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@ -11,7 +11,7 @@ File: plzip.info, Node: Top, Next: Introduction, Up: (dir)
Plzip Manual
************
This manual is for Plzip (version 1.8, 5 January 2019).
This manual is for Plzip (version 1.9, 3 January 2021).
* Menu:
@ -28,10 +28,10 @@ This manual is for Plzip (version 1.8, 5 January 2019).
* Concept index:: Index of concepts
Copyright (C) 2009-2019 Antonio Diaz Diaz.
Copyright (C) 2009-2021 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission to
copy, distribute and modify it.
This manual is free documentation: you have unlimited permission to copy,
distribute, and modify it.

File: plzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top
@ -39,88 +39,89 @@ File: plzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top
1 Introduction
**************
Plzip is a massively parallel (multi-threaded) implementation of lzip,
fully compatible with lzip 1.4 or newer. Plzip uses the lzlib
compression library.
Plzip is a massively parallel (multi-threaded) implementation of lzip, fully
compatible with lzip 1.4 or newer. 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 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.
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, chosen to maximize safety and
interoperability. 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.
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::.
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::.
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
alignment between tar members and lzip members. *Note tarlz manual:
(tarlz)Top.
The lzip file format is designed for data sharing and long-term
archiving, taking into account both data integrity and decoder
availability:
archiving, taking into account both data integrity and decoder availability:
* The lzip format provides very safe integrity checking and some data
recovery means. The lziprecover 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. *Note Data safety:
(lziprecover)Data safety.
recovery means. The program lziprecover 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. *Note Data safety: (lziprecover)Data
safety.
* The lzip format is as simple as possible (but not simpler). The
lzip manual provides the source code of a simple decompressor
along with a detailed explanation of how it works, so that with
the only help of the lzip manual it would be possible for a
digital archaeologist to extract the data from a lzip file long
after quantum computers eventually render LZMA obsolete.
* The lzip format is as simple as possible (but not simpler). The lzip
manual provides the source code of a simple decompressor along with a
detailed explanation of how it works, so that with the only help of the
lzip manual it would be possible for a digital archaeologist to extract
the data from a lzip file long after quantum computers eventually
render LZMA obsolete.
* Additionally the lzip reference implementation is copylefted, which
guarantees that it will remain free forever.
A nice feature of the lzip format is that a corrupt byte is easier to
repair the nearer it is from the beginning of the file. Therefore, with
the help of lziprecover, losing an entire archive just because of a
corrupt byte near the beginning is a thing of the past.
repair the nearer it is from the beginning of the file. Therefore, with the
help of lziprecover, losing an entire archive just because of a corrupt
byte near the beginning is a thing of the past.
Plzip uses the same well-defined exit status values used by lzip,
which 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 uses the same well-defined exit status values used by lzip, which
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 will automatically use 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::.
Plzip will automatically use 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::.
When compressing, plzip replaces every file given in the command line
with a compressed version of itself, with the name "original_name.lz".
When decompressing, plzip attempts to guess the name for the
decompressed file from that of the compressed file as follows:
with a compressed version of itself, with the name "original_name.lz". When
decompressing, plzip attempts to guess the name for the decompressed file
from that of the compressed file as follows:
filename.lz becomes filename
filename.tlz becomes filename.tar
anyothername becomes anyothername.out
(De)compressing a file is much like copying or moving it; therefore
plzip preserves the access and modification dates, permissions, and,
when possible, ownership of the file just as 'cp -p' does. (If the user
ID or the group ID can't be duplicated, the file permission bits
S_ISUID and S_ISGID are cleared).
(De)compressing a file is much like copying or moving it; therefore plzip
preserves the access and modification dates, permissions, and, when
possible, ownership of the file just as 'cp -p' does. (If the user ID or
the group ID can't be duplicated, the file permission bits S_ISUID and
S_ISGID are cleared).
Plzip is able to read from some types of non regular files if the
'--stdout' option is specified.
Plzip is able to read from some types of non-regular files if either the
option '-c' or the option '-o' is specified.
If no file names are specified, plzip compresses (or decompresses)
from standard input to standard output. In this case, plzip will
decline to write compressed output to a terminal, as this would be
entirely incomprehensible and therefore pointless.
Plzip will refuse to read compressed data from a terminal or write
compressed data to a terminal, as this would be entirely incomprehensible
and might leave the terminal in an abnormal state.
