91662 for AIX 5.3. This will provide fileset bos.rte.date. This APAR is also included in level 5300-05-05.
APAR IY91985 for AIX 5.2. This will provide fileset bos.rte.date.
The zdump command and the /usr/share/lib/zoneinfo data did not exist in AIX prior to 5.2.
Be sure not to ignore the additional issues in IBM Java, described here:
Changes to Daylight Saving Time will affect IBM Java and AIX
AIX 6.1 takes the daylight timings automatically, when the date comes for time backward/forward, it does it automatically, see zdump
so there is no setting to turn on or turn off the DST in AIX 6.1 and higher.

CST6CDT (POSIX) and America/Chicago (Olson)

I have read both are same timezones, so what difference does it make ?

Each of the following examples shows the three different ways that the four American time zones can be specified:
America/New York or EST or EST5EDT
America/Chicago or CST or CST6CDT
America/Denver or MST or MST7MDT
America/Los_Angeles or PST or PST8PDT

For parts of the Unites States that do not observe daylight savings time or have different daylight savings time rules, specify the appropriate "America/City" selection, for example:
America/Indianapolis for those parts of the state of Indiana that are in the Eastern Time Zone.
America/Phoenix is used for the entire state of Arizona, which does not observe any daylight savings time.
# 6  
Old 12-20-2016
Originally Posted by filosophizer
CST6CDT (POSIX) and America/Chicago (Olson)

I have read both are same timezones, so what difference does it make?
Counter question: what is the difference between "17 (octal)" and "15 (decimal)" and "F (hex)"?

POSIX and Olson are two ways of describing a timezone. Olson does so by using a list of definitions and specifiyng a certain entry in that list. POSIX achieves the same in a slightly different way (see the Open Groups website for details).

Every timezone definition contains the following information:

1) an offset to GMT (or UTC, which is basically the same)
2) an amount of time (in hours) to correct this basic offset during the daylight savings period
3) a starting- and ending date (and time) for this DST period

In this regard, Olson and POSIX do the same. Olson just has a directory of such definitions, so that i.e. "Europe/Vienna" means GMT-1, a daylight savings adjustment of 1 hour and a DST period from the third(?) Sunday of March, 2:00 am until last Sunday in October, 3:00 am. When you specify "Europe/Vienna" then the driver looks this information up in the directory and sets the time accordingly. If you specify the TZ specification manually (the POSIX way) it uses that.

I hope this helps.

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