> explain how it could be more elaborate.

it's completely up to them (as it is to fossil or kfs, which use a file 
/adm/users that they maintain themselves).
the location and representation of group membership, and its interpretation are 
all independent things.
that is, all three aspects could be handled by different services: for instance 
something like google's Chubby could
store a group map in s-expression form [unknown to chubby] but read and 
interpreted by other servers, even with
different interpretations of what that representation meant)

as another example, in a flash file system we did for inferno, there wasn't an 
/adm/users but a ctl file
of some sort received requests to manage a group membership similar to fossil 
console requests.

as a further example, SPKI's public key certificates can be used in various 
ways to establish group membership,
typically by producing a certificate stating that a given principal 
(represented by a public key)
is a member of a local name (ie group) rooted at another principal's public 
key. the latter principal
might correspond to the `owner' of a resource.  this example is more 
interesting than some of the others
because there isn't (in general) a group membership list; also SPKI itself 
allows delegation and compound
group names.

in your case, however, a simple scheme might have the kernel (or just a device) 
accept a ctl request that added
or removed a user name from a local group table, and then system start up 
script(s) would load the table from some agreed source
(and presumably one that's adequately reliable).  i think something like that 
was mentioned,
if not discussed, many months ago on the list.

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