convert data cd -> iso file
dd if=/dev/cdrom of=isofile conv=sync
or
readcd dev="0,0,0" f=isofile

write copy (To burn):
cdrecord dev=0,0,0 -v isofile
or more opts...
cdrecord -s driveropts=burnproof -v dev=0,0,0 fs=16m -eject speed=52 isofile &


for audio CD or others...
dd does not work.
readcd dev=0,0,0 -clone f=imgfile
or 
readcd dev=0,0,0 -clone -nocorr f=imgfile
or
cdrdao read-cd --paranoia-mode 3 -n -v 2 --eject --remote 17 --datafile $target_file $target_file.toc

write copy:
cdrecord dev=0,0,0 -raw96r -clone -v imgfile

To erase:
cdrecord -v -dev=0,3,0 blank=fast