TZ ¶The geographical format names a time zone ruleset maintained by the Time Zone Database of time zone and daylight saving time information for most regions of the world. This public-domain database is maintained by a community of volunteers.
If the format’s characters begin with ‘/’ it is an absolute file name; otherwise the library looks for the file /usr/share/zoneinfo/characters. The zoneinfo directory contains data files describing time zone rulesets in many different parts of the world. The names represent major cities, with subdirectories for geographical areas; for example, America/New_York, Europe/London, Asia/Tokyo. These data files are installed by the system administrator, who also sets /etc/localtime to point to the data file for the local time zone ruleset.
If the file corresponding to characters cannot be read or has
invalid data, and characters are not in the proleptic format,
then the GNU C Library silently defaults to UTC. However, applications
should not depend on this, as TZ formats may be extended in the
future.