[root@ipfire ~]# ddrescue -h
GNU ddrescue - Data recovery tool.
Copies data from one file or block device to another,
trying hard to rescue data in case of read errors.

Usage: ddrescue [options] infile outfile [logfile]
You should use a logfile unless you know what you are doing.

Options:
-h, --help                    display this help and exit
-V, --version                 output version information and exit
-b, --block-size=<bytes>      sector size of input device [default 512]
-B, --binary-prefixes         show binary multipliers in numbers [SI]
-c, --cluster-size=<sectors>  sectors to copy at a time [128]
-C, --complete-only           do not read new data beyond logfile limits
-d, --direct                  use direct disc access for input file
-D, --synchronous             use synchronous writes for output file
-e, --max-errors=<n>          maximum number of error areas allowed
-F, --fill=<types>            fill given type blocks with infile data (?*/-+)
-g, --generate-logfile        generate approximate logfile from partial copy
-i, --input-position=<pos>    starting position in input file [0]
-m, --domain-logfile=<file>   restrict domain to finished blocks in file
-n, --no-split                do not try to split or retry failed blocks
-o, --output-position=<pos>   starting position in output file [ipos]
-q, --quiet                   suppress all messages
-r, --max-retries=<n>         exit after given retries (-1=infinity) [0]
-R, --retrim                  mark all failed blocks as non-trimmed
-s, --max-size=<bytes>        maximum size of input data to be copied
-S, --sparse                  use sparse writes for output file
-t, --truncate                truncate output file to zero size
-T, --try-again               mark non-split, non-trimmed blocks as non-tried
-v, --verbose                 verbose operation
Numbers may be followed by a multiplier: b = blocks, k = kB = 10^3 = 1000,
Ki = KiB = 2^10 = 1024, M = 10^6, Mi = 2^20, G = 10^9, Gi = 2^30, etc...

Report bugs to bug-ddrescue@gnu.org
Ddrescue home page: http://www.gnu.org/software/ddrescue/ddrescue.html
General help using GNU software: http://www.gnu.org/gethelp