.bz2 File Extension

What kind of file is a .bz2?

A .bz2 file contains one stream of data compressed with Bzip2. Compression is lossless, so decompression reproduces the original bytes. Unlike ZIP, Bzip2 does not bundle a directory tree or multiple named members. A filename such as logs.tar.bz2 normally means that a TAR archive was created first and then compressed with Bzip2.

The usual MIME label is application/x-bzip2. It is a widespread convention, but it is not registered in IANA's application media-type registry.¹ A real Bzip2 stream begins with ASCII BZh, hexadecimal 42 5A 68, followed by a digit from 1 through 9. That digit records a block size from 100,000 to 900,000 bytes.²

How do I open a .bz2 on my computer?

• On Windows, open or extract it with 7-Zip or PeaZip.
• On macOS and Linux, use bunzip2, bzip2 -d, or an archive utility that supports Bzip2.
• For package.tar.bz2, GNU tar can decompress the outer stream and extract the tar members in one operation.³

To keep the compressed source while writing the decompressed result, run bzip2 -dk report.txt.bz2. Use bzip2 -tv report.txt.bz2 to test integrity without saving decompressed output. For a tarball, list its members first with tar -tjf package.tar.bz2, then extract into a new directory only after reviewing the paths.

Poly support for .bz2

Poly recognizes .bz2 as Bzip2 data. It stores, syncs, shares, versions, and downloads the file, and you can find it by filename and ordinary file properties.

Poly does not decompress the stream, generate a content preview, index the decompressed data or tar members, or give the Poly agent access to content inside it. Download and decompress the file with a trusted local tool. Add the resulting files to Poly separately to receive the preview, search, and agent capabilities available for their formats.

History of .bz2

Julian Seward created Bzip2 as a successor to his earlier, incompatible bzip compressor. Bzip2 0.15 appeared in July 1996, and the stable 1.0 line followed in 2000.⁴ The command-line interface deliberately resembles gzip, while the format uses the Burrows-Wheeler block-sorting transform and Huffman coding.²

The 2 distinguishes Bzip2 and .bz2 from the older bzip format and .bz suffix. Modern Bzip2 versions retain compatibility with the original public Bzip2 data format.²

Working with .bz2 and alternatives

Choose compression based on the job:

Bzip2 always adds some overhead. Its manual notes that files smaller than about 100 bytes tend to grow, while already compressed or random data can expand by roughly 0.5%.² Test representative files instead of assuming one format will always be smallest.

A CRC can reveal accidental corruption, but it does not authenticate the sender or make decompressed content safe. Untrusted data may expand dramatically, and a tarball may contain absolute paths, parent-directory references, links, or executables. Set resource limits, inspect tar member names, and keep important originals. Converting requires decompression and recompression; changing the suffix changes no bytes.