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5.3 Levels of Backups

An archive containing all the files in the file system is called a full backup or full dump. You could insure your data by creating a full dump every day. This strategy, however, would waste a substantial amount of archive media and user time, as unchanged files are daily re-archived.

It is more efficient to do a full dump only occasionally. To back up files between full dumps, you can use incremental dumps. A level one dump archives all the files that have changed since the last full dump.

A typical dump strategy would be to perform a full dump once a week, and a level one dump once a day. This means some versions of files will in fact be archived more than once, but this dump strategy makes it possible to restore a file system to within one day of accuracy by only extracting two archives—the last weekly (full) dump and the last daily (level one) dump. The only information lost would be in files changed or created since the last daily backup. (Doing dumps more than once a day is usually not worth the trouble.)

GNU tar comes with scripts you can use to do full and level-one (actually, even level-two and so on) dumps. Using scripts (shell programs) to perform backups and restoration is a convenient and reliable alternative to typing out file name lists and tar commands by hand.

Before you use these scripts, you need to edit the file ‘backup-specs’, which specifies parameters used by the backup scripts and by the restore script. This file is usually located in ‘/etc/backup’ directory. See section Setting Parameters for Backups and Restoration, for its detailed description. Once the backup parameters are set, you can perform backups or restoration by running the appropriate script.

The name of the backup script is backup. The name of the restore script is restore. The following sections describe their use in detail.

Please Note: The backup and restoration scripts are designed to be used together. While it is possible to restore files by hand from an archive which was created using a backup script, and to create an archive by hand which could then be extracted using the restore script, it is easier to use the scripts. See section Using tar to Perform Incremental Dumps, before making such an attempt.

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