[OS X TeX] OT: users and groups on Leopard

[Bruno Voisin]

Sorry for abusing this list with such an OT question, but after 2  
hours of search I'm about to give up and try here as last-resort  
measure before giving up completely.

Does anybody know how on Leopard one can access the list of users and  
groups on a given Mac, together with their numeric equivalents (=  
ids)? Here I mean not just the account owners on the Mac, but all the  
users and groups defined by OS X for its various components and  
services. On Tiger and before (or was it Panther?) it was very easy  
using /Applications/Utilities/NetInfo Manager. On Leopard:

- There's /Applications/Utilities/Directory Utility, but it doesn't  
seem to do exactly the same job.

- Apparently, starting from Tiger, OS X is no longer using standard  
unix files such as /etc/passwd, /etc/master.passwd and /etc/group.  
Instead, it's using a database-like mechanism involving such things as  
Open Directory, Directory Services, and Access Control Lists. There's  
a command-line utility dscl (Directory Service Command Line) that is  
said to allow access to the list of users and the like, but after some  
time studying its man page I couldn't find how to operate it properly.  
Namely, typing in "dscl . -read /Users/bvoisin" returned all kinds of  
info on my user account (including my id which seems to be 501), more  
than I ever wanted to know, but how to get summary info on all the  
users?

- There's a massive amount of info inside <http://images.apple.com/server/macosx/docs/User_Management_v10.5.mnl.pdf 
 >, but it's really very technical and specific to OS X Server to some  
extent. There's list of predefined user accounts and ids on p. 56, a  
list of predefined group accounts and ids on pp. 90-91, and on p. 67  
there are some details on user ids (namely that 0-100 are reserved for  
system use while 501 and above correspond to users created via the  
Accounts panel in System Prefs), but nothing more specific.

Could somebody having knowledge on these matters just point me where  
to look?

My reason for asking that: an external hard drive I use for Time  
Machine backups and also for manual backups of some files has  
suddenly  started to refuse any manual copy. There's room enough on  
the drive for the copy, so that's not the issue. I traced this to  
files and directories having switched ownership, for some reason, to  
group 999 and for some of them to user 999, and to being only writable  
by that user and group. Before changing the permissions, I would just  
be sure that 999 hasn't some special meaning for OS X (like being  
reserved for Time Machine use).

Bruno Voisin