When installed, the Oracle Preinstallation RPM does the following:
Automatically downloads and installs any additional RPM packages needed for installing Oracle Grid Infrastructure and Oracle Database, and resolves any dependencies Creates an oracle user, and creates the oraInventory (oinstall) and OSDBA (dba) groups for that user As needed, sets sysctl.conf settings, system startup parameters, and driver parameters to values based on recommendations from the Oracle Preinstallation RPM program Sets hard and soft resource limits Sets other recommended parameters, depending on your kernel version Sets numa=off in the kernel for Linux x86_64 machines.
https://docs.oracle.com/cd/E11882_01/install.112/e41961/prelinux.htm#CWLIN172