Enightening sought: User-ID, Owner & Permission

[SYNass IT Ubuntu / Linux]

On Tue, 2008-06-10 at 10:10 -0700, David Fox wrote:
> On Mon, Jun 9, 2008 at 8:13 PM, SYNass IT Ubuntu / Linux
> <i-ubux at synass.net> wrote:
> > My data entered normally are: svobi & my full name !
> > With my future plan it thought of: sn & its full name ...
> > ... and the previously used one will be the second one !?
> 
> Adding users is pretty much a trivial thing. What is more important,
> especially when migrating or accessing data between systems, or even
> new installs, is the file ownership and group id. Permissions are
> checked by the user id, not the given name. Oftentimes (especially on
> new installs) the user id given in the installation (and in
> /etc/password) doesn't match the userid numbers stored in the files'
> metadata. Often this will happen when switching distributions, because
> not everyone starts their first  (default) user at user id 500, or
> 1000, or what have you. So you get a permission denied error even
> though it may appear you own the files.
> 
> So you could change the user name and as long as the user id is kept
> the same things should work.
> 
> Or you could chgrp everything that is in /home/$user to the users
> group (if it isn't already) and addgroup this new username to the
> users group. Then everybody in the users group has access to the same
> files.
> 
> The user id should be automatically assigned sequentially stating at 1000.

Hi David and Thilo
Thanks for your feedbacks and hints !

Yes, adding users is a trivial thing and this isn't the specific problem
I had asked for. ;-)

If not mistaken: 
The first user enlisted with the installation / setup shall have some
special privileges !?

If this is true:
What are the consequences when changing from first to second one ???

Again a sample as currently used:
his system w/single user: User-ID: his / User name: man
her system w/single user: User-ID: her / User name; woman

Intentioned use for future:
his system (still) w/single user: User: both / User name: fam as / at
installation / setup PLUS
to be used normally: User-ID: his / User name: man

his system (still) w/single user: User: both / User name: fam as / at
installation / setup PLUS
to be used normally: User-ID: her / User name: woman

The difference will only be in the first setup (common) user id and user
name ...
... the previously first / single ones remain and are being 2nd but
normally and most used 
for each one !!!

Sorry if my explanation gets too longwinded. ;-|

TIA for further enlightening and assistance. ;-)
Cheers, svobi