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<appref>
  <header>
    <copyright>
      <year>2012</year><year>2013</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    </legalnotice>

    <title>SSH</title>
    <prepared></prepared>
    <docno></docno>
    <checked></checked>
    <date></date>
    <rev></rev>
    <file>ssh_app.xml</file>
  </header>
  <app>SSH</app>
  <appsummary>The ssh application implements the Secure Shell (SSH) protocol and
  provides an SSH File Transfer Protocol (SFTP) client and server.</appsummary>
  <description>
    <p>The <c>ssh</c> application is an implementation of the SSH protocol in Erlang.
    <c>ssh</c> offers API functions to write customized SSH clients and servers as well as
    making the Erlang shell available over SSH. An SFTP client, <c>ssh_sftp</c>, and server,
    <c>ssh_sftpd</c>, are also included.</p>
  </description>

   <section>
    <title>DEPENDENCIES</title>
    <p>The <c>ssh</c> application uses the applications <c>public_key</c> and
    <c>crypto</c> to handle public keys and encryption. Hence, these
    applications must be loaded for the <c>ssh</c> application to work. In
    an embedded environment this means that they must be started with
    <c>application:start/[1,2]</c> before the <c>ssh</c> application is started.
    </p>
  </section>

  <section>
    <title>CONFIGURATION</title>

    <p>The <c>ssh</c> application does not have an application-
    specific configuration file, as described in <seealso marker="kernel:application">application(3)</seealso>.
    However, by default it use the following configuration files
    from OpenSSH:</p>
    <list type="bulleted">
      <item><c>known_hosts</c></item>
      <item><c>authorized_keys</c></item>
      <item><c>authorized_keys2</c></item>
      <item><c>id_dsa</c></item>
      <item><c>id_rsa</c></item>
      <item><c>ssh_host_dsa_key</c></item>
      <item><c>ssh_host_rsa_key</c></item>
    </list>
      <p>By default, <c>ssh</c> looks for <c>id_dsa</c>, <c>id_rsa</c>,
      <c>known_hosts</c>, and <c>authorized_keys</c> in ~/.ssh,
      and for the host key files in <c>/etc/ssh</c>. These locations can be changed
      by the options <c>user_dir</c> and <c>system_dir</c>.
      </p>
      <p>Public key handling can also be customized through a callback module that
      implements the behaviors
      <seealso marker="ssh_client_key_api">ssh_client_key_api</seealso> and
      <seealso marker="ssh_server_key_api">ssh_server_key_api</seealso>.
      </p>

  </section>
  <section>
    <title>Public Keys</title>
    <p><c>id_dsa</c> and <c>id_rsa</c> are the users private key files.
	Notice that the public key is part of the private key so the <c>ssh</c>
	application does not use the <c>id_&lt;*>.pub</c> files. These are
	for the user's convenience when it is needed to convey the user's
	public key.
      </p>
  </section>
 <section>
    <title>Known Hosts</title>
    <p>The <c>known_hosts</c> file contains a list of approved servers and
      their public keys. Once a server is listed, it can be verified
      without user interaction.
      </p>
  </section>
 <section>
    <title>Authorized Keys</title>
    <p>The <c>authorized_key</c> file keeps track of the user's authorized
      public keys. The most common use of this file is to let users
      log in without entering their password, which is supported by the
      Erlang <c>ssh</c> daemon.
      </p>
  </section>
 <section>
    <title>Host Keys</title>
    <p>RSA and DSA host keys are supported and are
       expected to be found in files named <c>ssh_host_rsa_key</c> and
       <c>ssh_host_dsa_key</c>.
       </p>
  </section>
  <section>
    <title>ERROR LOGGER AND EVENT HANDLERS</title>
    <p>The <c>ssh</c> application uses the default <seealso marker="kernel:error_logger">OTP error logger</seealso> to log unexpected errors or print information about special events.</p>
  </section>

  <section>
    <title>SEE ALSO</title>
    <p><seealso marker="kernel:application">application(3)</seealso></p>
  </section>

</appref>
