This document discusses compression utilities like compress, gzip, and bzip2, which reduce file sizes using different algorithms. It also covers various system backup utilities like tar, cpio, and dump/restore that are used to copy files and directories to an archive. Tar is one of the most common backup utilities and can create compressed archives, while cpio has additional features like backing up device files. The dump/restore utility is designed to backup entire filesystems incrementally or in full backups.

1. COMPRESSION, SYSTEM
BACKUP & RESTORE

2. 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
2

3. Compression
 Compression: process in which files are
reduced in size by stripping out
characters
 Compression algorithm: standard set of
instructions used to compress a file
 Compression ratio: percentage by which
the file size was decreased
 Common compression utilities include
compress, gzip, and bzip2
3

4. The compress Utility
 Use to compress files using the Adaptive
Lempel Ziv coding (LZW) compression
algorithm
 Average compression ratio of 40-50%
 compress command: used to compress files
 zcat command: used to display the contents
of an archive created with compress
 Can use zmore and zless commands to view
contents page-by-page
 uncompress command: used to decompress
files compressed by compress command
4

5. The gzip Utility
 GNU zip (gzip): used to compress files
using the Lempel-Ziv compression
algorithm (LZ77)
 Varies slightly from algorithm used by
compress
 Average compression ratio of 60-70%
 Uses .gz filename extension by default
 gunzip command: used to decompress
.gz files
5

6. 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
 Uses .bz2 filename extension by default
 bunzip2 command: used to decompress
files compressed via bzip2
6

7. 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
Linux+ Guide to Linux Certification, 3e 7

8. System Backup (continued)
Linux+ Guide to Linux Certification, 3e 8
Table 11-4: Common tape device files

9. 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
 tar command: activates tar utility
 Arguments list the files to place in the
archive
 Accepts options to determine location of
archive and action to perform on archive
Linux+ Guide to Linux Certification, 3e 9

10. The tar Utility (continued)
Linux+ Guide to Linux Certification, 3e 10
-x Extract Archive
-c Create New Archive
-r Append to Archive
-v verbose
-f Write/Read File
-t List Archive Contents
-z Compress using gzip (c mode only)

11. 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
 Use options of the tar command to compress
an archive immediately after creation
Linux+ Guide to Linux Certification, 3e 11

12. The cpio Utility
 Copy in/out (cpio): common backup
utility
 Activated by the cpio command
○ Has various options
 Includes options similar to tar utility
 Has added features
○ Ability to back up device files
○ Long filenames
 Uses absolute pathnames by default when
archiving
Linux+ Guide to Linux Certification, 3e 12

13. The dump/restore Utility
 dump/restore: Used to back up files and
directories to device or file on filesystem
 Works only with files on ext2 and ext3
filesystems
 Designed to backup entire filesystems to
an archive
 /etc/dumpdates: file used to store
information about incremental and full
backups
Linux+ Guide to Linux Certification, 3e 13

14. The dump/restore Utility
(continued)
 Full backup: archiving all data on
filesystem
 Incremental backup: backs up only data
that has changed since last backup
 Can perform up to nine different incremental
backups
 dump command: create archives for full
or incremental backup
 restore command: extract archives
created with dump
Linux+ Guide to Linux Certification, 3e 14

15. Summary
 Many compression utilities are available for
Linux systems; each uses a different
compression algorithm and produces a
different compression ratio
 Files can be backed up to an archive using
a
backup utility
 To back up files to CD-RW or DVD-RW, use
burning software instead of a backup utility
Linux+ Guide to Linux Certification, 3e 15

16. Summary (continued)
 tar is the most common backup utility
used today
 Typically used to create compressed
archives called tarballs
Linux+ Guide to Linux Certification, 3e 16