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@@ -0,0 +1,94 @@ +Description + +Lziprecover is a data recovery tool and decompressor for files in the lzip +compressed data format (.lz). Lziprecover is able to repair slightly damaged +files (up to one single-byte error per member), produce a correct file by +merging the good parts of two or more damaged copies, reproduce a missing +(zeroed) sector using a reference file, extract data from damaged files, +decompress files, and test integrity of files. + +Lziprecover can remove the damaged members from multimember files, for +example multimember tar.lz archives. + +Lziprecover provides random access to the data in multimember files; it only +decompresses the members containing the desired data. + +Lziprecover facilitates the management of metadata stored as trailing data +in lzip files. + +Lziprecover is not a replacement for regular backups, but a last line of +defense for the case where the backups are also damaged. + +The lzip file format is designed for data sharing and long-term archiving, +taking into account both data integrity and decoder availability: + + * The lzip format provides very safe integrity checking and some data + recovery means. The program lziprecover can repair bit flip errors + (one of the most common forms of data corruption) in lzip files, and + provides data recovery capabilities, including error-checked merging + of damaged copies of a file. + + * The lzip format is as simple as possible (but not simpler). The lzip + manual provides the source code of a simple decompressor along with a + detailed explanation of how it works, so that with the only help of the + lzip manual it would be possible for a digital archaeologist to extract + the data from a lzip file long after quantum computers eventually + render LZMA obsolete. + + * Additionally the lzip reference implementation is copylefted, which + guarantees that it will remain free forever. + +A nice feature of the lzip format is that a corrupt byte is easier to repair +the nearer it is from the beginning of the file. Therefore, with the help of +lziprecover, losing an entire archive just because of a corrupt byte near +the beginning is a thing of the past. + +Compression may be good for long-term archiving. For compressible data, +multiple compressed copies may provide redundancy in a more useful form and +may have a better chance of surviving intact than one uncompressed copy +using the same amount of storage space. This is specially true if the format +provides recovery capabilities like those of lziprecover, which is able to +find and combine the good parts of several damaged copies. + +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. + +If the cause of file corruption is a damaged medium, the combination +GNU ddrescue + lziprecover is the recommended option for recovering data +from damaged lzip files. + +If a file is too damaged for lziprecover to repair it, all the recoverable +data in all members of the file can be extracted in one step with the +command 'lziprecover -cd -i file.lz > file'. + +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 kept unchanged. + +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. (Supposing that the errors are randomly located +inside each copy). + +The lziprecover package also includes unzcrash, a program written to test +robustness to decompression of corrupted data, inspired by unzcrash.c from +Julian Seward's bzip2. Type 'make unzcrash' in the lziprecover source +directory to build it. Then try 'unzcrash --help'. + + +Copyright (C) 2009-2022 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. |