Re: Change in logical link behaviour

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Feb 29 14:10, Rainer Emrich wrote:
> I try to reliably determine if native Windows symlink are working for a
> current cygwin environment in a shell script.
> 
> Therefor I used a powershell snipped:
> 
> mkdir asdfgh
> ln -s asdfgh/ asdfgh-1
> powershell "& {Get-Item -Path asdfgh-1 | Select-Object}"
> 
> On cygwin 3.0.7 the output is as follows:
> 
> 
>     Directory: D:\cygwin\home\rainer\temp
> 
> 
> Mode                LastWriteTime         Length Name
> ----                -------------         ------ ----
> d----l       29.02.2020     13:58                asdfgh-1
> 
> On cygwin 3.1.4 I get:
> 
> 
>     Directory: D:\cygwin\home\rainer\temp
> 
> 
> Mode                LastWriteTime         Length Name
> ----                -------------         ------ ----
> d----        29.02.2020     13:58                asdfgh-1
> 
> So now there is no indication that this is a link. Is this new behaviour
> intended or a bug?
> 
> I did not try on Windows 10, I'm still on windows 7.
> 
> Rainer
> 

I can't reproduce this behaviour.  Keep in mind that, by default, you
*have to* run in an elevated shell to be able to create native NTFS
symlinks, *and* you *have to* set the environment variable CYGWIN(*) to
contain "winsymlinks:native" or "winsymlinks:nativestrict".  The latter
is nice for testing, it refuses to fall back silently to the default
Cygwin-only symlinks but fails instead if it can't create a native
NTFS symlink.

So, on Windows 7 in an elevated shell:

  # id -G | grep -Eq '\<544\>' && echo elevated || echo non-elevated
  elevated
  # uname -a
  CYGWIN_NT-6.1 vmbert764 3.1.4(0.340/5/3) 2020-02-19 08:49 x86_64 Cygwin
  # mkdir qwe
  # cd qwe
  # export CYGWIN="winsymlinks:nativestrict"
  # touch foo
  # ln -s foo bar
  # cmd /c dir /a
   Volume in drive C has no label.
   Volume Serial Number is A8E0-A24E

   Directory of C:\cygwin64\home\corinna\qwe

  2020-03-02  17:31    <DIR>          .
  2020-03-02  17:31    <DIR>          ..
  2020-03-02  17:31    <SYMLINK>      bar [foo]
  2020-03-02  17:31                 0 foo
                 2 File(s)              0 bytes
		 2 Dir(s)   7.907.352.576 bytes free

In a non-elevated shell:

  $ id -G | grep -Eq '\<544\>' && echo elevated || echo non-elevated
  non-elevated
  $ uname -r
  CYGWIN_NT-6.1 vmbert764 3.1.4(0.340/5/3) 2020-02-19 08:49 x86_64 Cygwin
  $ cd qwe
  $ export CYGWIN="winsymlinks:nativestrict"
  $ rm bar
  $ ln -s foo bar
  ln: failed to create symbolic link 'bar': Operation not permitted
  $ export CYGWIN="winsymlinks:native"  # !!!
  $ ln -s foo bar
  $ cmd /c dir /a
   Volume in drive C has no label.
   Volume Serial Number is A8E0-A24E

   Directory of C:\cygwin64\home\corinna\qwe

  2020-03-02  17:31    <DIR>          .
  2020-03-02  17:31    <DIR>          ..
  2020-03-02  17:38                20 bar
  2020-03-02  17:31                 0 foo
                 2 File(s)             20 bytes
		 2 Dir(s)   7.907.352.576 bytes free

The symlink created last is a Cygwin-only symlink (special file
with SYSTEM attribute), not a native symlink.


Corinna

(*) https://cygwin.com/cygwin-ug-net/using-cygwinenv.html
(*) https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks


-- 
Corinna Vinschen
Cygwin Maintainer

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