On 9/16/2020 7:12 AM, Thomas Wolff wrote:
Am 16.09.2020 um 13:04 schrieb marco atzeri via Cygwin:
On Wed, Sep 16, 2020 at 10:53 AM Kristian Ivarsson via Cygwin
<cygwin@cygwin.com> wrote:
Dear folks

Does anyone know why cygwin annex the TMP (and TEMP) environment variable(s)
and sets them to /tmp for cygwin-built-applications (executables) ?

This results in that when you want the current users TMP-folder you end up
with the /tmp path. As a result,when writing to that, without having cygwin
installed (e.g. C:\cygwin64\), it seems like it refers to ${CWD}/../tmp/ and
that is not always accessible by all users


Does anyone know the rational with this behaviour and what can be done to
get hold of the (real) Windows TMP/TEMP environment-variable-values (in a
(hopefully) platform independent way) ?


Best regards,
Kristian

the logic behind is that the program should be located
in
     $YOUR_ROOT/bin

and the temp will be
     $YOUR_ROOT/tmp

so if you are making your custom tree, try to stick on that expectation
and have both directories.
In general, you are free to set TMP to a directory of your choice, that's the purpose of that variable, no need to sync it with some root.
There is a comment in /etc/profile:
   # TMP and TEMP as defined in the Windows environment
   # can have unexpected consequences for cygwin apps,
but it does not explain what consequences that might be; probably some trouble with ACL/access permissions for temporary files.

That's right. There was an issue in 2009 in which 'patch' was unexpectedly changing permissions. See the long thread starting at

  https://cygwin.com/pipermail/cygwin/2009-November/181760.html

and continuing at

  https://sourceware.org/pipermail/cygwin/2009-December/181829.html

The problem was caused by the inheritable permissions on a temporary directory that patch was using, based on the value of the Windows TMP environment variable.

Ken
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