.. include:: ../header.txt

.. _hostComm:

Communication Between Hosts
===============================

:title:`Linux for Programmers and Users`, Section 9.6

Here we list two commands for copying files betweens host (``rcp`` and
``scp``) and two commands to remotely use a remote host (``rsh`` and 
``ssh``). The commands ``rcp`` and ``rsh`` are not secure (data is not
encrypted), while ``scp`` and ``ssh`` are secure.  Only secure communication
commands should be run on networks, such as over the Internet, where untrusted
users might be present.

It is possible with both the secure and unsecure versions of these programs to
use them without the needed to type a password. The ``scp`` and ``ssh``
programs do so using public and private key files.  Instructions for how
to set this up can be found on various web pages on the Internet.

:command:`rcp`
-----------------

.. index:: rcp
.. program:: rcp
.. describe:: rcp

    Copy file(s) between hosts.

:command:`scp`
-----------------

.. index:: scp
.. program:: scp
.. describe:: scp

    Secure copy file(s) between hosts.
    


:command:`rsh`
-----------------

.. index:: rsh
.. program:: rsh
.. describe:: rsh

    Run a command (including a shell) on a remote computer.

:command:`ssh`
-----------------

.. index:: ssh
.. program:: ssh
.. describe:: ssh

    Securely run a command (including a shell) on a remote computer.

SYNOPSIS

    ssh [userid@]hostname [command]

When not command is run on the remote host a login is attempted.

With both ``rsh`` and ``ssh``, in addition to running a command on a remote
computer, data may be passed over the communication channel. See :ref:`dd` for
some examples.