cp /boot/initrd-$(uname -r).img /boot/initrd-$(uname -r).img.bak
mkinitrd -f -v /boot/initrd-$(uname -r).img $(uname -r

Rebuilding the initramfs (RHEL 6)
dracut -f initramfs-2.6.32-71.el6.x86_64.img 2.6.32-71.el6.x86_64