Merging upstream version 1.25~rc1.
Signed-off-by: Daniel Baumann <daniel@debian.org>
This commit is contained in:
parent
1d67e88e3c
commit
b8e73cb85f
GPG key ID:
FBB4F0E80A80222F
39 changed files with 978 additions and 742 deletions
|
|
@ -6,8 +6,8 @@
|
|||
@finalout
|
||||
@c %**end of header
|
||||
|
||||
@set UPDATED 1 October 2024
|
||||
@set VERSION 1.25-pre1
|
||||
@set UPDATED 18 November 2024
|
||||
@set VERSION 1.25-rc1
|
||||
|
||||
@dircategory Compression
|
||||
@direntry
|
||||
|
|
@ -38,6 +38,7 @@ This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}).
|
|||
@menu
|
||||
* Introduction:: Purpose and features of lziprecover
|
||||
* Invoking lziprecover:: Command-line interface
|
||||
* Argument syntax:: By convention, options start with a hyphen
|
||||
* File format:: Detailed format of the compressed file
|
||||
* Data safety:: Protecting data from accidental loss
|
||||
* Fec files:: Forward Error Correction
|
||||
|
|
@ -139,8 +140,16 @@ pdlzip.
|
|||
|
||||
If the cause of file corruption is a damaged medium, the combination
|
||||
@w{GNU ddrescue + lziprecover} is the recommended option for recovering data
|
||||
from damaged lzip files. @xref{ddrescue-example}, and
|
||||
@ref{ddrescue-example2}, for examples.
|
||||
from damaged files. @xref{ddrescue-example}, @ref{ddrescue-example2}, and
|
||||
@ref{ddrescue-example3}, for examples.
|
||||
@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.
|
||||
|
||||
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
|
||||
|
|
@ -186,11 +195,7 @@ standard output. Remember to prepend @file{./} to any file name beginning
|
|||
with a hyphen, or use @samp{--}.
|
||||
|
||||
@noindent
|
||||
lziprecover supports the following
|
||||
@uref{http://www.nongnu.org/arg-parser/manual/arg_parser_manual.html#Argument-syntax,,options}:
|
||||
@ifnothtml
|
||||
@xref{Argument syntax,,,arg_parser}.
|
||||
@end ifnothtml
|
||||
lziprecover supports the following options: @xref{Argument syntax}.
|
||||
|
||||
@table @code
|
||||
@item -h
|
||||
|
|
@ -211,12 +216,12 @@ garbage that can be safely ignored. @xref{concat-example}.
|
|||
|
||||
@item -A
|
||||
@itemx --alone-to-lz
|
||||
Convert lzma-alone files to lzip format without recompressing, just
|
||||
adding a lzip header and trailer. The conversion minimizes the
|
||||
dictionary size of the resulting file (and therefore the amount of
|
||||
memory required to decompress it). Only streamed files with default LZMA
|
||||
properties can be converted; non-streamed lzma-alone files lack the "End
|
||||
Of Stream" marker required in lzip files.
|
||||
Convert lzma-alone files to lzip format without recompressing, just adding a
|
||||
lzip header and trailer. The conversion minimizes the dictionary size of the
|
||||
resulting file (and therefore the amount of memory required to decompress
|
||||
it). Only streamed files with default LZMA properties can be converted;
|
||||
non-streamed lzma-alone files lack the 'End Of Stream' marker required in
|
||||
lzip files.
|
||||
|
||||
The name of the converted lzip file is derived from that of the original
|
||||
lzma-alone file as follows:
|
||||
|
|
@ -258,24 +263,27 @@ already exists and @option{--force} has not been specified, lziprecover
|
|||
continues decompressing the rest of the files and exits with error status 1.
|
||||
If a file fails to decompress, or is a terminal, lziprecover exits
|
||||
immediately with error status 2 without decompressing the rest of the files.
|
||||
A terminal is considered an uncompressed file, and therefore invalid.
|
||||
A terminal is considered an uncompressed file, and therefore invalid. A
|
||||
multimember file with one or more empty members is accepted if redirected to
|
||||
standard input or if '-i' is given.
