localtime - Man Page
Local timezone configuration file
/etc/localtime -> ../usr/share/zoneinfo/...
The /etc/localtime file configures the system-wide timezone of the local system that is used by applications for presentation to the user. It should be an absolute or relative symbolic link pointing to /usr/share/zoneinfo/, followed by a timezone identifier such as "Europe/Berlin" or "Etc/UTC". The resulting link should lead to the corresponding binary tzfile(5) timezone data for the configured timezone.
Because the timezone identifier is extracted from the symlink target name of /etc/localtime, this file may not be a normal file or hardlink.
If /etc/localtime is missing, the default "UTC" timezone is used.
The timezone may be overridden for individual programs by using the $TZ environment variable. See environ(7).
You may use timedatectl(1) to change the settings of this file from the command line during runtime. Use systemd-firstboot(1) to initialize the time zone on mounted (but not booted) system images.
systemd(1), tzset(3), localtime(3), timedatectl(1), systemd-timedated.service(8), systemd-firstboot(1)
systemd.directives(7), systemd-firstboot(1), systemd.index(7), systemd-timedated.service(8), systemd-timesyncd.service(8), timedatectl(1).