Thursday, February 11, 2010

Automating backups with tar

SkyHi @ Thursday, February 11, 2010

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 
    # and modified by Gerhard Mourani 
    
    #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
    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.