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Signed-off-by: Daniel Baumann <daniel@debian.org>
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@ -11,21 +11,22 @@ File: plzip.info, Node: Top, Next: Introduction, Up: (dir)
Plzip Manual
************
This manual is for Plzip (version 1.11, 21 January 2024).
This manual is for Plzip (version 1.12-rc1, 19 November 2024).
* Menu:
* Introduction:: Purpose and features of plzip
* Output:: Meaning of plzip's output
* Invoking plzip:: Command-line interface
* Program design:: Internal structure of plzip
* Memory requirements:: Memory required to compress and decompress
* Minimum file sizes:: Minimum file sizes required for full speed
* File format:: Detailed format of the compressed file
* Trailing data:: Extra data appended to the file
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept index:: Index of concepts
* Introduction:: Purpose and features of plzip
* Output:: Meaning of plzip's output
* Invoking plzip:: Command-line interface
* Argument syntax:: By convention, options start with a hyphen
* File format:: Detailed format of the compressed file
* Program design:: Internal structure of plzip
* Memory requirements:: Memory required to compress and decompress
* Minimum file sizes:: Minimum file sizes required for full speed
* Trailing data:: Extra data appended to the file
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept index:: Index of concepts
Copyright (C) 2009-2024 Antonio Diaz Diaz.
@ -39,27 +40,27 @@ File: plzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top
1 Introduction
**************
Plzip is a massively parallel (multi-threaded) implementation of lzip,
compatible with lzip 1.4 or newer. Plzip uses the compression library lzlib.
Plzip is a massively parallel (multi-threaded) implementation of lzip.
Plzip uses the compression library lzlib.
Lzip is a lossless data compressor with a user interface similar to the
one of gzip or bzip2. Lzip uses a simplified form of the 'Lempel-Ziv-Markov
chain-Algorithm' (LZMA) stream format to maximize interoperability. The
maximum dictionary size is 512 MiB so that any lzip file can be decompressed
on 32-bit machines. Lzip provides accurate and robust 3-factor integrity
checking. Lzip can compress about as fast as gzip (lzip -0) or compress most
files more than bzip2 (lzip -9). Decompression speed is intermediate between
gzip and bzip2. Lzip is better than gzip and bzip2 from a data recovery
perspective. Lzip has been designed, written, and tested with great care to
replace gzip and bzip2 as the standard general-purpose compressed format for
Unix-like systems.
one of gzip or bzip2. Lzip uses a simplified form of LZMA (Lempel-Ziv-Markov
chain-Algorithm) designed to achieve complete interoperability between
implementations. The maximum dictionary size is 512 MiB so that any lzip
file can be decompressed on 32-bit machines. Lzip provides accurate and
robust 3-factor integrity checking. 'lzip -0' compresses about as fast as
gzip, while 'lzip -9' compresses most files more than bzip2. Decompression
speed is intermediate between gzip and bzip2. Lzip provides better data
recovery capabilities than gzip and bzip2. Lzip has been designed, written,
and tested with great care to replace gzip and bzip2 as general-purpose
compressed format for Unix-like systems.
Plzip can compress/decompress large files on multiprocessor machines much
faster than lzip, at the cost of a slightly reduced compression ratio (0.4
to 2 percent larger compressed files). Note that the number of usable
threads is limited by file size; on files larger than a few GB plzip can use
hundreds of processors, but on files of only a few MB plzip is no faster
than lzip. *Note Minimum file sizes::.
hundreds of processors, but on files smaller than 1 MiB plzip is no faster
than lzip (even at compression level -0). *Note Minimum file sizes::.
For creation and manipulation of compressed tar archives tarlz can be
more efficient than using tar and plzip because tarlz is able to keep the
@ -96,9 +97,9 @@ makes it safer than compressors returning ambiguous warning values (like
gzip) when it is used as a back end for other programs like tar or zutils.
Plzip automatically uses for each file the largest dictionary size that
does not exceed neither the file size nor the limit given. Keep in mind
that the decompression memory requirement is affected at compression time
by the choice of dictionary size limit. *Note Memory requirements::.
does not exceed neither the file size nor the limit given. The dictionary
size used for decompression is the same dictionary size used for
compression. *Note Memory requirements::.
When compressing, plzip replaces every file given in the command line
with a compressed version of itself, with the name "original_name.lz". When
@ -174,7 +175,7 @@ have been compressed. Decompressed is used to refer to data which have
undergone the process of decompression.

