Bzip2

File Format
Name	bzip2
Ontology	Electronic File Formats Compression bzip2
Extension(s)	.bz2
MIME Type(s)	application/x-bzip2
PRONOM	x-fmt/268
Released	1997

bzip2 is a data compression algorithm and compressed file format.

Identification

Files begin with magic number "BZ" (bytes 42 5A). Then either an "h" (0x68; Huffman coding) or "0" (0x30; deprecated original version), then the block size, in 100kb units (TODO: clarify this).

Each compressed block starts with a magic number 0x314159265359 (yes, that is the start of decimal π, but in hex.)

The end of file marker uses magic number 0x177245385090 (square root of π, in the same ... interesting ... format.)

Software

• bzip2 and libbzip2
• 7-Zip

Sample files

• https://telparia.com/fileFormatSamples/archive/bz2/sm.tar.bz2

See also

• Burrows–Wheeler transform
• bzip

Links

• Wikipedia article
• Chart of format details
• bzip.org changes hands (LWN article from August 9, 2018)
• ForensicsWiki entry (also includes more details on the headers)