|
||||
|
||||
@item -D @var{range}
|
||||
@itemx --range-decompress=@var{range}
|
||||
Decompress only a range of bytes starting at decompressed byte position
|
||||
@var{begin} and up to byte position @w{@var{end} - 1}. Byte positions start
|
||||
at 0. This option provides random access to the data in multimember files;
|
||||
it only decompresses the members containing the desired data. 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 checked.
|
||||
at 0. The bytes produced are sent to standard output unless the option
|
||||
@option{-o} is used. This option provides random access to the data in
|
||||
multimember files; it only decompresses the members containing the desired
|
||||
data. 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 checked.
|
||||
|
||||
@anchor{range-format}
|
||||
Four formats of @var{range} are recognized, @samp{@var{begin}},
|
||||
@samp{@var{begin}-@var{end}}, @samp{@var{begin},@var{size}}, and
|
||||
@samp{,@var{size}}. If only @var{begin} is specified, @var{end} is taken as
|
||||
the end of the file. If only @var{size} is specified, @var{begin} is taken
|
||||
as the beginning of the file. The bytes produced are sent to standard output
|
||||
unless the option @option{--output} is used.
|
||||
as the beginning of the file.
|
||||
|
||||
@anchor{--reproduce}
|
||||
@item -e
|
||||
|
|
@ -371,7 +379,8 @@ last) may be wrong.
|
|||
|
||||
@item -k
|
||||
@itemx --keep
|
||||
Keep (don't delete) input files during decompression.
|
||||
Keep (don't delete) input files during decompression or conversion from
|
||||
lzma-alone.
|
||||
|
||||
@item -l
|
||||
@itemx --list
|
||||
|
|
@ -381,9 +390,11 @@ even for multimember files. If more than one file is given, a final line
|
|||
containing the cumulative sizes is printed. With @option{-v}, the dictionary
|
||||
size, the number of members in the file, and the amount of trailing data (if
|
||||
any) are also printed. With @option{-vv}, the positions and sizes of each
|
||||
member in multimember files are also printed. With @option{-i}, format errors
|
||||
are ignored, and with @option{-ivv}, gaps between members are shown. The
|
||||
member numbers shown coincide with the file numbers produced by @option{--split}.
|
||||
member in multimember files are also printed. A multimember file with one or
|
||||
more empty members is accepted if redirected to standard input or if '-i' is
|
||||
given. With @option{-i}, format errors are ignored, and with @option{-ivv},
|
||||
gaps between members are shown. The member numbers start at 1 and coincide
|
||||
with the file numbers produced by @option{--split}.
|
||||
|
||||
If any file is damaged, does not exist, can't be opened, or is not regular,
|
||||
the final exit status is @w{> 0}. @option{-lq} can be used to check quickly
|
||||
|
|
@ -402,8 +413,8 @@ the merge mode.
|
|||
@item -n @var{n}
|
||||
@itemx --threads=@var{n}
|
||||
Set the maximum number of worker threads for @option{--fec=create},
|
||||
overriding the system's default. Valid values range from 1 to "as many as
|
||||
your system can support". If this option is not used, lziprecover tries to
|
||||
overriding the system's default. Valid values range from 1 to as many as
|
||||
your system can support. If this option is not used, lziprecover tries to
|
||||
detect the number of processors in the system and use it as default value.
|
||||
@w{@samp{lziprecover --help}} shows the system's default value.
|
||||
|
||||
|
|
@ -411,7 +422,7 @@ detect the number of processors in the system and use it as default value.
|
|||
@itemx --output=@var{file}[/]
|
||||
If repairing, place the repaired output into @var{file} instead of into
|
||||
@var{file}_fixed.lz. If splitting, the names of the files produced are in
|
||||
the form @file{rec01@var{file}}, @file{rec02@var{file}}, etc.
|
||||
the form @file{rec1@var{file}}, @file{rec2@var{file}}, etc.
|
||||
|
||||
If creating FEC data and @option{-c} has not been also specified, write the
|
||||
FEC data to @var{file}. If @var{file} ends with a slash, it is interpreted
|
||||
|
|
@ -458,8 +469,8 @@ members with corrupt headers or trailers. If other lziprecover functions
|
|||
fail to work on a multimember @var{file} because of damage in headers or
|
||||
trailers, try to split @var{file} and then work on each member individually.
