For the second question: There doesn't seem to be an explicit reason for the difference of treatment. The code that does it has been there since 1996, and hasn'

For the second question: There doesn't seem to be an explicit reason for the difference of treatment. The code that does it has been there since 1996, and hasn't changed since. The only reason given is "Caching happens based on the contents of the environment variable TZ.". https://sourceware.org/git/?p=glibc.git;a=commit;h=68dbb3a69e78e24a778c6602c8cc91d715839d08 https://sourceware.org/git/?p=glibc.git;a=commit;h=68dbb3a69... I'd argue it should cache the same when both old_tz and tz are NULL (but start with an old_tz that is not NULL). I was about to file an upstream bug, but found https://sourceware.org/bugzilla/show_bug.cgi?id=5184 https://sourceware.org/bugzilla/show_bug.cgi?id=5184 and https://sourceware.org/bugzilla/show_bug.cgi?id=5186 https://sourceware.org/bugzilla/show_bug.cgi?id=5186 The latter actually implies the opposite should be happening: files given in TZ should be stat()ed just as much as /etc/localtime.