File: plzip.info, Node: Invoking plzip, Next: Program design, Prev: Output, Up: Top
File: plzip.info, Node: Invoking plzip, Next: Argument syntax, Prev: Output, Up: Top
3 Invoking plzip
****************
@ -189,8 +190,7 @@ means standard input. It can be mixed with other FILES and is read just
once, the first time it appears in the command line. Remember to prepend
'./' to any file name beginning with a hyphen, or use '--'.
plzip supports the following options: *Note Argument syntax:
(arg_parser)Argument syntax.
plzip supports the following options: *Note Argument syntax::.
'-h'
'--help'
@ -235,7 +235,8 @@ once, the first time it appears in the command line. Remember to prepend
status 1. If a file fails to decompress, or is a terminal, plzip exits
immediately with error status 2 without decompressing the rest of the
files. A terminal is considered an uncompressed file, and therefore
invalid.
invalid. A multimember file with one or more empty members is accepted
if redirected to standard input.
'-f'
'--force'
@ -259,7 +260,8 @@ once, the first time it appears in the command line. Remember to prepend
'-v', the dictionary size, the number of members in the file, and the
amount of trailing data (if any) are also printed. With '-vv', the
positions and sizes of each member in multimember files are also
printed.
printed. A multimember file with one or more empty members is accepted
if redirected to standard input.
If any file is damaged, does not exist, can't be opened, or is not
regular, the final exit status is > 0. '-lq' can be used to check
@ -278,8 +280,8 @@ once, the first time it appears in the command line. Remember to prepend
'-n N'
'--threads=N'
Set the maximum number of worker threads, overriding the system's
default. Valid values range from 1 to "as many as your system can
support". If this option is not used, plzip tries to detect the number
default. Valid values range from 1 to as many as your system can
support. If this option is not used, plzip tries to detect the number
of processors in the system and use it as default value. When
compressing on a 32 bit system, plzip tries to limit the memory use to
under 2.22 GiB (4 worker threads at level -9) by reducing the number
@ -338,7 +340,8 @@ once, the first time it appears in the command line. Remember to prepend
fails the test, does not exist, can't be opened, or is a terminal,
plzip 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.
testing multiple files. A multimember file with one or more empty
members is accepted if redirected to standard input.
'-v'
'--verbose'
@ -368,6 +371,7 @@ once, the first time it appears in the command line. Remember to prepend
'-s64MiB -m273'
Level Dictionary size (-s) Match length limit (-m)
------------------------------------------------------
-0 64 KiB 16 bytes
-1 1 MiB 5 bytes
-2 1.5 MiB 6 bytes
@ -387,7 +391,7 @@ once, the first time it appears in the command line. Remember to prepend
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
triggers a 'corrupt header' error and the cause is not indeed a
corrupt header.
'--in-slots=N'
@ -421,6 +425,7 @@ and may be followed by a multiplier and an optional 'B' for "byte".
Table of SI and binary prefixes (unit multipliers):
Prefix Value | Prefix Value
----------------------------------------------------------------------
k kilobyte (10^3 = 1000) | Ki kibibyte (2^10 = 1024)
M megabyte (10^6) | Mi mebibyte (2^20)
G gigabyte (10^9) | Gi gibibyte (2^30)
@ -439,9 +444,131 @@ corrupt or invalid input file, 3 for an internal consistency error (e.g.,
bug) which caused plzip to panic.

File: plzip.info, Node: Program design, Next: Memory requirements, Prev: Invoking plzip, Up: Top
File: plzip.info, Node: Argument syntax, Next: File format, Prev: Invoking plzip, Up: Top
4 Internal structure of plzip
4 Syntax of command-line arguments
**********************************
POSIX recommends these conventions for command-line arguments.
* A command-line argument is an option if it begins with a hyphen ('-').
* Option names are single alphanumeric characters.
* Certain options require an argument.
* 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, '-o foo' and '-ofoo' are
equivalent.
* 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,
'-abc' is equivalent to '-a -b -c'.
* Options typically precede other non-option arguments.
* The argument '--' terminates all options; any following arguments are
treated as non-option arguments, even if they begin with a hyphen.
* 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 '-'.
GNU adds "long options" to these conventions:
* A long option consists of two hyphens ('--') 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.
* 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 '='.
Thus, '--foo bar' and '--foo=bar' are equivalent.
The syntax of options with an optional argument is
'-<short_option><argument>' (without whitespace), or
'--<long_option>=<argument>'.