Plzip will correctly decompress a file which is the concatenation of
two or more compressed files. The result is the concatenation of the
Plzip will correctly decompress a file which is the concatenation of two
or more compressed files. The result is the concatenation of the
corresponding decompressed files. Integrity testing of concatenated
compressed files is also supported.
@ -135,41 +136,40 @@ The output of plzip looks like this:
plzip -v foo
foo: 6.676:1, 14.98% ratio, 85.02% saved, 450560 in, 67493 out.
plzip -tvv foo.lz
foo.lz: 6.676:1, 14.98% ratio, 85.02% saved. ok
plzip -tvvv foo.lz
foo.lz: 6.676:1, 14.98% ratio, 85.02% saved. 450560 out, 67493 in. ok
The meaning of each field is as follows:
'N:1'
The compression ratio (uncompressed_size / compressed_size), shown
as N to 1.
The compression ratio (uncompressed_size / compressed_size), shown as
N to 1.
'ratio'
The inverse compression ratio
(compressed_size / uncompressed_size), shown as a percentage. A
decimal ratio is easily obtained by moving the decimal point two
places to the left; 14.98% = 0.1498.
The inverse compression ratio (compressed_size / uncompressed_size),
shown as a percentage. A decimal ratio is easily obtained by moving the
decimal point two places to the left; 14.98% = 0.1498.
'saved'
The space saved by compression (1 - ratio), shown as a percentage.
'in'
The size of the uncompressed data. When decompressing or testing,
it is shown as 'decompressed'. Note that plzip always prints the
uncompressed size before the compressed size when compressing,
decompressing, testing or listing.
Size of the input data. This is the uncompressed size when
compressing, or the compressed size when decompressing or testing.
Note that plzip always prints the uncompressed size before the
compressed size when compressing, decompressing, testing, or listing.
'out'
The size of the compressed data. When decompressing or testing, it
is shown as 'compressed'.
Size of the output data. This is the compressed size when compressing,
or the decompressed size when decompressing or testing.
When decompressing or testing at verbosity level 4 (-vvvv), the
dictionary size used to compress the file is also shown.
LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may
never have been compressed. Decompressed is used to refer to data which
have undergone the process of decompression.
LANGUAGE NOTE: Uncompressed = not compressed = plain data; it may never
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
@ -181,11 +181,13 @@ The format for running plzip is:
plzip [OPTIONS] [FILES]
'-' used as a FILE argument means standard input. It can be mixed with
other FILES and is read just once, the first time it appears in the
command line.
If no file names are specified, plzip compresses (or decompresses) from
standard input to standard output. A hyphen '-' used as a FILE argument
means standard input. It can be mixed with other FILES and is read just
once, the first time it appears in the command line.
plzip supports the following options:
plzip supports the following options: *Note Argument syntax:
(arg_parser)Argument syntax.
'-h'
'--help'
@ -199,32 +201,33 @@ command line.
'-a'
'--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. *Note
concat-example::.
decompressing the last member. Such remaining input is usually trailing
garbage that can be safely ignored. *Note concat-example::.
'-B BYTES'
'--data-size=BYTES'
When compressing, set the size of the input data blocks in bytes.
The input file will be divided in chunks of this size before
compression is performed. Valid values range from 8 KiB to 1 GiB.
Default value is two times the dictionary size, except for option
'-0' where it defaults to 1 MiB. Plzip will reduce the dictionary
size if it is larger than the chosen data size.
When compressing, set the size of the input data blocks in bytes. The
input file will be divided in chunks of this size before compression is
performed. Valid values range from 8 KiB to 1 GiB. Default value is
two times the dictionary size, except for option '-0' where it
defaults to 1 MiB. Plzip will reduce the dictionary size if it is
larger than the data size specified. *Note Minimum file sizes::.
'-c'
'--stdout'
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.
Compress or decompress to standard output; keep input files unchanged.
If compressing several files, each file is compressed independently.
This option (or '-o') is needed when reading from a named pipe (fifo)
or from a device. Use 'lziprecover -cd -i' to recover as much of the
decompressed data as possible when decompressing a corrupt file. '-c'
overrides '-o'. '-c' has no effect when testing or listing.
