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Signed-off-by: Daniel Baumann <daniel@debian.org>
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165
doc/clzip.texi
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@ -6,8 +6,8 @@
@finalout
@c %**end of header
@set UPDATED 7 July 2015
@set VERSION 1.7
@set UPDATED 13 May 2016
@set VERSION 1.8
@dircategory Data Compression
@direntry
@ -39,13 +39,14 @@ This manual is for Clzip (version @value{VERSION}, @value{UPDATED}).
* Invoking clzip:: Command line interface
* File format:: Detailed format of the compressed file
* Algorithm:: How clzip compresses the data
* Trailing data:: Extra data appended to the file
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept index:: Index of concepts
@end menu
@sp 1
Copyright @copyright{} 2010-2015 Antonio Diaz Diaz.
Copyright @copyright{} 2010-2016 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission
to copy, distribute and modify it.
@ -78,7 +79,7 @@ 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.
@ifnothtml
@ref{Data safety,,,lziprecover}.
@xref{Data safety,,,lziprecover}.
@end ifnothtml
@item
@ -101,14 +102,14 @@ corrupt byte near the beginning is a thing of the past.
The member trailer stores the 32-bit CRC of the original data, the size
of the original data and the size of the member. These values, together
with the value remaining in the range decoder and the end-of-stream
marker, provide a 4 factor integrity checking which guarantees that the
decompressed version of the data is identical to the original. This
guards against corruption of the compressed data, and against undetected
bugs in clzip (hopefully very unlikely). The chances of data corruption
going undetected are microscopic. Be aware, though, that the check
occurs upon decompression, so it can only tell you that something is
wrong. It can't help you recover the original uncompressed data.
with the end-of-stream marker, provide a 3 factor integrity checking
which guarantees that the decompressed version of the data is identical
to the original. This guards against corruption of the compressed data,
and against undetected bugs in clzip (hopefully very unlikely). The
chances of data corruption going undetected are microscopic. Be aware,
though, that the check occurs upon decompression, so it can only tell
you that something is wrong. It can't help you recover the original
uncompressed data.
Clzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer than compressors returning ambiguous warning
@ -157,14 +158,14 @@ or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.
Clzip can produce multi-member files and safely recover, with
Clzip can produce multimember files and safely recover, with
lziprecover, the undamaged members in case of file damage. Clzip can
also split the compressed output in volumes of a given size, even when
reading from standard input. This allows the direct creation of
multivolume compressed tar archives.
Clzip is able to compress and decompress streams of unlimited size by
automatically creating multi-member output. The members so created are
automatically creating multimember output. The members so created are
large, about 2 PiB each.
@ -181,6 +182,11 @@ The format for running clzip is:
clzip [@var{options}] [@var{files}]
@end example
@noindent
@samp{-} used as a @var{file} argument means standard input. It can be
mixed with other @var{files} and is read just once, the first time it
appears in the command line.
Clzip supports the following options:
@table @code
@ -192,6 +198,13 @@ Print an informative help message describing the options and exit.
@itemx --version
Print the version number of clzip on the standard output and exit.
@anchor{--trailing-error}
@item -a
@itemx --trailing-error
Exit with error status 2 if any remaining input is detected after
decompressing the last member. Such remaining input is usually trailing
garbage that can be safely ignored. @xref{concat-example}.
@item -b @var{bytes}
@itemx --member-size=@var{bytes}
Set the member size limit to @var{bytes}. A small member size may
@ -200,13 +213,18 @@ range from 100 kB to 2 PiB. Defaults to 2 PiB.
@item -c
@itemx --stdout
Compress or 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.
Compress or decompress to standard output; keep input files unchanged.
If compressing several files, each file is compressed independently.
This option is needed when reading from a named pipe (fifo) or from a
device. Use it also to recover as much of the uncompressed data as
possible when decompressing a corrupt file.
@item -d
@itemx --decompress
Decompress.
Decompress the specified file(s). If a file does not exist or can't be
opened, clzip continues decompressing the rest of the files. If a file
fails to decompress, clzip exits immediately without decompressing the
rest of the files.
@item -f
@itemx --force
@ -242,11 +260,13 @@ Quiet operation. Suppress all messages.
@item -s @var{bytes}
@itemx --dictionary-size=@var{bytes}
Set the dictionary size limit in bytes. Valid values range from 4 KiB to
512 MiB. Clzip will use the smallest possible dictionary size for each
file without exceeding this limit. Note that dictionary sizes are
quantized. If the specified size does not match one of the valid sizes,
it will be rounded upwards by adding up to (@var{bytes} / 16) to it.
Set the dictionary size limit in bytes. Clzip will use the smallest
possible dictionary size for each file without exceeding this limit.
Valid values range from 4 KiB to 512 MiB. Values 12 to 29 are
interpreted as powers of two, meaning 2^12 to 2^29 bytes. Note that
dictionary sizes are quantized. If the specified size does not match one
of the valid sizes, it will be rounded upwards by adding up to
@w{(@var{bytes} / 8)} to it.
For maximum compression you should use a dictionary size limit as large
as possible, but keep in mind that the decompression memory requirement
@ -257,7 +277,7 @@ is affected at compression time by the choice of dictionary size limit.
Split the compressed output into several volume files with names
@samp{original_name00001.lz}, @samp{original_name00002.lz}, etc, and set
the volume size limit to @var{bytes}. Each volume is a complete, maybe
multi-member, lzip file. A small volume size may degrade compression
multimember, lzip file. A small volume size may degrade compression
ratio, so use it only when needed. Valid values range from 100 kB to 4
EiB.
@ -265,7 +285,8 @@ EiB.
@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.
Use it together with @samp{-v} to see information about the file(s). If
a file fails the test, clzip continues checking the rest of the files.
