/etc/TIMEZONE will have little effect on the system while it is running. This file (along with other config files in /etc) are sourced (executed in place) by /etc/rc.config, a script that starts all processes as the system boots. The inherited value of $TZ for all automatically-stated procsses will be unaffected if the TIMEZONE file is changed without a reboot.
The kernel parameters: timezone and dst should always be changed to match your local time. When $TZ is not inherited (special daemons or background processes), then exec calls to time routines will use the kernel parameters to select the time representation. Here is a quick review of time on HP-UX:
Time in Unix is always maintained as UTC or Zulu time. That's what the internal clock maintains. It makes perfect sense since this is the only universally recognized time reference. All other time zones very poor definitions of what is essentially an astronomic definition. Timezones follow political boundaries, not solar references.
And to make things worse, Daylight savings time is completely uncoordinated even in the U.S. and thus, Unix addresses the issue with the (in?)famous /usr/lib/tztab file. The good news is that you can edit it and create any timezone you like with any DST values you'd like, even rules that change from year to year.
Unix is unique in that any user can log in remotely from any location on earth, set the value of $TZ to the local timezone and from then on, all date and time references will be accurate for the local timezone. This includes daylight savings time. The Unix clock *never* skips forward or backward--only the interpretation changes based on the value on $TZ in the environment. This means that a database that uses a date stamp will obtain it's date stamp after being filtered by $TZ and the tztab rules. While the time will seem to jump, it is just the interpretation of Zulu/UTC time in that timezone.
The key is /etc/TIMEZONE where the current value of the tztab entry is kept for the host system. When the system starts, the script:
/etc/rc.config
is run and sources (executes locally) all the scripts in /etc/rc.config.d and also sources /etc/TIMEZONE. This sets all the ENV variables used by the startup scripts. Thus, when a network service such as inetd is started, it inherits the current values listed in /etc/TIMEZONE and so do the child processes of inetd.
One additional note: Some background processes may not inherit a $TZ value (for example, certain daemons, cronjobs, etc) and in this case, the kernel parameters timezone and dst need to be set for the local timezone. This is a less precise method as dst only has 6 formats but at least there will be a known timezone value for the date/time routines in these unique cases.
Bill Hassell, sysadmin
