Description

GNU ddrescue is a data recovery tool. It copies data from one file or
block device (hard disc, cdrom, etc) to another, trying hard to rescue
data in case of read errors.

The basic operation of ddrescue is fully automatic. That is, you don't
have to wait for an error, stop the program, read the log, run it in
reverse mode, etc.

If you use the logfile feature of ddrescue, the data is rescued very
efficiently, (only the needed blocks are read). Also you can interrupt
the rescue at any time and resume it later at the same point.

Ddrescue does not write zeros to the output when it finds bad sectors in
the input, and does not truncate the output file if not asked to. So,
every time you run it on the same output file, it tries to fill in the
gaps without wiping out the data already rescued.

Automatic merging of backups: If you have two or more damaged copies of
a 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. This is so because the probability of having damaged
areas at the same places on different input files is very low. Using
the logfile, only the needed blocks are read from the second and
successive copies.

Ddrescue recommends lzip for compression of backups because of its
reliability and data recovery capabilities, including error-checked
merging of backup copies. The combination ddrescue + lziprecover is the
best option for recovering data from multiple damaged copies.

Recordable CD and DVD media keep their data only for a finite time
(typically for many years). After that time, data loss develops slowly
with read errors growing from the outer media region towards the inside.
Just make two (or more) copies of every important CD/DVD you burn so
that you can later recover them with ddrescue.

The logfile is periodically saved to disc. So in case of a crash you can
resume the rescue with little recopying.

Also, the same logfile can be used for multiple commands that copy
different areas of the file, and for multiple recovery attempts over
different subsets.

Because ddrescue needs to read and write at random places, it only works
on seekable (random access) input and output files.

If your system supports it, ddrescue can use direct disc access to read
the input file, bypassing the kernel cache.

Ddrescue aligns its I/O buffer to the sector size so that it can be used
for direct disc access or to read from raw devices. For efficiency
reasons, also aligns it to the memory page size if page size is a
multiple of sector size. Read the info file to learn how to use direct
disc access or raw devices with ddrescue.

Ddrescue also features a "fill mode" able to selectively overwrite parts
of the output file, which has a number of interesting uses like wiping
data, marking bad areas or even, in some cases, "repair" damaged
sectors.


Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011
Antonio Diaz Diaz.

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

The file Makefile.in is a data file used by configure to produce the
Makefile. It has the same copyright owner and permissions that configure
itself.
