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Comments and suggestions concerning this book should be mailed to gmourani@videotron.ca © Copyright 1999-2000 Gerhard Mourani and Open Network Architecture ® 452 Notice how a filename, which contains the current date, is derived, simply by enclosing the “date” command between two back-quote characters. A common naming convention is to add a “tar” suffix for non-compressed archives, and a “tar.gz” suffix for compressed ones. Since we aren't able to specify a filename for the backup set, the "--label" option can be used to write some information about the backup set into the archive file itself. Finally, only the files contained in the "/home" are written to the tape. Because the tape drive is a character device, it is not possible to specify an actual file name. Therefore, the file name used as an argument to tar is simply the name of the device "/dev/st0", the first tape device. The "/dev/st0" device does not rewind after the backup set is written; therefore it is possible to write multiple sets on one tape. You may also refer to the device as “/dev/st0”, in which case the tape is automatically rewound after the backup set is written. When working with tapes, you can use the following commands to rewind, and eject your tape: [root@deep /]# mt -f /dev/st0 rewind [root@deep /]# mt -f /dev/st0 offline Caution: To reduce the space needed on a tar archive, the backups can be compressed with the “z” option of tar program. Unfortunately, using this option to compress backups can cause trouble. Due to the nature of how compression works, if a single bit in the compressed backup is wrong, all the rest of the compressed data will be lost. It’s recommended to NOT using compression (the “z” option) to make backups with the tar command. · If your backup doesn't fit on one tape, you’ll need to use the  --multi-volume (-M) option: [root@deep /]# cd / [root@deep /]# tar cMpf /dev/st0 /home Prepare volume #2 for /dev/st0 and hit return: · After you have made a backup, you should check that it is OK, using the --compare (-d) option as show bellow: [root@deep /]# cd / [root@deep /]# tar dvf /dev/st0 · To perform a backup of your entire system, use the following command: [root@deep /]# cd / [root@deep /]# tar cpf /archive/full-backup-`date '+%d-%B-%Y'`.tar \ --directory / --exclude=proc --exclude=mnt --exclude=archive \ --exclude=cache --exclude=*/lost+found . The ”--directory” option tells tar to first switch to the following directory path (the “/” directory in this example) prior to starting the backup. The “--exclude” options tell tar not to bother backing up the specified directories or files. Finally, the “.” character at the end of the command tells tar that it should back up everything in the current directory. Caution: When backing up your file systems, do not include the "/proc" pseudo-file-system! The files in "/proc" are not actually files but are simply file-like links which describe and point to kernel data structures, also do not include the “/mnt”, “/archive”, and all “lost+found” directories. Automating tasks of backups made with tar It is always interesting to automate the tasks of a backup. Automation offers enormous opportunities for using your Linux server to achieve the goals you set. The following example bellow is our backup script - named “backup.cron”. This script is designed to run on any computer by changing only the four variables: COMPUTER, DIRECTORIES, BACKUPDIR, and TIMEDIR.