Before we start to explain deep, let me introduce rsync 
What is Rsync ? 
rsync is a file transfer program for Unix systems. rsync uses the “rsync algorithm” which provides a very fast method for bringing remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand 
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Rsync features
- Can update whole directory trees and filesystems
- Optionally preserves symbolic links, hard links, file ownership, permissions, devices and times
- Requires no special privileges to install
- Internal pipelining reduces latency for multiple files
- Can use rsh, ssh or direct sockets as the transport
- Supports anonymous rsync which is ideal for mirroring
The Basic command rsync. 
rsync -av <source> <target>
eg.
rsync -av 192.168.1.100:/home/henry/ /backup/home/
or you can specify user
rsync -av henry@192.168.1.100:/home/henry/ /backup/home/
Rsync via ssh
rsync -ave ssh henry@192.168.1.100:/home/henry/ /backup/home/
Rsync with a non-standart ssh port
eg. ssh server listen on port 22222
rsync -av ‘ssh -p 22222′ henry@192.168.1.100:/home/henry/ /backup/home/
