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Date: Wed, 8 Jan 2014 16:58:50 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Re: Windows 8 group won't respect /etc/passwd or /etc/group
Message-ID: <20140108155850.GG1336@calimero.vinschen.de>
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On Jan  8 10:34, John Smith wrote:
> Hi there,
>=20
> First, thanks for the detailed reply!!
>=20
> >>I've been struggling with an issue trying to figure out why Windows
> >>8.1 won't seem to respect the trick of setting your /etc/password to
> >>use a default group such as users instead of 'none'.  There are a
> >>few other discussions on this board around changing the group to
> >>"Users" and modifying the /etc/passwd to have a default group.
> >
> >Not sure if the User's Guide is explaining it badly or not, but "None"
> >*is* a group.  It's the primary (what you call "default") group for all
> >users on a local machine not connected to a Windows domain, and it has
> >the SID S-1-5-21-<xxx>-<yyy>-<zzz>-513.  If you call mkgroup -l it shows
> >up like this:
> >
> >  None:S-1-5-21-3229976424-329291882-2774727752-513:513:
> >
> >assuming you have an english system, otherwise you see a localized
> >group name.
>=20
> Yes, I understand this part.  And I would be happy to see this group
> show up, but it does not seem to be able to identify "None" as the
> group.>
>=20
> >Yes, of course.  Changing the primary group via /etc/passwd only
> >works for Cygwin processes and their child processes.  It does not
> >change the default user token of all processes.  How should that
> >work, especially since the OS itself doesn't allow to change the
> >primary group of local user accounts.
>=20
> Interesting -- so we can change permissions via cygwin, (unless
> we're mounted as noacl) but not groups?

The primary group membership of a file is determined by the processes
user token at the time of writing a file.  Native processes not started
by Cygwin processes will have the "none" primary group, unless you're
a domain user.

> I'm not trying to change
> the default group necessarily - that would be convenient, of course,
> but the most frustrating part is that it's changing it *back*.

That's not how it works for me, even with Notepad.  It only changes
the file content, not the ownership.

> In *nix, once you change a group, just editing a file won't change
> the group back to something else.

That doesn't happen on Cygwin, too.

> Optimally I would find a way to change the default created group,
> but I can survive if cygwin (the OS?) will at least remember the
> group when I change it to something else.

The OS is Windows.  Cygwin does know the primary group and it won't
change it at a whim either.

> >>Well, technically
> >>it's coming back as 4294967295.  (64 bit cygwin)
> >
> >This can only happen if you dropped the "None" group from your
> >/etc/group file.  mkgroup -l > /etc/group will rectify it.
>=20
> See, this is why I'm so baffled: I *do* have this group.  It's the
> last entry in my /etc/groups:
>=20
> None:S-1-5-21-339652832-68357117-3096367938-513:513:

And your account is a local user account, not a domain account?
If so, the None entry won't be used, and the group information
is ???? because your real primary group is missing in /etc/group.
Recreate your /etc/passwd and /etc/group files using=20
mkpasswd -l -d and mkgroup -l -d.

> >Except for the 4294967295, which is just a missing entry for "None" in
> >/et/cgroup, this is normal.  See above.  It's not a problem of the OS or
> >Cygwin, you're just misunderstanding how this works.  User tokens
> >are propagated from process to child process.  The parent processes
> >of any first Cygwin process is a native Windows process with an
> >unchanged user token, so it has "None" as primary group.  At startup
> >of the first Cygwin process, it reads /etc/passwd and /etc/group
> >and changes the primary group in its user token if requested by your
> >settings.  This changed user token will be inherited by child processes
>=20
> Ah, I see.  So do you know if there is anyway to tell applications
> to change groups, to avoid this issue of the None/blank/missing
> group?

I'm thoroughly confused by this question.  This doesn't happen.  You
seem to be interpreting something you see the wrong way but I can't make
out what that is, sorry.

> >started from this process and subsequent processes, but it does not
> >affect the user tokens of unrelated processes, especially not of
> >non-CYgwin processes started from Explorer.  If you want Notepad to
> >use your group setting, start it from a Cygwin process.
>=20
> Just tested this, and yes, that definitely works.  OK, thank you for
> this.  It's not the solution yet but it's on the right track.
>=20
> Do you have any suggestions or thoughts as to why I'm still seeing
> that group of ??????????? even though "none" exists in my
> /etc/group?  I was assuming that the default group must be something
> else, not "None", maybe some virtual group that cygwin can't detect
> with mkgroup.

mkgroup doesn't print all existing groups, especially not most of
the predefined groups like "Local", "Createor Owner", etc., see
http://msdn.microsoft.com/en-us/library/windows/desktop/aa379649%28v=3Dvs.8=
5%29.aspx
These groups are not used for group membership usually, even if they
are part of a user token.  Try the icacls command on a file to see
what it prints and compare the info with your passwd and group files.


Corinna

--=20
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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