ANSWER:

After you have set up your SSH keys. Install RSYNC using your package manager

apt-get install rsync (Ubuntu)
yum install rsync (Centos)

You can then use RSYNC to copy (Synchronise) the files with this command

rsync -e ‘ssh -p 9999′ -avl –delete –stats –progress demo@999.45.67.890:/home/demo /backup

where 9999 is the port number. SSH bydefault uses port 22 if you have setup a different port mention it here.

and ‘demo’ is your user name on the source server.

and ’999.45.67.890′ is the ip address of your source server

and ‘/home/demo’ is the directory on your source server you want to backup/synchronise

and /backup is the directory on the destination server

sridhar pandurangiah from http://serverfault.com/questions/509448