90 lines
4 KiB
Text
90 lines
4 KiB
Text
Description
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Lziprecover is a data recovery tool and decompressor for files in the lzip
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compressed data format (.lz). Lziprecover is able to repair slightly damaged
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files, produce a correct file by merging the good parts of two or more
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damaged copies, extract data from damaged files, decompress files and test
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integrity of files.
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Lziprecover can remove the damaged members from multimember files, for
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example multimember tar.lz archives.
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Lziprecover provides random access to the data in multimember files; it only
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decompresses the members containing the desired data.
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Lziprecover facilitates the management of metadata stored as trailing data
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in lzip files.
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Lziprecover is not a replacement for regular backups, but a last line of
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defense for the case where the backups are also damaged.
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The lzip file format is designed for data sharing and long-term archiving,
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taking into account both data integrity and decoder availability:
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* The lzip format provides very safe integrity checking and some data
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recovery means. The lziprecover program can repair bit flip errors
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(one of the most common forms of data corruption) in lzip files,
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and provides data recovery capabilities, including error-checked
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merging of damaged copies of a file.
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* The lzip format is as simple as possible (but not simpler). The
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lzip manual provides the source code of a simple decompressor
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along with a detailed explanation of how it works, so that with
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the only help of the lzip manual it would be possible for a
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digital archaeologist to extract the data from a lzip file long
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after quantum computers eventually render LZMA obsolete.
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* Additionally the lzip reference implementation is copylefted, which
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guarantees that it will remain free forever.
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A nice feature of the lzip format is that a corrupt byte is easier to
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repair the nearer it is from the beginning of the file. Therefore, with
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the help of lziprecover, losing an entire archive just because of a
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corrupt byte near the beginning is a thing of the past.
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For compressible data, multiple lzip-compressed copies have a better
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chance of surviving intact than one uncompressed copy using the same
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amount of storage space.
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Lziprecover is able to recover or decompress files produced by any of
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the compressors in the lzip family; lzip, plzip, minilzip/lzlib, clzip
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and pdlzip.
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If the cause of file corruption is damaged media, the combination
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GNU ddrescue + lziprecover is the best option for recovering data from
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multiple damaged copies.
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If a file is too damaged for lziprecover to repair it, all the
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recoverable data in all members of the file can be extracted in one step
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with the '-D' option.
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When recovering data, lziprecover takes as arguments the names of the
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damaged files and writes zero or more recovered files depending on the
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operation selected and whether the recovery succeeded or not. The
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damaged files themselves are kept unchanged.
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When decompressing or testing file integrity, lziprecover behaves like
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lzip or lunzip.
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To give you an idea of its possibilities, when merging two copies, each
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of them with one damaged area affecting 1 percent of the copy, the
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probability of obtaining a correct file is about 98 percent. With three
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such copies the probability rises to 99.97 percent. For large files (a
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few MB) with small errors (one sector damaged per copy), the probability
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approaches 100 percent even with only two copies. (Supposing that the
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errors are randomly located inside each copy).
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The lziprecover package also includes unzcrash, a program written to
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test robustness to decompression of corrupted data, inspired by
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unzcrash.c from Julian Seward's bzip2. Type 'make unzcrash' in the
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lziprecover source directory to build it. Then try 'unzcrash --help'.
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Copyright (C) 2009-2019 Antonio Diaz Diaz.
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This file is free documentation: you have unlimited permission to copy,
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distribute and modify it.
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The file Makefile.in is a data file used by configure to produce the
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Makefile. It has the same copyright owner and permissions that configure
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itself.
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