Please be a good citizen and only rip media that you own!
Install dvdbackup and ffmpeg:
sudo apt install dvdbackup ffmpeg
Most commercial DVDs are encrypted with CSS (the Content Scramble System), which attempts to restrict the software that can play a DVD. To enable reading of encrypted DVDs, you’ll also need to compile and install libdvdcss. This will step you through it:
sudo apt install libdvd-pkg && sudo dpkg-reconfigure libdvd-pkg
More info here.
Insert DVD and note mount path, e.g., /media/username/SIDEWAYS_169.
Extract VOB files for feature:
dvdbackup -i /media/username/SIDEWAYS_169 -o output -F -n "Sideways" -p
Browse to output/Sideways/VIDEO_TS.
Determine which .VOB files contain the actual movie. You can use Celluloid to preview. Remove non-feature .VOB files like trailers, making-of, etc.
Combine the remaining .VOB files into one:
cat *.VOB > Sideways.VOB
Convert the .VOB file to .mp4:
ffmpeg -i Sideways.VOB Sideways.mp4