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Date:	Fri, 16 Jul 2021 06:59:46 +0300
From:	Andrey Repin <anrdaemon AT yandex DOT ru>
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To:	Doug Henderson <djndnbvg AT gmail DOT com>, cygwin AT cygwin DOT com
Subject:	Re: Setup shows errors from gnuplot-base.dash and python38-devel.sh
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Greetings, Doug Henderson!

>> >>> When I do that in an elevated shell:
>> >>>
>> >>> $ cd /etc/postinstall/
>> >>>
>> >>> $ cat gnuplot-base.dash
>> >>> /usr/sbin/alternatives --install /usr/bin/gnuplot gnuplot
>> >>> /usr/bin/gnuplot-base.exe 10
>> >>>
>> >>> $ . gnuplot-base.dash
>> >>> failed to read link /usr/bin/gnuplot: No such file or directory
>> >>> failed to link /usr/bin/gnuplot -> /etc/alternatives/gnuplot: No such
>> >>> file or directory
>> >>
>> >> Something seems to be confusing 'alternatives'.  Can you show a listing of
>> >> /etc/alternatives?
>> >
>> > $ cd /etc/alternatives/
>> >
>> > $ ls -l
>> > total 2.0K
>> > lrwxrwxrwx 1 Admin None  35 Oct  3  2017 automake-doc ->
>> > /usr/share/info/automake1.9.info.gz
>> > lrwxrwxrwx 1 Admin None  19 Jun 16 17:48 lua -> /usr/bin/lua5.3.exe*
>> > lrwxrwxrwx 1 Admin None  31 Jun 16 17:48 lua.1.gz ->
>> > /usr/share/man/man1/lua5.3.1.gz
>> > lrwxrwxrwx 1 Admin None  20 Jun 16 17:48 luac -> /usr/bin/luac5.3.exe*
>> > lrwxrwxrwx 1 Admin None  32 Jun 16 17:48 luac.1.gz ->
>> > /usr/share/man/man1/luac5.3.1.gz
>> > lrwxrwxrwx 1 Admin None  15 Jun  5 08:46 pip3 -> /usr/bin/pip3.8*
>> > lrwxrwxrwx 1 Admin None  22 Jun 16 07:34 python -> /usr/bin/python3.8.exe*
>> > -rw-r--r-- 1 Admin None 163 Apr  4  2013 README
>>
>> This shows that alternatives worked in June.  Have you changed anything since
>> then that might be related to symlinks (e.g., the CYGWIN environment variable)?
>>
>> Here are a few other things you could try:
>>
>> 1. Attach cygcheck output as requested in https://cygwin.com/problems.html
>>
>> 2. Add --verbose to the alternatives call.
>>
>> 3. Run the alternatives call under strace and look for errors involving
>> symlinks.  Or post the output somewhere so that we can look at it.

> Now using setup-x86_64.exe version 2.909 (64 bit)
> Postinstall script errors:
> Package: _/Unknown package
>     gnuplot-base.dash exit code 2
>     python38-devel.sh exit code 2

> Here's what I did in an elevated shell.

> $ cd /etc/alternatives

> $ cat /etc/postinstall/gnuplot-base.dash
> /usr/sbin/alternatives --install /usr/bin/gnuplot gnuplot
> /usr/bin/gnuplot-base.exe 10

> $ /usr/sbin/alternatives --verbose --install /usr/bin/gnuplot gnuplot
> /usr/bin/gnuplot-base.exe 10
> reading /var/lib/alternatives/gnuplot
> failed to read link /usr/bin/gnuplot: No such file or directory
> failed to link /usr/bin/gnuplot -> /etc/alternatives/gnuplot: No such
> file or directory

> $ echo $CYGWIN
> winsymlinks:nativestrict

> *** changed system environment
> $ echo $CYGWIN
> winsymlinks:native

> $ /usr/sbin/alternatives --verbose --install /usr/bin/gnuplot gnuplot
> /usr/bin/gnuplot-base.exe 10
> reading /var/lib/alternatives/gnuplot


> *** Success
> Alternatives does not work correctly when CYGWIN=nativestrict. Perhaps
> it is trying to create a link before the link target exists. Unlike
> Linux, Windows does not allow creating symbolic links to non-existent
> targets.

> The /etc/postinstall/python38-devel.sh also works now.

> Also after changing env back to CYGWIN=winsymlinks:nativestrict the
> erroring postinstall scripts continue to work. This supports my
> suspicion that /usr/sbin/alternatives is trying to create a symbolic
> link to a target before it creates the target when it is performing
> the first install for an alternative. On subsequent runs, the target
> already exists.

> I have unattached the output from cygcheck, as I do not believe it
> will help now.

> Am I the only person that uses "CYGWIN=winsymlinks:nativestrict" ???

$ echo "$CYGWIN"
wincmdln winsymlinks:nativestrict glob:ignorecase

> Sorry for all the bother. My aging brain forgot how I made
> alternatives work for Lua last month.

I've stumbled upon the same problem earlier.
alternatives tries to create a link pointing to a nonexistent file. Which is
valid in Linux, but impossible in Windows.
IMO, this is a logical fallacy and should not be attempted, making it an
upstream bug.


-- 
With best regards,
Andrey Repin
Friday, July 16, 2021 6:56:55

Sorry for my terrible english...


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