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Date:	Mon, 3 Feb 2014 22:05:22 +0100
From:	Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: How big are your /etc/passwd and /etc/group files?
Message-ID:	<20140203210522.GR2821@calimero.vinschen.de>
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On Feb  3 17:52, Kurt Franke wrote:
> Corinna Vinschen <corinna-cygwin <at> cygwin.com> writes:
> > This means, a rewrite of the /etc/passwd, /etc/group reading code from
> > "all or nothing" to "one at a time when needed".  Maybe that's in fact
> > the way to go.
>=20
> dbm files was already used in yellow pages two dekades ago.
> maybe there are some good examples how to do this (yppasswd etc.)

We can't use dbm unless we provide the functions as part of the Cygwin DLL.

> > In theory, we don't want to keep the files around anyway.  I have
> > implemented ways to configure user settings from /etc/passwd (like
> > home dir or login shell) in the local SAM or in AD.  So the admin
> > can switch to centralized maintainance even for Cygwin stuff.
>=20
> how to handling setting of the the primary group in /etc/passwd ?

I don't understand the question.  If your user has an /etc/passwd entry,
you can simply change the pw_gid field in the file, just as today.

> is it possible to store in in SAM ?

In AD the primary group is what's defined in the primaryGroupID field,
just as for your Windows user account, so your Cygwin primary group is
always the same as the Windows primary group.  What your admin set it
to, or "Domain Users" by default.  In SAM it's always "None".  Override
is only possible via /etc/passwd for now.

So far, the overridable values are defined like this:

- In AD, Cygwin will utilize the PosixAccount/PosixGroup entries per
  RFC 2307, available since Server 2003 R2.  For a user

    uid                overrides Windows username
    gecos              adds gecos info
    unixHomeDirectory  sets the Cygwin home directory
    loginShell         sets the login shell
    uidNumber          is used for the mapping from NFS/Samba shares
                       to the Windows/Cygwin uid

  For a group

    cn                 overrides Windows groupname
    gidNumber          is used for the mapping from NFS/Samba shares
                       to the Windows/Cygwin gid
=20
- In SAM (only used for local accounts), there are no freely definable
  fields for users or groups, except for the "Description" field.
  Therefore, you can set values using a faux-XML syntax in the
  "Description" field.  Here's what is supported right now:

  <CYGWINNAME:bla/>    overrides Windows username/groupname
  <CYGWINHOME:path/>   sets the Cygwin home directory to "path"
  <CYGWINSHELL:shell/> sets the login shell to "shell"

- pw_uid, pw_gid and gr_gid are computed per the SFU rules.  Local
  accounts have a uid/gid of 0x30000 + RID, primary domain accounts have
  a uid/gid of 0x100000 + RID, accounts from a trusted domain have the
  uid/gid trusted_domain.posix_offset(*) + RID.

  If you want to override pw_uid, pw_gid, or gr_gid, you have to add an
  entry to /etc/passwd or /etc/group.  But given that the uid/gid values
  have no importance, this should not be necessary.

Please note that this is all work in progress.  Details can still change
for one reason or another.  The upcoming 1.7.28 Cygwin release will not
have any of this.  I'll check in the changes only after we released 1.7.28.

(*) http://msdn.microsoft.com/en-us/library/windows/desktop/ms722487%28v=3D=
vs.85%29.aspx

> > On the other hand, we'd like to keep passwd and group for home users
> > which don't feel comfortable to make changes to the SAM, but then
> > we only need very tiny files with one or two entries anyway.
> >=20
> > Reading the files on demand only might be the right thing to do.
> > Catching two birds with one stone...
>=20
> it may be possible to have both using SAM but with a frontend named
> /etc/passwd respective /etc/group
>=20
> how about setting up read/write devices for passwd and group contents
> in /dev/ directory and just create symobolic links to it in /etc/ ?
> changes written to the devices of should be allow only to admins.
> such changes then should go done to SAM behind it as only storage locatio=
n.
>=20
> (this would make cygwin have the most modern handling of theses files
>  and become an example for the different unices and linux :-) )

That's not feasible.  The /etc/passwd and /etc/group files are supposed
to stay real files which can be used to override the stuff from AD/SAM
for people feeling more comfortable with that.  You *can* utilize AD and
SAM, but you don't have to.


Corinna

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

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