[CentOS] (Solved) Booting CentOS 6 with Grub from CentOS 7

Thu Oct 11 04:36:10 UTC 2018
Peter <peter at pajamian.dhs.org>

On 11/10/18 15:50, Yves Bellefeuille wrote:
> I myself wrote:
>> Grub from CentOS 7 automatically created an entry for CentOS 6, but
>> I get an error if I try to boot CentOS 6.
> It turns out that Grub2 checks the version of the kernel and refuses
> to proceed if it thinks that the kernel is too old. I don't know how
> old is considered too old, but the latest centosplus kernel for CentOS
> 6, vmlinuz-2.6.32-754.3.5.el6.centos.plus.x86_64, apparently
> qualifies.
> The solution was to install the latest kernel-ml kernel from ELRepo,
> https://elrepo.org/ , to change grub.cfg to reflect the new versions,
> and to change linux and initrd to linuxefi and initrdefi.
> I'm surprised this has apparently never arisen before. Am I really the
> first person to dual-boot CentOS 6 and 7?

I think you'll find that in order to use linuxefi and initrdefi you need
a kernel that is new enough to have efi support.  If you have an older
kernel (such as that which comes with CentOS 6) then you need to use
linux16 and initrd16.