After installing the virtual machine, your Ubuntu may be in a very small size (this may or may not be).
If you want to click settings, check the resolution drop-down box in Display, but because this window is too big to click the Apply button. Tragedies!!!!
Ctrl + Alt + TOpen the terminal
The 1280×800 behind is the resolution size. As long as the enter is struck, the result will be displayed immediately.
It should be noted that the two digit number is the X letter, not the number key of the numeric keypad. In addition, this effect can only be effective under the current running virtual machine. If the virtual machine is turned off, then it will be useless.
So you need to click display in system setting immediately to find the resolution modification and click apply to apply.
In addition, just after the virtual machine is finished, there is no root password, you need to set it up.
Then enter the new password about 3 times to complete the modification.