'-d'
'--decompress'
Decompress the specified files. If a file does not exist or can't
be opened, plzip continues decompressing the rest of the files. If
a file fails to decompress, or is a terminal, plzip exits
immediately without decompressing the rest of the files.
Decompress the files specified. If a file does not exist or can't be
opened, plzip continues decompressing the rest of the files. If a file
fails to decompress, or is a terminal, plzip exits immediately without
decompressing the rest of the files.
'-f'
'--force'
@ -232,59 +235,69 @@ command line.
'-F'
'--recompress'
When compressing, force re-compression of files whose name already
has the '.lz' or '.tlz' suffix.
When compressing, force re-compression of files whose name already has
the '.lz' or '.tlz' suffix.
'-k'
'--keep'
Keep (don't delete) input files during compression or
decompression.
Keep (don't delete) input files during compression or decompression.
'-l'
'--list'
Print the uncompressed size, compressed size and percentage saved
of the specified files. Trailing data are ignored. The values
produced are correct even for multimember files. If more than one
file is given, a final line containing the cumulative sizes is
printed. With '-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. '-lq' can be used to verify
quickly (without decompressing) the structural integrity of the
specified files. (Use '--test' to verify the data integrity).
'-alq' additionally verifies that none of the specified files
contain trailing data.
Print the uncompressed size, compressed size, and percentage saved of
the files specified. Trailing data are ignored. The values produced
are correct even for multimember files. If more than one file is
given, a final line containing the cumulative sizes is printed. With
'-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.
'-lq' can be used to verify quickly (without decompressing) the
structural integrity of the files specified. (Use '--test' to verify
the data integrity). '-alq' additionally verifies that none of the
files specified contain trailing data.
'-m BYTES'
'--match-length=BYTES'
When compressing, set the match length limit in bytes. After a
match this long is found, the search is finished. Valid values
range from 5 to 273. Larger values usually give better compression
ratios but longer compression times.
When compressing, set the match length limit in bytes. After a match
this long is found, the search is finished. Valid values range from 5
to 273. Larger values usually give better compression ratios but longer
compression times.
'-n N'
'--threads=N'
Set the 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 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 of threads below the system's default. 'plzip --help'
shows the system's default value.
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
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
of threads below the system's default. 'plzip --help' shows the
system's default value.
Note that the number of usable threads is limited to
ceil( file_size / data_size ) during compression (*note Minimum
file sizes::), and to the number of members in the input during
decompression.
Plzip starts the number of threads required by each file without
exceeding the value specified. Note that the number of usable threads
is limited to ceil( file_size / data_size ) during compression (*note
Minimum file sizes::), and to the number of members in the input
during decompression. You can find the number of members in a lzip
file by running 'plzip -lv file.lz'.
'-o FILE'
'--output=FILE'
When reading from standard input and '--stdout' has not been
specified, use 'FILE' as the virtual name of the uncompressed
file. This produces a file named 'FILE' when decompressing, or a
file named 'FILE.lz' when compressing. A second '.lz' extension is
not added if 'FILE' already ends in '.lz' or '.tlz'.
If '-c' has not been also specified, write the (de)compressed output to
FILE; keep input files unchanged. If compressing several files, each
file is compressed independently. This option (or '-c') is needed when
reading from a named pipe (fifo) or from a device. '-o -' is
equivalent to '-c'. '-o' has no effect when testing or listing.
In order to keep backward compatibility with plzip versions prior to
1.9, when compressing from standard input and no other file names are
given, the extension '.lz' is appended to FILE unless it already ends
in '.lz' or '.tlz'. This feature will be removed in a future version
of plzip. Meanwhile, redirection may be used instead of '-o' to write
the compressed output to a file without the extension '.lz' in its
name: 'plzip < file > foo'.
'-q'
'--quiet'
@ -292,30 +305,28 @@ command line.
'-s BYTES'
'--dictionary-size=BYTES'
When compressing, set the dictionary size limit in bytes. Plzip
will use for each file the largest dictionary size that does not
exceed neither the file size nor 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. Dictionary sizes are quantized
so that they can be coded in just one byte (*note
coded-dict-size::). If the specified size does not match one of
the valid sizes, it will be rounded upwards by adding up to
(BYTES / 8) to it.
