RHCSA - Understand and Use Essential Tools: Compression & Decompression Using bzip2

bzip2 Overview

bzip2 is a file compression and decompression tool used in Linux systems. The bzip2 command reduces the size of the named files using Burrows-Wheeler block sorting text compression algorithm and Huffman coding. bzip2 replaces the original file with a compressed version that has a .bz2 extension. Compressed files can be significantly smaller in size, saving storage space and reducing file transfer times.

Create a Practice File

To create a file for practicing bzip2 with, run:

Creating files with data using output from the dmesg & journalctl commands:

dmesg       > bzip2-test-default.txt
journalctl >> bzip2-test-default.txt
ls -lR /   >> bzip2-test-default.txt 2> /dev/null

cp bzip2-test-default.txt bzip2-test-fast.txt
cp bzip2-test-default.txt bzip2-test-best.txt

Note down the original size of the bzip2-test-default.txt file as this will be used to compare file sizes post compression in later exercises.

ls -lh bzip2-test-default.txt

24M in my case.

-rw-r--r--. 1 user1 user1 24M Jun 27 07:44 bzip2-test-default.txt

Compression Using bzip2

When using bzip2, you can use different flags to regulate the speed of compression (-1 to -9). Where -1 indicates the fastest compression method (less compression) and -9 indicates the slowest compression method (best compression). The default compression level is -9 (which is biased towards high compression at the expense of speed).

Using the -v flag will show the compression percentage as well as the new file name.

Using bzip2 with default compression:

bzip2 -v bzip2-test-default.txt

Using bzip2 with fastest compression:

bzip2 -v -1 bzip2-test-fast.txt

Using bzip2 with the best compression:

bzip2 -v -9 bzip2-test-best.txt

Comparing compressed file sizes:

ls -lh bzip2-test-*.txt.bz2

In my case, we can see that -9 has been confirmed as the being the default option with file sizes matching, both of which have a significant improvement over the -1 option.

-rw-r--r--. 1 user1 user1 1.4M Jun 27 07:44 bzip2-test-best.txt.bz2
-rw-r--r--. 1 user1 user1 1.4M Jun 27 07:44 bzip2-test-default.txt.bz2
-rw-r--r--. 1 user1 user1 1.8M Jun 27 07:44 bzip2-test-fast.txt.bz2

Decompression Using bzip2/bunzip2

There are two ways to decompress files that were compressed using bzip2. You can either use bzip2 itself with the -d or --decompress option, or you can use the bunzip2 command.

Using the -v flag will show the compression percentage.

Using bzip2 -d to decompress a file:

bzip2 -v -d bzip2-test-default.txt.bz2

Using bzip2 --decompress to decompress a file:

bzip2 -v --decompress bzip2-test-best.txt.bz2

Using bunzip2 to decompress a file:

bunzip2 -v bzip2-test-fast.txt.bz2

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