File: plzip.info, Node: File format, Next: Program design, Prev: Argument syntax, Up: Top
5 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
In the diagram below, a box like this:
+---+
| | <-- the vertical bars might be missing
+---+
represents one byte; a box like this:
+==============+
| |
+==============+
represents a variable number of bytes.
A lzip file consists of one or more independent "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 can
encode in compressed form up to 16 EiB - 1 byte of uncompressed data. The
size of a multimember file is unlimited. Empty members (data size = 0) are
not allowed in multimember files.
Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 | Data size | Member size |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All multibyte values are stored in little endian order.
'ID string (the "magic" bytes)'
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).
'VN (version number, 1 byte)'
Just in case something needs to be modified in the future. 1 for now.
'DS (coded dictionary size, 1 byte)'
The dictionary size is calculated by taking a power of 2 (the base
size) and subtracting from it a fraction between 0/16 and 7/16 of the
base size.
Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).
Bits 7-5 contain the numerator of the fraction (0 to 7) to subtract
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.
'LZMA stream'
The LZMA stream, terminated by an 'End Of Stream' marker. Uses default
values for encoder properties. *Note Stream format: (lzip)Stream
format, for a complete description.
'CRC32 (4 bytes)'
Cyclic Redundancy Check (CRC) of the original uncompressed data.
'Data size (8 bytes)'
Size of the original uncompressed data.
'Member size (8 bytes)'
Total size of the member, including header and trailer. This field acts
as a distributed index, improves the checking of stream integrity, and
facilitates the safe recovery of undamaged members from multimember
files. Lzip limits the member size to 2 PiB to prevent the data size
field from overflowing.

File: plzip.info, Node: Program design, Next: Memory requirements, Prev: File format, Up: Top
6 Internal structure of plzip
*****************************
When compressing, plzip divides the input file into chunks and compresses as
@ -456,8 +583,8 @@ because lzip usually produces single-member files, which can't be
decompressed in parallel.
For each input file, a splitter thread and several worker threads are
created, acting the main thread as muxer (multiplexer) thread. A "packet
courier" takes care of data transfers among threads and limits the maximum
created, acting the main thread as muxer (multiplexer) thread. A 'packet
courier' takes care of data transfers among threads and limits the maximum
number of data blocks (packets) being processed simultaneously.
The splitter reads data blocks from the input file, and distributes them
@ -486,7 +613,7 @@ only limited by the number of processors available and by I/O speed.

File: plzip.info, Node: Memory requirements, Next: Minimum file sizes, Prev: Program design, Up: Top
5 Memory required to compress and decompress
7 Memory required to compress and decompress
********************************************
The amount of memory required *per worker thread* for decompression or
@ -520,6 +647,7 @@ The following table shows the memory required *per thread* for compression
at a given level, using the default data size for each level:
Level Memory required
------------------------
-0 4.875 MiB
-1 17.75 MiB
-2 26.625 MiB
@ -532,9 +660,9 @@ Level Memory required
-9 568 MiB

File: plzip.info, Node: Minimum file sizes, Next: File format, Prev: Memory requirements, Up: Top
File: plzip.info, Node: Minimum file sizes, Next: Trailing data, Prev: Memory requirements, Up: Top
6 Minimum file sizes required for full compression speed
8 Minimum file sizes required for full compression speed
********************************************************
When compressing, plzip divides the input file into chunks and compresses
@ -569,85 +697,9 @@ Level
-9 128 MiB 256 MiB 512 MiB 1 GiB 4 GiB 16 GiB

File: plzip.info, Node: File format, Next: Trailing data, Prev: Minimum file sizes, Up: Top
File: plzip.info, Node: Trailing data, Next: Examples, Prev: Minimum file sizes, Up: Top
7 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
In the diagram below, a box like this:
+---+
| | <-- the vertical bars might be missing
+---+
represents one byte; a box like this:
+==============+
| |
+==============+
represents a variable number of bytes.
A lzip file consists of one or more independent "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 can
encode in compressed form up to 16 EiB - 1 byte of uncompressed data. The
size of a multimember file is unlimited.
Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 | Data size | Member size |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All multibyte values are stored in little endian order.
'ID string (the "magic" bytes)'
A four byte string, identifying the lzip format, with the value "LZIP"
(0x4C, 0x5A, 0x49, 0x50).
'VN (version number, 1 byte)'
Just in case something needs to be modified in the future. 1 for now.
'DS (coded dictionary size, 1 byte)'
The dictionary size is calculated by taking a power of 2 (the base
size) and subtracting from it a fraction between 0/16 and 7/16 of the
base size.
Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).
Bits 7-5 contain the numerator of the fraction (0 to 7) to subtract
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.
'LZMA stream'
The LZMA stream, finished by an "End Of Stream" marker. Uses default
values for encoder properties. *Note Stream format: (lzip)Stream
format, for a complete description.
'CRC32 (4 bytes)'
Cyclic Redundancy Check (CRC) of the original uncompressed data.
'Data size (8 bytes)'
Size of the original uncompressed data.
'Member size (8 bytes)'
Total size of the member, including header and trailer. This field acts
as a distributed index, improves the checking of stream integrity, and
facilitates the safe recovery of undamaged members from multimember
files. Lzip limits the member size to 2 PiB to prevent the data size
field from overflowing.

