Man page of SAFECOPY
Section: SAFECOPY (1)
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- rescue data from a source that causes IO errors
[OPTION]... SOURCE DEST
tries to get as much data from SOURCE as possible, even resorting to device
specific low level operations if applicable.
This is achieved by identifying problematic or damaged areas, skipping over
them and continuing reading afterwards. The corresponding area in the
destination file is either skipped (on initial creation that means padded with
zeros) or deliberately filled with a recognizable pattern to later find
affected files on a corrupted device.
Safecopy uses an incremental algorithm to identify the exact beginning and end
of bad areas, allowing the user to trade minimum accesses to bad areas for
thorough data resurrection.
Multiple passes over the same file are possible, to first retrieve as much data
from a device as possible with minimum harm, and then trying to retrieve some
of the remaining data with increasingly aggressive read attempts.
For this to work, the source device or file has to be seekable. For unseekable
devices (like tapes) you can try to use an external script to execute a
controlled skip over the damaged part for you.
(For example by using "mt seek" and "mt tell" on an SCSI tape device)
See the "-S <seekscript>" parameter for details.
Performance and success of this tool depend extremely on the device driver,
firmware and underlying hardware.
Currently safecopy supports RAW access to CDROM drives to read data directly of
a CD, bypassing some driver dependant error correction. This can speed up data
retrieval from CDs and reduce system load during recovery, as well as
increase the success rate. Safecopy uses the disc status syscall to determine
sector size and addressing of CDs. This fails on mixed-mode or multi-session
CDs, since the sector layout can change within the disk, but would still work
on the the big majority of disks. Other disks can still be recovered using
normal high level data access. Safecopy auto-detects the disk type involved
during scan for disk and block size.
Some CD/DVD drives are known to cause the ATAPI bus to crash on errors, causing
the device driver to freeze for times up to and beyond a minute per error. Try
to avoid using such drives for media recovery. Using safecopys low level access
features might help under some circumstances.
Some drives can read bad media better than others. Be sure to attempt data
recovery of CDs and DVDs on several different drives and computers.
You can use safecopys incremental recovery feature to read previously
unreadable sectors only.
Data recovery from damaged media is a delicate task, in the worst case its
success or failure can safe or ruin whole companies and seal affected peoples
personal fate. It is paramount that any tools written for that purpose are
reliable and trustworthy.
A user needs to know what exactly the software is doing to his hardware and
data. The outcome of any operation needs to be both understandable and
An "intelligent data resurrection wizard" with unknown complex internal
behaviour may be a nifty tool, but does not meet the above requirements of
predictable outcome, nor will the user know in advance what is done to his
The operation sequence of safecopy has been kept relatively simple to assure
this predictability. Unfortunately feature additions have risen the complexity
and lead to undefined outcome in the past when include and exclude lists had
been mixed, especially when mixing different block sizes. In the worst case
this could have lead to overwritten data in the destination file on a later
incremental run with the mark (-M) option.
From version 1.3 on, safecopy ships with a test suite that can be used to verify
safecopys behaviour in a set of test cases, simulating the combination of bad
blocks in input with different include and exclude lists, both with and without
marking. Releases are only made if safecopy passes those test cases according
to the specification.
This textual specification of behaviour of safecopy can be found in the file
specification.txt shipped with safecopy.
Preset to rescue most of the data fast,
using no retries and avoiding bad areas.
Presets: -f 10% -r 10% -R 1 -Z 0 -L 2 -M BaDbLoCk \
Preset to rescue more data, using no retries
but searching for exact ends of bad areas.
Presets: -f 128* -r 1* -R 1 -Z 0 -L 2 \
-I stage1.badblocks -o stage2.badblocks
Preset to rescue everything that can be rescued
using maximum retries, head realignment tricks
and low level access.
Presets: -f 1* -r 1* -R 4 -Z 1 -L 2 \
-I stage2.badblocks -o stage3.badblocks
All stage presets can be overridden by individual options.
- -b <size>
Blocksize for default read operations.
Set this to the physical sectorsize of your media.
Hardware block size if reported by OS, otherwise 4096
- -f <size>
Blocksize in bytes when skipping over badblocks.
Higher settings put less strain on your hardware,
but you might miss good areas in between two bad ones.
- -r <size>
Resolution in bytes when searching for the exact beginning or end of a bad
If you read data directly from a device there is no need to set this lower than
the hardware blocksize. On mounted filesystems however, read blocks and
physical blocks could be misaligned.
