(archive-rotation-shell-script)=
# Archive rotation shell script

The {ref}`simple backup shell script <basic-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:

```sh
#!/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 {ref}`how to back up using shell scripts <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:

```sh
#!/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`:

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