Automating Backups with cron

Automating Backups with cron

You can automate most of your backups with shell scripts and the cron daemon. Use the su command to become root, and then cd to the /usr/local/bin directory. Use any text editor to create a shell script called that looks similar to the following:

# - A simple backup script, by Thad Phetteplace
# This script takes one parameter, the dump level.
# If the dump level is not provided, it is
# automatically set to zero. For level zero (full)
# dumps, rewind and eject the tape when done.
if [ $1 ]; then
        # No dump level was provided, so set it
        # to zero
/sbin/dump $level'uf' /dev/nrft0 /
/sbin/dump $level'uf' /dev/nrft0 /home
/sbin/dump $level'uf' /dev/nrft0 /var
/sbin/dump $level'uf' /dev/nrft0 /usr
# If we are doing a full dump, rewind and eject
# the tape when done.
if [ $level = "0" ]; then
        # Note: We should replace this with the /bin/st command
        # instead if we ever switch to a SCSI tape drive.
        /bin/mt -f /dev/nrft0 rewind
        /bin/mt -f /dev/nrft0 offline

You may choose to change the partitions being backed up to match your situation, but this script should otherwise work quite well for you. After saving and exiting the editor, change the permissions on the file so that it is executable only by root:

# chmod 700

You can now back up your entire system by running the script when logged in as root. The script accepts the dump level as its only parameter. If you leave the parameter off, it will automatically assume a level zero dump. Thus, the following two commands are equivalent:

# 0

You may need to customize this script for your situation. For example, I am using the tape device /dev/nrft0. You may be using a different tape device. Whatever device you use, you should probably use the version of its device name that begins with a the letter n. That tells the system that after it finishes copying data to the tape, it should not rewind the tape. As an example, I used /dev/nrft0 instead of /dev/rst0 in the preceding script. If I had used /dev/rst0, each successive incremental backup would have overwritten the previous one.

Other things that you may change in this script include the partitions being backed up and the dump level at which the tape is ejected. It is not uncommon to eject the tape after the last incremental backup just before performing a full backup.

The most useful thing about this script is that you can easily configure your system to run it automatically. Simply add a few lines to the root crontab file, and the cron daemon will invoke the script on the days and times specified. While logged in as root, enter the crontab command with the -e option:

# crontab -e

This opens the root crontab file in an editor. Add the following lines at the end of the file:

0 22 * * 0 /usr/local/bin/ 0
0 22 * * 1 /usr/local/bin/ 9
0 22 * * 2 /usr/local/bin/ 8
0 22 * * 3 /usr/local/bin/ 7
0 22 * * 4 /usr/local/bin/ 6
0 22 * * 4 /usr/local/bin/ 5
0 22 * * 5 /usr/local/bin/ 4

Save and exit the file. The cron daemon will now run the backup script at 10:00 p.m. (22:00 in military time) every day of the week. This example implements the dump schedule outlined earlier. A full dump is performed on Sunday, and the tape is ejected when it is done. A new tape should be loaded on Monday, and then incremental backups will be written to that same tape for the rest of the week. The next full dump will be written to the end of that tape, unless someone is around on Sunday to eject and replace the tape before 10:00 p.m.

Part IV: Red Hat Linux Network and Server Setup