I have a 6.5 box that failed to boot after a kernel update. The reason is the first arg on the kernel line:
title CentOS (2.6.32-431.11.2.el6.x86_64) root (hd0,0) kernel /tboot.gz ro root=/dev/mapper/vol0-lvol1 intel_iommu=on rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD SYSFONT=latarcyrheb-sun16 crashkernel=auto rd_NO_DM KEYBOARDTYPE=pc KEYTABLE=us rd_LVM_LV=vol0/lv ol3 rd_LVM_LV=vol0/lvol1 rhgb quiet logging=vga,serial,memory module /vmlinuz-2.6.32-431.11.2.el6.x86_64 root=/dev/mapper/vol0-lvol1 crashkernel=auto SYSFONT=latarcyrheb-sun16 LANG=en_US.UTF-8 KEYTABLE=us module /initramfs-2.6.32-431.11.2.el6.x86_64.img
There is no such file /tboot.gz. This machine doesn't have tboot installed.
I removed the kernel and reinstalled it, yet the grub entry was recreated as above. Digging deeper, I found this in /etc/sysconfig/kernel:
# HYPERVISOR specifies the default multiboot kernel HYPERVISOR=/boot/tboot.gz HYPERVISOR_ARGS=logging=vga,serial,memory
Removing these lines results in a working grub.conf when the kernel is reinstalled. The question is now: what placed these entries there? It's not tboot, I checked the srpm.