LPI Linux Essentials Exam 010-160 - Topic 3.1 - Compression with xz

xz Overview

The xz command is a Linux utility used for file compression and decompression. It employs the LZMA (Lempel-Ziv-Markov chain-Algorithm) compression algorithm to reduce the size of files. When you use the xz command to compress a file, it replaces the original file with a compressed version, typically having a .xz extension. This compression process significantly reduces the file's size, which can be advantageous for conserving storage space and accelerating file transfers.

Create a Practice File

To create a file for practicing xz with in up coming exercises, follow the below:

Exercise: Creating files for practice with the xz command:

journalctl > xz-test-default.txt

ls -lR /etc /usr/bin /usr/share/doc >> xz-test-default.txt 2> /dev/null

cp xz-test-default.txt xz-test-fast.txt

cp xz-test-default.txt xz-test-best.txt

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

ls -lh xz-test-default.txt

60M in my case.

-rw-rw-r-- 1 dtvlinux dtvlinux 60M Oct 23 08:27 xz-test-default.txt

Compression Using xz

When using xz you can use different flags to regulate the speed of compression (-#, --fast, & --best). Where -1 or --fast indicates the fastest compression method, (less compression), and -9 or --best indicates the slowest compression method, (best compression). The default compression level is -6 (which is biased towards high compression at expense of speed).

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

Exercise: Using xz with default compression:

xz -v xz-test-default.txt

Exercise: Using xz with fastest compression:

xz -v --fast xz-test-fast.txt

Exercise: Using xz with the best compression:

xz -v --best xz-test-best.txt

Exercise: Comparing compressed file sizes:

ls -lh xz-test-*.txt.xz

In my case we can see that --best had a slight improvement over the default but a significant improvement over the --fast option.

-rw-rw-r-- 1 dtvlinux dtvlinux 2.3M Oct 23 08:27 xz-test-best.txt.xz
-rw-rw-r-- 1 dtvlinux dtvlinux 2.4M Oct 23 08:27 xz-test-default.txt.xz
-rw-rw-r-- 1 dtvlinux dtvlinux 6.6M Oct 23 08:27 xz-test-fast.txt.xz

Decompression Using xz/unxz

There are two ways to decompress files that were compressed using xz. You can either use xz itself with the -d, --decompress or --uncompress options, or you can use the unxz command.

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

Exercise: Using xz -d to decompress a file:

xz -v -d xz-test-default.txt.xz

Exercise: Using xz --decompress to decompress a file:

xz -v --decompress xz-test-fast.txt.xz

Exercise: Using gunzip to decompress a file:

unxz -v xz-test-best.txt.xz

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