How to change some GID

[ZIYAD A. M. AL-BATLY]

On Sat, 2005-04-02 at 02:37 +0200, Olivier Vogel wrote:
> Let me first explain my situation.
> 
> I would like to introduce Ubuntu in my school. All the computers are
> Macintosh, working with Mac OS X. There is a ldap database of users and
> all the home directories are on a server (with Mac OS X Server). I did
> success to manage the login to the server. So the problem is not here.
> 
> The problem begins with the authorizations of the users. I have
> understand that the users must belong to the groups:
> gid 24 for cdrom (access to cdrom)
> gid 25 for floppy (access to floppy)
> gid 29 for audio (have sound and listen music)
> gid 46 for plugdev (can mount usb stick and so on) 
> gid 108 for scanner (can use a scanner)
> 
> BUT, the administrator of Mac OS X Server is unable to create such
> groups with the same gid on the ldap database. All the groups that he
> can create have a gid > 500.
> 
> So, I have tried to change the gid of these groups:
> cdrom -> 2024
> floppy -> 2025
> audio -> 2029
> plugdev -> 2046
> scanner -> 2108
> 
> Only the change for the audio group has succeeded and not the others. I
> have tried with Terminal
> sudo groupmod -g 2024 cdrom (without success)
> sudo groupmod -o -g 2024 cdrom (seems to success)
> 
> But, after these changes, the automounting of cdrom doesn't work
> anymore. So I have to restore cdrom to gid 24.
> 
> Please help me to solve this problem; otherwise my school will never
> know Ubuntu!!!
> 
> Thanks for your help.
> 
> Olivier
> 
> 
I have an (not-so-great) idea: Why don't you create (on the Ubuntu
system) a new groups with the same GID of those on the Mac OS X:
Group cdrom2 with GID 2024 and add all those whom belong to the original
cdrom group to this new group. In result each user will be in group
cdrom and cdrom2 and thus problem solved (that is: if I did understand
the problem correctly in the first place). Do the same with the other
groups and you're set.

As a side note: It is a very *BAD* idea to change the users/groups that
are preset by the system for various reasons. In  a nutshell: Don't ever
change any UID or GID below 100 under Debian or any derivate
distributions (this includes Ubuntu).

Another note: I think there is a better solution (sadly I don't know
it). I think your problem should be solved by a means of mapping
UIDs/GIDs from the Ubuntu systems to the Mac OS X and vis versa.

As always: I hope this helps even a little.
Ziyad.