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Subject: Re: Python for Windows reports wrong local time when run under Cygwin
 on Europe/Moscow TZ
To: cygwin AT cygwin DOT com
References: <CAAHpriO6A+6bLXt0Qe-xpdXT1CiLjk7=7G31cHBtnVJ0kXb2Eg AT mail DOT gmail DOT com>
From: Brian Inglis <Brian DOT Inglis AT SystematicSw DOT ab DOT ca>
Organization: Systematic Software
Message-ID: <a5de1ef8-ee5a-01b8-ca4c-76087a645dbe@SystematicSw.ab.ca>
Date: Tue, 8 Jun 2021 21:43:15 -0600
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On 2021-06-08 11:37, Keith Thompson via Cygwin wrote:
> There is a known problem with the $TZ environment variable.
> 
> Here's a discussion from 2017:
> https://cygwin.com/pipermail/cygwin/2017-May/232675.html
> 
> The problem is that both Cygwin and Windows use the $TZ environment
> variable, but they interpret it differently.
> 
> The Windows handling of $TZ (or %TZ%) is documented here:
> https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/tzset?view=msvc-160
> 
> For example, Pacific Time is represented as TZ=PST8PDT.
> 
> In Cygwin, my $TZ is set by default to "America/Los_Angeles".
> Any Windows applications that I invoke from Cygwin, if they attempt
> to determine the time zone, will behave inconsistently because they
> don't see "America/Los_Angeles" as a valid time zone string.
> 
> I've worked around this by unsetting TZ in my .bash_profile .
> Cygwin applications are still able to determine the correct time zone.
> 
> I suggest that Cygwin should *not* set the TZ environment variable.

In that case, those affected should comment out the last line of each:

$ tail /etc/profile.d/tzset.*sh
==> /etc/profile.d/tzset.csh <==
# Modifying /etc/profile.d/tzset.csh directly will prevent
# setup from updating it.

# System-wide tzset.csh file

#Uses the geographical location setting of the user to find the right
#mapping, rather than the locale setting.  Only on Windows 2000 which
#doesn't know about the user's geographical location, or if fetching
#the geographical location fails, it falls back to the user's locale.
if ( $?TZ == 0 ) setenv TZ `/usr/bin/tzset`

==> /etc/profile.d/tzset.sh <==
# Modifying /etc/profile.d/tzset.sh directly will prevent
# setup from updating it.

# System-wide tzset.sh file

#Uses the geographical location setting of the user to find the right
#mapping, rather than the locale setting.  Only on Windows 2000 which
#doesn't know about the user's geographical location, or if fetching
#the geographical location fails, it falls back to the user's locale.
test -z "$TZ" && export TZ=$(/usr/bin/tzset)

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada

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