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=92dcc576-4e61-41f3-ae42-d06b3aec01ae rd_NO_LUKS KEYBOARDTYPE=pc KEYTABLE=cf rd_NO_MD LANG=fr_FR.UTF-8 SYSFONT=latarcyrheb-sun16 rd_NO_LVM rd_NO_DM crashkernel=auto initrd /boot/initramfs-2.6.32-754.3.5.el6.centos.plus.x86_64.img }
When I try to boot, I get a message that "linux" and "initrd" aren't valid commands. If I change them to "linuxefi" and initrdefi", I get this error:
error: kernel too old error: you need to load the kernel first
The information in the entry seems correct (partition, UUID, etc.).
I've searched on Google quite a bit, but didn't find anything useful. Are there any suggestions?