Thursday, February 11, 2010

Backup script for Linux using tar and find

Category: — SkyHi @ Thursday, February 11, 2010

Backup script for Linux using tar and find

Every Linux distribution provides a range of utilities that you can use to make backups of your files. Here is the how I get the job done with crontab and a shell script using tar and find

Goal

I wanted to secure all the data-files on my system on a regular basis. Regular for me implies on an automated basis. I've tried doing a manual backup every week or so but that caused too much hassle, so effectively I stopped making backups....
Further, I wanted to have an up-to-date backup of the most essential configuration settings on my system. This would help me in case I accidentally lost some datafiles or setting on my system. In case of losing everything I would need to reinstall my Linux distribution (plus extra installed software) and restore data files and settings. I decided that a full backup of the whole system wouldn't be worth the effort (and resources!).

Choice of hardware

Say "backup" and most Unix people think "tapedrive". However, nowadays harddrives come that cheap that I chose to add an extra harddrive to my AMD 400 machine. This cheap option has the advantage that a harddrive can be mounted automatically, no need for manually inserting tapes. A disadvantage is that the backup resides in the same physical unit as the very data it is supposed to secure. However, since I do have a CD-writer om my local network I still have the option to copy a backup to a CD once in a while.
My main HD is 6Mb. The backup HD has 10Mb.

Script

After adding the drive to my machine I wrote a little shell script (for bash) that basically does the following:
  • it mounts my backupdrive
  • it checks the date
  • every sunday it makes a full backup of some datafiles and some configuration settings, older incremental backups are removed. other days it backups files that have been accessed the last day
  • it dumps all the contents of a mysql database to the backup drive and zips the file
  • it unmounts the backup drive
This script (I've stored it in /root/scripts) is called every night at 3:01 AM by cron. The crontab file looks like: 
1 3 * * * /root/scripts/daily_backup
Add this line using contab -e when root.

Code

Here's the actual code: 
#!/bin/bash
#
# creates backups of essential files
#
DATA="/home /root /usr/local/httpd"
CONFIG="/etc /var/lib /var/named"
LIST="/tmp/backlist_$$.txt"
#
mount /mnt/backup
set $(date)
#
if test "$1" = "Sun" ; then
        # weekly a full backup of all data and config. settings:
        #
        tar cfz "/mnt/backup/data/data_full_$6-$2-$3.tgz" $DATA
        rm -f /mnt/backup/data/data_diff*
        #
        tar cfz "/mnt/backup/config/config_full_$6-$2-$3.tgz" $CONFIG
        rm -f /mnt/backup/config/config_diff*
else
        # incremental backup:
        #
        find $DATA -depth -type f \( -ctime -1 -o -mtime -1 \) -print > $LIST
        tar cfzT "/mnt/backup/data/data_diff_$6-$2-$3.tgz" "$LIST"
        rm -f "$LIST"
        #
        find $CONFIG -depth -type f  \( -ctime -1 -o -mtime -1 \) -print > $LIST
        tar cfzT "/mnt/backup/config/config_diff_$6-$2-$3.tgz" "$LIST"
        rm -f "$LIST"
fi
#
# create sql dump of databases:
mysqldump -u root --password=mypass --opt mydb > "/mnt/backup/database/mydb_$6-$2-$3.sql"
gzip "/mnt/backup/database/mydb_$6-$2-$3.sql"
#
umount /mnt/backup

Discussion

data files:
All my data files are in /root, /home or /usr/local/httpd.

settings:
I chose to backup all the setting in /etc (where most essential settings are stored), /var/named (nameserver settings) and /var/lib (not sure about the importance of this one...). I might need to add more to the list but I still far from being a Unix-guru ;-). All suggestions are welcome!

tar versus cpio
The first version of this script used cpio to create backups iso tar. However, I found the cpio format not very handy for restoring single files so I chang ed it to tar. A disadvantage of using tar is that you can't (as far as I know) simply pipe the output of a find to it.
Using a construct like tar cvfz archive.tgz `find /home -ctime -1 -depth -print` caused errors for files that contained a space " " character. This problem was solved by wring the output of find to a file first (and using tar with the -T option).

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