When compressing, set the dictionary size limit in bytes. Plzip will
use for each file the largest dictionary size that does not exceed
neither the file size nor 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. Dictionary sizes are quantized so that they can be
coded in just one byte (*note coded-dict-size::). If the size specified
does not match one of the valid sizes, it will be rounded upwards by
adding up to (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 is affected at compression time by the choice of
dictionary size limit.
For maximum compression you should use a dictionary size limit as large
as possible, but keep in mind that the decompression memory requirement
is affected at compression time by the choice of dictionary size limit.
'-t'
'--test'
Check integrity of the specified files, but don't decompress them.
This really performs a trial decompression and throws away the
result. Use it together with '-v' to see information about the
files. If a file does not exist, can't be opened, or is a
terminal, plzip continues checking the rest of the files. If a
file fails the test, plzip may be unable to check the rest of the
files.
Check integrity of the files specified, but don't decompress them. This
really performs a trial decompression and throws away the result. Use
it together with '-v' to see information about the files. If a file
fails the test, does not exist, can't be opened, or is a terminal,
plzip continues checking 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.
'-v'
'--verbose'
@ -323,26 +334,26 @@ command line.
When compressing, show the compression ratio and size for each file
processed.
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary
size, decompressed size, and compressed size.
Two or more '-v' options show the progress of (de)compression,
except for single-member files.
verbosity level, showing status, compression ratio, dictionary size,
decompressed size, and compressed size.
Two or more '-v' options show the progress of (de)compression, except
for single-member files.
'-0 .. -9'
Compression level. Set the compression parameters (dictionary size
and match length limit) as shown in the table below. The default
compression level is '-6', equivalent to '-s8MiB -m36'. Note that
'-9' can be much slower than '-0'. These options have no effect
when decompressing, testing or listing.
Compression level. Set the compression parameters (dictionary size and
match length limit) as shown in the table below. The default
compression level is '-6', equivalent to '-s8MiB -m36'. Note that '-9'
can be much slower than '-0'. These options have no effect when
decompressing, testing, or listing.
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 '--dictionary-size' and
'--match-length' options directly to achieve optimal performance.
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 options '--dictionary-size' and
'--match-length' directly to achieve optimal performance.
If several compression levels or '-s' or '-m' options are given,
the last setting is used. For example '-9 -s64MiB' is equivalent
to '-s64MiB -m273'
If several compression levels or '-s' or '-m' options are given, the
last setting is used. For example '-9 -s64MiB' is equivalent to
'-s64MiB -m273'
Level Dictionary size (-s) Match length limit (-m)
-0 64 KiB 16 bytes
@ -361,23 +372,33 @@ command line.
Aliases for GNU gzip compatibility.
'--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.
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.
'--in-slots=N'
Number of 1 MiB input packets buffered per worker thread when
decompressing from non-seekable input. Increasing the number of
packets may increase decompression speed, but requires more
memory. Valid values range from 1 to 64. The default value is 4.
decompressing from non-seekable input. Increasing the number of packets
may increase decompression speed, but requires more memory. Valid
values range from 1 to 64. The default value is 4.
'--out-slots=N'
Number of 1 MiB output packets buffered per worker thread when
decompressing to non-seekable output. Increasing the number of
packets may increase decompression speed, but requires more
memory. Valid values range from 1 to 1024. The default value is 64.
decompressing to non-seekable output. Increasing the number of packets
may increase decompression speed, but requires more memory. Valid
values range from 1 to 1024. The default value is 64.
'--check-lib'
Compare the version of lzlib used to compile plzip with the version
actually being used at run time and exit. Report any differences
found. Exit with error status 1 if differences are found. A mismatch
may indicate that lzlib is not correctly installed or that a different
version of lzlib has been installed after compiling plzip.
'plzip -v --check-lib' shows the version of lzlib being used and the
value of 'LZ_API_VERSION' (if defined). *Note Library version:
(lzlib)Library version.
Numbers given as arguments to options may be followed by a multiplier
@ -396,36 +417,36 @@ Z zettabyte (10^21) | Zi zebibyte (2^70)
Y yottabyte (10^24) | Yi yobibyte (2^80)
Exit status: 0 for a normal exit, 1 for environmental problems (file
not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or
invalid input file, 3 for an internal consistency error (eg, bug) which
caused plzip to panic.
Exit status: 0 for a normal exit, 1 for environmental problems (file not
found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid
input file, 3 for an internal consistency error (eg, bug) which caused
plzip to panic.

