HYPER-V VMs: Cygwin /bin/getent group 'Virtual Machines' cannot find the group

[Brian Inglis]

On 2026-03-04 23:35, Jakob Bohm via Cygwin wrote:
> On 03/03/2026 10:49, Brian Inglis via Cygwin wrote:
>> On 2026-03-03 01:26, Aurélien Couderc via Cygwin wrote:
>>> On Mon, Mar 2, 2026 at 8:19 PM Martin Wege via Cygwin <cygwin@cygwin.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> we use HYPER-V virtual machines on Windows 10 and Windows 11. It seems
>>>> they use a "special" kind of group called 'Virtual Machines', which
>>>> Cygwin (3.6.5) /bin/getent cannot lookup:
>>>>
>>>> getent group 'Virtual Machines'
>>>> <nothing>
>>>>
>>>> Does anyone have ideas or clues how to get getent group to work with
>>>> this kind of Windows group?
>>>>
>>>> We want the Cygwin gid for that group, and use Cygwin commands to work
>>>> with those files...
>>>
>>> Déjà vu
>>>
>>> 1. Please read https://cygwin.com/pipermail/cygwin/2025-July/258505.html
>>>
>>> 2. Try this:
>>> getent group "NT VIRTUAL MACHINE+Virtual Machines"
>>> For me, with default (empty, except comments) /etc/nsswitch.conf, it
>>> does not work. Which I consider a bug.
>>
>> The defaults are chosen so that required system components work.
>> If you have additional requirements, such as interactive lookup, or your own 
>> scripts, you may add to the defaults, which adds to the overhead on every 
>> lookup, reduced if you run the `cygserver` cache.
>>
>> This is the default installed conf file:
>> <snip large config file default>

> OP isn't asking about enumeration, but direct lookup.  You answer is as inept
> as responding with hosts file settings when asked about why certain DNS
> lookups fail.  If lookup of a system built in group fails, core cygwin tools 
> such as /bin/ls fail.

All responses in these mailing lists are from subscribers who try to help in 
their spare time - disparaging comments just get posts ignored or posters 
killfiled!
As with emails, if responses are unhelpful, you have the same options.

Builtins are limited to those seven documented - five users - two groups - and 
everything else is looked up via the NS sources switch.
Lookup is otherwise either done from files or configured DB sources under 
db_enum, so the example below disables direct user lookups completely, and 
settings allow access to other sources:

# Examples:
# db_enum: none
#       No output from getpwent/getgrent at all.

Try setting `db_enum: all` and see if you can access the desired entries.

If not, please attach as text a Simple Test Case, unfiltered strace output, and 
complete output from `cygcheck -hrsv`, as per problem reporting guidelines below.

> The CYGWIN library implementation of getent functions need to be agile
> enough to handle any values handled by the similar Win32 functions. This in
> turn requires hardcoded logic for any values of the enum first DWORD after
> the uint48_t authority field in SID values, in this case "83". Alternatively, grow
> the uid_t type to 560 bits, which seems to be the limit of current Win32
> implementations (max 15 DWORDS after the authority and version byte fixed at
> 1).
Patches submitted according to guidelines below will be gratefully accepted and 
thoughtfully considered when some interested subscriber has spare time.

-- 
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 retrancher  but when there is no more to cut
                                 -- Antoine de Saint-Exupéry