https://bugzilla.kernel.org/show_bug.cgi?id=218711

--- Comment #1 from Alejandro Colomar (alx@kernel.org) ---

On Thu, Apr 11, 2024 at 07:44:43PM +0000, bugzilla-daemon@kernel.org wrote:

https://bugzilla.kernel.org/show_bug.cgi?id=218711

            Bug ID: 218711
           Summary: strftime man page incorrectly claims that TZ is used
           Product: Documentation
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P3
         Component: man-pages
          Assignee: documentation_man-pages@kernel-bugs.osdl.org
          Reporter: gharris@sonic.net
        Regression: No

The strftime man page says, in the ENVIRONMENT section, that "The environment
variables TZ and LC_TIME are used."

strftime(), in Linux, does not use the TZ environment variable.  It is passed
a
pointer to a struct tm, which contains a time stamp that can reflect either
local time or UTC, and formats a string based on the values in that
structure. 
If the structure reflects local time, there is no need for any conversion of
POSIX time to local time, so TZ is not used.  If the structure reflects UTC,
the string will reflect UTC, meaning that, again, there is no need for any
conversion to local time, so TZ is not used.

TZ is *indirectly* used, because, to quote the Single UNIX Specification page
for strftime(), "Local timezone information is used as though strftime()
called
tzset().", and, to quote the Single UNIX Specification page for tzset(), "The
tzset() function shall use the value of the environment variable TZ to set
time
conversion information used by ctime, localtime, mktime, and strftime."

The reason why strftime is mentioned is that the %Z format specifier is
"Replaced by the timezone name or abbreviation, or by no bytes if no timezone
information exists."  In systems in which struct tm includes the tm_zone
member, %Z can use the tm_zone member as the timezone abbreviation, but, in
systems where it does *not* include the tm_zone member, strftime() might, for
example, have to fall back on using the tzname[] array and the tm_isdst
member
to select an element of that array.

Hi Guy,

Would you mind sending a patch to the mailing list, according to the
guidelines?

<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING>.
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/mail>
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/patches>

It would be wise to CC Paul Eggert [off-list ref].

Have a lovely day!
Alex

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