As for others live cd/dvd to set the root password you just need to: 

1) Open a terminal (in the Accessories menu) and write "sudo su" (without brackets)

2) Set the new password with "passwd" 

Basically if you just need to run an application as a root you should write in a terminal: 

1) As the normal user "xhost +"

2) "sudo blender" to start Blender as root. 

That's all!

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