Issues with ACL settings after updating to the latest cygwin.dll

Issues with ACL settings after updating to the latest cygwin.dll

[K Stahl]

I've discovered that when I use cvs to pull a module, the security
settings on the created files and directories are incorrect.  When I
view the security settings of the files, I noticed an invalid "NULL
SID" group permission was added.  If I delete this value, I can
properly execute the file, but if I leave it there, the file I'm
trying to execute will not run.

NOTE:
If I use wincvs, the files are fine.  This only happens within the
cygwin environment.

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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Jan 29 17:52, K Stahl wrote:
> I've discovered that when I use cvs to pull a module, the security
> settings on the created files and directories are incorrect.  When I
> view the security settings of the files, I noticed an invalid "NULL
> SID" group permission was added.  If I delete this value, I can
> properly execute the file, but if I leave it there, the file I'm
> trying to execute will not run.

I'm not quite sure what you observe there.  The NULL SID ACE only
contains extra information about some POSIX bits and the MASK value.
It's existence and setting should not influence what you can do with the
file.  The permission bits are explicitely set elsewhere in the ACL.

Can you reproduce the issue so that I can see what's going on?  I need
the icacls output for the file and its parent directory, as well as the
output from getfacl for both.


Thanks,
Corinna

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Re[2]: Issues with ACL settings after updating to the latest cygwin.dll

[xnor]

>I'm not quite sure what you observe there.  The NULL SID ACE only
>contains extra information about some POSIX bits and the MASK value.
>It's existence and setting should not influence what you can do with 
>the
>file.  The permission bits are explicitely set elsewhere in the ACL.
>
>Can you reproduce the issue so that I can see what's going on?  I need
>the icacls output for the file and its parent directory, as well as the
>output from getfacl for both.
I have the same problem with Transmission.

I noticed this first when I tried to execute an exe that was downloaded 
with Transmission compiled in cygwin. When trying to start the exe from 
Explorer an error dialog will appear:
"Windows cannot access the specified device, path, or file. You may not 
have the appropriate permissions to access the item."

When going to file properties - security I get an information dialog 
window:
"The permissions on <program> are incorrectly ordered, which may cause 
some entries to be ineffective."

Proper permissions (of parent folder) look like this:
Authenticated Users: modify
SYSTEM: Full control
Administrators: Full control
Users: Read & execute


The permissions of the cygwin/transmission created files are (manually 
translated from German):
NULL SID: special
<My User>: special
Authenticated Users: Browse folder / Execute file
SYSTEM: Browse folder / Execute file
Administrators: Browse folder / Execute file
Users: Browse folder / Execute file
Nobody: Read
Authenticated Users: Read, write, execute
SYSTEM: Read, write, execute
Administrators: Read, write, execute
Users: Read, Execute
Everyone: Read


Also when going to advanced permissions it shows the same incorrectly 
ordered warning and asks me to re-order permissions.




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Re[3]: Issues with ACL settings after updating to the latest cygwin.dll

[xnor]

>Nobody: Read
Small correction, this entry is actually
S-1-5-21-559282050-488988736-2019639472-513

which actually stalls the file properties window when switching to the 
security tab for a while. I guess Windows is trying to resolve this SID 
but gives up (there is no such SID on my system) and eventually replaces 
the display name with Nobody.

Something is seriously broken here.


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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Feb  8 18:12, xnor wrote:
> 
> >Nobody: Read
> Small correction, this entry is actually
> S-1-5-21-559282050-488988736-2019639472-513
> 
> which actually stalls the file properties window when switching to the
> security tab for a while. I guess Windows is trying to resolve this SID but
> gives up (there is no such SID on my system) and eventually replaces the
> display name with Nobody.

No idea why this is stalling your machine, but the above group SID
always exists on all machines and is perfectly valid (SID == machine SID
+ RID 513).  It's the primary group of all local (non-AD) user accounts,
and it's called "None" in English, with a localized name in other locales.

> Something is seriously broken here.

Not that.


Corinna

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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Feb  8 17:48, xnor wrote:
> 
> >I'm not quite sure what you observe there.  The NULL SID ACE only
> >contains extra information about some POSIX bits and the MASK value.
> >It's existence and setting should not influence what you can do with the
> >file.  The permission bits are explicitely set elsewhere in the ACL.
> >
> >Can you reproduce the issue so that I can see what's going on?  I need
> >the icacls output for the file and its parent directory, as well as the
> >output from getfacl for both.
> I have the same problem with Transmission.
> 
> I noticed this first when I tried to execute an exe that was downloaded with
> Transmission compiled in cygwin. When trying to start the exe from Explorer
> an error dialog will appear:
> "Windows cannot access the specified device, path, or file. You may not have
> the appropriate permissions to access the item."