Smaller values lead to very thorough attempts to read data at the edge of
damaged areas, but increase the strain on the damaged media.
- -R <number>
At least that many read attempts are made on the first bad block of a damaged
area with minimum resolution. More retries can sometimes recover a weak
sector, but at the cost of additional strain.
- -Z <number>
On each error, force seek the read head from start to end of the source device
as often as specified. That takes time, creates additional strain and might
not be supported by all devices or drivers.
- -L <mode>
Use low level device calls as specified:
0 Do not use low level device calls
1 Attempt low level device calls
for error recovery only
2 Always use low level device calls
Supported low level features in this version are:
SYSTEM DEVICE TYPE FEATURE
Linux cdrom/dvd bus/device reset
Linux cdrom read sector in raw mode
Linux floppy controller reset, twaddle
Use synchronized read calls (disable driver buffering).
Safecopy will use O_DIRECT if supported by the OS and O_SYNC otherwise.
Default: Asynchronous read buffering by the OS is allowed
- -s <blocks>
Start position where to start reading.
Will correspond to position 0 in the destination file.
Default: block 0
- -l <blocks>
Maximum length of data to be read.
Default: Entire size of input file
- -I <badblockfile>
Incremental mode. Assume the target file already exists and has holes specified
in the badblockfile. It will be attempted to retrieve more data from the
listed blocks or from beyond the file size of the target file only.
Without this option, the destination file will be emptied prior to writing.
Use -I /dev/null if you want to continue a previous run of safecopy without a
- -i <bytes>
Blocksize to interpret the badblockfile given with -I.
Default: Blocksize as specified by -b
- -X <badblockfile>
Exclusion mode. If used together with -I, excluded blocks override included
blocks. Safecopy will not read or write any data from areas covered by exclude
- -x <bytes>
Blocksize to interpret the badblockfile given with -X.
Default: Blocksize as specified by -b
- -o <badblockfile>
Write a badblocks/e2fsck compatible bad block file.
- -S <seekscript>
Use external script for seeking in input file.
(Might be useful for tape devices and similar).
Seekscript must be an executable that takes the number of blocks to be skipped
as argv1 (1-64) the blocksize in bytes as argv2 and the current position (in
bytes) as argv3. Return value needs to be the number of blocks successfully
skipped, or 0 to indicate seek failure. The external seekscript will only be
used if lseek() fails and we need to skip over data.
- -M <string>
Mark unrecovered data with this string instead of skipping it. This helps in
later finding corrupted files on rescued file system images. The default is to
zero unreadable data on creation of output files, and leaving the data as it is
on any later run.
When used in combination with incremental mode (-I) this may overwrite data in
any block that occurs in the -I file. Blocks not in the -I file, or covered
by the file specified with -X are save from being overwritten.
- --debug <level>
Enable debug output. Level is a bit field, add values together for more information:
program flow: 1
IO control: 2
badblock marking: 4
incremental mode: 16
exclude mode: 32
or for all debug output: 255
- -T <timingfile>
Write sector read timing information into this file for later analysis.
- -h, --help
Show the program help text.
valid parameters for -f -r -b <size> options are:
Amount in bytes - i.e. 1024
Percentage of whole file/device size - e.g. 10%
-b only, number times blocksize reported by OS
-f and -r only, number times the value of -b
description of output symbols:
Between 1 and 1024 blocks successfully read.
Read of block was incomplete. (possibly end of file) The blocksize is now
reduced to read the rest.
Seek failed, source can only be read sequentially.
Read failed, reducing blocksize to read partial data.
A low level error on read attempt of smallest allowed size leads to a retry
Current block and number of bytes continuously read successfully up to this
Read failed on a block with minimum blocksize and is skipped.
Unrecoverable error, destination file is padded with zeros.
Data is now skipped until end of the unreadable area is reached.
Successful read after the end of a bad area causes backtracking with smaller
blocksizes to search for the first readable data.
current block and number of bytes of recent continuous unreadable data.
How do I...
