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-\input texinfo @c -*-texinfo-*-
-@c %**start of header
-@setfilename lziprecover.info
-@documentencoding ISO-8859-15
-@settitle Lziprecover Manual
-@finalout
-@c %**end of header
-
-@set UPDATED 14 September 2013
-@set VERSION 1.15
-
-@dircategory Data Compression
-@direntry
-* Lziprecover: (lziprecover). Data recovery tool for lzip files
-@end direntry
-
-
-@ifnothtml
-@titlepage
-@title Lziprecover
-@subtitle Data recovery tool for lzip files
-@subtitle for Lziprecover version @value{VERSION}, @value{UPDATED}
-@author by Antonio Diaz Diaz
-
-@page
-@vskip 0pt plus 1filll
-@end titlepage
-
-@contents
-@end ifnothtml
-
-@node Top
-@top
-
-This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}).
-
-@menu
-* Introduction:: Purpose and features of lziprecover
-* Invoking lziprecover:: Command line interface
-* Repairing files:: Fixing bit-flip and similar errors
-* Merging files:: Fixing several damaged copies
-* File format:: Detailed format of the compressed file
-* Examples:: A small tutorial with examples
-* Unzcrash:: Testing the robustness of decompressors
-* Problems:: Reporting bugs
-* Concept index:: Index of concepts
-@end menu
-
-@sp 1
-Copyright @copyright{} 2009, 2010, 2011, 2012, 2013 Antonio Diaz Diaz.
-
-This manual is free documentation: you have unlimited permission
-to copy, distribute and modify it.
-
-
-@node Introduction
-@chapter Introduction
-@cindex introduction
-
-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
-@w{GNU ddrescue + lziprecover} is the best option for recovering data
-from multiple damaged copies. @xref{ddrescue-example}, for an example.
-
-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
-following command (the resulting file may contain errors and some
-garbage data may be produced at the end of each member):
-
-@example
-lziprecover -D0 -i -o file -q file.lz
-@end example
-
-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.
-
-Lziprecover is not a replacement for regular backups, but a last line of
-defense for the case where the backups are also damaged.
-
-
-@node Invoking lziprecover
-@chapter Invoking lziprecover
-@cindex invoking
-
-The format for running lziprecover is:
-
-@example
-lziprecover [@var{options}] [@var{files}]
-@end example
-
-Lziprecover supports the following options:
-
-@table @samp
-@item -h
-@itemx --help
-Print an informative help message describing the options and exit.
-
-@item -V
-@itemx --version
-Print the version number of lziprecover on the standard output and exit.
-
-@item -c
-@itemx --stdout
-Decompress to standard output. Needed when reading from a named pipe
-(fifo) or from a device. Use it to recover as much of the uncompressed
-data as possible when decompressing a corrupt file.
-
-@item -d
-@itemx --decompress
-Decompress.
-
-@item -D @var{range}
-@itemx --range-decompress=@var{range}
-Decompress only a range of bytes starting at decompressed byte position
-@samp{@var{begin}} and up to byte position @w{@samp{@var{end} - 1}}.
-Three formats of @var{range} are recognized, @samp{@var{begin}},
-@samp{@var{begin}-@var{end}}, and @samp{@var{begin},@var{size}}. If only
-@var{begin} is specified, @var{end} is taken as the end of the file. The
-produced bytes are sent to standard output unless the @samp{--output}
-option is used. In order to guarantee the correctness of the data
-produced, all members containing any part of the desired data are
-decompressed and their integrity is verified. This operation is more
-efficient in multi-member files because it only decompresses the members
-containing the desired data.
-
-@item -f
-@itemx --force
-Force overwrite of output files.
-
-@item -i
-@itemx --ignore-errors
-Make @samp{--range-decompress} ignore data errors and continue
-decompressing the remaining members in the file. For example,
-@w{@samp{lziprecover -i -D0 file.lz > file}} decompresses all the
-recoverable data in all members of @samp{file.lz} without having to
-split it first.
-
-@item -k
-@itemx --keep
-Keep (don't delete) input files during decompression.
-
-@item -l
-@itemx --list
-Print total file sizes and ratios. The values produced are correct even
-for multi-member files. Use it together with @samp{-v} to see
-information about the members in the file.
-
-@item -m
-@itemx --merge
-Try to produce a correct file merging the good parts of two or more
-damaged copies. If successful, a repaired copy is written to the file
-@samp{@var{file}_fixed.lz}. The exit status is 0 if a correct file could
-be produced, 2 otherwise. See the chapter @samp{Merging files}
-(@pxref{Merging files}) for a complete description of the merge mode.
