Hello,
We have RHEL 7.5 server with latest updates. We needed to install Oracle 12 DB on it so chose "easy method" of installing "oracle-database-server-12cR2-preinstall-1.0-3.el7.x86_64.rpm" and then installed oracle DB. Everything went smooth and all OK but later we noticed that it has Oracle Kernel ver 4.14 uek installed instead of using Redhat's 3.10 ver. and using updates from Oracle rep. I managed to configure it back to use updates from Redhat (as we have support from RH) but not sure how to switch the kernel back to Redhat's by keeping all the software (esp Oracle) intact. Redhat is NOT providing any support as this server running Oracle kernel.

We can see both Oracle kernel entries & Redhat entries in grub.conf but not sure If I can simply boot Redhat 3.x kernel with oracle too working fine.

Could anyone please advise how to switch back to RH kernel without breaking anything else? I know rebuilding the server from scratch and not choosing "preinstall rpm" method will fix that but that's a too long process.

Thanks!

you might have to "shut down" for testing, then switch them in grub to see what actually takes place. That is as far as I can go on this issue. good luck.

I presume that the Orace kernel is but a version of Red Hat...
That said, I find it difficult to believe that RH and/or Oracle won't provide support if you have a contract with them, even if it's your fault things got messed up.

I'm surprised to read that you have a grub.conf file since Red Hat switched to Grub2 with release 7.0. Do you have different options for the different kernels in this file?

Thanks everyone for your replies

Very good question. I actually upgraded to RHEL 7.5 from RHEL 6.10 version and later I didn't upgrade grub to grub2 (which I need to do manually as RH upgrade doesn't do it)

So, as asked before: why don't you contact Red Hat support and ask them?? As said, both Oracle and RHEL are pay-for distros...either can give you support since you're paying for them. Personally, I'd reload the box from scratch, since doing an in place upgrade from 6.x to 7.x is NOT a good idea...jumping major versions (and several minor ones), isn't trivial, and is bound to cause issues.

I've never used either Red Hat or Oracle so I'm not sure exactly what your system does. I notice that all of your Red Hat root entries in grub.conf show root(hd0,0) as does the Oracle entry. So what is the default set to? If it is 0, it should boot the Red Hat kernel, if it is 1 it would boot the Oracle kernel.

Don't know that either, I suppose the simple test is to try it?