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, produce a correct file by merging the good parts of two or more
damaged copies, 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 lziprecover program 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.

For compressible data, multiple lzip-compressed copies have a better
chance of surviving intact than one uncompressed copy using the same
amount of storage space.

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 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 in one step
with the '-D' option.

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) 2009-2019 Antonio Diaz Diaz.

This file is free documentation: you have unlimited permission to copy,
distribute and modify it.

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