|
||||
|
||||
The names of the files produced are in the form @file{rec01@var{file}},
|
||||
@file{rec02@var{file}}, etc, and are designed so that the use of wildcards
|
||||
The names of the files produced are in the form @file{rec1@var{file}},
|
||||
@file{rec2@var{file}}, etc, and are designed so that the use of wildcards
|
||||
in subsequent processing, for example,
|
||||
@w{@samp{lziprecover -cd rec*@var{file} > recovered_data}}, processes the
|
||||
files in the correct order. The number of digits used in the names varies
|
||||
|
|
@ -473,7 +484,8 @@ together with @option{-v} to see information about the files. If a file
|
|||
fails the test, does not exist, can't be opened, or is a terminal, lziprecover
|
||||
continues testing the rest of the files. A final diagnostic is shown at
|
||||
verbosity level 1 or higher if any file fails the test when testing multiple
|
||||
files.
|
||||
files. A multimember file with one or more empty members is accepted if
|
||||
redirected to standard input or if '-i' is given.
|
||||
|
||||
@item -v
|
||||
@itemx --verbose
|
||||
|
|
@ -489,8 +501,8 @@ operations, and extra information (for example, the failed areas).
|
|||
@item --dump=[@var{member_list}][:damaged][:empty][:tdata]
|
||||
Dump the members listed, the damaged members (if any), the empty members (if
|
||||
any), or the trailing data (if any) of one or more regular multimember files
|
||||
to standard output, or to a file if the option @option{--output} is used. If
|
||||
more than one file is given, the elements dumped from all the files are
|
||||
to standard output, or to a file if the option @option{-o} is used. If more
|
||||
than one file is given, the elements dumped from all the files are
|
||||
concatenated. If a file does not exist, can't be opened, or is not regular,
|
||||
lziprecover continues processing the rest of the files. If the dump fails in
|
||||
one file, lziprecover exits immediately without processing the rest of the
|
||||
|
|
@ -547,7 +559,7 @@ attempting the removal of trailing data.
|
|||
|
||||
@item --strip=[@var{member_list}][:damaged][:empty][:tdata]
|
||||
Copy one or more regular multimember files to standard output (or to a file
|
||||
if the option @option{--output} is used), stripping the members listed, the
|
||||
if the option @option{-o} is used), stripping the members listed, the
|
||||
damaged members (if any), the empty members (if any), or the trailing data
|
||||
(if any) from each file. If all members in a file are selected to be
|
||||
stripped, the trailing data (if any) are also stripped even if @samp{tdata}
|
||||
|
|
@ -559,22 +571,11 @@ the rest of the files. If a file fails to copy, lziprecover exits
|
|||
immediately without processing the rest of the files. See @option{--dump}
|
||||
above for a description of the argument.
|
||||
|
||||
@item --ignore-empty
|
||||
When decompressing, testing, or listing, ignore empty members in multimember
|
||||
files. By default lziprecover exits with error status 2 if any empty member
|
||||
is found in a multimember file.
|
||||
|
||||
@item --ignore-nonzero
|
||||
When decompressing or testing, ignore a nonzero first byte in the LZMA
|
||||
stream. By default lziprecover exits with error status 2 if the first LZMA
|
||||
byte is nonzero in any member of the input files.
|
||||
Use @w{@samp{lziprecover --nonzero-repair}} to repair any such nonzero bytes.
|
||||
|
||||
@item --loose-trailing
|
||||
When decompressing, testing, or listing, allow trailing data whose first
|
||||
bytes are so similar to the magic bytes of a lzip header that they can
|
||||
be confused with a corrupt header. Use this option if a file triggers a
|
||||
"corrupt header" error and the cause is not indeed a corrupt header.
|
||||
'corrupt header' error and the cause is not indeed a corrupt header.
|
||||
|
||||
@item --nonzero-repair
|
||||
Repair in place a nonzero first LZMA byte in the files specified. With
|
||||
|
|
@ -666,13 +667,14 @@ Load the compressed @var{file} into memory, set the byte at @var{position}
|
|||
to @var{value}, and decompress the modified compressed data to standard
|
||||
output. If the damaged member can be decompressed to the end (just fails
|
||||
with a CRC mismatch), the members following it are also decompressed.
|
||||
@xref{--set-byte}, for a description of @var{value}.
