Archive rotation shell script

Server Guide
1

The simple backup shell script only allows for seven different archives. For a server whose data doesn’t change often, this may be enough. If the server has a large amount of data, a more complex rotation scheme should be used.

Rotating NFS archives

Here, the shell script is slightly modified to implement a grandparent-parent-child rotation scheme (monthly-weekly-daily):

  • The rotation will do a daily backup from Sunday to Friday.

  • On Saturday, a weekly backup is done – giving four weekly backups per month.

  • The monthly backup is done on the first day of the month, rotating two monthly backups based on whether the month is odd or even.

Here is the new script:

#!/bin/bash
####################################
#
# Backup to NFS mount script with
# grandparent-parent-child rotation.
#
####################################
    
# What to backup. 
backup_files="/home /var/spool/mail /etc /root /boot /opt"
    
# Where to backup to.
dest="/mnt/backup"
    
# Setup variables for the archive filename.
day=$(date +%A)
hostname=$(hostname -s)
    
# Find which week of the month 1-4 it is.
day_num=$(date +%-d)
if (( $day_num <= 7 )); then
        week_file="$hostname-week1.tgz"
elif (( $day_num > 7 && $day_num <= 14 )); then
        week_file="$hostname-week2.tgz"
elif (( $day_num > 14 && $day_num <= 21 )); then
        week_file="$hostname-week3.tgz"
elif (( $day_num > 21 && $day_num < 32 )); then
        week_file="$hostname-week4.tgz"
fi
    
# Find if the Month is odd or even.
month_num=$(date +%m)
month=$(expr $month_num % 2)
if [ $month -eq 0 ]; then
        month_file="$hostname-month2.tgz"
else
        month_file="$hostname-month1.tgz"
fi
    
# Create archive filename.
if [ $day_num == 1 ]; then
        archive_file=$month_file
elif [ $day != "Saturday" ]; then
        archive_file="$hostname-$day.tgz"
else 
        archive_file=$week_file
fi
    
# Print start status message.
echo "Backing up $backup_files to $dest/$archive_file"
date
echo
    
# Backup the files using tar.
tar czf $dest/$archive_file $backup_files
    
# Print end status message.
echo
echo "Backup finished"
date
    
# Long listing of files in $dest to check file sizes.
ls -lh $dest/

The script can be executed using the same methods as in our guide on how to back up using shell scripts.

As discussed in the introduction, a copy of the backup archives and/or media can then be transferred off-site.

Backing up to tape drives

A tape drive attached to the server can be used instead of an NFS share. Using a tape drive simplifies archive rotation, and makes taking the media off-site easier as well.

When using a tape drive, the filename portions of the script aren’t needed because the data is sent directly to the tape device. Some commands to manipulate the tape are needed, however. This is accomplished using mt, a magnetic tape control utility – part of the cpio package.

Here is the shell script modified to use a tape drive:

#!/bin/bash
####################################
#
# Backup to tape drive script.
#
####################################
    
# What to backup. 
backup_files="/home /var/spool/mail /etc /root /boot /opt"
    
# Where to backup to.
dest="/dev/st0"
    
# Print start status message.
echo "Backing up $backup_files to $dest"
date
echo
    
# Make sure the tape is rewound.
mt -f $dest rewind
    
# Backup the files using tar.
tar czf $dest $backup_files
    
# Rewind and eject the tape.
mt -f $dest rewoffl
    
# Print end status message.
echo
echo "Backup finished"
date

Note:
The default device name for a SCSI tape drive is /dev/st0. Use the appropriate device path for your system.

Restoring from a tape drive is basically the same as restoring from a file. Simply rewind the tape and use the device path instead of a file path. For example, to restore the /etc/hosts file to /tmp/etc/hosts:

mt -f /dev/st0 rewind
tar -xzf /dev/st0 -C /tmp etc/hosts
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