polynomial-c@gentoo.org Lars Wendler mgorny@gentoo.org Michał Górny Lziprecover is a data recovery tool and decompressor for files in the lzip compressed data format (.lz), able to repair slightly damaged files, recover badly damaged files from two or more copies, extract data from damaged files, decompress files and test integrity of files. The lzip file format is designed for long-term data archiving. It is clean, provides very safe 4 factor integrity checking, and is backed by the recovery capabilities of lziprecover. Lziprecover is able to recover or decompress files produced by any of the compressors in the lzip family; lzip, plzip, minilzip/lzlib, clzip and pdlzip. Lziprecover makes lzip files resistant to bit-flip (one of the most common forms of data corruption), and can safely merge multiple damaged backup copies. If the cause of file corruption is damaged media, the combination GNU ddrescue + lziprecover is the best option for recovering data from multiple damaged copies. If a file is too damaged for lziprecover to repair it, all the recoverable data in all members of the file can be extracted with the '-D' option. Lziprecover is able to efficiently extract a range of bytes from a multi-member file, because it only decompresses the members containing the desired data. Lziprecover can print correct total file sizes and ratios even for multi-member files. When recovering data, lziprecover takes as arguments the names of the damaged files and writes zero or more recovered files depending on the operation selected and whether the recovery succeeded or not. The damaged files themselves are never modified. When decompressing or testing file integrity, lziprecover behaves like lzip or lunzip. To give you an idea of its possibilities, when merging two copies, each of them with one damaged area affecting 1 percent of the copy, the probability of obtaining a correct file is about 98 percent. With three such copies the probability rises to 99.97 percent. For large files (a few MB) with small errors (one sector damaged per copy), the probability approaches 100 percent even with only two copies. Lziprecover is not a replacement for regular backups, but a last line of defense for the case where the backups are also damaged.