|
||||
|
||||
@item -X[@var{position},@var{value}]
|
||||
@itemx --show-packets[=@var{position},@var{value}]
|
||||
Load the compressed @var{file} into memory, optionally set the byte at
|
||||
@var{position} to @var{value}, decompress the modified compressed data
|
||||
(discarding the output), and print to standard output descriptions of the
|
||||
LZMA packets being decoded.
|
||||
LZMA packets being decoded. @xref{--set-byte}, for a description of @var{value}.
|
||||
|
||||
@item -Y @var{range}
|
||||
@itemx --debug-delay=@var{range}
|
||||
|
|
@ -689,6 +691,7 @@ description of @var{range}.
|
|||
@itemx --debug-byte-repair=@var{position},@var{value}
|
||||
Load the compressed @var{file} into memory, set the byte at @var{position}
|
||||
to @var{value}, and then try to repair the byte error. @xref{--byte-repair}.
|
||||
@xref{--set-byte}, for a description of @var{value}.
|
||||
|
||||
@item --gf16
|
||||
Forces the use of GF(2^16) when creating FEC blocks even if the number of
|
||||
|
|
@ -723,6 +726,59 @@ indicate a corrupt or invalid input file, 3 for an internal consistency
|
|||
error (e.g., bug) which caused lziprecover to panic.
|
||||
|
||||
|
||||
@node Argument syntax
|
||||
@chapter Syntax of command-line arguments
|
||||
@cindex argument syntax
|
||||
|
||||
POSIX recommends these conventions for command-line arguments.
|
||||
|
||||
@itemize @bullet
|
||||
@item A command-line argument is an option if it begins with a hyphen
|
||||
(@samp{-}).
|
||||
|
||||
@item Option names are single alphanumeric characters.
|
||||
|
||||
@item Certain options require an argument.
|
||||
|
||||
@item An option and its argument may or may not appear as separate tokens.
|
||||
(In other words, the whitespace separating them is optional, unless the
|
||||
argument is the empty string).
|
||||
Thus, @w{@option{-o foo}} and @option{-ofoo} are equivalent.
|
||||
|
||||
@item One or more options without arguments, followed by at most one option
|
||||
that takes an argument, may follow a hyphen in a single token.
|
||||
Thus, @option{-abc} is equivalent to @w{@option{-a -b -c}}.
|
||||
|
||||
@item Options typically precede other non-option arguments.
|
||||
|
||||
@item The argument @samp{--} terminates all options; any following arguments
|
||||
are treated as non-option arguments, even if they begin with a hyphen.
|
||||
|
||||
@item A token consisting of a single hyphen character is interpreted as an
|
||||
ordinary non-option argument. By convention, it is used to specify standard
|
||||
input, standard output, or a file named @samp{-}.
|
||||
@end itemize
|
||||
|
||||
@noindent
|
||||
GNU adds @dfn{long options} to these conventions:
|
||||
|
||||
@itemize @bullet
|
||||
@item A long option consists of two hyphens (@samp{--}) followed by a name
|
||||
made of alphanumeric characters and hyphens. Option names are typically one
|
||||
to three words long, with hyphens to separate words. Abbreviations can be
|
||||
used for the long option names as long as the abbreviations are unique.
|
||||
|
||||
@item A long option and its argument may or may not appear as separate
|
||||
tokens. In the latter case they must be separated by an equal sign @samp{=}.
|
||||
Thus, @w{@option{--foo bar}} and @option{--foo=bar} are equivalent.
|
||||
@end itemize
|
||||
|
||||
@noindent
|
||||
The syntax of options with an optional argument is
|
||||
@option{-<short_option><argument>} (without whitespace), or
|
||||
@option{--<long_option>=<argument>}.
|
||||
|
||||
|
||||
@node File format
|
||||
@chapter File format
|
||||
@cindex file format
|
||||
|
|
@ -785,7 +841,7 @@ 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
|
||||
The LZMA stream, terminated by an 'End Of Stream' marker. Uses default values
|
||||
for encoder properties.
|
||||
@ifnothtml
|
||||
@xref{Stream format,,,lzip},
|
||||
|
|
@ -932,12 +988,11 @@ identical backups (@pxref{performance-of-merge}).
