I'd not given any thought to this before, but as I am trying to create a sandbox system to mimic as closely as possible one of my prod systems and comb through any possible differences, I noticed this.
It seems that in all of my 'real' systems, across several versions of *nix, across several shops, user 'oracle' always comes up with UID=501, group oinstall has gid=501, dba gid=502. But when I build my sandbox I got
oracle:orcl$ id
uid=54321(oracle) gid=54321(oinstall) groups=54321(oinstall),54322(dba)
In this case, the oracle user and groups were actually created as part of 'yum install oracle-validated'.
Just as an expreriment, I just restored one of my vm's to a snapshot prior to installing oracle-validated, where there is no user 'oracle', and created it manually with 'useradd oracle'. That produced a uid=500 and a gid (oracle) of 501. Of course, with that simple experiment, I had no 'dba' or 'oinstall' groups.
Not a problem, just a curiosity as to how the system assigns UID and GID, and why allowing the oracle user and associated groups to be created with the oracle-validated package would be so different than when created directly with 'useradd'.
And does that present any 'unknown unknowns' I need to become aware of, to move to the 'known unknowns' ...