Cygwin tool to differ junctions from soft links?

Cygwin tool to differ junctions from soft links?

[Martin Wege]

Good morning!

Does Cygwin have a command line tool (Scriptable!) which can be used
to differ between soft links and Windows junctions?

Thanks,
Martin

Re: Cygwin tool to differ junctions from soft links?

[Martin Wege]

?

On Wed, Nov 1, 2023 at 10:14 AM Martin Wege <martin.l.wege@gmail.com> wrote:
>
> Good morning!
>
> Does Cygwin have a command line tool (Scriptable!) which can be used
> to differ between soft links and Windows junctions?
>
> Thanks,
> Martin

Re: Cygwin tool to differ junctions from soft links?

[Andrey Repin]

Greetings, Martin Wege!

> Does Cygwin have a command line tool (Scriptable!) which can be used
> to differ between soft links and Windows junctions?

It would be easier to help you, if you specify the purpose of your request.
I.e. what you want to achieve with such tool.


-- 
With best regards,
Andrey Repin
Thursday, November 16, 2023 11:46:09

Sorry for my terrible english...

Re: Cygwin tool to differ junctions from soft links?

[matthew patton]

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AFAIK no. what I do is re-implement 'ln' with a wrapper because the Cygwin behavior (Junctions) was driving me up the wall.
https://github.com/tb3088/shell-environment/blob/ccf7aa161899c2c4ebe2d9e980e674bc726a3ef3/.functions_os.CYGWIN_NT#L9

============
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“Ours may become the first civilization destroyed, not by the power of our enemies, but by the ignorance of our teachers and the dangerous nonsense they are teaching our children. In an age of artificial intelligence, they are creating artificial stupidity.' - Thomas Sowell
 

    On Thursday, November 16, 2023 at 03:50:24 AM EST, Andrey Repin via Cygwin <cygwin@cygwin.com> wrote:  
 
 Greetings, Martin Wege!

> Does Cygwin have a command line tool (Scriptable!) which can be used
> to differ between soft links and Windows junctions?

It would be easier to help you, if you specify the purpose of your request.
I.e. what you want to achieve with such tool.


-- 
With best regards,
Andrey Repin
Thursday, November 16, 2023 11:46:09

Sorry for my terrible english...


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Re: Cygwin tool to differ junctions from soft links?

[Brian Inglis]

On 2023-11-16 11:55, matthew patton via Cygwin wrote:
> On Thursday, November 16, 2023 at 03:50:24 AM EST, Andrey Repin wrote:
>>> Does Cygwin have a command line tool (Scriptable!) which can be used to
>>> differ between soft links and Windows junctions?

Distinguishing between types of Windows reparse points is not a POSIX or 
emulation function, so not of interest to Cygwin developers.

I thought about it when support was added, but then realized there was no nice 
place to add it within the platform, without going the non-portable Windows 
specific utility route, as in lsattr.

You could in a function or script by running lsattr -d which seems to fail on 
reparse points, then ls -dl which shows a Symbolic Link with a relative path, 
and a Junction with an absolute path, although it could just be a Symbolic Link 
with an absolute path.

Perhaps something like the following would be useful to Windows users who want 
to know this stuff:

	https://schinagl.priv.at/nt/hardlinkshellext/hardlinkshellext.html

>> It would be easier to help you, if you specify the purpose of your
>> request. I.e. what you want to achieve with such tool.
> AFAIK no. what I do is re-implement 'ln' with a wrapper because the Cygwin
> behavior (Junctions) was driving me up the wall.
> https://github.com/tb3088/shell-environment/blob/ccf7aa161899c2c4ebe2d9e980e674bc726a3ef3/.functions_os.CYGWIN_NT#L9

Cygwin never creates Windows Directory or Filesystem Junction reparse points, 
and by default it uses its own version of Unix path symlink files, preceded by a 
flag ("magic cookie") value, and with system attribute, to allow compatibility 
with FAT file system limitations, or else NFS symlinks on NFS filesystems.

