做mount掛載時，修改了 /etc/fstab 文件，導致Centos7重啟時出現如下圖所示錯誤：
Welcome to emergency mode! After logging in, type "journalctl -xb" to view system logs,"systemctl reboot" to reboot ,"systemctl default" or ^D to try again to boot into default mode. Give root password for maintenance (or type Control-D to continue):
輸如root權限密碼， vi /etc/fstab 將自己多配置的一行內容刪除，wq保存,之后reboot重啟虛擬機，就恢復正常了。