Often I get a new server to clone an instance. This is the way I setup the user so that I don't have to do any change ownership to the files being cloned as they get the same id as the PROD system. This obviously will only work with single instances on a server.
groupmod -g 500 dba
useradd -gdba -s/bin/bash -poratest -d/home/oratest -m oratest
usermod -u 500 oratest