CYGWIN env var settings allow creation of Windows shortcuts and symbolic link 
reparse points instead of its default (equivalent to winsymlinks:sys), when 
supported by the file system and Windows release:

	https://cygwin.com/cygwin-ug-net/using-cygwinenv.html

	https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

Re: Cygwin tool to differ junctions from soft links?

[Doug Henderson]

> On Wed, Nov 1, 2023 at 10:14 AM Martin Wege <martin.l.wege@gmail.com> wrote:
> >
> > Good morning!
> >
> > Does Cygwin have a command line tool (Scriptable!) which can be used
> > to differ between soft links and Windows junctions?
> >
> > Thanks,
> > Martin

Cygwin itself does not have a command, that I know of, to do this.

However, you can use the windows command shell to call its internal
commands. In bash, e.g.

$ /cygdrive/c/Windows/System32/cmd.exe /c dir /a:l /b

shows all the junctions in my windows user home folder when  I am there.

The windows dir command can list links and junctions. The mklink
command documentation at https://ss64.com/nt/mklink.html has more
information than the "mklink/?" help text about links.

HTH

Doug

-- 
Doug Henderson, Calgary, Alberta, Canada - from gmail.com

Re: Cygwin tool to differ junctions from soft links?

[Thomas Wolff]

Am 16.11.2023 um 21:30 schrieb Brian Inglis via Cygwin:
> On 2023-11-16 11:55, matthew patton via Cygwin wrote:
>> On Thursday, November 16, 2023 at 03:50:24 AM EST, Andrey Repin wrote:
>>>> Does Cygwin have a command line tool (Scriptable!) which can be 
>>>> used to
>>>> differ between soft links and Windows junctions?
>
> Distinguishing between types of Windows reparse points is not a POSIX 
> or emulation function, so not of interest to Cygwin developers.
>
> I thought about it when support was added, but then realized there was 
> no nice place to add it within the platform, without going the 
> non-portable Windows specific utility route, as in lsattr.
>
> You could in a function or script by running lsattr -d which seems to 
> fail on reparse points, then ls -dl which shows a Symbolic Link with a 
> relative path, and a Junction with an absolute path, although it could 
> just be a Symbolic Link with an absolute path.
lsattr has an explicit flag:
              'r', 'Reparse':       file or directory that has a reparse 
point
I don't know whether it's the same as a junction, otherwise a 'j' flag 
could be added.

>
> Perhaps something like the following would be useful to Windows users 
> who want to know this stuff:
>
>     https://schinagl.priv.at/nt/hardlinkshellext/hardlinkshellext.html
>
>>> It would be easier to help you, if you specify the purpose of your
>>> request. I.e. what you want to achieve with such tool.
>> AFAIK no. what I do is re-implement 'ln' with a wrapper because the 
>> Cygwin
>> behavior (Junctions) was driving me up the wall.
>> https://github.com/tb3088/shell-environment/blob/ccf7aa161899c2c4ebe2d9e980e674bc726a3ef3/.functions_os.CYGWIN_NT#L9 
>>
>
> Cygwin never creates Windows Directory or Filesystem Junction reparse 
> points, and by default it uses its own version of Unix path symlink 
> files, preceded by a flag ("magic cookie") value, and with system 
> attribute, to allow compatibility with FAT file system limitations, or 
> else NFS symlinks on NFS filesystems.
>
> CYGWIN env var settings allow creation of Windows shortcuts and 
> symbolic link reparse points instead of its default (equivalent to 
> winsymlinks:sys), when supported by the file system and Windows release:
>
>     https://cygwin.com/cygwin-ug-net/using-cygwinenv.html
>
>     https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks
>

Re: Cygwin tool to differ junctions from soft links?

