转自: Ubuntu 14.04 LTS very slow on VirtualBox

Got the solution from here:
Shut down the guest machine

1. Select the Ubuntu 14.04 virtual machine and click the Settings button
2. Select the ‘Display’ item from the list on the left
3. In the Video tab on the right, check the ‘Enable 3D Video
   Acceleration’ option
4. Select the ‘Storage’ item from the list on the left
5. In the ‘Storage Tree’ view on the right, select the Controller:SATA
   item
6. In the corresponding attributes to it’s right, check the ‘Use Host I/O Cache’ option
7. Close the settings and restart the virtual machine. It should be
   considerably faster now.

reference: Speed up Ubuntu in VirtualBox