File: plzip.info, Node: Trailing data, Next: Examples, Prev: File format, Up: Top
8 Extra data appended to the file
9 Extra data appended to the file
*********************************
Sometimes extra data are found appended to a lzip file after the last
@ -657,7 +709,7 @@ member. Such trailing data may be:
example when writing to a tape. It is safe to append any amount of
padding zero bytes to a lzip file.
* Useful data added by the user; an "End Of File" string (to check that
* 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
@ -693,8 +745,8 @@ where a file containing trailing data must be rejected, the option

File: plzip.info, Node: Examples, Next: Problems, Prev: Trailing data, Up: Top
9 A small tutorial with examples
********************************
10 A small tutorial with examples
*********************************
WARNING! Even if plzip is bug-free, other causes may result in a corrupt
compressed file (bugs in the system libraries, memory errors, etc).
@ -706,38 +758,32 @@ comparing the compressed file with the original because the corruption
happens before plzip compresses the RAM contents, resulting in a valid
compressed file containing wrong data.
Example 1: Extract all the files from archive 'foo.tar.lz'.
tar -xf foo.tar.lz
or
plzip -cd foo.tar.lz | tar -xf -
Example 2: Replace a regular file with its compressed version 'file.lz' and
show the compression ratio.
plzip -v file
Example 3: Like example 2 but the created 'file.lz' has a block size of
1 MiB. The compression ratio is not shown.
plzip -B 1MiB file
Example 4: Restore a regular file from its compressed version 'file.lz'. If
the operation is successful, 'file.lz' is removed.
plzip -d file.lz
Example 5: Check the integrity of the compressed file 'file.lz' and show
status.
plzip -tv file.lz
Example 6: The right way of concatenating the decompressed output of two or
more compressed files. *Note Trailing data::.
@ -746,19 +792,16 @@ more compressed files. *Note Trailing data::.
Do this instead
plzip -cd file1.lz file2.lz file3.lz
Example 7: Decompress 'file.lz' partially until 10 KiB of decompressed data
are produced.
plzip -cd file.lz | dd bs=1024 count=10
Example 8: Decompress 'file.lz' partially from decompressed byte at offset
10000 to decompressed byte at offset 14999 (5000 bytes are produced).
plzip -cd file.lz | dd bs=1000 skip=10 count=5
Example 9: Compress a whole device in /dev/sdc and send the output to
'file.lz'.
@ -769,7 +812,7 @@ Example 9: Compress a whole device in /dev/sdc and send the output to

File: plzip.info, Node: Problems, Next: Concept index, Prev: Examples, Up: Top
10 Reporting bugs
11 Reporting bugs
*****************
There are probably bugs in plzip. There are certainly errors and omissions
@ -790,6 +833,7 @@ Concept index
[index]
* Menu:
* argument syntax: Argument syntax. (line 6)
* bugs: Problems. (line 6)
* examples: Examples. (line 6)
* file format: File format. (line 6)
@ -809,21 +853,22 @@ Concept index

Tag Table:
Node: Top217
Node: Introduction1156
Node: Output5934
Node: Invoking plzip7497
Ref: --trailing-error8372
Ref: --data-size8610
Node: Program design19519
Node: Memory requirements21818
Node: Minimum file sizes23503
Node: File format25506
Ref: coded-dict-size26945
Node: Trailing data28195
Node: Examples30531
Ref: concat-example31964
Node: Problems32721
Node: Concept index33276
Node: Introduction1207
Node: Output5956
Node: Invoking plzip7519
Ref: --trailing-error8365
Ref: --data-size8603
Node: Argument syntax19941
Node: File format21886
Ref: coded-dict-size23386
Node: Program design24637
Node: Memory requirements26933
Node: Minimum file sizes28643
Node: Trailing data30648
Node: Examples32991
Ref: concat-example34420
Node: Problems35174
Node: Concept index35729

End Tag Table