-
-@item -o @var{file}
-@itemx --output=@var{file}
-Place the output into @samp{@var{file}} instead of into
-@samp{@var{file}_fixed.lz}. If splitting, the names of the files
-produced are in the form @samp{rec01@var{file}}, @samp{rec02@var{file}},
-etc. If decompressing from standard input and @samp{--stdout} has not
-been specified, use @samp{@var{file}} as the name of the decompressed
-file.
-
-@item -q
-@itemx --quiet
-Quiet operation. Suppress all messages.
-
-@item -R
-@itemx --repair
-Try to repair a file with small errors (up to one byte error per
-member). If successful, a repaired copy is written to the file
-@samp{@var{file}_fixed.lz}. @samp{@var{file}} is not modified at all.
-The exit status is 0 if the file could be repaired, 2 otherwise. See the
-chapter @samp{Repairing files} (@pxref{Repairing files}) for a complete
-description of the repair mode.
-
-@item -s
-@itemx --split
-Search for members in @samp{@var{file}} and write each member in its own
-@samp{.lz} file. You can then use @samp{lziprecover -t} to test the
-integrity of the resulting files, decompress those which are undamaged,
-and try to repair or partially decompress those which are damaged.
-
-The names of the files produced are in the form
-@samp{rec01@var{file}.lz}, @samp{rec02@var{file}.lz}, etc, and are
-designed so that the use of wildcards in subsequent processing, for
-example, @w{@samp{lziprecover -cd rec*@var{file}.lz > recovered_data}},
-processes the files in the correct order. The number of digits used in
-the names varies depending on the number of members in @samp{@var{file}}.
-
-@item -t
-@itemx --test
-Check integrity of the specified file(s), but don't decompress them.
-This really performs a trial decompression and throws away the result.
-Use it together with @samp{-v} to see information about the file.
-
-@item -v
-@itemx --verbose
-Verbose mode.@*
-When decompressing or testing, further -v's (up to 4) increase the
-verbosity level, showing status, compression ratio, dictionary size,
-trailer contents (CRC, data size, member size), and up to 6 bytes of
-trailing garbage (if any).
-
-@end table
-
-Numbers given as arguments to options may be followed by a multiplier
-and an optional @samp{B} for "byte".
-
-Table of SI and binary prefixes (unit multipliers):
-
-@multitable {Prefix} {kilobyte (10^3 = 1000)} {|} {Prefix} {kibibyte (2^10 = 1024)}
-@item Prefix @tab Value @tab | @tab Prefix @tab Value
-@item k @tab kilobyte (10^3 = 1000) @tab | @tab Ki @tab kibibyte (2^10 = 1024)
-@item M @tab megabyte (10^6) @tab | @tab Mi @tab mebibyte (2^20)
-@item G @tab gigabyte (10^9) @tab | @tab Gi @tab gibibyte (2^30)
-@item T @tab terabyte (10^12) @tab | @tab Ti @tab tebibyte (2^40)
-@item P @tab petabyte (10^15) @tab | @tab Pi @tab pebibyte (2^50)
-@item E @tab exabyte (10^18) @tab | @tab Ei @tab exbibyte (2^60)
-@item Z @tab zettabyte (10^21) @tab | @tab Zi @tab zebibyte (2^70)
-@item Y @tab yottabyte (10^24) @tab | @tab Yi @tab yobibyte (2^80)
-@end multitable
-
-@sp 1
-Exit status: 0 for a normal exit, 1 for environmental problems (file not
-found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
-invalid input file, 3 for an internal consistency error (eg, bug) which
-caused lziprecover to panic.
-
-
-@node Repairing files
-@chapter Repairing files
-@cindex repairing files
-
-Lziprecover is able to repair files with small errors (up to one byte
-error per member). The error may be located anywhere in the file except
-in the header (first 6 bytes of each member) or in the @samp{Member
-size} field of the trailer (last 8 bytes of each member). This makes
-lzip files resistant to bit-flip, one of the most common forms of data
-corruption.
-
-Bit-flip happens when one bit in the file is changed from 0 to 1 or vice
-versa. It may be caused by bad RAM or even by natural radiation. I have
-seen a case of bit-flip in a file stored in an USB flash drive.
-
-
-@node Merging files
-@chapter Merging files
-@cindex merging files
-
-If you have several copies of a file but all of them are too damaged to
-repair them (@pxref{Repairing files}), lziprecover can try to produce a
-correct file merging the good parts of the damaged copies.
-
-The merge may succeed even if some copies of the file have all the
-headers and trailers damaged, as long as there is at least one copy of
-every header and trailer intact, even if they are in different copies of
-the file.
