PhotoRec

src: i.ytimg.com

PhotoRec is a free and open-source file carver data recovery software tool designed to recover lost files from digital camera memory (CompactFlash, Memory Stick, Secure Digital, SmartMedia, Microdrive, MMC, USB flash drives, etc.), hard disks and CD-ROMs. It recovers most common photo formats, including JPEG, and also recovers audio files, including MP3, document formats such as OpenDocument, Microsoft Office, PDF and HTML, and archive formats including ZIP.

PhotoRec does not attempt to write to the damaged media the user is about to recover from. Recovered files are instead written to the directory from which PhotoRec is run, any other directory may be chosen. It can be used for data recovery or in a digital forensics context. PhotoRec is shipped with TestDisk.

PhotoRec is compatible with:

• DOS (either real or in a Windows 9x DOS box)
• Microsoft Windows: NT4, 2000, XP, 2003, 2008, Vista, Windows 7
• Linux
• FreeBSD, NetBSD, OpenBSD
• SunOS
• Mac OS X

Video PhotoRec

How PhotoRec works

FAT, NTFS, ext2/ext3/ext4 filesystems store files in data blocks (also called data clusters under Windows). The cluster or block size remains at a constant number of sectors after being initialized during the formatting of the filesystem. In general, most operating systems try to store the data in a contiguous way so as to minimize data fragmentation. The seek time of mechanical drives is significant for writing and reading data to/from a hard disk, so that is why it is important to keep the fragmentation to a minimum level.

When a file is deleted, the meta-information about this file (filename, date/time, size, location of the first data block/cluster, etc.) is lost; e.g., in an ext3/ext4 filesystem, the names of deleted files are still present, but the location of the first data block is removed. This means the data is still present on the filesystem, but only until some or all of it is overwritten by new file data.

To recover these "lost" files, PhotoRec first tries to find the data block (or cluster) size. If the filesystem is not corrupted, this value can be read from the superblock (ext2/ext3/ext4) or volume boot record (FAT, NTFS). Otherwise, PhotoRec reads the media, sector by sector, searching for the first ten files, from which it calculates the block/cluster size from their locations. Once this block size is known, PhotoRec reads the media block by block (or cluster by cluster). Each block is checked against a signature database; which comes with the program and has been growing in the type of files it can recover ever since PhotoRec's first version came out. It is a common data recovery method called file carving.

For example, PhotoRec identifies a JPEG file when a block begins with:

• Start Of Image + APP0: 0xff, 0xd8, 0xff, 0xe0
• Start Of Image + APP1: 0xff, 0xd8, 0xff, 0xe1
• or Start Of Image + Comment: 0xff, 0xd8, 0xff, 0xfe

If PhotoRec has already started to recover a file, it stops its recovery, checks the consistency of the file when possible and starts to save the new file (which it determined from the signature it found).

If the data is not fragmented, the recovered file should be identical to (or possibly larger than) the original file in size. In some cases, PhotoRec can learn the original file size from the file header, so the recovered file is truncated to the correct size. If, however, the recovered file ends up being smaller than its header specifies, it is discarded. Some files, such as *.MP3 types, are data streams. In this case, PhotoRec parses the recovered data, then stops the recovery when the stream ends.

When a file is recovered successfully, PhotoRec checks the previous data blocks to see whether a file signature was found but the file was not able to be successfully recovered (i.e., the file was too small), and it tries again. This way, some fragmented files can be successfully recovered.

Maps PhotoRec

Distribution

PhotoRec and TestDisk are shipped together. They can be downloaded from CGSecurity website. These utilities can be found on various Linux Live CDs:

• GParted Live CD
• Parted Magic
• Slax-LFI, a Slax-derived distribution
• SystemRescueCD
• Trinity Rescue Kit
• Ubuntu Rescue Remix, an Ubuntu derivation

They are also packaged for numerous *nix (mostly Linux based) distributions:

• ALT Linux
• ArchLinux Extra Repository
• Debian contrib
• Fedora Extras
• Red Hat Epel
• FreeBSD port
• OpenBSD port
• Gentoo and Gentoo Portage
• Mandriva contrib
• Source Mage GNU/Linux
• Ubuntu

src: www.cgsecurity.org

See also

• Photo recovery

src: qnapsupport.net

References

src: i.ytimg.com

External links

• Official website

Source of article : Wikipedia