发现昨天不能进入grub的原因居然是: guestOS 的grub.conf 中timeout 被设置为 0
2
刚刚把host OS的kernel 放到 guestOS ,并且修改了grub.conf ，之后重启guest OS ,显示：
This kernel requires the following features not present on the CPU:
pae
Unable to boot - please use a kernel appropriate for your CPU;
解决办法：需要修改guestOS 的setting ==> system ==> processor : ENABLE PAE/NX;