As a system administrator, you may find it useful to create and maintain an operable backup machine that contains all the files you use regularly. Your and/or your end users may also want to keep their desktop and laptop machines synchronized.
Linux enables you to synchronize the filesystems of the local host and a remote machine. You can use the rdist and rsync commands to synchronize and transfer data. However, if security is a concern, using rsync with ssh is preferable.
ssh, the secure shell, is a utility that allows log in to a remote system using encrypted data transfer.

Rdist is an older facility for synchronizing files. rdist works by connecting to a machine over the network that trusts^[1] the local machine and sending the filesystems across the wire that you instruct rdist to send. The remote host must be running an rdist server that handles the connection from the rdist client on the local machine.
The rdist client consults a configuration file^[2] whenever it is invoked. The configuration file knows which files are to be mirrored as well as other information necessary to do the synchronization. The filesystem on the remote host is updated to match the source filesystem's contents on the local host.

It is not trivial to secure rdist. The remote machine must trust the local machine, which opens it to spoofing attacks . Data flowing from the local machine to the remote machine is also available for packet sniffers or other forms of eavesdropping.
The MouseOver below illustrates the differences between a trusted and untrusted connection.

Trusted Untrusted Networks
The next lesson explains how to use rsync to synchronize filesystems.

[1] Trust: Trust is a basic concept in security. The ability to trust means relying on the availability of another computer and the integrity of information provided by the other computer.

[2] Configuration file: A configuration file contains information such as settings or options to be used by a hardware device or program.