Below are the list of packages you must install before Oracle 12c installation on RHEL/Linux.
yum install binutils -y yum install compat-libcap1 -y yum install compat-libstdc++-33 -y yum install compat-libstdc++-33.i686 -y yum install gcc -y yum install gcc-c++ -y yum install glibc -y yum install glibc.i686 -y yum install glibc-devel -y yum install glibc-devel.i686 -y yum install ksh -y yum install libgcc -y yum install libgcc.i686 -y yum install libstdc++ -y yum install libstdc++.i686 -y yum install libstdc++-devel -y yum install libstdc++-devel.i686 -y yum install libaio -y yum install libaio.i686 -y yum install libaio-devel -y yum install libaio-devel.i686 -y yum install libXext -y yum install libXext.i686 -y yum install libXtst -y yum install libXtst.i686 -y yum install libX11 -y yum install libX11.i686 -y yum install libXau -y yum install libXau.i686 -y yum install libxcb -y yum install libxcb.i686 -y yum install libXi -y yum install libXi.i686 -y yum install make -y yum install sysstat -y yum install unixODBC -y yum install unixODBC-devel -y