[Corinna Vinschen]

On Nov 17 06:54, Thomas Wolff via Cygwin wrote:
> 
> 
> Am 16.11.2023 um 21:30 schrieb Brian Inglis via Cygwin:
> > On 2023-11-16 11:55, matthew patton via Cygwin wrote:
> > > On Thursday, November 16, 2023 at 03:50:24 AM EST, Andrey Repin wrote:
> > > > > Does Cygwin have a command line tool (Scriptable!) which can
> > > > > be used to
> > > > > differ between soft links and Windows junctions?
> > 
> > Distinguishing between types of Windows reparse points is not a POSIX or
> > emulation function, so not of interest to Cygwin developers.
> > 
> > I thought about it when support was added, but then realized there was
> > no nice place to add it within the platform, without going the
> > non-portable Windows specific utility route, as in lsattr.
> > 
> > You could in a function or script by running lsattr -d which seems to
> > fail on reparse points, then ls -dl which shows a Symbolic Link with a
> > relative path, and a Junction with an absolute path, although it could
> > just be a Symbolic Link with an absolute path.
> lsattr has an explicit flag:
>              'r', 'Reparse':       file or directory that has a reparse
> point
> I don't know whether it's the same as a junction, otherwise a 'j' flag could
> be added.

lsattr is basically a frontend for the ioctl(FS_IOC_GETFLAGS) call.
It centers around showing file attributes.  DOS attributes as per
https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants
know about reparse points, but only as a flag.

Just as its Linux counterpart showing ext[234] attributes, lsattr only
works on regular files and directories.  If you try to run it on
a file Cygwin handles as a symbolic link, you get an error:

  $ mkdir foo
  $ ln -s foo bar
  $ lsattr -d foo bar
  ------------ foo
  lsattr: Not supported on bar

  $ cmd /c mklink /j baz foo
  Junction created for baz <<===>> foo
  $ ls -l
  total 0
  lrwxrwxrwx 1 corinna vinschen  3 Nov 17 11:28 bar -> foo
  lrwxrwxrwx 1 corinna vinschen 23 Nov 17 11:29 baz -> /home/corinna/tmp/x/foo
  drwxr-xr-x 1 corinna vinschen  0 Nov 17 11:28 foo
  $ lsattr -d foo bar baz
  ------------ foo
  lsattr: Not supported on bar
  lsattr: Not supported on baz

Actually, even if you run lsattr on a reparse point NOT handled as a
symlink, you probably won't see the Reparse attribute at all.

The reason is that the open(2) call doesn't expose a way to POSIX apps
to open a reparse point as reparse point.  There's just no POSIX flag
for that, given the entire concept of reparse points is alien.

As a result, the underlying Windows kernel NtCreateFile call will try to
reparse.  If the reparse point is one known to the OS, or a reparse point
which is handled by some driver, you'll see the attributes of the reparse
target.  Volume mount points are a known variety not handled as symlink
by Cygwin.  Open the volume mount point with open(2), and you actually
opened the root directory of the mounted filesystem.

Funny enough, same goes for Windows attrib.exe tool...

Having said that, I don't see an easy way to provide the required
information from inside Cygwin by providing an API for stuff like that.

If you want to see this kind of information, there are ways.  For
instance, a tool can do something like that:

  lstat("foo");
  if (S_ISLNK("foo"))
    {
      HANDLE h = CreateFile("foo", ..., FILE_FLAG_OPEN_REPARSE_POINT, ...);
      if (h != INVALID_HANDLE_VALUE)
	{
	  FILE_ATTRIBUTE_TAG_INFO at;
	  if (GetFileInformationByHandleEx (h, FileAttributeTagInfo,
					    &at, sizeof at))
	    {
	      if (at.FileAttributes & FILE_ATTRIBUTE_REPARSE_POINT)
	        {
		  /* Check at.ReparseTag:
		  IO_REPARSE_TAG_LX_SYMLINK: WSL symlink
		  IO_REPARSE_TAG_SYMLINK: Windows symlink
		  IO_REPARSE_TAG_MOUNT_POINT: Volume mount point
					      or directory junction
		  IO_REPARSE_TAG_APPEXECLINK: App execution alias
		  Anything else: *shrug*
		}
	    }
	}
    }



Corinna

Re: Cygwin tool to differ junctions from soft links?

