Booting CentOS 6 With Grub From CentOS 7

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I had CentOS 6 installed on an MBR hard disk. I converted the disk to GPT (with UEFI) and installed CentOS 7 on a new partition.

CentOS 7 itself seems to work properly.

Grub from CentOS 7 automatically created an entry for CentOS 6, but I
get an error if I try to boot CentOS 6.

The menu entry is:

menuentry ‘CentOS release 6.10 (Final) (on /dev/sda7)’ –class gnu-linux –class gnu –class os $menuentry_id_option
‘osprober-gnulinux-simple-92dcc576-4e61-41f3-ae42-d06b3aec01ae’ {
insmod part_gpt
insmod ext2
set root=’hd0,gpt7′
if [ x$feature_platform_search_hint = xy ]; then
search –no-floppy –fs-uuid –set=root –hint-bios=hd0,gpt7
–hint-efi=hd0,gpt7 –hint-baremetal=ahci0,gpt7
92dcc576-4e61-41f3-ae42-d06b3aec01ae
else
search –no-floppy –fs-uuid –set=root
92dcc576-4e61-41f3-ae42-d06b3aec01ae
fi
linux /boot/vmlinuz-2.6.32-754.3.5.el6.CentOS.plus.x86_64 ro root=UUID

3 thoughts on - Booting CentOS 6 With Grub From CentOS 7

  • Was CentOS6 bootable after you converted the disk to GPT? My luck with getting it to work has not been good as the conversion usually changes something very important to the underlying OS which needs a reinstall or a bunch of ‘fiddling’ in rescue mode before I could get it to work at all.

    The EL6 kernel and initrd probably do not have the tools in them to deal with a GPT partition. Your ‘best’ bet is to boot into an EL6
    rescue iso, edit the fstab to know it needs to mount a /boot/efi and make sure the kernel/initrd images in /boot are efi aware and stick the right stuff into /boot/efi that is needed. [There are several different people who have posted similar things in 2016 and such. I am not sure how much work they will take.]

    I am not sure if the /boot/efi partition needs to be different from the one you got for EL7. From various posts on mailing lists and such… it confuses a lot of tools when they are the same and on other systems it breaks if they are different.

    I don’t have much more I can add to this. I would normally just backup the EL6, blow it away and run EL6 as a virtual machine from then on. I
    know this might not work for most people, but it is what I have ended up doing.

  • Stephen John Smoogen wrote:

    Um, say *what*?! This wasn’t a complete rebuild? Next you’ll tell us you buy hardware from Acme, the company that Wile E. Coyote buys hardware.

    I think they can. However, several things: what I’ve had to do on our new rebranded Supermicro boxen is to go into the BIOS, and tell it *not* to dual boot (that is, legacy BIOS or UEFI), and *not* legacy, but *only*
    UEFI.

    I will note that we’ve been using GPT on secondary drives since we started buying drives > 2TB, and that’s been a number of years now….

    mark