I use Crashplan as my offsite backup provider, and I provide offsite backup for several family members through Crashplan. Unfortunately, it isn’t a native linux program – it uses java, so that also has to be installed as part of the process. The steps are generally from http://support.crashplan.com/doku.php/getting_started/installing_crashplan#linux:

wget http://download.code42.com/installs/linux/install/CrashPlan/CrashPlan_3.6.3_Linux.tgz
tar -vxzf CrashPlan_3.6.3_Linux.tgz
cd CrashPlan-install/
sudo ./install.sh

Then following the prompts, you choose the directories for data, and other things. Here I chose the locally mounted samba/cifs share in /mnt/smb/Crashplan. During the installation, I was advised that:

Your Linux system is currently configured to watch 8192 files in real time.
We recommend using a larger value; see the CrashPlan support site for details.

That is important so that Crashplan can backup files as they change. You can update the value permanently by putting the following value in /etc/sysctl.conf and restarting:

fs.inotify.max_user_watches=1048576

I was then able to point Crashplan to my samba/cifs locally mounted greyhole shares, it found the matches and didn’t have to upload it all again.