ddrescue

Data recovery tool, save data from a crashed partition.

Syntax
      ddrescue [options] infile outfile [logfile]

Options:
   -b=bytes          Hardware block size of input device [512]
   --block-size=bytes

   -B                Show binary multipliers in numbers [default SI] 
   --binary-prefixes

   -c=blocks         Hardware blocks to copy at a time [128] 
   --cluster-size=blocks

   -C                Do not read new data beyond logfile limits 
   --complete-only

   -d                Use direct disc access for input file 
   --direct

   -e=n              Maximum number of error areas allowed
   --max-errors=n

   -i=pos            Starting position in input file [0]
   --input-position=pos

   -n                Do not try to split error areas 
   --no-split

   -o=pos            Starting position in output file [ipos] 
   --output-position=pos

   -q                Quiet operation 
   --quiet

   -r=n              Exit after given retries (-1=infinity) [0]
   --max-retries=n

   -s=bytes          Maximum size of data to be copied 
   --max-size=bytes

   -t                Truncate output file
   --truncate

   -v                Verbose operation
   --verbose

   -V                Output version information and exit
   --version

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...

Installation

Debian / Ubuntu Linux:
# apt-get install ddrescue

RedHat /Fedora /CentOS Linux:
# yum -y install ddrescue

ddrescue written by Antonio Diaz Diaz, download from the GNU web site.
Installs as /usr/bin/ddrescue

Example:

To copy /dev/sda (damaged \device\harddisk0) to another drive /dev/sdb (empty \device\harddisk1)

# ddrescue /dev/sda /dev/sdb

To recover the partition data run fsck, for example if /home (user data) is on /dev/sda2, run fsck on partition /dev/sdb2:
# fsck /dev/sdb2

This avoids touching the damaged /dev/sda, if the procedure fails you can send the original disk to a professional data recovery service.

Lastly mount the partition somewhere and see if you can access the data:
# mount /dev/sdb2 /mnt/data

"Rescue me, Oh take me in your arms, Rescue me" - Aretha Franklin

Related:

info ddrescue - full ddrescue manual
dd_rescue - written by Kurt Garloff for Debian
ddrescue for OS X - macosxhints
dd - Data Dump - Convert and copy a file