Here is the answer: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html https://www.gnu.org/software/libc/manual/html_node/TZ-Variab... The

Here is the answer: https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html https://www.gnu.org/software/libc/manual/html_node/TZ-Variab... The third format looks like this: :characters Each operating system interprets this format differently; in the GNU C Library, characters is the name of a file which describes the time zone. The other formats specify the timezone directly, such as EST+5EDT. Interestingly, it seems to work okay without the colon. Perhaps the leading slash implies a filename?