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Merging upstream version 1.17~rc1.

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Signed-off-by: Daniel Baumann <daniel@debian.org>
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Daniel Baumann 2025-02-21 11:23:37 +01:00
parent 97763bf5de
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GPG key ID: FBB4F0E80A80222F
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101
doc/lziprecover.info
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@ -12,12 +12,13 @@ File: lziprecover.info, Node: Top, Next: Introduction, Up: (dir)
Lziprecover Manual
******************
This manual is for Lziprecover (version 1.17-pre1, 16 October 2014).
This manual is for Lziprecover (version 1.17-rc1, 21 January 2015).
* Menu:
* Introduction:: Purpose and features of lziprecover
* Invoking lziprecover:: Command line interface
* Data safety:: Protecting data from accidental loss
* Repairing files:: Fixing bit-flip and similar errors
* Merging files:: Fixing several damaged copies
* File names:: Names of the files produced by lziprecover
@ -28,7 +29,7 @@ This manual is for Lziprecover (version 1.17-pre1, 16 October 2014).
* Concept index:: Index of concepts
Copyright (C) 2009-2014 Antonio Diaz Diaz.
Copyright (C) 2009-2015 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission to
copy, distribute and modify it.
@ -104,7 +105,7 @@ like lzip or lunzip.
line of defense for the case where the backups are also damaged.

File: lziprecover.info, Node: Invoking lziprecover, Next: Repairing files, Prev: Introduction, Up: Top
File: lziprecover.info, Node: Invoking lziprecover, Next: Data safety, Prev: Introduction, Up: Top
2 Invoking lziprecover
**********************
@ -252,20 +253,66 @@ invalid input file, 3 for an internal consistency error (eg, bug) which
caused lziprecover to panic.

File: lziprecover.info, Node: Repairing files, Next: Merging files, Prev: Invoking lziprecover, Up: Top
File: lziprecover.info, Node: Data safety, Next: Repairing files, Prev: Invoking lziprecover, Up: Top
3 Repairing files
3 Protecting data from accidental loss
**************************************
There are 3 main types of data corruption that may cause data loss:
single-byte errors, multi-byte errors (generally affecting a whole
sector in a block device), and total device failure.
Lziprecover protects natively against single-byte errors (*note
Repairing files::), as long as file integrity is checked frequently
enough that a second single-byte error does not develop in the same
member before the first one is repaired.
Lziprecover also protects against multi-byte errors (*note Merging
files::), if at least one backup copy of the file is made.
The only remedy for total device failure is storing backup copies in
separate media.
How does lzip compare with gzip and bzip2 with respect to data
safety? Lets suppose that you made a backup copy of your valuable
scientific data, compressed it, and stored two copies on separate
media. Years later you notice that both copies are corrupt.
If you compressed with gzip and both copies suffer any damage in the
data stream, even if it is just one altered bit, the original data can't
be recovered.
If you used bzip2, and if the file is large enough to contain more
than one compressed data block (usually larger than 900 kB), and if no
block is damaged in both files, then the data can be manually recovered
by splitting the files with bzip2recover, verifying every block and then
copying the right blocks in the right order in another file.
But if you used lzip, the data can be automatically recovered as
long as no byte is damaged in both files.
Note that each error in a bzip2 file makes a whole block unusable,
but each error in a lzip file only affects the damaged bytes, making it
possible to recover a file with thousands of errors.

File: lziprecover.info, Node: Repairing files, Next: Merging files, Prev: Data safety, Up: Top
4 Repairing files
*****************
Lziprecover can repair perfectly most files with small errors (up to one
single-byte error per member), without the need of any extra redundance
at all. If the reparation is successful, the repaired file will be
identical bit for bit to the original.
identical bit for bit to the original. This makes lzip files resistant
to bit-flip, one of the most common forms of data corruption.
The error may be located anywhere in the file except in the header
(first 6 bytes of each member) or in the '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.
trailer (last 8 bytes of each member). If the error is in the header it
can be easily repaired with a text editor like GNU Moe (*note File
format::). If the error is in the member size, it is enough to ignore
the message about 'bad member size' when decompressing.
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
@ -289,7 +336,7 @@ lziprecover repairs more efficiently the worst errors.

File: lziprecover.info, Node: Merging files, Next: File names, Prev: Repairing files, Up: Top
4 Merging files
5 Merging files
***************
If you have several copies of a file but all of them are too damaged to
@ -330,7 +377,7 @@ errors are randomly located inside each copy).

File: lziprecover.info, Node: File names, Next: File format, Prev: Merging files, Up: Top
5 Names of the files produced by lziprecover
6 Names of the files produced by lziprecover
********************************************
The name of the fixed file produced by '--merge' and '--repair' is made
@ -341,7 +388,7 @@ original file name ends with one of the extensions '.tar.lz', '.lz' or

File: lziprecover.info, Node: File format, Next: Examples, Prev: File names, Up: Top
6 File format
7 File format
*************
Perfection is reached, not when there is no longer anything to add, but
@ -414,7 +461,7 @@ additional information before, between, or after them.

File: lziprecover.info, Node: Examples, Next: Unzcrash, Prev: File format, Up: Top
7 A small tutorial with examples
8 A small tutorial with examples
********************************
Example 1: Restore a regular file from its compressed version
@ -485,7 +532,7 @@ correct file produced is saved in 'big_db_00001.lz'.

File: lziprecover.info, Node: Unzcrash, Next: Problems, Prev: Examples, Up: Top
8 Testing the robustness of decompressors
9 Testing the robustness of decompressors
*****************************************
The lziprecover package also includes unzcrash, a program written to
@ -562,8 +609,8 @@ caused unzcrash to panic.

File: lziprecover.info, Node: Problems, Next: Concept index, Prev: Unzcrash, Up: Top
9 Reporting bugs
****************
10 Reporting bugs
*****************
There are probably bugs in lziprecover. There are certainly errors and
omissions in this manual. If you report them, they will get fixed. If
@ -584,6 +631,7 @@ Concept index
* Menu:
* bugs: Problems. (line 6)
* data safety: Data safety. (line 6)
* examples: Examples. (line 6)
* file format: File format. (line 6)
* file names: File names. (line 6)
@ -598,17 +646,18 @@ Concept index

Tag Table:
Node: Top231
Node: Introduction1153
Node: Invoking lziprecover4249
Node: Repairing files9686
Node: Merging files11371
Node: File names13212
Node: File format13676
Node: Examples16183
Ref: ddrescue-example17384
Node: Unzcrash18493
Node: Problems21047
Node: Concept index21597
Node: Introduction1216
Node: Invoking lziprecover4312
Node: Data safety9745
Node: Repairing files11661
Node: Merging files13563
Node: File names15404
Node: File format15868
Node: Examples18375
Ref: ddrescue-example19576
Node: Unzcrash20685
Node: Problems23239
Node: Concept index23791

End Tag Table