On 2024-12-10 03:31, Florian Weimer via tz wrote:
* Guy Harris via tz:
On Dec 7, 2024, at 9:15 PM, Mark Davis Ⓤ <[email protected]> wrote:
That is, the API is returning a value indicating that what you asked for
doesn't have a well-defined answer.
Then, presumably, all that is needed is a guarantee from the tzdb
maintainers that "Etc/Unknown" will never be assigned to a timezone.
Given that tzset() does not return a success/failure indication, and
that the 2024 Single UNIX Specification's page for taste() says
nothing about the behavior if TZ isn't set to a valid value (for some
definition of "valid"):
https://pubs.opengroup.org/onlinepubs/9799919799/functions/tzset.html
nor does the 2024 Single UNIX Specification page on environment
variables specify the the value of TZ in a fashion that permits all
possible values to be determined to be valid or invalid:
https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap08.html
the behavior after calling tzset() if TZ is set to Etc/Unknown isn't
specified anywhere, and it could be the same as the behavior if
tzset("This/Does/Not/Exist") is called on a system that just uses the
tzdb files, so there doesn't appear to be any need to put Etc/Unknown
into the database - a guarantee that Etc/Unknown will never be used
for any timezone in the tzdb should suffice
It's also not possible to detect on some POSIX-like systems (that use
the IANA database) whether the system administrator has used a specific
IANA identifier to configure the system. Applications only see the data
blob describing the time zone behavior and (sometimes) abbreviations,
and that doesn't include the identifier.
You should be able to figure it out whether using symlinks, hardlinks, or check
sums of some kind:
$ head -v /etc/timezone; \
tail -vn1 /etc/localtime; echo; \
llgo /etc/localtime; echo; \
find /usr/share/zoneinfo/ -inum `stat -L -c%i /etc/localtime`; echo; \
cksum /etc/localtime; echo; \
find /usr/share/zoneinfo/ -size `cksum /etc/localtime | cut -d' ' -f2`c \
| xargs cksum
==> /etc/timezone <==
America/Edmonton
==> /etc/localtime <==
MST7MDT,M3.2.0,M11.1.0
lrwxrwxrwx 1 31 May 25 2020 /etc/localtime -> ../usr/share/zoneinfo/localtime
/usr/share/zoneinfo/America/Edmonton
/usr/share/zoneinfo/Canada/Mountain
/usr/share/zoneinfo/Etc/localtime
/usr/share/zoneinfo/localtime
/usr/share/zoneinfo/posix/America/Edmonton
/usr/share/zoneinfo/posix/Canada/Mountain
1365654935 2332 /etc/localtime
1365654935 2332 /usr/share/zoneinfo/America/Edmonton
1365654935 2332 /usr/share/zoneinfo/Canada/Mountain
1365654935 2332 /usr/share/zoneinfo/Etc/localtime
1365654935 2332 /usr/share/zoneinfo/localtime
1365654935 2332 /usr/share/zoneinfo/posix/America/Edmonton
1365654935 2332 /usr/share/zoneinfo/posix/Canada/Mountain
--
Take care. Thanks, Brian Inglis Calgary, Alberta, Canada
La perfection est atteinte Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer but when there is no more to cut
-- Antoine de Saint-Exupéry
