bzip2 - Unix, Linux Command


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bzip2 - a block-sorting file compressor.



bzip2 is used to compress a file in order to reduce disk space, it is quite popular in Linux and UNIX operating systems for this reason.

bzip2 expects a list of file names to accompany the command-line flags. Each file is replaced by a compressed version of itself, with the name "original_name.bz2". Each compressed file has the same modification date, permissions, and, when possible, ownership as the corresponding original, so that these properties can be correctly restored at decompression time. File name handling is naive in the sense that there is no mechanism for preserving original file names, permissions, ownerships or dates in filesystems which lack these concepts, or have serious file name length restrictions, such as MS-DOS.

bzip2 and bunzip2 will by default not overwrite existing files. If you want this to happen, specify the -f flag.

If no file names are specified, bzip2 compresses from standard input to standard output. In this case, bzip2 will decline to write compressed output to a terminal.


Tag Description
-c --stdout Compress or decompress to standard output.
--d --decompress 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..
-z --compress The complement to -d: forces compression, regardless of the invocation name.
-t --test Check integrity of the specified files, but don't decompress them. This really performs a trial decompression and throws away the result.
-f --force 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.
-k --keep Keep don't delete input files during compression or decompression.
-s --small Reduce memory usage, for compression, decompression and testing. Files are decompressed and tested using a modified algorithm which only requires 2.5 bytes per block byte. This means any file can be decompressed in 2300k of memory, albeit at about half the normal speed.

During compression, -s selects a block size of 200k, 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.

-q --quiet Suppress non-essential warning messages. Messages pertaining to I/O errors and other critical events will not be suppressed.
-v --verbose Verbose mode -- show the compression ratio for each file processed. Further -v's increase the verbosity level, spewing out lots of information which is primarily of interest for diagnostic purposes..
-L --license -V --version Display the software version, license terms and conditions.
-h --help print a help message and exit
-1 (or --fast) to -9 (or --best) Set the block size to 100 k, 200 k .. 900 k when compressing. Has no effect when decompressing. The --fast and --best aliases are primarily for GNU gzip compatibility. In particular, --fast doesn't make things significantly faster. And --best merely selects the default behavior.
-- 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.
--repetitive-fast --repetitive-best These flags are redundant in versions 0.9.5 and above. They provided some coarse control over the behavior of the sorting algorithm in earlier versions, which was sometimes useful. 0.9.5 and above have an improved algorithm which renders these flags irrelevant.



 To compress a single file.

$ bzip2 system_1


(No output will be shown unless any error occoured)
ls -lrt
-rw-rw-r--  1 nubo nubo   53 Jan  7 18:20 system_1.bz2 This will compress system_1 and create system_1.bz2, note that this will remove the original system_1 file.


 To compress multiple files at once

$ bzip2  system_1 system_2

 This will compress all files specified in the command.


(No output will be shown unless any error occoured)
ls -lrt
-rw-rw-r-- 1 nubo nubo 53 Jan 7 18:20 system_1.bz2
-rw-rw-r-- 1 nubo nubo 53 Jan 7 18:20 system_2.bz2


 To compress a single file and keep the original.

 $ bzip2 -c system_1 >
 The -c flag outputs the compressed copy of system_1 to stdout, this is then sent to system_1.bz2, 
 keeping the original system_1 file in place.
 Can also be written with -k option.
 $ bzip2 -k system_1


-rw-rw-r-- 1 nubo nubo 53 Jan 7 18:20 system_1.bz2
-rw-rw-r-- 1 nubo nubo 21 Jan 7 18:20 system_1
-rw-rw-r-- 1 nubo nubo 53 Jan 7 18:20 system_2.bz2
-rw-rw-r-- 1 nubo nubo 19 Jan 7 18:20 system_2


 To decompress a bzip2 compressed file

 $ bzip2 -d system_1.bz2

 $ bunzip2 system_1.bz2
 Both of these commands will produce the same result, decompressing system_1.bz2 to system_1, 
 removing the compressed system_1.bz2 file.


 List compression information:

  $ bzip2 -v linux-3.18.19.tar
  linux-3.18.19.tar:  6.015:1,  1.330 bits/byte, 83.37% saved, 580761600 in, 96552670 out.

$ ls -lah -rw-r--r--. 1 root root 554M Jul 22 10:38 linux-3.18.19.tar -rw-r--r--. 1 root root 93M Jul 22 10:38 linux-3.18.19.tar.bz2


 Integrity test

 The -t or --test flag can be used to check the integrity of a compressed file.  
  $ bzip2 -tv system_1.bz2


system_1.bz2: ok


 Concatenate multiple files

 Multiple files can be concatenated into a single .bz2 file.

$ bzip2 -c system_1 > system.bz2
$ bzip2 -c system_2 >> system.bz2

To check output :

$ bzcat system.bz2
line 1
line 2
line 3
line 3
The system.bz2 now contains the contents of both system_1 and system_2, if you decompress system.bz2 you will get a file named ‘system’ which contains the content of both files.

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