It is highly recommended you keep regular backups of any important files. Backups often shouldn't be limited to user files; they could include configuration files, databases, installed software, settings, and even an entire snapshot of a system.
Here we'll guide you through some backup techniques for your Raspberry Pi system.
A sensible way to keep your home folder backed up is to use the tar command to make a snapshot archive of the folder, and keep a copy of it on your home PC or in cloud storage. To do this enter the following commands:
cd /home/
tar czf pi_home.tar.gz pi
This creates a tar archive called pi_home.tar.gz in /home/. You should copy this file to a USB stick or transfer it to another machine on your network.
If you have MySQL databases running on your Raspberry Pi, it would be wise to keep them backed up too. To back up a single database, use the mysqldump command:
mysqldump recipes > recipes.sql
This command will back up the recipes database to the file recipes.sql. Note that in this case no username and password have been supplied to the mysqldump command. If you do not have your MySQL credentials in a .my.cnf configuration file in your home folder, then supply the username and password with flags:
mysqldump -uroot -ppass recipes > recipes.sql
To restore a MySQL database from a dumpfile, pipe the dumpfile into the mysql command; provide credentials if necessary and the database name. Note that the database must exist, so create it first:
mysql -Bse "create database recipes"
cat recipes.sql | mysql recipes
Alternatively, you can use the pv command (not installed by default, so install with apt-get install pv) to see a progress meter as the dumpfile is processed by MySQL. This is useful for large files:
pv recipes | mysql recipes
It may be sensible for you to keep a copy of the entire SD card image, so you can restore the whole SD card if you lose it or it becomes corrupt. You can do this using the same method you'd use to write an image to a new card, but in reverse.
In Linux or Mac, for example:
sudo dd bs=4M if=/dev/sdb of=raspbian.img
This will create an image file on your PC which you can use to write to another SD card, and keep exactly the same contents and settings. To restore or clone to another card, use dd in reverse:
sudo dd bs=4M if=raspbian.img of=/dev/sdb
See more about installing SD card images.
You could write a Bash script to perform each of these processes automatically, and even have it performed periodically using cron.