- - resurrect a file from a mounted but damaged media, that copy will fail on:
- - create an filesystem image of a damaged disk/cdrom:
- - resurrect data as thoroughly as possible?
source dest -f 1* -R 8 -Z 2
(assuming logical misalignment of blocks to sectors)
source dest -f 1* -r 1 -R 8 -Z 2
- - resurrect data as fast as possible, or
- - resurrect data with low risk of damaging the media further:
(you can use even higher values for -f and -r)
source dest -f 10% -R 0 -Z 0
- - resurrect some data fast, then read more data thoroughly later:
source dest -f 10% -R 0 -Z 0 -o badblockfile
source dest -f 1* -R 8 -Z 2 -I badblockfile
Alternate approach using the new preset features:
source dest --stage1
source dest --stage2
source dest --stage3
- - utilize some friends CD-ROM drives to complete the data from my damaged CD:
/dev/mydrive imagefile <someoptions> -b <myblocksize> -o myblockfile
/dev/otherdrive imagefile <someoptions> -b <otherblocksize> -I myblockfile -i <myblocksize> -o otherblockfile
/dev/anotherdrive imagefile <someoptions> -b <anotherblocksize> -I otherblockfile -i <otherblocksize>
- - interrupt and later resume a data rescue operation:
source dest -I /dev/null
- - interrupt and later resume a data rescue operation with correct badblocks output:
source dest <options> -o badblockfile
source dest -I /dev/null -o badblockfile
- - interrupt and resume in incremental mode:
(this needs a bit of bash scripting to get the correct badblock lists)
source dest <options> -o badblockfile1
source dest <options> -I badblockfile1 -o badblockfile2
latest=$( tail -n 1 badblockfile2 )
if [ -z $latest ]; then latest=-1; fi;
cat badblockfile1 | while read block; do
[ $block -gt $latest ] && echo $block >>badblockfile2;
source dest <options> -I badblockfile2 -o badblockfile3
- - find the corrupted files on a partially successful rescued file system:
/dev/filesystem image -M CoRrUpTeD
-o loop image /mnt/mountpoint
-R /mnt/mountpoint "CoRrUpTeD"
(hint: this might not find all affected files if the unreadable
parts are smaller in size than your marker string)
- - exclude the previously known badblocks list of a filesystem from filesystem image creation:
-b /dev/filesystem >badblocklist
/dev/filesystem image -X badblocklist -x <blocksize of your fs>
- - create an image of a device that starts at X and is Y in size:
/dev/filesystem -b <bsize> -s <X/bsize> -l <Y/bsize>
- - combine two partial images of rescued data without access to the actual (damaged) source data:
(This is a bit tricky. You need to get badblocks lists for both files somehow
to make safecopy know where the missing data is. If you used the -M (mark)
feature you might be able to automatically compute these, however this feature
is not provided by safecopy. Lets assume you have two badblocks files.
The file size of image1 needs to be greater or equal to that of image2. (If
not, swap them)
image1.dat combined.dat -I image2.badblocks -i blocksize2 -X image1.badblocks -x blocksize1
(This gets you the combined data, but no output badblocklist.
The resulting badblocks list would be the badblocks that are
a: in both badblocks lists, or
b: in image1.badblocks and beyond the file size of image2 It should be
reasonably easy to solve this logic in a short shell script. One day this might
be shipped with safecopy, until then consider this your chance to contribute to
a random open source project.)
- - rescue data of a tape device:
If the tape device driver supports lseek(), treat it as any file,
otherwise utilize the "-S" option of safecopy with a to be
self-written script to skip over the bad blocks.
(for example using "mt seek")
Make sure your tape device doesn't auto-rewind on close.
Send me feedback if you had any luck doing so, so I can update
Why create this tool if there already is something like dd-rescue and
other tools for that purpose?
Because I didn't know of dd(-)rescue when I started, and I felt like it. Also I
think safecopy suits the needs of a user in data loss peril better due to more
readable output and more understandable options than some of the other tools.
(Then again I am biased. Compare them yourself)
Meanwhile safecopy supports low level features other tools don't.
What exactly does the -Z option do?
Remember back in MS-DOS times when a floppy would make a "neek nark" sound 3
times every time when running into a read error? This happened when the BIOS
or DOS disk driver moved the IO head to its boundaries to possibly correct
small cylinder misalignment, before it tried again. Linux doesn't do that by
default, neither do common CDROM drives or drivers. Nevertheless forcing this
behaviour can increase your chance of reading bad sectors from a CD __BIG__
time. (Unlike floppies where it usually has little effect)
Whats my best chance to resurrect a CD that has become unreadable?
