Copying a DVD under Linux wasn't a problem for a long time. I always used k3b. However lately I failed to copy a DVD.
k3b would say:
"failed to retireve all CSS keys" or in german
"es konnten nicht alle CSS Schlüssel geholt werden". k9copy would say:
"libdvdread: Error cracking CSS key for /VIDEO_TS/VTS_03_1.VOB (0x0031ccb6)!!"
First I thought k3b didn't have access to libdvdcss. However it turns out that aparently some DVD drives won't return data from some sections of a disc if the region code of the drive is not set.
My drive is a “HL-DT-ST DVDRAM GSA-T20N”. After setting the region code with
"regionset" I was able to copy the DVD. Thanks a lot to the population of the internet that allowed me to slowly progress to a solution…
Region codes can be found here