[CentOS] What happened if install a el7 package on a el6 system

Tue May 7 12:22:01 UTC 2019
Robert Heller <heller at deepsoft.com>

At Tue, 7 May 2019 05:50:35 -0400 CentOS mailing list <centos at centos.org> wrote:

> On Tue, 7 May 2019 at 04:06, wuzhouhui <wuzhouhui14 at mails.ucas.ac.cn> wrote:
> > Hi,
> >
> > Recently, I encountered a interesting phenomenon that CentOS 6.3
> > running as normal even if I (my colleague, actually) installed a
> > kernel that build for CentOS 7.x (e.g. kernel-3.10.0-327.el7.x86_64.rpm).
> >
> > I found kernel is mismatch accidentally when I using "uname -r" to
> > check kernel version. So my question is what the harmness we will
> > get if I install a el7 rpm into a el6 system?
> >
> >
> Many CentOS-7 packages will not install because they will need dependencies
> that the EL-6 does not have. The kernel is different because it is mostly
> self-contained and meant to be parallel installed. 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.

And I wonder if the EL7 kernel will even show up as an available kernel.  EL7 
uses Grub 2 and EL6 uses Grub [1].  *Different* config files. Because (unlike 
Lilo), grub is not updated in the MBR each time its config is updated (eg 
installing a new kernel), it is very likely the EL7 kernel rpm install might 
not touch /boot/grub/grub.conf, since it is expecting to update 
/boot/grub/grub.cfg instead.

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).

> > Thanks.
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> >

Robert Heller             -- 978-544-6933
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