|
|||
@chapter Forward Error Correction
|
||||
@cindex forward error correction
|
||||
|
||||
"Forward Error Correction" (FEC) is any way of protecting data from
|
||||
corruption by creating redundant data that can be used later to repair
|
||||
errors in the protected data. Lziprecover uses a Hilbert-based Reed-Solomon
|
||||
code to create one fec file (with extension @file{.fec}) for each file that
|
||||
needs to be protected. The fec files created by lziprecover are
|
||||
reproducible.
|
||||
Forward Error Correction (FEC) is any way of protecting data from corruption
|
||||
by creating redundant data that can be used later to repair errors in the
|
||||
protected data. Lziprecover uses a Hilbert-based Reed-Solomon code to create
|
||||
one fec file (with extension @file{.fec}) for each file that needs to be
|
||||
protected. The fec files created by lziprecover are reproducible.
|
||||
|
||||
Reed-Solomon is the most space-efficient Error Correcting Code (ECC) for
|
||||
data stored in block devices. It creates redundant FEC blocks in such a way
|
||||
|
|
@ -945,8 +1000,7 @@ that X FEC blocks allow the recuperation of any combination of up to X lost
|
|||
data blocks. All the blocks (data and FEC) are of the same size, which in
|
||||
fec files must be a multiple of 512 bytes. Reed-Solomon is not optimum for
|
||||
corruption affecting random single bits in a file because each corrupt bit
|
||||
invalidates the whole block containing it. But in block devices, scattered
|
||||
bit flips should not happen.
|
||||
invalidates the whole block containing it.
|
||||
|
||||
Usually, a corrupt file does not provide an indication of where the
|
||||
corruption is located. Therefore, each fec file stores one or two arrays of
|
||||
|
|
@ -1000,8 +1054,7 @@ If we have that x = 1, y = 2, and z = 3, then p = 6, q = 14, and r = 13:
|
|||
|
||||
Now, if the values of x and y are lost because of data corruption, they can
|
||||
be recomputed by using any two of the three equations above. For example, if
|
||||
we replace the known values of z, p, q, and r in equations (1) and (2) we
|
||||
get:
|
||||
we replace the known values of z, p, and q in equations (1) and (2) we get:
|
||||
|
||||
@example
|
||||
x + y + 3 = 6 (1b)
|
||||
|
|
@ -1076,13 +1129,12 @@ missing data blocks.
|
|||
Lziprecover implements GF(2^8) with polynomial 0x11D and GF(2^16) with
|
||||
polynomial 0x1100B.
|
||||
|
||||
A Hilbert matrix is defined as @w{@samp{A[i][j] = 1 / (i + j + 1)}} for i
|
||||
and j >= 0. But as in a Galois Field addition is exclusive or, applying the
|
||||
Hilbert definition produces a singular (non invertible) matrix. To avoid
|
||||
this problem, lziprecover uses a Hilbert matrix starting at row
|
||||
@w{@samp{gf_size / 2}}. I.e., @w{@samp{A[i][j] = 1 / (i + gf_size / 2 + j)}}
|
||||
for @w{@samp{0 <= i,j < gf_size / 2}}. (gf_size is the size of the Galois
|
||||
Field).
|
||||
A Hilbert matrix is defined as @w{A[i][j] = 1 / (i + j + 1)} for
|
||||
@w{i,j >= 0}. But, as in a Galois Field the addition is the exclusive or
|
||||
operation, applying the Hilbert definition produces a singular (non
|
||||
invertible) matrix. To avoid this problem, lziprecover uses a Hilbert matrix
|
||||
starting at row @w{r0 = gf_size / 2}. I.e., @w{A[i][j] = 1 / (i + j + r0)}
|
||||
for @w{0 <= i,j < r0}. (@samp{gf_size} is the size of the Galois Field).
|
||||
|
||||
|
||||
@node Creating fec files
|
||||
|
|
@ -1113,6 +1165,14 @@ Example 3: Create recursively one fec file for each file in the directory
|
|||
lziprecover -v -r -Fc -o fec/ datadir
|
||||
@end example
|
||||
|
||||
@noindent
|
||||
Example 4: Create fec files for a collection of photos stored in directory
|
||||
@file{photos} and store them in the directory @file{photos-fec}.
