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Subject: Re: TMP/TEMP environment variable and /tmp
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From: Ken Brown via Cygwin <cygwin@cygwin.com>
Reply-To: Ken Brown <kbrown@cornell.edu>
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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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