摘自国外论坛亲测可用：
1) Restart Machine
2) HOLD Shift Button ( You will get message “GRUB Loading“)
3) Select the Kernel ( Don’t select Recovery Mode)
4) Press the e key to edit the entry
5) Select the line starting with the word “linux”
6) Append the init=/bin/bash to the end of the linux line.
7) Now Press F10 to boot with provided option.
Now You need to mount File System ( / ) into Read-Write Mode
8) mount -o remount,rw /
Now execute passwd command to Reset root password.
9) For root User passwd
Other User passwd <user-name>