This little article describe how to setup an automatic backup procedure to a remote machine via the rsync tool.

Prerequisites

• A distant server, where backup will be stored (homeserver.com in this case),
• A user account on this server (mine was kevin),
• A ssh deamon running on the server that allow the user to log in.

Setup rsync

First, install rsync on the client and on the server using:

urpmi rsync

Synchronization

Then, to synchronise from the local machine to the distant server, just do:

rsync -avz -e ssh /home/client_user/Documents kevin@homeserver.com:/mnt/raid2/

• /home/client_user/Documents is the local folder we want to save (located in the home folder of the client user client_user),
• homeserver.com is the distant server name (could be en IP address),
• kevin is the distant user,
• /mnt/raid2/ is the distant folder where we want to save the local one.

Croned synchronization

First, create a pair of cryptographic keys (public, private):

ssh-keygen -t rsa

Then, from the local machine as user client_user, register you on the distant server:

ssh-copy-id -i ~/.ssh/id_rsa.pub kevin@homeserver.com

In case your distant machine’s SSH server is running on another port than 22 (which is the default port), let’s said 222, here is the command that emulate ssh-copy-id (as the later doesn’t have a port parameter):

cat ~/.ssh/id_rsa.pub | ssh -p 222 kevin@homeserver.com "cat >> ~/.ssh/authorized_keys"

Create a script named rsync_data_backup.sh that contain the command you’ve used previously to synchronize your data:

rsync -avz -e ssh /home/client_user/Documents kevin@homeserver.com:/mnt/raid2/

To run this script with a cron entry, the (unsecure) solution found is to create a key without a passphrase. The cron entry could be something like:

15 13 * * 1-5 client_user /home/client_user/rsync_data_backup.sh > /home/client_user/rsync_data_backup.log

This crontab entry will automaticcaly synchronise our data each first-5 days of the week, at 13:15.