Try making a backup image on many different computers and drives. The
abilities to read from bad media vary extremely. I have a 6 year old Lite On
CDRW drive, that even reads deeply and purposely scratched CDs (as in with my
key, to make it unreadable) flawlessly. A CDRW drive of the same age at work
doesn't read any data from that part of the CD at all, while most DVD and combo
drives have bad blocks every couple hundred bytes. Make full use of safecopys
RAW access features if applicable. (-L 2 option)
As a general guideline:
-CDRW drives usually do better than read-only CD drives.
-CD only drives sometimes do better on CDs than DVD drives.
-PC drives are sometimes better than laptop ones.
-A drive with a clean lens does better than a dirtball.
-Cleaning up CDs helps.
-Unless you use chemicals.
-Using sticky tape on a CD will rip of the reflective layer permanently
rendering the disk unreadable.
Whats my best chance to resurrect a floppy that became unreadable?
Again try different floppy drives. Keep in mind that it might be easier to
further damage data on a bad floppy than on a CD. (Don't overdo read attempts)
What about BlueRay/HDDVD disks?
Hell if I knew, but generally they should be similar to DVDs. It probably
depends how the drives firmware acts up.
My hard drive suddenly has many bad sectors, what should I do?
Speed is an essential factor when rescuing data from a bad hard drive.
Accesses to bad areas or even just time running can further damage the
drive and make formerly readable areas unreadable, be it due to
temperature rise, damaged heads scratching still good parts of the
surface, bearings degrading due to vibration, etc. Its advisable to
shut the system down and remove the hard drive from the computer as soon
as errors occur and as fast as possible without causing further damage.
(Don't pull the plug! Press reset to force reboot and then power down
via power button/ACPI)
Set up a rescue system with enough disk space to store all the data
from the damaged drive (and possibly multiple copies of it). If you
have an external hard drive case that connects via USB SATA or SCSI,
allowing a hot plug of the drive into a running system, use it. This
allows you to prepare everything without the need for the drive to power
up and possibly BIOS or operating system involuntarily accessing it.
You also get easier access to the drive to check temperature or noise
When you rescue data, rescue good data first before attempting to
access bad sectors. Safecopy allows you to skip known problem sectors
using a badblock exclude file (-X) which you might be able to retrieve
from system logs or from the drive internal logs, via smartmontools or
similar software. Be aware that you might possibly need to convert
physical sector numbers into logical block numbers depending on your
Also you should tell safecopy to jump out of any problematic areas ASAP
and continue somewhere else. Parameters "-f 10% -r 10% -R 0 -Z 0" would
do the trick by making safecopy skip 10% of the device content and
continue there without backtracking. You can always attempt to get the
data in between later, first get the supposedly good data on the rest
of the drive. Depending on the method of data recovery you plan on
using, it may make sense to mark the bad data with the "-M" option.
This allows you to later find files affected by data corruption more
easily. Use the "-o" option to make safecopy write a badblock list
with all blocks skipped or unreadable.
When safecopy is done with this first run, you can attempt a second go
trying to get more data. Using smaller values for "-f" and allowing
safecopy to backtrack for the end of the affected area "-r 1*".
Be sure to use incremental mode "-I" to only read the blocks skipped
in the first run.
It may make sense to let the drive cool down between runs.
Once you got all the data from the "good" areas of the drive you can
risk more "thorough" access to it. Increase the numbers of retries
"-R" in case of bad blocks, maybe together with a head realignment
"-Z 1". "-f 1*" would make safecopy try to read on every single block,
not skipping over bad areas at all.
If your drive stops responding, power it down, let it cool down for a
while, then try again.
(I heard from people who brought dead drives back to live for a short
time by cooling them to low temperatures with ice-packs.)
If the data is really important, go to a professional data recovery specialist
right away, before doing further damage to the drive.
safecopy always returns 0 (zero) regardless of success rate and/or aborted
safecopy and its manpage have been designed and written by CorvusCorax.
Please use the project page on sourceforge
<http://www.sf.net/projects/safecopy> to get in contact with project
development if you encounter bugs or want to contribute to safecopy.
Copyright © 2009 CorvusCorax
This is free software. You may redistribute copies of it under the terms of
the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
There is NO WARRANTY, to the extent permitted by law.
Programs with a similar scope are among others
- ddrescue(1), dd-rescue(1), ...
- EXIT STATUS
- SEE ALSO
This document was created by
using the manual pages.
Time: 07:34:21 GMT, September 13, 2011
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