Timezone issues -- Daylight savings

filosophizer · December 19, 2016, 6:36am

Hello,

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

 cat /etc/environment | grep TZ
TZ=CST6CDT

Now looking at date:

root@test8:/>date
Tue Dec 20 05:34:45 CST 2016

How can I make it from CST to CDT ?

thanks

agent.kgb · December 19, 2016, 7:30am

a little bit waiting (till summer 2017) would help, I think

Daylight saving time - Wikipedia

filosophizer · December 19, 2016, 8:09am

thanks agent.kgb,

but i need to change it to CDT for some testing with oracle EM, any help will be appreciated

rbatte1 · December 19, 2016, 8:43am

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 ;))

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

Kind regards,
Robin

filosophizer · December 20, 2016, 7:47am

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

DST for UNIX
IBM AIX
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.5.3.0.51. This APAR is also included in level 5300-05-05.
APAR IY91985 for AIX 5.2. This will provide fileset bos.rte.date.5.2.0.41.
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.

Question:
CST6CDT (POSIX) and America/Chicago (Olson)

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

bakunin · December 20, 2016, 9:27am

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.

bakunin