On Wed, 8 May 2019 at 07:08, Peter <peter at pajamian.dhs.org> wrote: > On 8/05/19 12:22 AM, Robert Heller wrote: > The >> are from me. > >> Many CentOS-7 packages will not install because they will need > dependencies > >> that the EL-6 does not have. > > Correct, and different versions of dependencies, and files go in > different locations, etc. > > >> The kernel is different because it is mostly > >> self-contained and meant to be parallel installed. > > Correct. > > > In most cases, it should > >> result in an unbootable system because the boot is going to be > >> dracut+systemd bits and the EL-6 has none of that. > > Older versions of dracut will run on newer kernels just fine. When you > install the kernel on CentOS 6 it will run the CentOS 6 version of > dracut at the time of the install and create a CentOS 6 compatible > initramfs image. > > I wasn't sure if this would work, but since the person has a working system and you have explained why.. I learned something new. Thank you. > Systemd is user-space and does not include components in the kernel (as > far as I'm aware). Even if it does, the kernel is still > backwards-compatible and would boot just fine to upstart (which is the > init system in CentOS 6), it simply would not use those modules and > features that are used for systemd. > > > And I wonder if the EL7 kernel will even show up as an available > kernel. EL7 > > uses Grub 2 and EL6 uses Grub . > > CentOS 7 does have grub legacy (1) as an option and does work fine with > grub legacy. I have set up CentOS 7 systems that use grub legacy in the > past. It stands to reason that a kernel that installs and configures > just fine in grub legacy on CentOS 7 will do the same in grub on CentOS 6. > > > I know that when I installed Ubuntu 18.04 as a *second* OS, that even > though > > the /boot file system is shared between CentOS 6 and Ubuntu 18.04 the > Ubuntu > > 18.04 installer did not touch /boot/grub/grub.conf and installed > > /boot/grub/grub.cfg along side (I manually reinstalled grub 1 and > manually > > hacked /boot/grub/grub.conf to put the Ubuntu 18.04 boot option in). > > This is not the case with CentOS. You can run dual-boot CentOS 6 and 7 > on the same grub legacy boot loader and CentOS 7 will boot up and run > just fine. > > While I cannot make any guarantees that a CentOS 7 kernel will not cause > issues running in CentOS 6, and indeed I would not support a system that > used such, the Linux kernel, being self-contained and largely > backwards-compatible should in theory, at least, not have issues running > a CentOS 7 kernel on CentOS 6, and indeed there are newer kernels that > are specifically built for CentOS 6 (elrepo kernel-ml) that run just > fine as well. > > The main thing that might stand in your way would be any changes to the > rpm file format (which does happen from time to time) that prevent an > rpm built for CentOS 7 from being recognized and installible by rpm or > yum in older versions of CentOS 6. I am aware of such changes from > older versions of CentOS but none between CentOS 6 and 7. > > So in summary, it would probably work just fine, but I wouldn't do it, > recommend it or support it. > > > Peter > _______________________________________________ > CentOS mailing list > CentOS at centos.org > https://lists.centos.org/mailman/listinfo/centos > -- Stephen J Smoogen.