@item -v
@itemx --verbose
@ -274,18 +295,19 @@ When compressing, show the compression ratio for each file processed. A
second @samp{-v} shows the progress of compression.@*
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary size,
and trailer contents (CRC, data size, member size).
trailer contents (CRC, data size, member size), and up to 6 bytes of
trailing data (if any).
@item -0 .. -9
Set the compression parameters (dictionary size and match length limit)
as shown in the table below. Note that @samp{-9} can be much slower than
@samp{-0}. These options have no effect when decompressing.
as shown in the table below. The default compression level is @samp{-6}.
Note that @samp{-9} can be much slower than @samp{-0}. These options
have no effect when decompressing.
The bidimensional parameter space of LZMA can't be mapped to a linear
scale optimal for all files. If your files are large, very repetitive,
etc, you may need to use the @samp{--match-length} and
@samp{--dictionary-size} options directly to achieve optimal
performance.
etc, you may need to use the @samp{--dictionary-size} and
@samp{--match-length} options directly to achieve optimal performance.
@multitable {Level} {Dictionary size} {Match length limit}
@item Level @tab Dictionary size @tab Match length limit
@ -364,14 +386,14 @@ 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 |
| 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
@item ID string (the "magic" bytes)
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).
@ -388,8 +410,8 @@ 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
@item LZMA stream
The LZMA stream, finished by an end of stream marker. Uses default
values for encoder properties.
@ifnothtml
@xref{Stream format,,,lzip},
@ -409,7 +431,7 @@ 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.
facilitates safe recovery of undamaged members from multimember files.
@end table
@ -480,6 +502,44 @@ range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI).
@node Trailing data
@chapter Extra data appended to the file
@cindex trailing data
Sometimes extra data is found appended to a lzip file after the last
member. Such trailing data may be:
@itemize @bullet
@item
Padding added to make the file size a multiple of some block size, for
example when writing to a tape.
@item
Garbage added by some not totally successful copy operation.
@item
Useful data added by the user; a cryptographically secure hash, a
description of file contents, etc.
@item
Malicious data added to the file in order to make its total size and
hash value (for a chosen hash) coincide with those of another file.
@item
In very rare cases, trailing data could be the corrupt header of another
member. In multimember or concatenated files the probability of
corruption happening in the magic bytes is 5 times smaller than the
probability of getting a false positive caused by the corruption of the
integrity information itself. Therefore it can be considered to be below
the noise level.
@end itemize
Trailing data can be safely ignored in most cases. In some cases, like
that of user-added data, it is expected to be ignored. In those cases
where a file containing trailing data must be rejected, the option
@samp{--trailing-error} can be used. @xref{--trailing-error}.
@node Examples
@chapter A small tutorial with examples
@cindex examples
@ -487,7 +547,7 @@ LZMA), and Julian Seward (for bzip2's CLI).
WARNING! Even if clzip is bug-free, other causes may result in a corrupt
compressed file (bugs in the system libraries, memory errors, etc).
Therefore, if the data you are going to compress are important, give the
@samp{--keep} option to clzip and do not remove the original file until
@samp{--keep} option to clzip and don't remove the original file until
you verify the compressed file with a command like
@w{@samp{clzip -cd file.lz | cmp file -}}.
@ -502,7 +562,7 @@ clzip -v file
@sp 1
@noindent
Example 2: Like example 1 but the created @samp{file.lz} is multi-member
Example 2: Like example 1 but the created @samp{file.lz} is multimember
with a member size of 1 MiB. The compression ratio is not shown.
@example
@ -530,16 +590,29 @@ clzip -tv file.lz
@sp 1
@noindent
Example 5: Compress a whole floppy in /dev/fd0 and send the output to
Example 5: Compress a whole device in /dev/sdc and send the output to
@samp{file.lz}.
@example
clzip -c /dev/fd0 > file.lz
clzip -c /dev/sdc > file.lz
@end example
@sp 1
@anchor{concat-example}
@noindent
Example 6: The right way of concatenating compressed files.
@xref{Trailing data}.
@example
Don't do this
cat file1.lz file2.lz file3.lz | clzip -d
Do this instead
clzip -cd file1.lz file2.lz file3.lz
@end example
@sp 1
@noindent
Example 6: Decompress @samp{file.lz} partially until 10 KiB of
Example 7: Decompress @samp{file.lz} partially until 10 KiB of
decompressed data are produced.
@example
@ -548,7 +621,7 @@ clzip -cd file.lz | dd bs=1024 count=10
@sp 1
@noindent
Example 7: Decompress @samp{file.lz} partially from decompressed byte
Example 8: Decompress @samp{file.lz} partially from decompressed byte
10000 to decompressed byte 15000 (5000 bytes are produced).
@example
@ -557,7 +630,7 @@ clzip -cd file.lz | dd bs=1000 skip=10 count=5
@sp 1
@noindent
Example 8: Create a multivolume compressed tar archive with a volume
Example 9: Create a multivolume compressed tar archive with a volume
size of 1440 KiB.
@example
@ -566,7 +639,7 @@ tar -c some_directory | clzip -S 1440KiB -o volume_name
@sp 1
@noindent
Example 9: Extract a multivolume compressed tar archive.
Example 10: Extract a multivolume compressed tar archive.
@example
clzip -cd volume_name*.lz | tar -xf -
@ -574,8 +647,8 @@ clzip -cd volume_name*.lz | tar -xf -
@sp 1
@noindent
Example 10: Create a multivolume compressed backup of a large database
file with a volume size of 650 MB, where each volume is a multi-member
Example 11: Create a multivolume compressed backup of a large database
file with a volume size of 650 MB, where each volume is a multimember
file with a member size of 32 MiB.
@example