Superuser password in Ubuntu 12.04 Desktop?

[LincolnB]

Summary: What is the password needed to get superuser privileges with the 'su' command in Canonical's Ubuntu Linux 12.04 Desktop Virtual Appliance?

I am an almost total newbie to Linux. Yesterday I downloaded Canonical's Virtual Appliance for Ubuntu Linux 12.04 Desktop. When I booted the VM for the first time, the status line of Parallels Desktop 8 said "Parallels Tools is outdated". PD8's Help facility said,

Installing Parallels Tools in the most recent versions of Linux systems
If you have one of the most recent versions of Linux OSs (Ubuntu, Fedora) in your virtual machine, the prl-tools-lin.iso image file will be mounted automatically after you connect it to the CD/DVD drive. To install Parallels Tools, do the following:
• Start the virtual machine.
• When the operating system boots up, click Virtual Machine and choose Install Parallels Tools. ... 
The prl-tools-lin.iso image file will be mounted to the virtual machine's CD/DVD drive.
You can connect and mount the Parallels Tools ISO image file manually. Right-click the CD/DVD drive icon in the virtual machine's window status bar and choose Connect Image. In the Finder window, go to the hard disk folder (normally named "Macintosh HD"), select the /Library/Parallels/Tools/ folder, select the prl-tools-lin.iso file, and click Open to connect it to the virtual machine.
• Start a terminal in your Linux guest OS. Type the following command to gain the root privileges:su
• Change the directory to the CD/DVD drive directory usingcd /media/cdrom/
Note: In some of the Linux operating systems, the mount point for the virtual CD/DVD drive may appear as /media/Parallels\ Tools/.
• In the CD/DVD drive directory, enter the following command to launch Parallels Tools installation:./install
• Follow the Parallels Tools Installer instructions to complete the installation.
• When the installation of Parallels Tools is complete, restart your virtual machine.

I was able to do the first three steps ok, but when I got to Terminal and typed 'su', Terminal asked me for a password. I was logged in as user parallels with administrative privileges and had previously set that user's login password. I tried typing parallel's login password as the superuser password, but got back the error message 'Authentication failure'. I also tried just hitting the [Enter] key, but got the same Authentication failure error message:

parallels@parallels-Parallels-Virtual-Platform:~$ su
Password:
su: Authentication failure

In the meantime, I have discovered a workaround using the 'sudo ./install' command. However, for future use of the 'su' command, I wonder what is the password on Canonical's Ubuntu 12.04 Desktop Virtual Appliance?

Thanks,
LincolnB

Host config: 17-inch, Late 2011 MacBook Pro 8,3 with 8 Gb RAM, running OS X 10.7.5 Lion and Parallels Desktop 8.
Guest config: Canonical's Virtual Appliance for 64-bit Ubuntu Linux 12.04 Desktop