This class tries the following methods of determining the local time zone, in the order listed here:
• $ENV{TZ}
It checks $ENV{TZ} for a valid time zone name.
• /etc/timezone
If this file exists, it is read and its contents are used as a time zone name.
Note that this file may be out of date on many systems, as modern distros may not do a good job of
updating this file. If you find that this file is not being updated, you may want to consider
deleting it so that one of the following methods can be used.
• /etc/localtime
If this file is a symlink to an Olson database time zone file (usually in /usr/share/zoneinfo) then
it uses the target file's path name to determine the time zone name. For example, if the path is
/usr/share/zoneinfo/America/Chicago, the time zone is "America/Chicago".
Some systems just copy the relevant file to /etc/localtime instead of making a symlink. In this
case, we look in /usr/share/zoneinfo for a file that has the same size and content as /etc/localtime
to determine the local time zone.
• /etc/TIMEZONE
If this file exists, it is opened and we look for a line starting like "TZ = ...". If this is found,
it should indicate a time zone name.
• /etc/sysconfig/clock
If this file exists, it is opened and we look for a line starting like "TIMEZONE = ..." or "ZONE =
...". If this is found, it should indicate a time zone name.
• /etc/default/init
If this file exists, it is opened and we look for a line starting like "TZ=...". If this is found, it
should indicate a time zone name.
Note: Some systems such as virtual machine boxes may lack any of these files. You can confirm that this
is case by running:
$ ls -l /etc/localtime/etc/timezone /etc/TIMEZONE \
/etc/sysconfig/clock /etc/default/init
If this is the case, then when checking for timezone handling you are likely to get an exception:
$ perl -wle 'use DateTime; DateTime->now( time_zone => "local" )'
Cannot determine local time zone
In that case, you should consult your system man pages for details on how to address that problem. In one
such case reported to us, a FreeBSD virtual machine had been built without any of these files. The user
was able to run the FreeBSD tzsetup utility. That installed /etc/localtime, after which the above
timezone diagnostic ran silently, i.e., without throwing an exception.