Lessons learnt from fresh ebs r12.2 installation on Oracle Linux 7

1. Preinstaller rpms are great and your files are backed up under /var/log/oracle-ebs-server-R12-preinstall/backup
sysctl.conf
resolv.conf
grub.cfg

2. orakernel.log often ignored should be reviewed after installing both rpms
oracle-rdbms-server-12cR1-preinstall
oracle-ebs-server-R12-preinstall

3. applmgr and oracle have oinstall as common primary OS group. applmgr does not have dba as secondary group.

4. Starting from OL7, user limits are not stored in /etc/security/limits.conf. There will be .conf files created under /etc/security/limits.d 
that are read by systemd during server startup 

5. resolve.conf file will be overridden if you have DNS1/2 directives in your network configuration files -
/etc/sysconfig/network-scripts/ifcfg-*
You can make resolv.conf immutable to changes or remove directives DNS1/2 in your network configuration files.