Compression
- 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