File: plzip.info, Node: Program design, Next: File format, Prev: Invoking plzip, Up: Top
4 Program design
****************
4 Internal structure of plzip
*****************************
When compressing, plzip divides the input file into chunks and
compresses as many chunks simultaneously as worker threads are chosen,
creating a multimember compressed file.
When compressing, plzip divides the input file into chunks and compresses as
many chunks simultaneously as worker threads are chosen, creating a
multimember compressed file.
When decompressing, plzip decompresses as many members
simultaneously as worker threads are chosen. Files that were compressed
with lzip will not be decompressed faster than using lzip (unless the
'-b' option was used) because lzip usually produces single-member
files, which can't be decompressed in parallel.
When decompressing, plzip decompresses as many members simultaneously as
worker threads are chosen. Files that were compressed with lzip will not be
decompressed faster than using lzip (unless the option '-b' was used)
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 number of data blocks (packets) being processed simultaneously.
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 to the workers. The workers (de)compress the blocks received from
the splitter. The muxer collects processed packets from the workers, and
writes them to the output file.
The splitter reads data blocks from the input file, and distributes them
to the workers. The workers (de)compress the blocks received from the
splitter. The muxer collects processed packets from the workers, and writes
them to the output file.
,------------,
,-->| worker 0 |--,
@ -438,13 +459,12 @@ writes them to the output file.
`-->| worker N-1 |--'
`------------'
When decompressing from a regular file, the splitter is removed and
the workers read directly from the input file. If the output file is
also a regular file, the muxer is also removed and the workers write
directly to the output file. With these optimizations, the use of RAM
is greatly reduced and the decompression speed of large files with many
members is only limited by the number of processors available and by
I/O speed.
When decompressing from a regular file, the splitter is removed and the
workers read directly from the input file. If the output file is also a
regular file, the muxer is also removed and the workers write directly to
the output file. With these optimizations, the use of RAM is greatly
reduced and the decompression speed of large files with many members is
only limited by the number of processors available and by I/O speed.

File: plzip.info, Node: File format, Next: Memory requirements, Prev: Program design, Up: Top
@ -458,11 +478,13 @@ when there is no longer anything to take away.
In the diagram below, a box like this:
+---+
| | <-- the vertical bars might be missing
+---+
represents one byte; a box like this:
+==============+
| |
+==============+
@ -471,10 +493,11 @@ when there is no longer anything to take away.
A lzip file consists of a series of "members" (compressed data sets).
The members simply appear one after another in the file, with no
additional information before, between, or after them.
The members simply appear one after another in the file, with no additional
information before, between, or after them.
Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID string | VN | DS | LZMA stream | CRC32 | Data size | Member size |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
@ -482,17 +505,16 @@ additional information before, between, or after them.
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).
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.
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.
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.
@ -501,20 +523,20 @@ additional information before, between, or after them.
'LZMA stream'
The LZMA stream, finished by an end of stream marker. Uses default
values for encoder properties. *Note Stream format: (lzip)Stream
values for encoder properties. *Note Stream format: (lzip)Stream
format, for a complete description.
'CRC32 (4 bytes)'
CRC of the uncompressed original data.
Cyclic Redundancy Check (CRC) of the uncompressed original data.
'Data size (8 bytes)'
Size of the uncompressed original data.
'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
multimember files.
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 multimember
files.

@ -526,20 +548,20 @@ File: plzip.info, Node: Memory requirements, Next: Minimum file sizes, Prev:
The amount of memory required *per worker thread* for decompression or
testing is approximately the following:
* For decompression of a regular (seekable) file to another regular
file, or for testing of a regular file; the dictionary size.
* For decompression of a regular (seekable) file to another regular file,
or for testing of a regular file; the dictionary size.
* For testing of a non-seekable file or of standard input; the
dictionary size plus 1 MiB plus up to the number of 1 MiB input
packets buffered (4 by default).
* For testing of a non-seekable file or of standard input; the dictionary
size plus 1 MiB plus up to the number of 1 MiB input packets buffered
(4 by default).
* For decompression of a regular file to a non-seekable file or to
standard output; the dictionary size plus up to the number of 1 MiB
output packets buffered (64 by default).
* For decompression of a non-seekable file or of standard input; the
dictionary size plus 1 MiB plus up to the number of 1 MiB input
and output packets buffered (68 by default).
dictionary size plus 1 MiB plus up to the number of 1 MiB input and
output packets buffered (68 by default).
