Automated rsync backups from a webserver to Qnap NAS

How to make a daily copy of backup files from a webserver on Debian to a local NAS using rsync over SSH.

On my webserver I make a dump of most databases every day, using a command like this:

mysqldump dbName --opt --user=dbUsername --password=dbPassword | gzip > "/home/backups/dbName/dbName_`date +%d`.sql.gz"

This creates nicely gzipped files, one for each day of the month. The command is in a shell script which is executed by a cron task. As an extra backup, I wanted to have a copy of these files on a different server: my Qnap NAS. The NAS runs a version of Linux, so all required tools are present: rsync, SSH and cron. rsync will compare the local and remote directories and synchronize them as needed. It’s a smart tool: it only copies new or modified files, saving time and bandwidth.

Set up the rsync script

Log in to the NAS as the admin user, preferably over SSH with a tool like Putty.

On the NAS, I created a shell script backup.sh containing these lines:

#!/bin/sh
rsync -ae ssh tom@www.example.com:/home/backups/ /share/toms/serverbackups/

-a puts rsync into archive mode, which makes the operation recursive and keeps timestamps, amongst others.

-e ssh makes rsync run through an SSH tunnel, making the operation pretty secure.

The command will sync /home/backups/ on www.example.com with /share/toms/serverbackups on the NAS. toms is a shared folder on the NAS; serverbackups is where I want to store the backups. tom is the user on the webserver who created and owns the database backups.

You’ll need to write the script using the lovely vi, which is the only text editor available on Qnap NAS. Or just create the script on your PC and copy it to the NAS. (Update 4-4-2016: don’t do that. It may append unwanted characters to the command, such as \#015. Use vi on the NAS.)

Store backup.sh somewhere in a shared folder but definitely not in the root folder, as that one is recreated at every server reboot. I stored it in /share/toms/scripts/ and made it executable to admin only with

chmod u+x /share/toms/scripts/backup.sh

Check that the rsync command works by running it from the NAS command line. It should prompt for tom‘s server password, and then start copying files.

If that works, the next step is to enable login without you entering the password all the time: authorize with keys.

SSH keys

On the NAS, run the ssh-keygen command to generate a set of keys. It will prompt for a passphrase: don’t enter anything, just hit enter.

Copy the contents of ~/.ssh/id_rsa.pub (the public key) on the NAS to /home/tom/.ssh/authorized_keys on the webserver. Create the directory and file if they don’t yet exist and set tom as the owner. chmod the directory to 0700 and the file to 0600, so only the user tom can read them.

Next, test the password-free login:

ssh -l tom www.example.com

If that works, the next step is to automate the task.

Setting up the cron task on the Qnap NAS

Run this to add a command to the crontab’s config file:

echo "45 15 * * * /share/toms/scripts/backup.sh" >> /etc/config/crontab

The command will run the script every day at 15:45.

Finally, reload the running cron daemon with the altered config file:

crontab /etc/config/crontab

This way our added command will persist over NAS reboots, contrary to using crontab -e.