-
-The merge will fail if the damaged areas overlap (at least one byte is
-damaged in all copies), or are adjacent and the boundary can't be
-determined, or if the copies have too many damaged areas.
-
-All the copies must have the same size. If some of them have been
-truncated and are therefore smaller than they should, you can extend
-them to the correct size with the following command before merging them
-with the other copies:
-
-@example
-ddrescue --extend-outfile=<correct_size> small_file.lz extended_file.lz
-@end example
-
-If some of the copies have got garbage data at the end and are therefore
-larger than they should, you can reduce their sizes to the correct value
-with the following command before merging them with the other copies:
-
-@example
-ddrescue --size=<correct_size> large_file.lz reduced_file.lz
-@end example
-
-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.
-
-
-@node File format
-@chapter File format
-@cindex file format
-
-Perfection is reached, not when there is no longer anything to add, but
-when there is no longer anything to take away.@*
---- Antoine de Saint-Exupery
-
-@sp 1
-In the diagram below, a box like this:
-@verbatim
-+---+
-| | <-- the vertical bars might be missing
-+---+
-@end verbatim
-
-represents one byte; a box like this:
-@verbatim
-+==============+
-| |
-+==============+
-@end verbatim
-
-represents a variable number of bytes.
-
-@sp 1
-A lzip file consists of a series of "members" (compressed data sets).
-The members simply appear one after another in the file, with no
-additional information before, between, or after them.
-
-Each member has the following structure:
-@verbatim
-+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size |
-+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-@end verbatim
-
-All multibyte values are stored in little endian order.
-
-@table @samp
-@item ID string
-A four byte string, identifying the lzip format, with the value "LZIP"
-(0x4C, 0x5A, 0x49, 0x50).
-
-@item VN (version number, 1 byte)
-Just in case something needs to be modified in the future. 1 for now.
-
-@item DS (coded dictionary size, 1 byte)
-Lzip divides the distance between any two powers of 2 into 8 equally
-spaced intervals, named "wedges". The dictionary size is calculated by
-taking a power of 2 (the base size) and substracting from it a number of
-wedges between 0 and 7. The size of a wedge is (base_size / 16).@*
-Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).@*
-Bits 7-5 contain the number of wedges (0 to 7) to substract from the
-base size to obtain the dictionary size.@*
-Example: 0xD3 = 2^19 - 6 * 2^15 = 512 KiB - 6 * 32 KiB = 320 KiB@*
-Valid values for dictionary size range from 4 KiB to 512 MiB.
-
-@item Lzma stream
-The lzma stream, finished by an end of stream marker. Uses default values
-for encoder properties. See the lzip manual for a full description.
-
-@item CRC32 (4 bytes)
-CRC of the uncompressed original data.
-
-@item Data size (8 bytes)
-Size of the uncompressed original data.
-
-@item Member size (8 bytes)
-Total size of the member, including header and trailer. This field acts
-as a distributed index, allows the verification of stream integrity, and
-facilitates safe recovery of undamaged members from multi-member files.
-
-@end table
-
-
-@node Examples
-@chapter A small tutorial with examples
-@cindex examples
-
-Example 1: Restore a regular file from its compressed version
-@samp{file.lz}. If the operation is successful, @samp{file.lz} is
-removed.
-
-@example
-lziprecover -d file.lz
-@end example
-
-@sp 1
-@noindent
-Example 2: Verify the integrity of the compressed file @samp{file.lz}
-and show status.
-
-@example
-lziprecover -tv file.lz
-@end example
-
-@sp 1
-@noindent
-Example 3: Decompress @samp{file.lz} partially until 10 KiB of
-decompressed data are produced.
-
-@example
-lziprecover -D 0,10KiB file.lz
-@end example
-
-@sp 1
-@noindent
-Example 4: Decompress @samp{file.lz} partially from decompressed byte
-10000 to decompressed byte 15000 (5000 bytes are produced).
-
-@example
-lziprecover -D 10000-15000 file.lz
-@end example
-
-@sp 1
-@noindent
-Example 5: Repair small errors in the file @samp{file.lz}. (Indented
-lines are abridged diagnostic messages from lziprecover).
-
-@example
-lziprecover -v -R file.lz
- Copy of input file repaired successfully.
-mv file_fixed.lz file.lz
-@end example
-
-@sp 1
-@noindent
-Example 6: Split the multi-member file @samp{file.lz} and write each
-member in its own @samp{recXXXfile.lz} file. Then use
-@w{@samp{lziprecover -t}} to test the integrity of the resulting files.
