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 LBZIP2(1)                       lbzip2-2.3                        LBZIP2(1)
 User commands                                                 User commands

                              22 September 2013

      lbzip2 - parallel bzip2 utility

      lbzip2|bzip2 [-n WTHRS] [-k|-c|-t [-S] [ FILE ... ]

      lbunzip2|bunzip2 [-n WTHRS] [-k|-c|-t [-S] [ FILE ... ]

      lbzcat|bzcat [-n WTHRS] [-z] [-f] [-v [-S] [ FILE ... ]


      Compress or decompress FILE operands or standard input to regular
      files or standard output using the Burrows-Wheeler block-sorting text
      compression algorithm. The lbzip2 utility employs multiple threads and
      an input-bound splitter even when decompressing .bz2 files created by
      standard bzip2.

      Compression is generally considerably better than that achieved by
      more conventional LZ77/LZ78-based compressors, and competitive with
      all but the best of the PPM family of statistical compressors.

      Compression is always performed, even if the compressed file is
      slightly larger than the original. The worst case expansion is for
      files of zero length, which expand to fourteen bytes. Random data
      (including the output of most file compressors) is coded with
      asymptotic expansion of around 0.5%.

      The command-line options are deliberately very similar to those of
      bzip2 and gzip, but they are not identical.

      The default mode of operation is compression. If the utility is
      invoked as lbunzip2 or bunzip2, the mode is switched to decompression.
      Calling the utility as lbzcat or bzcat selects decompression, with the
      decompressed byte-stream written to standard output.

      -n WTHRS
           Set the number of (de)compressor threads to WTHRS.  If this
           option is not specified, lbzip2 tries to query the system for the

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           number of online processors (if both the compilation environment
           and the execution environment support that), or exits with an
           error (if it's unable to determine the number of processors

      -k, --keep
           Don't remove FILE operands after successful (de)compression. Open
           regular input files with more than one link.

      -c, --stdout
           Write output to standard output, even when FILE operands are
           present. Implies -k and excludes -t.

      -t, --test
           Test decompression; discard output instead of writing it to files
           or standard output. Implies -k and excludes -c.  Roughly
           equivalent to passing -c and redirecting standard output to the
           bit bucket.

      -d, --decompress
           Force decompression over the mode of operation selected by the
           invocation name.

      -z, --compress
           Force compression over the mode of operation selected by the
           invocation name.

      -1 .. -9
           Set the compression block size to 100K .. 900K, in 100K
           increments.  Ignored during decompression. See also the BLOCK
           SIZE section below.

           Alias for -1.

           Alias for -9.  This is the default.

      -f, --force
           Open non-regular input files. Open input files with more than one

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           link, breaking links when -k isn't specified in addition. Try to
           remove each output file before opening it.  By default lbzip2
           will not overwrite existing files; if you want this to happen,
           you should specify -f.  If -c and -d are also given don't reject
           files not in bzip2 format, just copy them without change; without
           -f lbzip2 would stop after reaching a file that is not in bzip2

      -v, --verbose
           Be more verbose. Print more detailed information about
           (de)compression progress to standard error: before processing
           each file, print a message stating the names of input and output
           files; during (de)compression, print a rough percentage of
           completeness and estimated time of arrival (only if standard
           error is connected to a terminal); after processing each file
           print a message showing compression ratio, space savings, total
           compression time (wall time) and average (de)compression speed
           (bytes of plain data processed per second).

      -S   Print condition variable statistics to standard error for each
           completed (de)compression operation. Useful in profiling.

      -s, --small, -q,
           Accepted for compatibility with bzip2, otherwise ignored.

      -h, --help
           Print help on command-line usage on standard output and exit

      -L, --license, -V,
           Print license and version information on standard output and exit

           Before parsing the command line, lbzip2 inserts the contents of
           these variables, in the order specified, between the invocation
           name and the rest of the command line. Tokens are separated by
           spaces and tabs, which cannot be escaped.

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 LBZIP2(1)                       lbzip2-2.3                        LBZIP2(1)
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      FILE Specify files to compress or decompress.

           FILEs with .bz2, .tbz, .tbz2 and name suffixes will be skipped
           when compressing. When decompressing, .bz2 suffixes will be
           removed in output filenames; .tbz, .tbz2 and .tz2 suffixes will
           be replaced by .tar; other filenames will be suffixed with .out.
           If an INT or TERM signal is delivered to then it removes the
           regular output file currently open before exiting.

           If no FILE is given, lbzip2 works as a filter, processing
           standard input to standard output. In this case, lbzip2 will
           decline to write compressed output to a terminal (or read
           compressed input from a terminal), as this would be entirely
           incomprehensible and therefore pointless.

      0    if lbzip2 finishes successfully. This presumes that whenever it
           tries, lbzip2 never fails to write to standard error.

      1    if lbzip2 encounters a fatal error.

      4    if lbzip2 issues warnings without encountering a fatal error.
           This presumes that whenever it tries, lbzip2 never fails to write
           to standard error.

           if lbzip2 intends to exit with status 1 due to any fatal error,
           but any such signal with inherited SIG_DFL action was generated
           for lbzip2 previously, then lbzip2 terminates by way of one of
           said signals, after cleaning up any interrupted output file.

           if a runtime assertion fails (i.e.  lbzip2 detects a bug in
           itself). Hopefully whoever compiled your binary wasn't bold
           enough to #define NDEBUG.

           lbzip2 catches these signals so that it can remove an interrupted
           output file. In such cases, lbzip2 exits by re-raising (one of)
           the received signal(s).

