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diff --git a/doc/plzip.1 b/doc/plzip.1 index 99dfd8b..694a99d 100644 --- a/doc/plzip.1 +++ b/doc/plzip.1 @@ -1,12 +1,28 @@ .\" DO NOT MODIFY THIS FILE! It was generated by help2man 1.46.1. -.TH PLZIP "1" "February 2018" "plzip 1.7" "User Commands" +.TH PLZIP "1" "January 2019" "plzip 1.8" "User Commands" .SH NAME plzip \- reduces the size of files .SH SYNOPSIS .B plzip [\fI\,options\/\fR] [\fI\,files\/\fR] .SH DESCRIPTION -Plzip \- Parallel compressor compatible with lzip. +Plzip is a massively parallel (multi\-threaded) implementation of lzip, fully +compatible with lzip 1.4 or newer. Plzip uses the lzlib compression library. +.PP +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 \fB\-0\fR) +or compress most files more than bzip2 (lzip \fB\-9\fR). 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. +.PP +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. .SH OPTIONS .TP \fB\-h\fR, \fB\-\-help\fR @@ -71,6 +87,12 @@ alias for \fB\-9\fR .TP \fB\-\-loose\-trailing\fR allow trailing data seeming corrupt header +.TP +\fB\-\-in\-slots=\fR<n> +number of 1 MiB input packets buffered [4] +.TP +\fB\-\-out\-slots=\fR<n> +number of 1 MiB output packets buffered [64] .PP If no file names are given, or if a file is '\-', plzip compresses or decompresses from standard input to standard output. @@ -95,8 +117,8 @@ Plzip home page: http://www.nongnu.org/lzip/plzip.html .SH COPYRIGHT Copyright \(co 2009 Laszlo Ersek. .br -Copyright \(co 2018 Antonio Diaz Diaz. -Using lzlib 1.10 +Copyright \(co 2019 Antonio Diaz Diaz. +Using lzlib 1.11 License GPLv2+: GNU GPL version 2 or later <http://gnu.org/licenses/gpl.html> .br This is free software: you are free to change and redistribute it. diff --git a/doc/plzip.info b/doc/plzip.info index c8d7387..2b7aa52 100644 --- a/doc/plzip.info +++ b/doc/plzip.info @@ -2,7 +2,7 @@ This is plzip.info, produced by makeinfo version 4.13+ from plzip.texi. INFO-DIR-SECTION Data Compression START-INFO-DIR-ENTRY -* Plzip: (plzip). Parallel compressor compatible with lzip +* Plzip: (plzip). Massively parallel implementation of lzip END-INFO-DIR-ENTRY @@ -11,7 +11,7 @@ File: plzip.info, Node: Top, Next: Introduction, Up: (dir) Plzip Manual ************ -This manual is for Plzip (version 1.7, 7 February 2018). +This manual is for Plzip (version 1.8, 5 January 2019). * Menu: @@ -28,7 +28,7 @@ This manual is for Plzip (version 1.7, 7 February 2018). * Concept index:: Index of concepts - Copyright (C) 2009-2018 Antonio Diaz Diaz. + Copyright (C) 2009-2019 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -39,20 +39,25 @@ File: plzip.info, Node: Introduction, Next: Output, Prev: Top, Up: Top 1 Introduction ************** -Plzip is a massively parallel (multi-threaded) lossless data compressor -based on the lzlib compression library, with a user interface similar to -the one of lzip, bzip2 or gzip. +Plzip is a massively parallel (multi-threaded) implementation of lzip, +fully compatible with lzip 1.4 or newer. Plzip uses the lzlib +compression library. + + 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. 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 uses the lzip file format; the files produced by plzip are -fully compatible with lzip-1.4 or newer, and can be rescued with -lziprecover. +plzip is no faster than lzip. *Note Minimum file sizes::. The lzip file format is designed for data sharing and long-term archiving, taking into account both data integrity and decoder @@ -80,15 +85,16 @@ 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 and -bzip2, 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 the smallest possible dictionary size -for each file without exceeding the given limit. 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". @@ -101,7 +107,7 @@ 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 +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). @@ -188,6 +194,7 @@ command line. '-V' '--version' Print the version number of plzip on the standard output and exit. + This version number should be included in all bug reports. '-a' '--trailing-error' @@ -286,12 +293,14 @@ command line. '-s BYTES' '--dictionary-size=BYTES' When compressing, set the dictionary size limit in bytes. Plzip - 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 (BYTES / 8) to it. + 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. For maximum compression you should use a dictionary size limit as large as possible, but keep in mind that the decompression memory @@ -320,27 +329,32 @@ command line. except for single-member files. '-0 .. -9' - Set the compression parameters (dictionary size and match length - limit) as shown in the table below. The default compression level - is '-6'. 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. - Level Dictionary size Match length limit - -0 64 KiB 16 bytes - -1 1 MiB 5 bytes - -2 1.5 MiB 6 bytes - -3 2 MiB 8 bytes - -4 3 MiB 12 bytes - -5 4 MiB 20 bytes - -6 8 MiB 36 bytes - -7 16 MiB 68 bytes - -8 24 MiB 132 bytes - -9 32 MiB 273 bytes + 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 + -1 1 MiB 5 bytes + -2 1.5 MiB 6 bytes + -3 2 MiB 8 bytes + -4 3 MiB 12 bytes + -5 4 MiB 20 bytes + -6 8 MiB 36 bytes + -7 16 MiB 68 bytes + -8 24 MiB 132 bytes + -9 32 MiB 273 bytes '--fast' '--best' @@ -353,6 +367,18 @@ command line. 