|
||||
|
||||
@example
|
||||
lziprecover -v -Fc -o photos-fec/ photos/*
|
||||
@end example
|
||||
|
||||
|
||||
@node Testing with fec files
|
||||
@section How to test files using fec files
|
||||
|
|
@ -1143,6 +1203,14 @@ directory @file{fec}.
|
|||
lziprecover -v -r -Ft --fec-file=fec/ datadir
|
||||
@end example
|
||||
|
||||
@noindent
|
||||
Example 4: Test the integrity of a collection of photos stored in directory
|
||||
@file{photos} using fec files from directory @file{photos-fec}.
|
||||
|
||||
@example
|
||||
lziprecover -v -Ft --fec-file=photos-fec/ photos/*
|
||||
@end example
|
||||
|
||||
|
||||
@node Repairing with fec files
|
||||
@section How to repair files using fec files
|
||||
|
|
@ -1174,6 +1242,22 @@ directory @file{fec}.
|
|||
lziprecover -v -r -Fr --fec-file=fec/ datadir
|
||||
@end example
|
||||
|
||||
@anchor{ddrescue-example}
|
||||
@noindent
|
||||
Example 4: Recover a collection of photos from a damaged external drive
|
||||
(@file{/dev/sdc1}). The photos are in directory @file{photos}, and the fec
|
||||
files are in directory @file{photos-fec}.
|
||||
|
||||
@example
|
||||
ddrescue -b4096 -r10 /dev/sdc1 hdimage mapfile
|
||||
mount -o loop,ro hdimage /mnt/hdimage
|
||||
cp -a /mnt/hdimage/photos photos
|
||||
cp -a /mnt/hdimage/photos-fec photos-fec
|
||||
umount /mnt/hdimage
|
||||
lziprecover -v -Fr --fec-file=photos-fec/ photos/*
|
||||
(Check and rename repaired files. They are named @file{photos/*_fixed})
|
||||
@end example
|
||||
|
||||
|
||||
@node Fec file format
|
||||
@section Fec file format
|
||||
|
|
@ -1274,9 +1358,9 @@ The first chksum packet contains an array of CRC32s, while the second chksum
|
|||
packet (if present) contains an array of CRC32-Cs.
|
||||
|
||||
For the expected thousands of bit flips caused by a zeroed sector, a
|
||||
"symmetric" CRC like CRC32 is probably better than CRC32-C, which detects
|
||||
all the errors with an odd number of bit flips at the expense of a larger
|
||||
number of undetected errors with an even number of bit flips.
|
||||
symmetric CRC like CRC32 is probably better than CRC32-C, which detects all
|
||||
the errors with an odd number of bit flips at the expense of a larger number
|
||||
of undetected errors with an even number of bit flips.
|
||||
|
||||
@item payload_crc
|
||||
CRC32 of the crc_array.
|
||||
|
|
@ -1334,9 +1418,9 @@ The file is repaired in memory. Therefore, enough virtual memory
|
|||
@w{(RAM + swap)} to contain the largest damaged member is required. Member
|
||||
size is limited to @w{2 GiB} on 32-bit systems.
|
||||
|
||||
The error may be located anywhere in the file except in the first 5
|
||||
bytes of each member header or in the @samp{Member size} field of the
|
||||
trailer (last 8 bytes of each member). If the error is in the header it
|
||||
The error may be located anywhere in the file except in the first 5 bytes of
|
||||
each member header (magic and version) or in the @samp{Member size} field of
|
||||
the 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 (@pxref{File
|
||||
format}). If the error is in the member size, it is enough to ignore the
|
||||
message about @samp{bad member size} when decompressing.
|
||||
|
|
@ -1349,7 +1433,7 @@ One byte may seem small, but most file corruptions not produced by
|
|||
transmission errors or I/O errors just affect one byte, or even one bit,
|
||||
of the file. Also, unlike magnetic media, where errors usually affect a
|
||||
whole sector, solid-state storage devices tend to produce single-byte
|
||||
errors, making of lzip the perfect format for data stored on such devices.
|
||||
errors, which lziprecover can repair.
|
||||
|
||||
Repairing a file can take some time. Small files or files with the error
|
||||
located near the beginning can be repaired in a few seconds. But
|
||||
|
|
@ -1421,19 +1505,10 @@ Note that the number of errors reported by lziprecover (2552) is lower
|
|||
than the number of corrupt bytes (3104) because contiguous corrupt bytes
|
||||
are counted as a single multibyte error.