Not sure what Transmission is, but files downloaded with POSIX
tools are usually not executable.  For instance, download Cygwin's
setup-x86.exe with wget.  Then try to execute it.  It won't since
the permissions are set according to your umask and without execute
permissions, e.g., 0644.  This is normal.

> When going to file properties - security I get an information dialog window:
> "The permissions on <program> are incorrectly ordered, which may cause some
> entries to be ineffective."
> 
> Proper permissions (of parent folder) look like this:
> Authenticated Users: modify
> SYSTEM: Full control
> Administrators: Full control
> Users: Read & execute
> 
> 
> The permissions of the cygwin/transmission created files are (manually
> translated from German):
> NULL SID: special
> <My User>: special
> Authenticated Users: Browse folder / Execute file
> SYSTEM: Browse folder / Execute file
> Administrators: Browse folder / Execute file
> Users: Browse folder / Execute file
> Nobody: Read
> Authenticated Users: Read, write, execute
> SYSTEM: Read, write, execute
> Administrators: Read, write, execute
> Users: Read, Execute
> Everyone: Read
> 
> 
> Also when going to advanced permissions it shows the same incorrectly
> ordered warning and asks me to re-order permissions.

The permissions must *not* be reordered.  If Cygwin creates permissions
incorrectly it's one thing, but the order to emulate POSIX permissions
is non-canonical.  Reordering them will break them.

Please provide the exact output from icacls.


Thanks,
Corinna

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Corinna Vinschen                  Please, send mails regarding Cygwin to
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Red Hat

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Re[2]: Issues with ACL settings after updating to the latest cygwin.dll

[xnor]

>Not sure what Transmission is, but files downloaded with POSIX
>tools are usually not executable.  For instance, download Cygwin's
>setup-x86.exe with wget.  Then try to execute it.  It won't since
>the permissions are set according to your umask and without execute
>permissions, e.g., 0644.  This is normal.
The behavior has changed with the ACL change in Cygwin and I would not 
consider that "normal". The warning from Windows is not normal.

I realize that the previous implementation was already problematic and 
messed with permissions but I did not notice it since it never denied 
executing executables.


>The permissions must *not* be reordered.  If Cygwin creates permissions
>incorrectly it's one thing, but the order to emulate POSIX permissions
>is non-canonical.  Reordering them will break them.
>
>Please provide the exact output from icacls.
They *have* to be reordered to be modifiable in Windows/Explorer. In 
other words, if I want to change permission the new ACL behavior ensures 
that it breaks the Cygwin permissions?


Here is the output from icacls /saveacl for some file:
D:P(D;;RPWPDTRC;;;S-1-0-0)(A;;0x1f019f;;;S-1-5-21-559282050-488988736-2019639472-1001)(D;;WP;;;AU)(D;;WP;;;SY)(D;;WP;;;BA)(D;;WP;;;BU)(A;;FR;;;S-1-5-21-559282050-488988736-2019639472-513)(A;;0x1201bf;;;AU)(A;;0x1201bf;;;SY)(A;;0x1201bf;;;BA)(A;;0x1200a9;;;BU)(A;;FR;;;WD)

After letting Windows fix the order:
D:PAI(D;;RPWPDTRC;;;S-1-0-0)(D;;WP;;;AU)(D;;WP;;;SY)(D;;WP;;;BA)(D;;WP;;;BU)(A;;0x1f019f;;;S-1-5-21-559282050-488988736-2019639472-1001)(A;;FR;;;S-1-5-21-559282050-488988736-2019639472-513)(A;;0x1201bf;;;AU)(A;;0x1201bf;;;SY)(A;;0x1201bf;;;BA)(A;;0x1200a9;;;BU)(A;;FR;;;WD)

Here is what's "normal" for Windows if I create a file under a new 
folder on C: in Explorer:
D:AI(A;ID;FA;;;BA)(A;ID;FA;;;SY)(A;ID;0x1200a9;;;BU)(A;ID;0x1301bf;;;AU)

Strangely enough this is displayed as "-rwxrwx---+ MyUser None" with `ls 
-l` even though my user is in the group Administrators.


Here is what I would expect:
MyUser is in the group Administrators. Given the inherited permissions 
above a Windows-created file should be shown as "-rwxrwxr--+ MyUser 
Administrators"?

After chmod 664 I would expect this:
- still inherit all the permissions
- add permission MyUser DENY execute
- add permission Administrators DENY execute
- add permission Everyone ALLOW read

Instead Cygwin copies all permissions, drops the inheritance, copies 
them again, adds None, adds NULL SID ...

After a consecutive chmod 770 I would expect the above non-inherited 
permissions to be removed again.



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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Andrey Repin]

Greetings, xnor!

>>The permissions must *not* be reordered.  If Cygwin creates permissions
>>incorrectly it's one thing, but the order to emulate POSIX permissions
>>is non-canonical.  Reordering them will break them.
>>
>>Please provide the exact output from icacls.
> They *have* to be reordered to be modifiable in Windows/Explorer. In 
> other words, if I want to change permission the new ACL behavior ensures 
> that it breaks the Cygwin permissions?

It was always the case.
Permissions are NOT REQUIRED to be ordered in a specific way, but Explorer is
only capable of editing them in the only one way.
Means, Explorer is deficient. Explorer. Not Windows. Windows is perfectly
capable of handling the Cygwin ACL in the intended way.


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With best regards,
Andrey Repin
Wednesday, February 10, 2016 05:05:14

Sorry for my terrible english...


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Re[2]: Issues with ACL settings after updating to the latest cygwin.dll

[xnor]

>It was always the case.
>Permissions are NOT REQUIRED to be ordered in a specific way, but 
>Explorer is
>only capable of editing them in the only one way.
>Means, Explorer is deficient. Explorer. Not Windows. Windows is 
>perfectly
>capable of handling the Cygwin ACL in the intended way.
No, it really wasn't.

The ACLs were fine until the change in the new Cygwin version. Now there 
are 12 ACL entries, all non inherited / inheritance is broken, for each 
file...

Also, I always ways able to change ACLs through Explorer without 
warnings, which I need to do from time to time.

I'm sorry but all of this can be summed up as bad design.


I've explained what ACLs should be added by Cygwin in a related message. 
By making use of default, inherited ACLs, at most 3 (+1 for whatever 
NULL SID is doing ...) are needed. At least I see no reason why there 
should be such a bloat.

Besides, if cygwin set ACLs properly on the root folder this could be 
reduced to 0 additional non-inherited ACLs for many files.


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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Andrey Repin]

Greetings, xnor!


>>It was always the case.
>>Permissions are NOT REQUIRED to be ordered in a specific way, but 
>>Explorer is
>>only capable of editing them in the only one way.
>>Means, Explorer is deficient. Explorer. Not Windows. Windows is 
>>perfectly
>>capable of handling the Cygwin ACL in the intended way.
> No, it really wasn't.

> The ACLs were fine until the change in the new Cygwin version. Now there 
> are 12 ACL entries, all non inherited / inheritance is broken, for each 
> file...

That's normal POSIX behavior.
If you want Windows behavior, mount your outside-Cygwin FS with noacl flag.


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Andrey Repin
Wednesday, February 10, 2016 21:20:45

Sorry for my terrible english...


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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Feb  9 20:53, xnor wrote:
> 
> >Not sure what Transmission is, but files downloaded with POSIX
> >tools are usually not executable.  For instance, download Cygwin's
> >setup-x86.exe with wget.  Then try to execute it.  It won't since
> >the permissions are set according to your umask and without execute
> >permissions, e.g., 0644.  This is normal.
> The behavior has changed with the ACL change in Cygwin and I would not
> consider that "normal". The warning from Windows is not normal.

Which warning do you mean here?

> I realize that the previous implementation was already problematic and
> messed with permissions but I did not notice it since it never denied
> executing executables.

No, but either way, the created ACL is not necessarily what Microsoft
describes as "canonical".  POSIX permissions just don't map well with
canonical-only ACLs.

The problem right now is that I can't reproduce what you encounter.
That's why I'm asking for the details in terms of the ACL, that is,
output from icacls and getfacl to compare the output and ideally
being able to reproduce and, even more ideal, fix it.

Come on, be fair.  The new ACL handling started out early 2015, got a
break when I realized that it doesn't work as is, and then got a new
test phase starting back in September.  Except for minor bugs it seemed
to work rather well.  Nobody reported this effect in all the 4 months of
test period.  You don't actually think I wouldn't have fixed it prior
to the release if I had known about it, do you?

> >The permissions must *not* be reordered.  If Cygwin creates permissions
> >incorrectly it's one thing, but the order to emulate POSIX permissions
> >is non-canonical.  Reordering them will break them.
> >
> >Please provide the exact output from icacls.
> They *have* to be reordered to be modifiable in Windows/Explorer. In other
> words, if I want to change permission the new ACL behavior ensures that it
> breaks the Cygwin permissions?

They are not supposed to be modifiable in Explorer.  If you want to
change permissions on a Cygwin ACL, use chmod or setfacl.

> Here is the output from icacls /saveacl for some file:
> D:P(D;;RPWPDTRC;;;S-1-0-0)(A;;0x1f019f;;;S-1-5-21-559282050-488988736-2019639472-1001)(D;;WP;;;AU)(D;;WP;;;SY)(D;;WP;;;BA)(D;;WP;;;BU)(A;;FR;;;S-1-5-21-559282050-488988736-2019639472-513)(A;;0x1201bf;;;AU)(A;;0x1201bf;;;SY)(A;;0x1201bf;;;BA)(A;;0x1200a9;;;BU)(A;;FR;;;WD)

Doh, I'm sorry, but I can't read this format very well.  Can you please
again send the standard icacls output as well as the output from getfacl
of the parent dir and the created file?  I'd like to have this problem
fixed, but I need your help.  As I said, it works fine for me and without
being able to reproduce I'm somewhat at a loss.

> Here is what's "normal" for Windows if I create a file under a new folder on
> C: in Explorer:

If you don't want POSIX perms, but standard Windows perms, use the "noacl"
mount option.  See https://cygwin.com/cygwin-ug-net/using.html#mount-table

> Here is what I would expect:
> MyUser is in the group Administrators. Given the inherited permissions above
> a Windows-created file should be shown as "-rwxrwxr--+ MyUser
> Administrators"?

Sorry, can't do that, *unless* you make "Administrators" the primary
group in your user token(*).  Even though your account is *member* of
the Administrators group, the group is *never* your primary group per
Windows.  All local accounts, independently of their group memberships,
have the group "None" as their primary group.  That's how Windows works,
and that hasn't changed since at least NT4.

Unless, of course, if you use a so-called "Windows account", one of
those accounts which you login with using your email address (was that
introduced with Windows 8?  I'm not sure).  In that case, the primary
group in your user token is set to your user account itself.  So your
primary group SID is your own user SID.  Duh!


Corinna

(*) There *is* a way to do that, but only inside Cygwin, see
    https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-mapping-passwdinfo

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Corinna Vinschen                  Please, send mails regarding Cygwin to
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Re: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Feb 10 12:55, Corinna Vinschen wrote:
> On Feb  9 20:53, xnor wrote:
> > Here is what I would expect:
> > MyUser is in the group Administrators. Given the inherited permissions above
> > a Windows-created file should be shown as "-rwxrwxr--+ MyUser
> > Administrators"?
> 
> Sorry, can't do that, *unless* you make "Administrators" the primary
> group in your user token(*).  Even though your account is *member* of
> the Administrators group, the group is *never* your primary group per
> Windows.  All local accounts, independently of their group memberships,
> have the group "None" as their primary group.  That's how Windows works,
> and that hasn't changed since at least NT4.
> 
> Unless, of course, if you use a so-called "Windows account", one of
> those accounts which you login with using your email address (was that
> introduced with Windows 8?  I'm not sure).  In that case, the primary
> group in your user token is set to your user account itself.  So your
> primary group SID is your own user SID.  Duh!
> 
> 
> Corinna
> 
> (*) There *is* a way to do that, but only inside Cygwin, see
>     https://cygwin.com/cygwin-ug-net/ntsec.html#ntsec-mapping-passwdinfo

Oh, and if it's not clear how this works under the hood, it's like this:

The Windows user token contains a couple of SID entries:

- The "user" SID
- The "owner" SID       (user and owner are not necessarily the same,
                         but, never mind)
- The primary group SID (which, it has to be said, is meaningless
                         in the Windows context and only kept for
                         POSIX compatibility)
- A list of group SIDs the user is member in.

For a local account, the primary group SID is set to "None", the local
group with RID 513.  For domain accounts this is typically the group
"Domain Users", the domain account with RID 513 (hmm...)

However, every process is allowed to switch the primary group entry of
its user token to *any* group mentioned in the group list, *or* even to
its user or owner SID.  If you use the aforementioned method to change
the primary group, what happens is that the first Cygwin process in a
process chain changes the primary group in its user token.  If the new
group is in the token's group list, this will work.

