From: Brian Inglis <Brian.Inglis@SystematicSW.ab.ca>
To: cygwin@cygwin.com
Subject: Re: Switching groups with newgrp - how to get the new group with |GetTokenInformation()| ?
Date: Sun, 10 Mar 2024 21:49:13 -0600 [thread overview]
Message-ID: <8073a531-0e17-43e3-9620-b485edf16d69@SystematicSW.ab.ca> (raw)
In-Reply-To: <CAAvCNcC=RpUgEia3vcZXqRD4CgyYnFRWXA3O+Kwfi3kQTNjD8A@mail.gmail.com>
On 2024-03-10 19:30, Dan Shelton via Cygwin wrote:
> On Sat, 9 Mar 2024 at 22:27, Glenn Strauss via Cygwin <cygwin@cygwin.com> wrote:
>> On Wed, Mar 06, 2024 at 02:01:06PM +0100, Corinna Vinschen via Cygwin wrote:
>>> On Mar 5 23:38, Dan Shelton via Cygwin wrote:
>>>> On Sat, 24 Feb 2024 at 14:11, Corinna Vinschen via Cygwin wrote:
>>>>> On Feb 23 22:15, Dan Shelton via Cygwin wrote:
>>>>>> HOWEVER, there is another Cygwin bug:
>>>>>> "getent group mywingrp1" does not list any group members, even after
>>>>>> "net localgroup mywingrp1 mywinuser44 /add", which is a POSIX
>>>>>> violation.
>>>>>
>>>>> Not a bug. Two problems:
>>>>>
>>>>> - Getting members of a group can be an extremly costly operation
>>>>> in a domain or, worse, a domain forest, or even worse, if the
>>>>> domain or domain forest is remote.
>>>>>
>>>>> - Alonmg the same lines, getting members of a group can be extremly
>>>>> costly in big orgs with thousands of users. Nobody want's to clutter
>>>>> up space with the list of members in the "Domain Users" group.
>>>>>
>>>>> - Permissions to enumerate members of a group are restricted.
>>>>> By default only admins and group members are allow to enumerate
>>>>> members and this can be restricted further by domain admins.
>>>>>
>>>>> Therefore we dropped even trying to populate gr_mem, considering
>>>>> that even in its original form on Unix systems, it's used only
>>>>> to add supplementary groups. To do this right on Windows is even
>>>>> more costly than blindly enumerating.
>>>>>
>>>>> It's not a bug, it's a feature :)
>>>>
>>>> Could you add an option to getent so that the full lookup can be
>>>> requested via command line, pls?
>>>
>>> That's not possible. getent just calls getpwent/getgrent.
>>>
>>>> Always editing /etc/nsswitch.conf
>>>> forth and back is not a elegant solution, aside from race conditions
>>>> with other users on a system
>>>
>>> So, here we go again.
>>>
>>> - What exactly are you trying to accomplish by enumerating the accounts?
>>> Maybe you won't actually need it for your task at hand.
>>>
>>> - Why do you have to change nsswitch.conf "back and forth"?
>>> Just change it once and you're done.
>>>> Always editing /etc/nsswitch.conf
>>>> forth and back is not a elegant solution, aside from race conditions
>>>> with other users on a system
Plus you need to terminate all processes in a tree and/or restart cygserver to
pick up any changed information.
>> Please check the man page for getent.
>>
>> man getent
>> getent --help
>>
>> You can use -s or --service to override the service used without
>> editing nsswitch.conf. The man page on Linux provides an example
>> with a bit more details than the man page for getent under cygwin.
>> https://www.man7.org/linux/man-pages/man1/getent.1.html
That web page does not even define services (and it is not the same as the
services database), better info is available on the linked page:
https://man7.org/linux/man-pages/man5/nsswitch.conf.5.html
but none of those Linux services/sources apply on Cygwin.
The Cygwin getent man page does not document the current implementation; and
getent --help does not explain what a service configuration is: possibly the
same as the line you specify after db_enum, or maybe just one source?
Rely on /etc/nsswitch.conf; a bit better explanation is available if you install
Cygwin man-pages-linux then run:
$ man -m linux getent
and, as above, none of those Linux services/sources apply on Cygwin.
> Is this feature supported under Cygwin /usr/bin/getent?
>
> I tried it, but did not see any change. Even putting garbage into it,
> e.g. /usr/bin/getent -s "$(man man)" group foo does not yield an
> error.
This facility is a generic lookup using certain sets of functions accessing
information from various sources defined in comments in Cygwin's
/etc/nsswitch.conf, so if you pass in nonsense, you just will not get a match,
and nothing will be output.
You will only get an error if information required to perform a lookup is
unrecognized, for example option, database, or missing, for example key, where
enumeration is not supported.
Perhaps using meaningful commands on existing but elusive groups above like:
$ getent -s local group mywingrp1
$ getent -s primary group mywingrp1
may produce results that match what you should expect, and possibly even
$ getent -s 'local primary' group mywingrp1
may produce output.
--
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
next prev parent reply other threads:[~2024-03-11 3:49 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-22 17:38 Roland Mainz
2024-02-22 19:11 ` Corinna Vinschen
2024-02-23 13:03 ` Roland Mainz
2024-02-23 15:47 ` Corinna Vinschen
2024-02-23 18:45 ` Roland Mainz
2024-02-23 21:15 ` Dan Shelton
2024-02-24 13:11 ` Corinna Vinschen
2024-03-05 22:38 ` Dan Shelton
2024-03-06 13:01 ` Corinna Vinschen
2024-03-09 21:26 ` Glenn Strauss
2024-03-11 1:30 ` Dan Shelton
2024-03-11 3:49 ` Brian Inglis [this message]
2024-03-11 16:54 ` Corinna Vinschen
2024-03-11 1:28 ` Dan Shelton
2024-03-11 16:56 ` Corinna Vinschen
2024-04-19 23:44 ` Dan Shelton
2024-04-26 9:04 ` Andrey Repin
2024-02-24 16:57 ` Brian Inglis
2024-02-24 12:53 ` Corinna Vinschen
2024-02-24 14:38 ` Will all SIDs fit into |SECURITY_MAX_SID_SIZE| bytes ? / was: " Roland Mainz
2024-02-24 18:57 ` Corinna Vinschen
2024-02-25 21:04 ` Roland Mainz
2024-02-25 22:32 ` gs-cygwin.com
2024-02-26 4:17 ` gs-cygwin.com
2024-02-26 16:12 ` [EXTERNAL] " Lavrentiev, Anton (NIH/NLM/NCBI) [C]
2024-02-26 9:20 ` Corinna Vinschen
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8073a531-0e17-43e3-9620-b485edf16d69@SystematicSW.ab.ca \
--to=brian.inglis@systematicsw.ab.ca \
--cc=cygwin@cygwin.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).