Re: Problem with tar version 1.29 (in Cygwin 3.6 64 bit) in extracting sym-link files

[Hamish McIntyre-Bhatty <hamishmb@live.co.uk>]

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On 05/10/2020 18:29, Brian Inglis wrote:
> On 2020-10-05 09:23, Hamish McIntyre-Bhatty via Cygwin wrote:
>> On 04/10/2020 11:28, Andrey Repin via Cygwin wrote:
>>> Greetings, vinay Hegde!
>>>
>>> Please no top-posting in this list.
>>>
>>>> On Fri, Oct 2, 2020 at 9:13 PM Eliot Moss wrote:
>>>>> On 10/2/2020 11:26 AM, vinay Hegde via Cygwin wrote:
>>>>>> Hi Cygwin Team,
>>>>>> In Cygwin 3.6, I am facing an issue while using tar.exe for extracting
>>>>>> .tar.z file.
>>>>>>
>>>>>> Issue summary:
>>>>>> When I use 'tar.exe' to extract the .tar.z file, it extracts all files
>>>>>> including symlinks. But symlink file size will be 0KB & it throws
>>>>>> error 'The file cannot be accessed by the system', if I try to open in
>>>>>> any Windows editor like notepad or notepad++
>>>>>>
>>>>>> Below are the details:
>>>>>> -   OS: Windows 2019
>>>>>> -   Cygwin version installed: 3.6 (tar version: 1.29)
>>>>>> -   Command used to extract the tar file is: tar -zxvf jre64.tar.Z
>>>>>> -   'ls -l' on the extracted directory shows:
>>>>>> lrwxrwxrwx  1 etbuild Domain Users      8 Jul 10  2017 ControlPanel -> jcontrol
>>>>>> -rwxr-xr-x+ 1 etbuild Domain Users   7734 Mar 15  2017 java
>>>>>> -rwxr-xr-x+ 1 etbuild Domain Users 128791 Mar 15  2017 javaws
>>>>>> -rwxr-xr-x+ 1 etbuild Domain Users   6264 Mar 15  2017 jcontrol
>>>>>>
>>>>>> -     As you can see 'ControlPanel' is a symlink file with 0KB
>>>>>> (8Bytes) size. This file, I cannot open in any Windows editor. It
>>>>>> throws error like ''The file cannot be accessed by the system'
>>>>>>
>>>>>> -    However, I can open this file in vi editor or I can 'cat' this.
>>>>>>
>>>>>> -    Earlier, I was using Cygwin version 1.7 (tar version: 1.27) & in
>>>>>> that, this issue was not there. Symlink file size was 1KB & I could
>>>>>> open it with any Windows editor.
>>>>>>
>>>>>> Please suggest what needs to be done to fix this issue.
>>>>> Hi, Vinay - Cygwin can use, and create, a variety of forms of links.  Some of these are understood
>>>>> by Windows tools, some not.  I suggest you read in the Cygwin documentation about symlinks and
>>>>> decide what kind are best for you.  Then you'll need to set that up, delete the existing link, and
>>>>> re-create it.  I personally run with CYGWIN=winsymlinks:native, but as we say in Internet land, YMMV.
>>>>>
>>>> Hi Eliot Moss,
>>>> Thank you very much for the quick response & the information.It really helped.
>>>> I just set 'CYGWIN=winsymlinks:lnk' & I am now able to open sym-link
>>>> file. Both 'CYGWIN=winsymlinks:lnk' & 'CYGWIN=winsymlinks' are working
>>>> for me.
>>>> But it creates a shortcut(not the regular file). Hope it won't impact
>>>> my existing setup.
>>>> But both  'CYGWIN=winsymlinks:native' (which is default I believe) &
>>>> 'CYGWIN=winsymlinks:nativestrict' are not working for me. Just to
>>>> understand, In what OS environment/File System 'native' will work?
>>> Given enough permissions, "native" will work everywhere, it will create native
>>> symlink, but failing that, it will fall back to creating Cygwin link.
>>>
>>> LNK is an Explorer shortcut, which would work with many programs outside
>>> Cygwin, but not necessarily with your one.
>>>
>>> See https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks as well as
>>> https://cygwin.com/cygwin-ug-net/using-cygwinenv.html 
>> Does anyone happen to know if there's a way to automatically regenerate
>> existing symlinks after changing these settings?
> Example: remove the "echo" after checking it will update only the desired links:
>
> $ for link in `find . -type l`
>> do
>>   targ=`readlink $link`
>>   echo ln -fsv $targ $link
>> done
> ln -fsv linux-kernel/linux-next/cpufeatures.h ./cpufeatures.h
> ln -fsv linux-kernel/linux-next/cpufeatures.log ./cpufeatures.log
> ln -fsv ../../cygwin/newlib-cygwin/winsup/cygwin/fhandler_proc.cc
> ./cpuinfo/fhandler_proc.cc
> ln -fsv ../../cygwin/newlib-cygwin/winsup/cygwin/sysconf.cc ./cpuinfo/sysconf.cc
> ln -fsv ../cygwin/cpuid ./cygwin
> ln -fsv CPUID_Explorer/CPUID/Debug Static/CPUID.exe ./explorer
> ln -fsv /lib/gcc/x86_64-pc-cygwin/9.3.0/include/cpuid.h ./gcc/cpuid.h
> ln -fsv linux-kernel/linux-prev-next.diff ./linux-prev-next.diff
> ln -fsv linux-kernel/linux-next/scattered.log ./scattered.log

Cheers, worked for me.

In my case, I'm bundling Cygwin in an installer package for one of my
programs, so I used this trick to regenerate all my Cygwin symlinks as
Windows .lnk files (using 32-bit Cygwin to run that on C:\cygwin64 and
vice versa). I'm aware that it was probably Not Recommended (TM) to do
that so I made backups first. All seems fine so far.

I was having problems with the bundles and I figured Cygwin might be
using WSL symlinks (my dev VM is running Windows 10), so I thought it
was worth a try. Cheers.

Hamish


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