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