The amount of memory required *per worker thread* for compression is
approximately the following:
@ -550,9 +572,8 @@ approximately the following:
* For compression at other levels; 11 times the dictionary size plus
3.375 times the data size. Default is 142 MiB.
The following table shows the memory required *per thread* for
compression at a given level, using the default data size for each
level:
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
@ -572,22 +593,22 @@ File: plzip.info, Node: Minimum file sizes, Next: Trailing data, Prev: Memory
7 Minimum file sizes required for full compression speed
********************************************************
When compressing, plzip divides the input file into chunks and
compresses as many chunks simultaneously as worker threads are chosen,
creating a multimember compressed file.
When compressing, plzip divides the input file into chunks and compresses
as many chunks simultaneously as worker threads are chosen, creating a
multimember compressed file.
For this to work as expected (and roughly multiply the compression
speed by the number of available processors), the uncompressed file
must be at least as large as the number of worker threads times the
chunk size (*note --data-size::). Else some processors will not get any
data to compress, and compression will be proportionally slower. The
maximum speed increase achievable on a given file is limited by the
ratio (file_size / data_size). For example, a tarball the size of gcc or
linux will scale up to 8 processors at level -9.
For this to work as expected (and roughly multiply the compression speed
by the number of available processors), the uncompressed file must be at
least as large as the number of worker threads times the chunk size (*note
--data-size::). Else some processors will not get any data to compress, and
compression will be proportionally slower. The maximum speed increase
achievable on a given file is limited by the ratio (file_size / data_size).
For example, a tarball the size of gcc or linux will scale up to 10 or 14
processors at level -9.
The following table shows the minimum uncompressed file size needed
for full use of N processors at a given compression level, using the
default data size for each level:
The following table shows the minimum uncompressed file size needed for
full use of N processors at a given compression level, using the default
data size for each level:
Processors 2 4 8 16 64 256
------------------------------------------------------------------
@ -612,43 +633,40 @@ File: plzip.info, Node: Trailing data, Next: Examples, Prev: Minimum file siz
Sometimes extra data are found appended to a lzip file after the last
member. Such trailing data may be:
* Padding added to make the file size a multiple of some block size,
for example when writing to a tape. It is safe to append any
amount of padding zero bytes to a lzip file.
* Padding added to make the file size a multiple of some block size, for
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; 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 match the corresponding byte in the string "LZIP", and
the text does not contain any zero bytes (null characters).
Nonzero bytes and zero bytes can't be safely mixed in trailing
data.
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
match the corresponding byte in the string "LZIP", and the text does
not contain any zero bytes (null characters). Nonzero bytes and zero
bytes can't be safely mixed in trailing data.
* Garbage added by some not totally successful copy operation.
* 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.
* 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.
* In 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. Additionally, the test
used by plzip to discriminate trailing data from a corrupt header
has a Hamming distance (HD) of 3, and the 3 bit flips must happen
in different magic bytes for the test to fail. In any case, the
option '--trailing-error' guarantees that any corrupt header will
be detected.
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. Additionally, the test used by plzip to
discriminate trailing data from a corrupt header has a Hamming
distance (HD) of 3, and the 3 bit flips must happen in different magic
bytes for the test to fail. In any case, the option '--trailing-error'
guarantees that any corrupt header will be detected.
Trailing data are in no way part of the lzip file format, but tools
reading lzip files are expected to behave as correctly and usefully as
possible in the presence of trailing data.
Trailing data can be safely ignored in most cases. In some cases,
like that of user-added data, they are expected to be ignored. In those
cases where a file containing trailing data must be rejected, the option
Trailing data can be safely ignored in most cases. In some cases, like
that of user-added data, they are expected to be ignored. In those cases
where a file containing trailing data must be rejected, the option
'--trailing-error' can be used. *Note --trailing-error::.

@ -660,62 +678,70 @@ File: plzip.info, Node: Examples, Next: Problems, Prev: Trailing data, Up: T
WARNING! Even if plzip 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
'--keep' option to plzip and don't remove the original file until you
option '--keep' to plzip and don't remove the original file until you
verify the compressed file with a command like
'plzip -cd file.lz | cmp file -'. Most RAM errors happening during
compression can only be detected by 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.
compression can only be detected by 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: Replace a regular file with its compressed version 'file.lz'
and show the compression ratio.
