Linux Compression, Backup, and Software Installation: A Comprehensive Guide, Slides of Advanced Operating Systems

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Chapter 12

Compression, System Backup, and

Software Installation

Objectives

• Outline the features of common compression utilities
• Compress and decompress files using common compression utilities
• Perform system backups using the tar, cpio, and dump commands
• View and extract archives using the tar, cpio, and restore commands

Compression

• Compression: Process in which files are reduced in size by a compression algorithm
• Compression algorithm: Set of instructions used to systematically reduce a file’s contents
• Compression ratio: Amount of compression occurring during compression
• Three most common compression utilities:
  • Compress
  • gzip
  • bzip

The compress Utility

• compress command: Used to compress files using Lempel-Ziv compression algorithm
• zcat command: Used to view contents of an archive created with compress or gzip to Standard Output
• uncompress command: Used to decompress files compressed by compress command

The gzip Utility

• GNU zip (gzip): Used to compress files using Lempel-Ziv compression algorithm - Varies slightly from algorithm used by compress - Typically yields better compression than compress - Uses .gz filename extension by default - Can control level of compression
• gunzip command: Used to decompress .gz files

The gzip Utility (continued)

Table 12-2: Common options used with the gzip utility

The gzip Utility (continued)

Table 12-2 (continued): Common options used with the gzip utility

The bzip2 Utility

• bzip2 command: Used to compress files using Burrows-Wheeler Block Sorting Huffman Coding compression algorithm - Cannot compress directory full of files - Cannot use zcat and zmore to view files - Must use bzcat command - Compression ratio is 50% to 75% on average
• bunzip2 command: Used to decompress files compressed via bzip

The bzip2 Utility (continued)

Table 12-3 (continued): Common options used with the bzip2 utility

System Backup

• System backup: Process whereby files are copied to an archive
• Archive: Location (file or device) that contains copy of files - Typically created by a backup utility
• Should backup user files from home directories and any important system configuration files - Possibly files used by system services, as well
• Several backup utilities available
  • tar, cpio, dump/restore, burning software

The tar Utility

• Tape archive (tar) utility: One of oldest and most common backup utilities - Can create archive in a file on a filesystem or directly on a device - Accepts options to determine location of archive and action to perform on archive

The tar Utility (continued)

Table 12-5: Common options used with the tar utility

The tar Utility (continued)

• tar utility does not compress files inside archive
  • Time needed to transfer archive across a network is high
  • Can compress archive
• Backing up files to compressed archive on a filesystem is useful when transferring data across a network - Ill suited to backing up large amounts of data for system recovery

The cpio Utility

• Copy in/out (cpio): Common backup utility
  • Includes options similar to tar utility
  • Has added features
    • Ability to back up device files
    • Long filenames
  • Uses absolute pathnames by default when archiving