Do you have access to a shell account on a unix server with some spare space? If so it's pretty easy to incrementally backup your files securely with SSH.

I titled this entry Howto Backup your Mac incrementally over SSH but this technique can also be used to backup any computer that can run rsync and ssh. They are already installed on Mac OS X, and most linux / unix servers.

Step 1 - Create a folder to store your backups on the remote server

mkdir backup

Make sure that your SSH user has permission to write to this directory.

Step 2 - Setup automatic authentication Optional

This step allows the backups to run without prompting you for a password when it runs. You can omit this step but you will have to type in your ssh password each you run backup.

I wrote an article called Setting up public key authentication over SSH that will guide you through this step.

If you own the server you might also want to create a user specifically for this process.

Step 3 - Use rsync to backup files incrementally

rsync -e "ssh" -rca --delete-after ~/test/ pete@myserver.example.com:backup

Now lets break it down a bit:

• rsync - this syncs the local directory to with the server directory.
• -e "ssh" - this tells rsync to use ssh if your want to pass in other ssh options such as port you can do that in the quotes: -e "ssh -p 12345"
• -rca recursive, checksum, and archive
• --delete-after - this will delete files on the server if you delete them locally.
• ~/test/ - I am backing up / syncing the test directory inside my home directory on my mac.
• pete@myserver.example.com:backup - my ssh username is pete, my remote ssh server hostname is myserver.example.com, and I am backing up into the directory ~pete/backup.

Excluding directories

Sometimes you might want to exclude a directory from being backed up, perhaps your Music directory since that is already backed up on your ipod.

rsync -e "ssh" -rca --delete-after --exclude=Music --delete-excluded ~/test/ pete@myserver.example.com:backup

Step 4 - Schedule it with cron Optional

Now lets create a cron job (scheduled task) to run this script every day. First make a new file called backup.sh in your home directory.

#!/bin/sh
rsync -e "ssh" -rca --delete-after ~/test/ pete@myserver.example.com:backup

Now sure make the file is executable: chmod ug+x backup.sh

Next type crontab -e this will open up your scheduled tasks list, in most cases it will open an empty file. Add the following to the file:

15 11 * * * yourusername ~yourusername/backup.sh

That's will schedule the script to run at 11:15am. If you don't want to do this step you can simply run the command whenever you want to run a backup.

DISCLAIMER You should test everything before performing the backups on your live data. If you would like to use the scripts above you must acknowledge that I'm not responsible for any loss of data.

I'd love to hear your feedback on this, please comment below. I'm use this technique to backup my two web servers on to each other.