[Brian Inglis]

On 2023-11-16 22:54, Thomas Wolff via Cygwin wrote:
> Am 16.11.2023 um 21:30 schrieb Brian Inglis via Cygwin:
>> On 2023-11-16 11:55, matthew patton via Cygwin wrote:
>>> On Thursday, November 16, 2023 at 03:50:24 AM EST, Andrey Repin wrote:
>>>>> Does Cygwin have a command line tool (Scriptable!) which can be used to
>>>>> differ between soft links and Windows junctions?
>> Distinguishing between types of Windows reparse points is not a POSIX or 
>> emulation function, so not of interest to Cygwin developers.
>> I thought about it when support was added, but then realized there was no nice 
>> place to add it within the platform, without going the non-portable Windows 
>> specific utility route, as in lsattr.
>> You could in a function or script by running lsattr -d which seems to fail on 
>> reparse points, then ls -dl which shows a Symbolic Link with a relative path, 
>> and a Junction with an absolute path, although it could just be a Symbolic 
>> Link with an absolute path.

> lsattr has an explicit flag:
>               'r', 'Reparse':       file or directory that has a reparse point
> I don't know whether it's the same as a junction, otherwise a 'j' flag could be 
> added.

Notice that the flag is the same as 'r' "Readonly" and lsattr does not work on 
Windows Reparse Points which are Junctions, Directory or File Symbolic Links 
[sanitized]:
$ cd ~
$ cmd /c dir /a:l | grep '>'
2021-04-13  10:41    <JUNCTION>     Application Data [$HOME/AppData/Roaming]
2021-06-21  21:07    <JUNCTION>     Bookshelf [...]
2021-04-13  10:41    <JUNCTION>     Cookies 
[$HOME/AppData/Local/Microsoft/Windows/INetCookies]
2021-09-15  10:23    <JUNCTION>     cygwin-64t [...]
2021-04-13  10:41    <JUNCTION>     Local Settings [$HOME/AppData/Local]
2020-04-21  03:33    <SYMLINKD>     Mail [AppData/Roaming/...]
2021-04-13  10:41    <JUNCTION>     My Documents [$HOME/Documents]
2021-04-13  10:41    <JUNCTION>     NetHood 
[$HOME/AppData/Roaming/Microsoft/Windows/Network Shortcuts]
2023-05-27  07:30    <JUNCTION>     ntp-dev [...]
2023-05-27  07:30    <JUNCTION>     ntp-stable [...]
2021-04-13  10:41    <JUNCTION>     PrintHood 
[$HOME/AppData/Roaming/Microsoft/Windows/Printer Shortcuts]
2021-04-13  10:41    <JUNCTION>     Recent 
[$HOME/AppData/Roaming/Microsoft/Windows/Recent]
2021-04-13  10:41    <JUNCTION>     SendTo 
[$HOME/AppData/Roaming/Microsoft/Windows/SendTo]
2021-04-13  10:41    <JUNCTION>     Start Menu 
[$HOME/AppData/Roaming/Microsoft/Windows/Start Menu]
2021-02-10  21:19    <JUNCTION>     Tech [...]
2021-04-13  10:41    <JUNCTION>     Templates 
[$HOME/AppData/Roaming/Microsoft/Windows/Templates]
2022-05-27  19:15    <JUNCTION>     weather [...]
2020-06-20  01:19    <SYMLINK>      _gvimrc [.vim/gvimrc]
2020-06-20  01:06    <SYMLINKD>     _vim [.vim]
2020-06-20  00:51    <SYMLINK>      _viminfo [.vim/viminfo]
2020-06-20  00:51    <SYMLINK>      _vimrc [.vim/vimrc]
$ cmd /c dir /a:l /b "$HOMEPATH" | d2u | xargs -I@ lsattr -d '@'
lsattr: Not supported on Application Data
lsattr: Not supported on Bookshelf
lsattr: Not supported on Cookies
lsattr: Not supported on cygwin-64t
lsattr: Not supported on Local Settings
lsattr: Not supported on Mail
lsattr: Not supported on My Documents
lsattr: Not supported on NetHood
lsattr: Not supported on ntp-dev
lsattr: Not supported on ntp-stable
lsattr: Not supported on PrintHood
lsattr: Not supported on Recent
lsattr: Not supported on SendTo
lsattr: Not supported on Start Menu
lsattr: Not supported on Tech
lsattr: Not supported on Templates
lsattr: Not supported on weather
lsattr: Not supported on _gvimrc
lsattr: Not supported on _vim
lsattr: Not supported on _viminfo
lsattr: Not supported on _vimrc