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 2: Like example 1 but the created 'file.lz' has a block size of
Example 3: Like example 1 but the created 'file.lz' has a block size of
1 MiB. The compression ratio is not shown.
plzip -B 1MiB file
Example 3: Restore a regular file from its compressed version
'file.lz'. If the operation is successful, 'file.lz' is removed.
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 4: Verify the integrity of the compressed file 'file.lz' and
show status.
Example 5: Verify the integrity of the compressed file 'file.lz' and show
status.
plzip -tv file.lz
Example 5: Compress a whole device in /dev/sdc and send the output to
Example 6: Compress a whole device in /dev/sdc and send the output to
'file.lz'.
plzip -c /dev/sdc > file.lz
plzip -c /dev/sdc > file.lz
or
plzip /dev/sdc -o file.lz
Example 6: The right way of concatenating the decompressed output of two
or more compressed files. *Note Trailing data::.
Example 7: The right way of concatenating the decompressed output of two or
more compressed files. *Note Trailing data::.
Don't do this
cat file1.lz file2.lz file3.lz | plzip -d
cat file1.lz file2.lz file3.lz | plzip -d -
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.
Example 8: 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 10000
to decompressed byte 15000 (5000 bytes are produced).
Example 9: 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
@ -725,14 +751,14 @@ File: plzip.info, Node: Problems, Next: Concept index, Prev: Examples, Up: T
10 Reporting bugs
*****************
There are probably bugs in plzip. There are certainly errors and
omissions in this manual. If you report them, they will get fixed. If
you don't, no one will ever know about them and they will remain unfixed
for all eternity, if not longer.
There are probably bugs in plzip. There are certainly errors and omissions
in this manual. If you report them, they will get fixed. If you don't, no
one will ever know about them and they will remain unfixed for all
eternity, if not longer.
If you find a bug in plzip, please send electronic mail to
<lzip-bug@nongnu.org>. Include the version number, which you can find
by running 'plzip --version'.
<lzip-bug@nongnu.org>. Include the version number, which you can find by
running 'plzip --version'.

File: plzip.info, Node: Concept index, Prev: Problems, Up: Top
@ -743,40 +769,40 @@ Concept index
[index]
* Menu:
* bugs: Problems. (line 6)
* examples: Examples. (line 6)
* file format: File format. (line 6)
* getting help: Problems. (line 6)
* introduction: Introduction. (line 6)
* invoking: Invoking plzip. (line 6)
* memory requirements: Memory requirements. (line 6)
* minimum file sizes: Minimum file sizes. (line 6)
* options: Invoking plzip. (line 6)
* output: Output. (line 6)
* program design: Program design. (line 6)
* trailing data: Trailing data. (line 6)
* usage: Invoking plzip. (line 6)
* version: Invoking plzip. (line 6)
* bugs: Problems. (line 6)
* examples: Examples. (line 6)
* file format: File format. (line 6)
* getting help: Problems. (line 6)
* introduction: Introduction. (line 6)
* invoking: Invoking plzip. (line 6)
* memory requirements: Memory requirements. (line 6)
* minimum file sizes: Minimum file sizes. (line 6)
* options: Invoking plzip. (line 6)
* output: Output. (line 6)
* program design: Program design. (line 6)
* trailing data: Trailing data. (line 6)
* usage: Invoking plzip. (line 6)
* version: Invoking plzip. (line 6)

Tag Table:
Node: Top222
Node: Introduction1158
Node: Output5456
Node: Invoking plzip6936
Ref: --trailing-error7563
Ref: --data-size7806
Node: Program design16267
Node: File format18419
Ref: coded-dict-size19719
Node: Memory requirements20849
Node: Minimum file sizes22531
Node: Trailing data24540
Node: Examples26823
Ref: concat-example28238
Node: Problems28813
Node: Concept index29341
Node: Introduction1159
Node: Output5788
Node: Invoking plzip7351
Ref: --trailing-error8146
Ref: --data-size8384
Node: Program design18364
Node: File format20542
Ref: coded-dict-size21840
Node: Memory requirements22995
Node: Minimum file sizes24677
Node: Trailing data26693
Node: Examples28961
Ref: concat-example30556
Node: Problems31153
Node: Concept index31681

End Tag Table