mount -t vboxsf tools /mnt/share
报错了：/sbin/mount.vboxsf: mounting failed with the error: No such device
解决办法：
yum clean all
yum update
yum install kernel
yum install kernel-devel
yum install kernel-headers
yum install gcc
yum install make
reboot
cd /opt/VBoxGuestAdditions-*/init
./vboxadd setup
reboot
也可以先尝试不更新，直接执行上面的安装命令