How to change the system time zone

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Abstract

It may be necesary to change a HP-UX system timezone. Normally, this occured when system are rellocated to new geographical regions. There are to ways to change the system time zone.

The available timezone are define on "/usr/lib/tztab" file. The format of the entries is the following. 

0   3   1-7     4     1987-2038        0      UCT5
|   |    |      |         |            |       |> time zone description
|   |    |      |         |            |> day of week (0-6, 0=Sunday)
|   |    |      |         |> year (range)
|   |    |      |> month of year
|   |    |> day of month (range)
|   |> hour
|> minute

Using "set_parms timezone" command

# set_parms timezone

_______________________________________________________________________________

The following procedure enables you to set the time zone.
Select your location from the following list:

  1) North America or Hawaii

  2) Central America

  3) South America

  4) Europe

  5) Africa

  6) Asia

  7) Australia, New Zealand

  8) Russia / CIS
_______________________________________________________________________________


Enter the number for your location (1-7) then press [Enter] 2 


_______________________________________________________________________________

You have selected the time zone for all of Central America.
_______________________________________________________________________________

Is this correct?

Press [y] for yes or [n] for no, then press [Enter] y

_______________________________________________________________________________


Your changes will not take effect until you reboot the system.

_______________________________________________________________________________

Do you want to reboot now?

Press [y] for yes or [n] for no, then press [Enter] y

Editing timezone files

To change the system timezone, is necesary to change the contents of two files: /etc/default/tz and /etc/TIMEZONE. The timezone must match between in both files.

The "/etc/TIMEZONE" file is used by daemons that don't have TZ shell variable exported into their environment when they are started. The "/etc/default/tz" is used by processes that relay on the TZ shell variable to keep time tracking.

Example: 

# cat /etc/default/tz
MST7MDT

# cat /etc/TIMEZONE
#!/sbin/sh
# @(#)B.11.31_LR
TZ=MST7MDT
export TZ

Notes:

  • While it is not strictly required to reboot the system after modifying the rules in the /usr/lib/tztab file, running processes using a timezone with a changed rule need to be restarted to apply the new rules.
  • Processes like cron(1M), which depend on proper interpretation of timestamps in the future, must be restarted as soon as possible.
  • Processes that only timestamp messages, should be restarted before the changes take effect.
  • While it's teoretical possible to establish every individual processes that needs to be restartated, is good policy not to trust that every last one was discovered. The effects of missing a process restart could produce incorrect time stamps or time calculations in the data and applications. Is much better to schedule a maintenance window to reboot the system after changing the system timezone.

References

Tunable Kernel Parameters
http://www.docs.hp.com/hpux/pdf/TKP-90202.pdf

HP-UX Reference Release 11.0 System Calls and File Formats
http://www.docs.hp.com/hpux/pdf/B2355-90682.pdf
On page 795 tztab file is explained.


DST Changes for HP High Availability Products
http://docs.hp.com/en/9704/ACSL_DST_Summary.pdf


Authors

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