ctl-d freed me up to use ctl-F1 etc. Then I tried ctl-alt-backspace. The xserver quit and the boot proceeded normally. I was even able to install!
** Bug 60316 has been marked a duplicate of this bug -- Black screen at the end of boot process https://launchpad.net/bugs/59772 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