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. + +'--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. + Numbers given as arguments to options may be followed by a multiplier and an optional 'B' for "byte". @@ -465,11 +491,11 @@ additional information before, between, or after them. 'DS (coded dictionary size, 1 byte)' The dictionary size is calculated by taking a power of 2 (the base - size) and substracting from it a fraction between 0/16 and 7/16 of + 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 - substract from the base size to obtain the dictionary size. + 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. @@ -497,22 +523,25 @@ File: plzip.info, Node: Memory requirements, Next: Minimum file sizes, Prev: 6 Memory required to compress and decompress ******************************************** -The amount of memory required *per thread* for decompression or testing -is approximately the following: +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 testing of a non-seekable file or of standard input; the - dictionary size plus up to 5 MiB. + 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 32 MiB. + 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 up to 35 MiB. + 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 thread* for compression is +The amount of memory required *per worker thread* for compression is approximately the following: * For compression at level -0; 1.5 MiB plus 3.375 times the data size @@ -561,7 +590,7 @@ 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 -------------------------------------------------------------------------- +------------------------------------------------------------------ Level -0 2 MiB 4 MiB 8 MiB 16 MiB 64 MiB 256 MiB -1 4 MiB 8 MiB 16 MiB 32 MiB 128 MiB 512 MiB @@ -633,7 +662,11 @@ 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 verify the compressed file with a command like -'plzip -cd file.lz | cmp file -'. +'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. Example 1: Replace a regular file with its compressed version 'file.lz' @@ -728,21 +761,22 @@ Concept index Tag Table: -Node: Top221 +Node: Top222 Node: Introduction1158 -Node: Output5134 -Node: Invoking plzip6614 -Ref: --trailing-error7177 -Ref: --data-size7420 -Node: Program design14938 -Node: File format17090 -Node: Memory requirements19522 -Node: Minimum file sizes20985 -Node: Trailing data23002 -Node: Examples25285 -Ref: concat-example26450 -Node: Problems27025 -Node: Concept index27553 +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 End Tag Table diff --git a/doc/plzip.texi b/doc/plzip.texi index 44cff75..b5469b9 100644 --- a/doc/plzip.texi +++ b/doc/plzip.texi @@ -6,19 +6,19 @@ @finalout @c %**end of header -@set UPDATED 7 February 2018 -@set VERSION 1.7 +@set UPDATED 5 January 2019 +@set VERSION 1.8 @dircategory Data Compression @direntry -* Plzip: (plzip). Parallel compressor compatible with lzip +* Plzip: (plzip). Massively parallel implementation of lzip @end direntry @ifnothtml @titlepage @title Plzip -@subtitle Parallel compressor compatible with lzip +@subtitle Massively parallel implementation of lzip @subtitle for Plzip version @value{VERSION}, @value{UPDATED} @author by Antonio Diaz Diaz @@ -49,7 +49,7 @@ This manual is for Plzip (version @value{VERSION}, @value{UPDATED}). @end menu @sp 1 -Copyright @copyright{} 2009-2018 Antonio Diaz Diaz. +Copyright @copyright{} 2009-2019 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -59,23 +59,28 @@ to copy, distribute and modify it. @chapter Introduction @cindex introduction -Plzip is a massively parallel (multi-threaded) lossless data compressor -based on the lzlib compression library, with a user interface similar to -the one of lzip, bzip2 or gzip. +@uref{http://www.nongnu.org/lzip/plzip.html,,Plzip} is a massively parallel +(multi-threaded) implementation of lzip, fully compatible with lzip 1.4 or +newer. Plzip uses the lzlib compression library. + +@uref{http://www.nongnu.org/lzip/lzip.html,,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 @w{(lzip -0)} or compress most files more +than bzip2 @w{(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 (@pxref{Minimum file sizes}). - -Plzip uses the lzip file format; the files produced by plzip are fully -compatible with lzip-1.4 or newer, and can be rescued with lziprecover. +plzip is no faster than lzip. @xref{Minimum file sizes}. -The lzip file format is designed for data sharing and long-term -archiving, taking into account both data integrity and decoder -availability: +The lzip file format is designed for data sharing and long-term archiving, +taking into account both data integrity and decoder availability: @itemize @bullet @item @@ -107,15 +112,14 @@ 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 and -bzip2, 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 the smallest possible dictionary size for -each file without exceeding the given limit. Keep in mind that the -decompression memory requirement is affected at compression time by the -choice of dictionary size limit (@pxref{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. @xref{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". @@ -130,7 +134,7 @@ file from that of the compressed file as follows: (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 +possible, ownership of the file just as @samp{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). @@ -142,10 +146,10 @@ 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 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. +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. @node Output @@ -225,6 +229,7 @@ Print an informative help message describing the options and exit. @item -V @itemx --version Print the version number of plzip on the standard output and exit. +This version number should be included in all bug reports. @anchor{--trailing-error} @item -a @@ -322,12 +327,13 @@ Quiet operation. Suppress all messages. @item -s @var{bytes} @itemx --dictionary-size=@var{bytes} When compressing, set the dictionary size limit in bytes. Plzip will use -the smallest possible dictionary size for each file without exceeding -this limit. Valid values range from @w{4 KiB} to @w{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 each file the largest dictionary size that does not exceed neither +the file size nor this limit. Valid values range from @w{4 KiB} to +@w{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 (@pxref{coded-dict-size}). 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 @@ -354,18 +360,23 @@ Two or more @samp{-v} options show the progress of (de)compression, except for single-member files. @item -0 .. -9 -Set the compression parameters (dictionary size and match length limit) -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, 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 @samp{-6}, equivalent to @w{@samp{-s8MiB -m36}}. Note that +@samp{-9} can be much slower than @samp{-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 @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 +If several compression levels or @samp{-s} or @samp{-m} options are +given, the last setting is used. For example @w{@samp{-9 -s64MiB}} is +equivalent to @w{@samp{-s64MiB -m273}} + +@multitable {Level} {Dictionary size (-s)} {Match length limit (-m)} +@item Level @tab Dictionary size (-s) @tab Match length limit (-m) @item -0 @tab 64 KiB @tab 16 bytes @item -1 @tab 1 MiB @tab 5 bytes @item -2 @tab 1.5 MiB @tab 6 bytes @@ -388,6 +399,18 @@ 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. +@item --in-slots=@var{n} +Number of @w{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. + +@item --out-slots=@var{n} +Number of @w{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. + @end table Numbers given as arguments to options may be followed by a multiplier @@ -506,12 +529,13 @@ A four byte string, identifying the lzip format, with the value "LZIP" @item VN (version number, 1 byte) Just in case something needs to be modified in the future. 1 for now. +@anchor{coded-dict-size} @item DS (coded dictionary size, 1 byte) The dictionary size is calculated by taking a power of 2 (the base size) -and substracting from it a fraction between 0/16 and 7/16 of the base +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 substract +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. @@ -546,8 +570,8 @@ facilitates safe recovery of undamaged members from multimember files. @chapter Memory required to compress and decompress @cindex memory requirements -The amount of memory required @strong{per thread} for decompression or -testing is approximately the following: +The amount of memory required @strong{per worker thread} for +decompression or testing is approximately the following: @itemize @bullet @item @@ -556,20 +580,23 @@ or for testing of a regular file; the dictionary size. @item For testing of a non-seekable file or of standard input; the dictionary -size plus up to @w{5 MiB}. +size plus @w{1 MiB} plus up to the number of @w{1 MiB} input packets +buffered (4 by default). @item For decompression of a regular file to a non-seekable file or to -standard output; the dictionary size plus up to @w{32 MiB}. +standard output; the dictionary size plus up to the number of @w{1 MiB} +output packets buffered (64 by default). @item For decompression of a non-seekable file or of standard input; the -dictionary size plus up to @w{35 MiB}. +dictionary size plus @w{1 MiB} plus up to the number of @w{1 MiB} input +and output packets buffered (68 by default). @end itemize @noindent -The amount of memory required @strong{per thread} for compression is -approximately the following: +The amount of memory required @strong{per worker thread} for compression +is approximately the following: @itemize @bullet @item @@ -696,9 +723,12 @@ where a file containing trailing data must be rejected, the option 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 -@samp{--keep} option to plzip and don't remove the original file until -you verify the compressed file with a command like -@w{@samp{plzip -cd file.lz | cmp file -}}. +@samp{--keep} option to plzip and don't remove the original file until you +verify the compressed file with a command like +@w{@samp{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. @sp 1 @noindent |