>> Perhaps something like the following would be useful to Windows users who want 
>> to know this stuff:
>>     https://schinagl.priv.at/nt/hardlinkshellext/hardlinkshellext.html
>>>> It would be easier to help you, if you specify the purpose of your
>>>> request. I.e. what you want to achieve with such tool.
>>> AFAIK no. what I do is re-implement 'ln' with a wrapper because the Cygwin
>>> behavior (Junctions) was driving me up the wall.
>>> https://github.com/tb3088/shell-environment/blob/ccf7aa161899c2c4ebe2d9e980e674bc726a3ef3/.functions_os.CYGWIN_NT#L9
>> Cygwin never creates Windows Directory or Filesystem Junction reparse points, 
>> and by default it uses its own version of Unix path symlink files, preceded by 
>> a flag ("magic cookie") value, and with system attribute, to allow 
>> compatibility with FAT file system limitations, or else NFS symlinks on NFS 
>> filesystems.
>> CYGWIN env var settings allow creation of Windows shortcuts and symbolic link 
>> reparse points instead of its default (equivalent to winsymlinks:sys), when 
>> supported by the file system and Windows release:
>>     https://cygwin.com/cygwin-ug-net/using-cygwinenv.html
>>     https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks

-- 
Take care. Thanks, Brian Inglis              Calgary, Alberta, Canada

La perfection est atteinte                   Perfection is achieved
non pas lorsqu'il n'y a plus rien à ajouter  not when there is no more to add
mais lorsqu'il n'y a plus rien à retirer     but when there is no more to cut
                                 -- Antoine de Saint-Exupéry

Re: Cygwin tool to differ junctions from soft links?

[matthew patton]

[-- Attachment #1: Type: text/plain, Size: 1406 bytes --]

>> Cygwin never creates Windows Directory or Filesystem Junction reparse points,
>> and by default it uses its own version of Unix path symlink files, preceded by 
>> a flag ("magic cookie") value, and with system attribute, to allow 
>> compatibility with FAT file system limitations, or else NFS symlinks on NFS 
>> filesystems.
>> CYGWIN env var settings allow creation of Windows shortcuts and symbolic link 
>> reparse points instead of its default (equivalent to winsymlinks:sys), when 
>> supported by the file system and Windows release:
>>     https://cygwin.com/cygwin-ug-net/using-cygwinenv.html
>>     https://cygwin.com/cygwin-ug-net/using.html#pathnames-symlinks

That ^^^ hasn't been true for how many years now? That was the OLD, deprecated mechanism which hasn't seen the light of day since what, WIndows 7 or 10?
13:36 45 $ unset CYGWIN; /bin/ln -s README.md test-link13:37 46 $ cmd /c dir /a: test-link
 Volume in drive C is Windows
 Directory of C:\Users\pattonma
11/17/2023  01:37 PM    <JUNCTION>     test-link [...]               1 File(s)              0 bytes               0 Dir(s)  241,024,512,000 bytes free
My environment is shared between Win10, Cygwin, and WSL and Dropbox for a bunch of targets of symlinks. Some 'DOS' tools, specifically AWS CLI can't follow Junctions so I had to take matters into my own hands.