If you can get to a console, hit enter before the boot process starts, or hit the space bar before it times out – usually there is a 10 second delay (default) allowing you to intervene in the boot process. Once you’ve interrupted you should see a list of kernels available, pick an older functioning hopefully functioning kernel.
Once you can boot – which kernel kernel you select can be modified as follows:
cd /boot/grub
#make a backup
cp -p grub.conf grub.conf.YYYYMMDD
vi grub.conf
#depends on what “default” is set to. Zero (0) is the first one, 1 the second etc. If 0 were corrupt – simply change as follows:
default=1
and save and reboot
Once you’ve rebooted doing a – “uname -a” will show you the kernel running – and cat /etc/redhat-release will show you Linux version for RHEL.