Offhand, and a quick google search; I was unable to find the exact definition / specification for how time-zone data must be obtained rather than how it happens

Offhand, and a quick google search; I was unable to find the exact definition / specification for how time-zone data must be obtained rather than how it happens to conventionally be obtained. It is entirely reasonable that any of the following _might_ be valid behavior. * Simple but syscall heavy approach which re-reads the env, and possibly /etc/localtime each call and has no stability. (Results may mutate as other processes / threads change things.) * Same as above, then caches the decision result for some application specific reasonable time; which may be until the application exits. * The elsewhere mentioned stat / inotify approaches that only track updates to /etc/localtime (and ideally update the cached decision result when notified). All approaches seem valid. It's sort of like the hostname or any other system level configuration where a reboot may be a reasonable expectation for a complete update.