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 LBZIP2(1)                       lbzip2-2.3                        LBZIP2(1)
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      lbzip2 compresses large files in blocks. It can operate at various
      block sizes, ranging from 100k to 900k in 100k steps, and it allocates
      only as much memory as it needs to. The block size affects both the
      compression ratio achieved, and the amount of memory needed both for
      compression and decompression.  Compression and decompression speed is
      virtually unaffected by block size, provided that the file being
      processed is large enough to be split among all worker threads.

      The flags -1 through -9 specify the block size to be 100,000 bytes
      through 900,000 bytes (the default) respectively. At decompression-
      time, the block size used for compression is read from the compressed
      file -- the flags -1 to -9 are irrelevant to and so ignored during

      Larger block sizes give rapidly diminishing marginal returns; most of
      the compression comes from the first two or three hundred k of block
      size, a fact worth bearing in mind when using lbzip2 on small
      machines. It is also important to appreciate that the decompression
      memory requirement is set at compression-time by the choice of block
      size. In general you should try and use the largest block size memory
      constraints allow.

      Another significant point applies to small files. By design, only one
      of lbzip2's worker threads can work on a single block. This means that
      if the number of blocks in the compressed file is less than the number
      of processors online, then some of worker threads will remain idle for
      the entire time. Compressing small files with smaller block sizes can
      therefore significantly increase both compression and decompression
      speed. The speed difference is more noticeable as the number of CPU
      cores grows.

      Dealing with error conditions is the least satisfactory aspect of
      lbzip2.  The policy is to try and leave the filesystem in a consistent
      state, then quit, even if it means not processing some of the files
      mentioned in the command line.

      `A consistent state' means that a file exists either in its compressed
      or uncompressed form, but not both. This boils down to the rule
      `delete the output file if an error condition occurs, leaving the
      input intact'. Input files are only deleted when we can be pretty sure
      the output file has been written and closed successfully.

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 LBZIP2(1)                       lbzip2-2.3                        LBZIP2(1)
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      lbzip2 needs various kinds of system resources to operate. Those
      include memory, threads, mutexes and condition variables. The policy
      is to simply give up if a resource allocation failure occurs.

      Resource consumption grows linearly with number of worker threads. If
      lbzip2 fails because of lack of some resources, decreasing number of
      worker threads may help. It would be possible for lbzip2 to try to
      reduce number of worker threads (and hence the resource consumption),
      or to move on to subsequent files in the hope that some might need
      less resources, but the complications for doing this seem more trouble
      than they are worth.

      lbzip2 attempts to compress data by performing several non-trivial
      transformations on it. Every compression of a file implies an
      assumption that the compressed file can be decompressed to reproduce
      the original. Great efforts in design, coding and testing have been
      made to ensure that this program works correctly.  However, the
      complexity of the algorithms, and, in particular, the presence of
      various special cases in the code which occur with very low but non-
      zero probability make it very difficult to rule out the possibility of
      bugs remaining in the program. That is not to say this program is
      inherently unreliable. Indeed, I very much hope the opposite is true
      -- lbzip2 has been carefully constructed and extensively tested.

      As a self-check for your protection, lbzip2 uses 32-bit CRCs to make
      sure that the decompressed version of a file is identical to the
      original. This guards against corruption of the compressed data, and
      against undiscovered bugs in lbzip2 (hopefully unlikely). The chances
      of data corruption going undetected is microscopic, about one chance
      in four billion for each file processed. Be aware, though, that the
      check occurs upon decompression, so it can only tell you that that
      something is wrong.

      CRCs can only detect corrupted files, they can't help you recover the
      original, uncompressed data. However, because of the block nature of
      the compression algorithm, it may be possible to recover some parts of
      the damaged file, even if some blocks are destroyed.

      Separate input files don't share worker threads; at most one input
      file is worked on at any moment.

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 LBZIP2(1)                       lbzip2-2.3                        LBZIP2(1)
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      lbzip2 was originally written by Laszlo Ersek <>, Versions 2.0 and later were written by Mikolaj

      Copyright (C) 2011, 2012, 2013 Mikolaj Izdebski
      Copyright (C) 2008, 2009, 2010 Laszlo Ersek
      Copyright (C) 1996 Julian Seward

      This manual page is part of lbzip2, version 2.3. lbzip2 is free
      software: you can redistribute it and/or modify it under the terms of
      the GNU General Public License as published by the Free Software
      Foundation, either version 3 of the License, or (at your option) any
      later version.

      lbzip2 is distributed in the hope that it will be useful, but WITHOUT
      ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
      FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
      for more details.

      You should have received a copy of the GNU General Public License
      along with lbzip2. If not, see <>.

      Adam Maulis at ELTE IIG; Julian Seward; Paul Sladen; Michael Thomas
      from Caltech HEP; Bryan Stillwell; Zsolt Bartos-Elekes; Imre Csatlos;
      Gabor Kovesdan; Paul Wise; Paolo Bonzini; Department of Electrical and
      Information Engineering at the University of Oulu; Yuta Mori.

      lbzip2 home page



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