Ubuntu contains a number of DVD backup applications (aka "DVD rippers"). To rip encrypted DVDs, you must install libdvdcss2 the same as you would to play encrypted DVDs (see Playing DVDs).
Libdvdcss2 may not be enough for playing DVDs produced by Warner Bros (they have a JACKET_P folder as well as a txtdt file). It would require libudf to be installed on the system.
There are several different utilities targeted at Ripping DVDs on Ubuntu Linux.