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Merging upstream version 1.15~pre1.

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Signed-off-by: Daniel Baumann <daniel@debian.org>
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doc/lziprecover.texinfo
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@ -6,8 +6,8 @@
@finalout
@c %**end of header
@set UPDATED 31 May 2013
@set VERSION 1.14
@set UPDATED 17 June 2013
@set VERSION 1.15-pre1
@dircategory Data Compression
@direntry
@ -35,12 +35,14 @@
This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}).
@menu
* Introduction:: Purpose and features of lziprecover
* Invoking Lziprecover:: Command line interface
* File Format:: Detailed format of the compressed file
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept Index:: Index of concepts
* 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
* Problems:: Reporting bugs
* Concept Index:: Index of concepts
@end menu
@sp 1
@ -56,14 +58,15 @@ to copy, distribute and modify it.
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 undamaged
members from multi-member files, decompress files and test integrity of
files.
recover badly damaged files from two or more copies, extract data from
damaged files, decompress files and test integrity of files.
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. This recovery capability contributes to make the lzip format
one of the best options for long-term data archiving.
and pdlzip. It makes lzip files resistant to bit-flip, one of the most
common forms of data corruption, and its recovery capabilities
contribute to make of the lzip format one of the best options for
long-term data archiving.
Lziprecover is able to efficiently extract a range of bytes from a
multi-member file, because it only decompresses the members containing
@ -80,23 +83,26 @@ damaged files themselves are never modified.
When decompressing or testing file integrity, lziprecover behaves like
lzip or lunzip.
If the files are too damaged for lziprecover to repair them, data from
damaged members can be partially recovered writing it to stdout as shown
in the following example (the resulting file may contain some garbage
data at the end):
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 -cd rec01file.lz > rec01file
lziprecover -D0 -i -o file -q file.lz
@end example
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.
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 lziprecover
@cindex invoking
The format for running lziprecover is:
@ -164,18 +170,10 @@ 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. The copies must be single-member files. The merge will
fail if the copies have too many damaged areas or if the same byte is
damaged in all copies. If successful, a repaired copy is written to the
file @samp{@var{file}_fixed.lz}. The exit status is 0 if the file could
be repaired, 2 otherwise.
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 with
small errors, the probability approaches 100 percent even with only two
copies.
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 Merging Files (@pxref{Merging
Files}) for a complete description of the merge mode.
@item -o @var{file}
@itemx --output=@var{file}
@ -192,10 +190,12 @@ Quiet operation. Suppress all messages.
@item -R
@itemx --repair
Try to repair a small error, affecting only one byte, in a single-member
@var{file}. If successful, a repaired copy is written to the file
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 Repairing Files (@pxref{Repairing Files}) for a complete
description of the repair mode.
@item -s
@itemx --split
@ -252,6 +252,47 @@ 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.
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 with
small errors, the probability approaches 100 percent even with only two
copies.
@node File Format
@chapter File Format
@cindex file format
@ -368,9 +409,8 @@ lziprecover -D 10000-15000 file.lz
@sp 1
@noindent
Example 5: Repair a one-byte corruption in the single-member file
@samp{file.lz}. (Indented lines are abridged error messages from
lziprecover).
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
@ -422,27 +462,12 @@ Example 8: Recover the first volume of those created with the command
@w{@code{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. Two correct copies are produced and
compared.
member 12 damaged in both copies. The correct file produced is saved in
@samp{big_db_00001.lz}.
@example
lziprecover -s big_db1_00001.lz
lziprecover -s big_db2_00001.lz
lziprecover -t rec*big_db1_00001.lz
rec07big_db1_00001.lz: crc mismatch
rec12big_db1_00001.lz: crc mismatch
lziprecover -t rec*big_db2_00001.lz
rec12big_db2_00001.lz: crc mismatch
rec18big_db2_00001.lz: crc mismatch
lziprecover -m -v rec12big_db1_00001.lz rec12big_db2_00001.lz
lziprecover -m -v -o big_db_00001.lz big_db1_00001.lz big_db2_00001.lz
Input files merged successfully
cp rec07big_db2_00001.lz rec07big_db1_00001.lz
cp rec12big_db1_00001_fixed.lz rec12big_db1_00001.lz
cp rec12big_db1_00001_fixed.lz rec12big_db2_00001.lz
cp rec18big_db1_00001.lz rec18big_db2_00001.lz
cat rec*big_db1_00001.lz > big_db3_00001.lz
cat rec*big_db2_00001.lz > big_db4_00001.lz
zcmp big_db3_00001.lz big_db4_00001.lz
@end example