|
||||
|
||||
@sp 1
|
||||
@anchor{ddrescue-example}
|
||||
@anchor{ddrescue-example2}
|
||||
@noindent
|
||||
Example 1: 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 -d -r1 -b2048 /dev/cdrom cdimage1 mapfile1
|
||||
|
|
@ -1451,7 +1526,6 @@ lziprecover -tv backup.tar.lz
|
|||
backup.tar.lz: ok
|
||||
@end example
|
||||
|
||||
@sp 1
|
||||
@noindent
|
||||
Example 2: Recover the first volume of those created with the command
|
||||
@w{@samp{lzip -b 32MiB -S 650MB big_db}} from two copies,
|
||||
|
|
@ -1608,8 +1682,7 @@ Member reproduced successfully.
|
|||
Copy of input file reproduced successfully.
|
||||
@end example
|
||||
|
||||
@sp 1
|
||||
@anchor{ddrescue-example2}
|
||||
@anchor{ddrescue-example3}
|
||||
@noindent
|
||||
Example 2: Recover a damaged backup with a zeroed sector of 4096 bytes at
|
||||
file position 1019904, using as reference a previous backup. The damaged
|
||||
|
|
@ -1634,7 +1707,6 @@ Member reproduced successfully.
|
|||
Copy of input file reproduced successfully.
|
||||
@end example
|
||||
|
||||
@sp 1
|
||||
@noindent
|
||||
Example 3: Recover a damaged backup with a zeroed sector of 4096 bytes at
|
||||
file position 1019904, using as reference a file from the filesystem. (If
|
||||
|
|
@ -1790,7 +1862,7 @@ example when writing to a tape. It is safe to append any amount of
|
|||
padding zero bytes to a lzip file.
|
||||
|
||||
@item
|
||||
Useful data added by the user; an "End Of File" string (to check that the
|
||||
Useful data added by the user; an 'End Of File' string (to check that the
|
||||
file has not been truncated), a cryptographically secure hash, a description
|
||||
of file contents, etc. It is safe to append any amount of text to a lzip
|
||||
file as long as none of the first four bytes of the text matches the
|
||||
|
|
@ -1844,7 +1916,6 @@ lziprecover --strip=tdata file.lz > stripped_file.lz
|
|||
lziprecover --remove=tdata file.lz
|
||||
@end example
|
||||
|
||||
@sp 1
|
||||
@noindent
|
||||
Example 2: Add and check a cryptographically secure hash. (This may be
|
||||
convenient, but a separate copy of the hash must be kept in a safe place
|
||||
|
|
@ -2036,10 +2107,11 @@ The number of N-bit errors per byte (N = 1 to 8) is:
|
|||
|
||||
@item -B[@var{size}][,@var{value}]
|
||||
@itemx --block[=@var{size}][,@var{value}]
|
||||
Test block errors of given @var{size}, simulating a whole sector I/O error.
|
||||
@var{size} defaults to 512 bytes. @var{value} defaults to 0. By default,
|
||||
only contiguous, non-overlapping blocks are tested, but this may be changed
|
||||
with the option @option{--delta}.
|
||||
Test block errors of given @var{size}, simulating a whole sector I/O error
|
||||
by setting all the bytes in the block to @var{value} before attempting
|
||||
decompression. @var{size} defaults to 512 bytes. @var{value} defaults to 0.
|
||||
By default, only contiguous, non-overlapping blocks are tested, but this may
|
||||
be changed with the option @option{--delta}.
|
||||
|
||||
@item -d @var{n}
|
||||
@itemx --delta=@var{n}
|
||||
|
|
@ -2049,6 +2121,7 @@ non-overlapping blocks, or truncation sizes. Values of @var{n} smaller than
|
|||
the block size result in overlapping blocks. (Which is convenient for
|
||||
testing because there are usually too few non-overlapping blocks in a file).
|
||||
|
||||
@anchor{--set-byte}
|
||||
@item -e @var{position},@var{value}
|
||||
@itemx --set-byte=@var{position},@var{value}
|
||||
Set byte at @var{position} to @var{value} in the internal buffer after
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue