{
    "mode": "man",
    "parameter": "bzip2",
    "section": "1",
    "url": "https://www.chedong.com/phpMan.php/man/bzip2/1/json",
    "generated": "2026-11-07T13:05:02Z",
    "synopsis": "bzip2 [ -cdfkqstvzVL123456789 ] [ filenames ...  ]\nbzip2 [ -h|--help ]\nbunzip2 [ -fkvsVL ] [ filenames ...  ]\nbunzip2 [ -h|--help ]\nbzcat [ -s ] [ filenames ...  ]\nbzcat [ -h|--help ]\nbzip2recover filename",
    "sections": {
        "NAME": {
            "content": "bzip2, bunzip2 - a block-sorting file compressor, v1.0.8\nbzcat - decompresses files to stdout\nbzip2recover - recovers data from damaged bzip2 files\n\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "bzip2 [ -cdfkqstvzVL123456789 ] [ filenames ...  ]\nbzip2 [ -h|--help ]\nbunzip2 [ -fkvsVL ] [ filenames ...  ]\nbunzip2 [ -h|--help ]\nbzcat [ -s ] [ filenames ...  ]\nbzcat [ -h|--help ]\nbzip2recover filename\n\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "bzip2  compresses  files  using the Burrows-Wheeler block sorting text compression algorithm,\nand Huffman coding.  Compression is generally considerably better than that achieved by  more\nconventional LZ77/LZ78-based compressors, and approaches the performance of the PPM family of\nstatistical compressors.\n\nThe command-line options are deliberately very similar to those of GNU gzip, but they are not\nidentical.\n\nbzip2  expects  a  list  of file names to accompany the command-line flags.  Each file is re‐\nplaced by a compressed version of itself, with the name \"originalname.bz2\".  Each compressed\nfile has the same modification date, permissions, and, when possible, ownership as the corre‐\nsponding original, so that these properties can be correctly restored at decompression  time.\nFile  name  handling is naive in the sense that there is no mechanism for preserving original\nfile names, permissions, ownerships or dates in filesystems which  lack  these  concepts,  or\nhave serious file name length restrictions, such as MS-DOS.\n\nbzip2  and bunzip2 will by default not overwrite existing files.  If you want this to happen,\nspecify the -f flag.\n\nIf no file names are specified, bzip2 compresses from standard input to standard output.   In\nthis  case, bzip2 will decline to write compressed output to a terminal, as this would be en‐\ntirely incomprehensible and therefore pointless.\n\nbunzip2 (or bzip2 -d) decompresses all specified files.  Files  which  were  not  created  by\nbzip2  will be detected and ignored, and a warning issued.  bzip2 attempts to guess the file‐\nname for the decompressed file from that of the compressed file as follows:\n\nfilename.bz2    becomes   filename\nfilename.bz     becomes   filename\nfilename.tbz2   becomes   filename.tar\nfilename.tbz    becomes   filename.tar\nanyothername    becomes   anyothername.out\n\nIf the file does not end in one of the recognised endings, .bz2, .bz, .tbz2  or  .tbz,  bzip2\ncomplains that it cannot guess the name of the original file, and uses the original name with\n.out appended.\n\nAs with compression, supplying no filenames causes decompression from standard input to stan‐\ndard output.\n\nbunzip2 will correctly decompress a file which is the concatenation of two or more compressed\nfiles.   The  result is the concatenation of the corresponding uncompressed files.  Integrity\ntesting (-t) of concatenated compressed files is also supported.\n\nYou can also compress or decompress files to the standard output by giving the -c flag.  Mul‐\ntiple files may be compressed and decompressed like this.  The resulting outputs are fed  se‐\nquentially  to  stdout.  Compression of multiple files in this manner generates a stream con‐\ntaining multiple compressed file representations.  Such a stream  can  be  decompressed  cor‐\nrectly  only  by bzip2 version 0.9.0 or later.  Earlier versions of bzip2 will stop after de‐\ncompressing the first file in the stream.\n\nbzcat (or bzip2 -dc) decompresses all specified files to the standard output.\n\nbzip2 will read arguments from the environment variables BZIP2 and BZIP, in that  order,  and\nwill  process  them before any arguments read from the command line.  This gives a convenient\nway to supply default arguments.\n\nCompression is always performed, even if the compressed file  is  slightly  larger  than  the\noriginal.   Files of less than about one hundred bytes tend to get larger, since the compres‐\nsion mechanism has a constant overhead in the region of 50 bytes.  Random data (including the\noutput of most file compressors) is coded at about 8.05 bits per byte, giving an expansion of\naround 0.5%.\n\nAs a self-check for your protection, bzip2 uses 32-bit CRCs to  make  sure  that  the  decom‐\npressed  version  of  a file is identical to the original.  This guards against corruption of\nthe compressed data, and against undetected bugs in bzip2  (hopefully  very  unlikely).   The\nchances  of data corruption going undetected is microscopic, about one chance in four billion\nfor each file processed.  Be aware, though, that the check occurs upon decompression,  so  it\ncan  only  tell  you  that something is wrong.  It can't help you recover the original uncom‐\npressed data.  You can use bzip2recover to try to recover data from damaged files.\n\nReturn values: 0 for a normal exit, 1 for environmental problems  (file  not  found,  invalid\nflags,  I/O  errors,  &c), 2 to indicate a corrupt compressed file, 3 for an internal consis‐\ntency error (eg, bug) which caused bzip2 to panic.\n\n",
            "subsections": []
        },
        "OPTIONS": {
            "content": "",
            "subsections": [
                {
                    "name": "-c --stdout",
                    "content": "Compress or decompress to standard output.\n",
                    "flag": "-c",
                    "long": "--stdout"
                },
                {
                    "name": "-d --decompress",
                    "content": "Force decompression.  bzip2, bunzip2 and bzcat are really the same  program,  and  the\ndecision  about what actions to take is done on the basis of which name is used.  This\nflag overrides that mechanism, and forces bzip2 to decompress.\n",
                    "flag": "-d",
                    "long": "--decompress"
                },
                {
                    "name": "-z --compress",
                    "content": "The complement to -d: forces compression, regardless of the invocation name.\n",
                    "flag": "-z",
                    "long": "--compress"
                },
                {
                    "name": "-t --test",
                    "content": "Check integrity of the specified file(s), but don't decompress them.  This really per‐\nforms a trial decompression and throws away the result.\n",
                    "flag": "-t",
                    "long": "--test"
                },
                {
                    "name": "-f --force",
                    "content": "Force overwrite of output files.  Normally, bzip2 will not overwrite  existing  output\nfiles.   Also  forces  bzip2 to break hard links to files, which it otherwise wouldn't\ndo.\n\nbzip2 normally declines to decompress files which don't have the correct magic  header\nbytes.   If forced (-f), however, it will pass such files through unmodified.  This is\nhow GNU gzip behaves.\n",
                    "flag": "-f",
                    "long": "--force"
                },
                {
                    "name": "-k --keep",
                    "content": "Keep (don't delete) input files during compression or decompression.\n",
                    "flag": "-k",
                    "long": "--keep"
                },
                {
                    "name": "-s --small",
                    "content": "Reduce memory usage, for compression, decompression and  testing.   Files  are  decom‐\npressed  and tested using a modified algorithm which only requires 2.5 bytes per block\nbyte.  This means any file can be decompressed in 2300 k of memory,  albeit  at  about\nhalf the normal speed.\n\nDuring  compression,  -s  selects  a  block  size of 200 k, which limits memory use to\naround the same figure, at the expense of your compression ratio.  In short,  if  your\nmachine  is  low  on  memory (8 megabytes or less), use -s for everything.  See MEMORY\nMANAGEMENT below.\n",
                    "flag": "-s",
                    "long": "--small"
                },
                {
                    "name": "-q --quiet",
                    "content": "Suppress non-essential warning messages.  Messages pertaining to I/O errors and  other\ncritical events will not be suppressed.\n",
                    "flag": "-q",
                    "long": "--quiet"
                },
                {
                    "name": "-v --verbose",
                    "content": "Verbose  mode -- show the compression ratio for each file processed.  Further -v's in‐\ncrease the verbosity level, spewing out lots of information which is primarily of  in‐\nterest for diagnostic purposes.\n",
                    "flag": "-v",
                    "long": "--verbose"
                },
                {
                    "name": "-h --help",
                    "content": "Print a help message and exit.\n",
                    "flag": "-h",
                    "long": "--help"
                },
                {
                    "name": "-L --license -V --version",
                    "content": "Display the software version, license terms and conditions.\n",
                    "flag": "-V",
                    "long": "--version"
                },
                {
                    "name": "-1 (or --fast) to -9 (or --best)",
                    "content": "Set  the  block  size to 100 k, 200 k ...  900 k when compressing.  Has no effect when\ndecompressing.  See MEMORY MANAGEMENT below.  The --fast and --best aliases  are  pri‐\nmarily for GNU gzip compatibility.  In particular, --fast doesn't make things signifi‐\ncantly faster.  And --best merely selects the default behaviour.\n\n--     Treats  all  subsequent arguments as file names, even if they start with a dash.  This\nis so you can handle files with names beginning with a dash,  for  example:  bzip2  --\n-myfilename.\n",
                    "flag": "-9"
                },
                {
                    "name": "--repetitive-fast --repetitive-best",
                    "content": "These flags are redundant in versions 0.9.5 and above.  They provided some coarse con‐\ntrol  over the behaviour of the sorting algorithm in earlier versions, which was some‐\ntimes useful.  0.9.5 and above have an improved algorithm which  renders  these  flags\nirrelevant.\n\n",
                    "long": "--repetitive-best"
                }
            ]
        },
        "MEMORY MANAGEMENT": {
            "content": "bzip2  compresses  large  files in blocks.  The block size affects both the compression ratio\nachieved, and the amount of memory needed for compression and decompression.   The  flags  -1\nthrough -9 specify the block size to be 100,000 bytes through 900,000 bytes (the default) re‐\nspectively.   At  decompression  time,  the  block size used for compression is read from the\nheader of the compressed file, and bunzip2 then allocates itself just enough memory to decom‐\npress the file.  Since block sizes are stored in compressed files, it follows that the  flags\n-1 to -9 are irrelevant to and so ignored during decompression.\n\nCompression and decompression requirements, in bytes, can be estimated as:\n\nCompression:   400 k + ( 8 x block size )\n\nDecompression: 100 k + ( 4 x block size ), or\n100 k + ( 2.5 x block size )\n\nLarger  block sizes give rapidly diminishing marginal returns.  Most of the compression comes\nfrom the first two or three hundred k of block size, a fact worth bearing in mind when  using\nbzip2  on  small  machines.  It is also important to appreciate that the decompression memory\nrequirement is set at compression time by the choice of block size.\n\nFor files compressed with the default 900 k block  size,  bunzip2  will  require  about  3700\nkbytes  to decompress.  To support decompression of any file on a 4 megabyte machine, bunzip2\nhas an option to decompress using approximately  half  this  amount  of  memory,  about  2300\nkbytes.   Decompression speed is also halved, so you should use this option only where neces‐\nsary.  The relevant flag is -s.\n\nIn general, try and use the largest block size memory constraints allow, since that maximises\nthe compression achieved.  Compression and decompression speed are  virtually  unaffected  by\nblock size.\n\nAnother  significant  point  applies  to files which fit in a single block -- that means most\nfiles you'd encounter using a large block size.  The amount of real memory touched is propor‐\ntional to the size of the file, since the file is smaller than a block.   For  example,  com‐\npressing  a  file  20,000  bytes  long with the flag -9 will cause the compressor to allocate\naround 7600 k of memory, but only touch 400 k + 20000 * 8 = 560 kbytes of it.  Similarly, the\ndecompressor will allocate 3700 k but only touch 100 k + 20000 * 4 = 180 kbytes.\n\nHere is a table which summarises the maximum memory usage for different  block  sizes.   Also\nrecorded is the total compressed size for 14 files of the Calgary Text Compression Corpus to‐\ntalling  3,141,622  bytes.  This column gives some feel for how compression varies with block\nsize.  These figures tend to understate the advantage of larger block sizes for larger files,\nsince the Corpus is dominated by smaller files.\n\nCompress   Decompress   Decompress   Corpus\nFlag     usage      usage       -s usage     Size\n\n-1      1200k       500k         350k      914704\n-2      2000k       900k         600k      877703\n-3      2800k      1300k         850k      860338\n-4      3600k      1700k        1100k      846899\n-5      4400k      2100k        1350k      845160\n-6      5200k      2500k        1600k      838626\n-7      6100k      2900k        1850k      834096\n-8      6800k      3300k        2100k      828642\n-9      7600k      3700k        2350k      828642\n\n",
            "subsections": []
        },
        "RECOVERING DATA FROM DAMAGED FILES": {
            "content": "bzip2 compresses files in blocks, usually 900 kbytes long.  Each block  is  handled  indepen‐\ndently.   If  a media or transmission error causes a multi-block .bz2 file to become damaged,\nit may be possible to recover data from the undamaged blocks in the file.\n\nThe compressed representation of each block is delimited by a 48-bit pattern, which makes  it\npossible to find the block boundaries with reasonable certainty.  Each block also carries its\nown 32-bit CRC, so damaged blocks can be distinguished from undamaged ones.\n\nbzip2recover  is  a  simple  program whose purpose is to search for blocks in .bz2 files, and\nwrite each block out into its own .bz2 file.  You can then use bzip2 -t to test the integrity\nof the resulting files, and decompress those which are undamaged.\n\nbzip2recover takes a single argument, the name of the damaged file, and writes  a  number  of\nfiles  \"rec00001file.bz2\",  \"rec00002file.bz2\", etc., containing the  extracted  blocks.  The\noutput filenames are designed so that the use of wildcards in subsequent  processing  --  for\nexample,  \"bzip2 -dc rec*file.bz2 > recovereddata\" -- processes the files in the correct or‐\nder.\n\nbzip2recover should be of most use dealing with large .bz2 files, as these will contain  many\nblocks.   It is clearly futile to use it on damaged single-block files, since a damaged block\ncannot be recovered.  If you wish to minimise any potential data loss through media or trans‐\nmission errors, you might consider compressing with a smaller block size.\n\n",
            "subsections": []
        },
        "PERFORMANCE NOTES": {
            "content": "The sorting phase of compression gathers together similar strings in the  file.   Because  of\nthis,  files containing very long runs of repeated symbols, like \"aabaabaabaab ...\" (repeated\nseveral hundred times) may compress more slowly than normal.  Versions 0.9.5 and  above  fare\nmuch  better  than previous versions in this respect.  The ratio between worst-case and aver‐\nage-case compression time is in the region of 10:1.  For previous versions, this  figure  was\nmore  like  100:1.   You can use the -vvvv option to monitor progress in great detail, if you\nwant.\n\nDecompression speed is unaffected by these phenomena.\n\nbzip2 usually allocates several megabytes of memory to operate in, and then charges all  over\nit  in a fairly random fashion.  This means that performance, both for compressing and decom‐\npressing, is largely determined by the speed at which your machine can service cache  misses.\nBecause of this, small changes to the code to reduce the miss rate have been observed to give\ndisproportionately  large performance improvements.  I imagine bzip2 will perform best on ma‐\nchines with very large caches.\n\n",
            "subsections": []
        },
        "CAVEATS": {
            "content": "I/O error messages are not as helpful as they could be.  bzip2 tries hard to detect  I/O  er‐\nrors  and exit cleanly, but the details of what the problem is sometimes seem rather mislead‐\ning.\n\nThis manual page pertains to version 1.0.8 of bzip2.  Compressed data created by this version\nis entirely forwards and backwards compatible with the  previous  public  releases,  versions\n0.1pl2,  0.9.0, 0.9.5, 1.0.0, 1.0.1, 1.0.2 and above, but with the following exception: 0.9.0\nand above can correctly decompress multiple concatenated compressed files.  0.1pl2 cannot  do\nthis; it will stop after decompressing just the first file in the stream.\n\nbzip2recover  versions prior to 1.0.2 used 32-bit integers to represent bit positions in com‐\npressed files, so they could not handle compressed files more than 512 megabytes long.   Ver‐\nsions  1.0.2  and  above  use 64-bit ints on some platforms which support them (GNU supported\ntargets, and Windows).  To establish whether or not bzip2recover was built with such a  limi‐\ntation,  run  it without arguments.  In any event you can build yourself an unlimited version\nif you can recompile it with MaybeUInt64 set to be an unsigned 64-bit integer.\n\n\n\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "Julian Seward, jseward@acm.org.\n\nhttps://sourceware.org/bzip2/\n\nThe ideas embodied in bzip2 are due to (at least) the following people: Michael  Burrows  and\nDavid  Wheeler  (for the block sorting transformation), David Wheeler (again, for the Huffman\ncoder), Peter Fenwick (for the structured coding model in the original bzip, and many refine‐\nments), and Alistair Moffat, Radford Neal and Ian Witten (for the  arithmetic  coder  in  the\noriginal  bzip).   I  am much indebted for their help, support and advice.  See the manual in\nthe source distribution for pointers to sources of documentation.  Christian von  Roques  en‐\ncouraged  me  to  look  for  faster  sorting algorithms, so as to speed up compression.  Bela\nLubkin encouraged me to improve the worst-case compression performance.  Donna  Robinson  XM‐\nLised  the  documentation.   The bz* scripts are derived from those of GNU gzip.  Many people\nsent patches, helped with portability problems, lent machines, gave advice and were generally\nhelpful.\n\nbzip2(1)",
            "subsections": []
        }
    },
    "summary": "bzip2, bunzip2 - a block-sorting file compressor, v1.0.8 bzcat - decompresses files to stdout bzip2recover - recovers data from damaged bzip2 files",
    "flags": [
        {
            "flag": "-c",
            "long": "--stdout",
            "arg": null,
            "description": "Compress or decompress to standard output."
        },
        {
            "flag": "-d",
            "long": "--decompress",
            "arg": null,
            "description": "Force decompression. bzip2, bunzip2 and bzcat are really the same program, and the decision about what actions to take is done on the basis of which name is used. This flag overrides that mechanism, and forces bzip2 to decompress."
        },
        {
            "flag": "-z",
            "long": "--compress",
            "arg": null,
            "description": "The complement to -d: forces compression, regardless of the invocation name."
        },
        {
            "flag": "-t",
            "long": "--test",
            "arg": null,
            "description": "Check integrity of the specified file(s), but don't decompress them. This really per‐ forms a trial decompression and throws away the result."
        },
        {
            "flag": "-f",
            "long": "--force",
            "arg": null,
            "description": "Force overwrite of output files. Normally, bzip2 will not overwrite existing output files. Also forces bzip2 to break hard links to files, which it otherwise wouldn't do. bzip2 normally declines to decompress files which don't have the correct magic header bytes. If forced (-f), however, it will pass such files through unmodified. This is how GNU gzip behaves."
        },
        {
            "flag": "-k",
            "long": "--keep",
            "arg": null,
            "description": "Keep (don't delete) input files during compression or decompression."
        },
        {
            "flag": "-s",
            "long": "--small",
            "arg": null,
            "description": "Reduce memory usage, for compression, decompression and testing. Files are decom‐ pressed and tested using a modified algorithm which only requires 2.5 bytes per block byte. This means any file can be decompressed in 2300 k of memory, albeit at about half the normal speed. During compression, -s selects a block size of 200 k, which limits memory use to around the same figure, at the expense of your compression ratio. In short, if your machine is low on memory (8 megabytes or less), use -s for everything. See MEMORY MANAGEMENT below."
        },
        {
            "flag": "-q",
            "long": "--quiet",
            "arg": null,
            "description": "Suppress non-essential warning messages. Messages pertaining to I/O errors and other critical events will not be suppressed."
        },
        {
            "flag": "-v",
            "long": "--verbose",
            "arg": null,
            "description": "Verbose mode -- show the compression ratio for each file processed. Further -v's in‐ crease the verbosity level, spewing out lots of information which is primarily of in‐ terest for diagnostic purposes."
        },
        {
            "flag": "-h",
            "long": "--help",
            "arg": null,
            "description": "Print a help message and exit."
        },
        {
            "flag": "-V",
            "long": "--version",
            "arg": null,
            "description": "Display the software version, license terms and conditions."
        },
        {
            "flag": "-9",
            "long": null,
            "arg": null,
            "description": "Set the block size to 100 k, 200 k ... 900 k when compressing. Has no effect when decompressing. See MEMORY MANAGEMENT below. The --fast and --best aliases are pri‐ marily for GNU gzip compatibility. In particular, --fast doesn't make things signifi‐ cantly faster. And --best merely selects the default behaviour. -- Treats all subsequent arguments as file names, even if they start with a dash. This is so you can handle files with names beginning with a dash, for example: bzip2 -- -myfilename."
        },
        {
            "flag": "",
            "long": "--repetitive-best",
            "arg": null,
            "description": "These flags are redundant in versions 0.9.5 and above. They provided some coarse con‐ trol over the behaviour of the sorting algorithm in earlier versions, which was some‐ times useful. 0.9.5 and above have an improved algorithm which renders these flags irrelevant."
        }
    ],
    "examples": [],
    "see_also": [],
    "tldr": {
        "source": "official",
        "description": "A block-sorting file compressor.",
        "examples": [
            {
                "description": "Compress a file",
                "command": "bzip2 {{path/to/file_to_compress}}"
            },
            {
                "description": "Decompress a file",
                "command": "bzip2 {{-d|--decompress}} {{path/to/compressed_file.bz2}}"
            },
            {
                "description": "Decompress a file to `stdout`",
                "command": "bzip2 {{-dc|--decompress --stdout}} {{path/to/compressed_file.bz2}}"
            },
            {
                "description": "Test the integrity of each file inside the archive file",
                "command": "bzip2 {{-t|--test}} {{path/to/compressed_file.bz2}}"
            },
            {
                "description": "Show the compression ratio for each file processed with detailed information",
                "command": "bzip2 {{-v|--verbose}} {{path/to/compressed_files.bz2}}"
            },
            {
                "description": "Decompress a file overwriting existing files",
                "command": "bzip2 {{-f|--force}} {{path/to/compressed_file.bz2}}"
            },
            {
                "description": "Display help",
                "command": "bzip2 {{-h|--help}}"
            }
        ]
    }
}