How to get to recovery mode if grub screen does not appear?

I cannot login my Ubuntu12.04 (which is VM running on OSX using VMWARE FUSION 6) because I have changed permission of /tmp for some purpose before rebooting the machine. Thus I tried to boot Ubuntu in recovery mode by pressing shift key while booting the machine (in order to change the permission of /tmp), but it was not possible because no grub screen appears while booting. How can I get into recovery mode if grub does not appear?