Automating backups with tar

Securing and Optimizing Linux: RedHat Edition -A Hands on Guide
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# 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:

1. COMPUTER

2. DIRECTORIES

3. BACKUPDIR

4. TIMEDIR

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:

       #!/bin/sh
       # 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

       PATH=/usr/local/bin:/usr/bin:/bin
       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
               NEWER=""
               $TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DM.tar $DIRECTORIES
       fi

       # Weekly full backup
       if [ $DOW = "Sun" ]; then
               NEWER=""
               NOW=`date +%d-%b`

               # Update full backup date
               echo $NOW > $TIMEDIR/$COMPUTER-full-date
               $TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DOW.tar $DIRECTORIES

       # Make incremental backup - overwrite last weeks
       else

               # Get date of last full backup
               NEWER="--newer `cat $TIMEDIR/$COMPUTER-full-date`"
               $TAR $NEWER -cf $BACKUPDIR/$COMPUTER-$DOW.tar $DIRECTORIES
       fi

   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

   > : 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

> : 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.

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