-
-@example
-lziprecover -s file.lz
-lziprecover -tv rec*file.lz
-@end example
-
-@sp 1
-@anchor{ddrescue-example}
-@noindent
-Example 7: Recover a compressed backup from two copies on CD-ROM with
-error-checked merging of copies
-@ifnothtml
-(@xref{Top,GNU ddrescue manual,,ddrescue},
-@end ifnothtml
-@ifhtml
-(See the
-@uref{http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html,,ddrescue manual}
-@end ifhtml
-for details about ddrescue).
-
-@example
-ddrescue -b2048 /dev/cdrom cdimage1 logfile1
-mount -t iso9660 -o loop,ro cdimage1 /mnt/cdimage
-cp /mnt/cdimage/backup.tar.lz rescued1.tar.lz
-umount /mnt/cdimage
- (insert second copy in the CD drive)
-ddrescue -b2048 /dev/cdrom cdimage2 logfile2
-mount -t iso9660 -o loop,ro cdimage2 /mnt/cdimage
-cp /mnt/cdimage/backup.tar.lz rescued2.tar.lz
-umount /mnt/cdimage
-lziprecover -m -v -o backup.tar.lz rescued1.tar.lz rescued2.tar.lz
-@end example
-
-@sp 1
-@noindent
-Example 8: Recover the first volume of those created with the command
-@w{@samp{lzip -b 32MiB -S 650MB big_db}} from two copies,
-@samp{big_db1_00001.lz} and @samp{big_db2_00001.lz}, with member 07
-damaged in the first copy, member 18 damaged in the second copy, and
-member 12 damaged in both copies. The correct file produced is saved in
-@samp{big_db_00001.lz}.
-
-@example
-lziprecover -m -v -o big_db_00001.lz big_db1_00001.lz big_db2_00001.lz
- Input files merged successfully
-@end example
-
-
-@node Unzcrash
-@chapter Testing the robustness of decompressors
-@cindex unzcrash
-
-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 @samp{make unzcrash} in the
-lziprecover source directory to build it.
-
-Unzcrash reads the specified file and then repeatedly decompresses it,
-increasing 256 times each byte of the compressed data, so as to test all
-possible one-byte errors. This should not cause any invalid memory
-accesses. If it does, please, report it as a bug.
-
-Unzcrash really executes as a subprocess the shell command specified in
-the first non-option argument, and then writes the file specified in the
-second non-option argument to the standard input of the subprocess,
-modifying the corresponding byte each time. Therefore you can use
-unzcrash to test any decompressor (not only lzip), or even other decoder
-programs with a suitable command line syntax.
-
-The format for running unzcrash is:
-
-@example
-unzcrash [@var{options}] "lzip -tv" @var{filename}.lz
-@end example
-
-Unzcrash supports the following options:
-
-@table @samp
-@item -h
-@itemx --help
-Print an informative help message describing the options and exit.
-
-@item -V
-@itemx --version
-Print the version number of unzcrash on the standard output and exit.
-
-@item -b @var{range}
-@itemx --bits=@var{range}
-Test N-bit errors only, instead of testing all the 255 wrong values for
-each byte. @samp{N-bit error} means any value differing from the
-original value in N bit positions, not a value differing from the
-original value in the bit position N.@*
-The number of N-bit errors per byte (N = 1 to 8) is: 8 28 56 70 56 28 8 1@*
-Examples of @var{range}: 1 1,2,3 1-4 1,3-5,8 1-3,5-8
-
-@item -p @var{bytes}
-@itemx --position=@var{bytes}
-First byte position to test in the file. Defaults to 0.
-
-@item -q
-@itemx --quiet
-Quiet operation. Suppress all messages.
-
-@item -s @var{bytes}
-@itemx --size=@var{bytes}
-Number of byte positions to test. If not specified, the whole file is
-tested.
-
-@item -v
-@itemx --verbose
-Verbose mode.
-
-@end table
-
-Exit status: 0 for a normal exit, 1 for environmental problems (file not
-found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
-invalid input file, 3 for an internal consistency error (eg, bug) which
-caused unzcrash to panic.
-
-
-@node Problems
-@chapter Reporting bugs
-@cindex bugs
-@cindex getting help
-
-There are probably bugs in lziprecover. There are certainly errors and
-omissions in this manual. If you report them, they will get fixed. If
-you don't, no one will ever know about them and they will remain unfixed
-for all eternity, if not longer.
-
-If you find a bug in lziprecover, please send electronic mail to
-@email{lzip-bug@@nongnu.org}. Include the version number, which you can
-find by running @w{@samp{lziprecover --version}}.
-
-
-@node Concept index
-@unnumbered Concept index
-
-@printindex cp
-
-@bye