33.3. Automating backups 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 below is our backup script, called backup.cron. This script is designed to run on any computer by changing only the four variables:





We suggest that you set this script up and run it at the beginning of the month for the first time, and then run it for a month before making major changes. In our example below we do the backup to a directory on the local server BACKUPDIR, but you could modify this script to do it to a tape on the local server or via an NFS mounted file system.

  1. Create the backup script backup.cron file, touch /etc/cron.daily/backup.cron and add the following lines to this backup file:
    # full and incremental backup script
    # created 07 February 2000
    # Based on a script by Daniel O'Callaghan <danny@freebsd.org>
    # and modified by Gerhard Mourani <gmourani@videotron.ca>
    #Change the 5 variables below to fit your computer/backup
    COMPUTER=deep                           	# name of this computer
    DIRECTORIES="/home"                     	# directoris to backup
    BACKUPDIR=/backups                      	# where to store the backups
    TIMEDIR=/backups/last-full              	# where to store time of full backup
    TAR=/bin/tar                            		# name and locaction of tar
    #You should not have to change anything below here
    DOW=`date +%a`              		# Day of the week e.g. Mon
    DOM=`date +%d`              		# Date of the Month e.g. 27
    DM=`date +%d%b`             	# Date and Month e.g. 27Sep
    # On the 1st of the month a permanet full backup is made
    # Every Sunday a full backup is made - overwriting last Sundays backup
    # The rest of the time an incremental backup is made. Each incremental
    # backup overwrites last weeks incremental backup of the same name.
    # if NEWER = "", then tar backs up all files in the directories
    # otherwise it backs up files newer than the NEWER date. NEWER
    # gets it date from the file written every Sunday.
    # Monthly full backup
    if [ $DOM = "01" ]; then
    # Weekly full backup
    if [ $DOW = "Sun" ]; then
            NOW=`date +%d-%b`
            # Update full backup date
            echo $NOW > $TIMEDIR/$COMPUTER-full-date
    # Make incremental backup - overwrite last weeks
            # Get date of last full backup
            NEWER="--newer `cat $TIMEDIR/$COMPUTER-full-date`"

    Example 33-1. Backup directory of a week

    Here is an abbreviated look of the backup directory after one week:
[root@deep] /# ls -l /backups/
total 22217
    -rw-r--r--   	1 root     root     	 10731288 	Feb  7 11:24 deep-01Feb.tar
    -rw-r--r--   	1 root     root            	6879 	Feb  7 11:24 deep-Fri.tar
    -rw-r--r--   	1 root     root         	2831 	Feb  7 11:24 deep-Mon.tar
    -rw-r--r--   	1 root     root            	7924 	Feb  7 11:25 deep-Sat.tar
    -rw-r--r--   	1 root     root     	 11923013 	Feb  7 11:24 deep-Sun.tar
    -rw-r--r--   	1 root     root            	5643 	Feb  7 11:25 deep-Thu.tar
    -rw-r--r--   	1 root     root            	3152 	Feb  7 11:25 deep-Tue.tar
    -rw-r--r--   	1 root     root            	4567 	Feb  7 11:25 deep-Wed.tar
    drwxr-xr-x	2 root     root         	1024 	Feb  7 11:20 last-full

    Important: The directory where to store the backups BACKUPDIR, and the directory where to store time of full backup TIMEDIR must exist or be created before the use of the backup-script, or you will receive an error message.

  2. If you are not running this backup script from the beginning of the month 01-month-year, the incremental backups will need the time of the Sunday backup to be able to work properly. If you start in the middle of the week, you will need to create the time file in the TIMEDIR. To create the time file in the TIMEDIR directory, use the following command:
[root@deep] /# date +%d%b < /backups/last-full/myserver-full-date
    Where /backups/last-full is our variable TIMEDIR wherein we want to store the time of the full backup, and myserver-full-date is the name of our server e.g. deep, and our time file consists of a single line with the present date i.e. 15-Feb.

  3. Make this script executable and change its default permissions to be writable only by the super-user root 755.
[root@deep] /# chmod 755 /etc/cron.daily/backup.cron

Note: Because this script is in the /etc/cron.daily directory, it will be automatically run as a cron job at one o'clock in the morning every day.