LBZIP2(1) lbzip2-2.3 LBZIP2(1)
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NAME
lbzip2 - parallel bzip2 utility
SYNOPSIS
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 ... ]
lbzip2|bzip2|lbunzip2|
DESCRIPTION
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.
INVOCATION
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.
OPTIONS
-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
online).
-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.
--fast
Alias for -1.
--best
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
format.
-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
successfully.
-L, --license, -V,
Print license and version information on standard output and exit
successfully.
ENVIRONMENT
LBZIP2, BZIP2, BZIP
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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OPERANDS
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.
EXIT STATUS
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.
SIGPIPE, SIGXFSZ
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.
SIGABRT
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.
SIGINT, SIGTERM
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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BLOCK SIZE
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
decompression.
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.
ERROR HANDLING
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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RESOURCE ALLOCATION
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.
DAMAGED FILES
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.
BUGS
Separate input files don't share worker threads; at most one input
file is worked on at any moment.
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AUTHORS
lbzip2 was originally written by Laszlo Ersek <lacos@caesar.elte.hu>,
http://lacos.hu/. Versions 2.0 and later were written by Mikolaj
Izdebski.
COPYRIGHT
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 <http://www.gnu.org/licenses/>.
THANKS
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.
SEE ALSO
lbzip2 home page
http://lbzip2.org/
bzip2(1)
http://www.bzip.org/
pbzip2(1)
http://compression.ca/pbzip2/
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bzip2smp(1)
http://bzip2smp.sourceforge.net/
smpbzip2(1)
http://home.student.utwente.nl/n.werensteijn/smpbzip2/
dbzip2(1)
http://www.mediawiki.org/wiki/Dbzip2
p7zip(1)
http://p7zip.sourceforge.net/
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