Child processes inherit the user token from their parent process, so
there's no reason to change the primary group again in a process tree.
Since that's a Windows property, this also works for non-Cygwin child
processes.

With the Administrators group there's a complication.  If you're running
a normal shell, it's running under UAC control.  UAC restricts the user
token of an admin user so that the admins group in the token group list
is "crippled":  The admins SID is still in the list, but with a flag
"DENY ONLY".  You're kind of not in the Administrators group anymore.
Only if an access check is performed, and the Admins group is denied
access to some object, this membership kicks in and denies the access.


HTH,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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Re[3]: Issues with ACL settings after updating to the latest cygwin.dll

[xnor]

>I have the same problem with Transmission.
Sorry for another mail, but I need to make another last correction:
It's not Transmission specific. A simple
$ cd /cygdrive/path/to/download/dir
$ touch test
will result in the same broken permissions for test.

Doing this in $HOME will result in these Windows permissions:
NULL SID
Everyone
<My User>
Nobody (actually non existent S-1-5-21-...)

There are also no warnings and no prompt to re-order permissions.


File permission for an older file (created before cygwin ACL changes):
Everyone
<My User>
Nobody (actually non existent S-1-5-21-...)


So the new ACL implementation simply messes up in directories with 
non-cygwin permissions.


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Re: Re[3]: Issues with ACL settings after updating to the latest cygwin.dll

[K Stahl]

On Feb 8, 2016 1:33 PM, "xnor" <xnoreq@gmail.com> wrote:
>
>
>> I have the same problem with Transmission.
>
> Sorry for another mail, but I need to make another last correction:
> It's not Transmission specific. A simple
> $ cd /cygdrive/path/to/download/dir
> $ touch test
> will result in the same broken permissions for test.
>
> Doing this in $HOME will result in these Windows permissions:
> NULL SID
> Everyone
> <My User>
> Nobody (actually non existent S-1-5-21-...)
>
> There are also no warnings and no prompt to re-order permissions.
>
>
> File permission for an older file (created before cygwin ACL changes):
> Everyone
> <My User>
> Nobody (actually non existent S-1-5-21-...)
>
>
> So the new ACL implementation simply messes up in directories with non-cygwin permissions.
>
>
>
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>

Thanks xnor for documenting the issue!  I've been on travel and didn't
have access to my cygwin installation.

In my case, I have to use CVS to download source code and executables.
Once a file is downloaded, the permissions are set.  Each file created
using the new ACL features has the NUL SID set and this in turn in
fine for regular files, but those that have an execution bit set will
not run unless I open their properties in Wnidows, change the security
permissions (which states there is a error).

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Re: Re[3]: Issues with ACL settings after updating to the latest cygwin.dll

[Corinna Vinschen]

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On Feb  9 10:01, K Stahl wrote:
> On Feb 8, 2016 1:33 PM, "xnor" <xnoreq@gmail.com> wrote:
> >
> >
> >> I have the same problem with Transmission.
> >
> > Sorry for another mail, but I need to make another last correction:
> > It's not Transmission specific. A simple
> > $ cd /cygdrive/path/to/download/dir
> > $ touch test
> > will result in the same broken permissions for test.
> >
> > Doing this in $HOME will result in these Windows permissions:
> > NULL SID
> > Everyone
> > <My User>
> > Nobody (actually non existent S-1-5-21-...)
> >
> > There are also no warnings and no prompt to re-order permissions.
> >
> >
> > File permission for an older file (created before cygwin ACL changes):
> > Everyone
> > <My User>
> > Nobody (actually non existent S-1-5-21-...)
> >
> >
> > So the new ACL implementation simply messes up in directories with non-cygwin permissions.
> >
> >
> >
> > --
> > Problem reports:       http://cygwin.com/problems.html
> > FAQ:                   http://cygwin.com/faq/
> > Documentation:         http://cygwin.com/docs.html
> > Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple
> >
> 
> Thanks xnor for documenting the issue!  I've been on travel and didn't
> have access to my cygwin installation.
> 
> In my case, I have to use CVS to download source code and executables.
> Once a file is downloaded, the permissions are set.  Each file created
> using the new ACL features has the NUL SID set and this in turn in
> fine for regular files, but those that have an execution bit set will
> not run unless I open their properties in Wnidows, change the security
> permissions (which states there is a error).

https://cygwin.com/ml/cygwin/2016-02/msg00077.html


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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