ddrescue copies data from one file or block device (hard disk, cdrom...)
to another, trying hard to rescue data in case of read errors.

ddrescue does not truncate the output file if not asked to. So everytime
you run it on the same output file it tries to fill in the gaps.

If you have two or more copies of a damaged file, cdrom, etc, and run
ddrescue on all of them, one at a time, with the same output file, you
will probably obtain a complete and error-free file.

1. build dependencies:
   1. gcc-c++
   2. lzip
   3. texinfo