path: root/lib/ssh/doc/src/ssh.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>2004</year><year>2014</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      The contents of this file are subject to the Erlang Public License,
      Version 1.1, (the "License"); you may not use this file except in
      compliance with the License. You should have received a copy of the
      Erlang Public License along with this software. If not, it can be
      retrieved online at http://www.erlang.org/.

      Software distributed under the License is distributed on an "AS IS"
      basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
      the License for the specific language governing rights and limitations
      under the License.

    </legalnotice>
    
    <title>ssh</title>
    <date>2007-10-06</date>
  </header>
  <module>ssh</module>
  <modulesummary>Main API of the SSH application</modulesummary>
  <description>
    <p>Interface module for the SSH application. </p>
  </description>

   <section>
    <title>SSH</title>

    <list type="bulleted">
      <item>SSH requires the crypto and public_key applications.</item>
      <item>Supported SSH version is 2.0 </item>
      <item>Supported MAC algorithms: hmac-sha2-256 and hmac-sha1</item>
      <item>Supported encryption algorithms: aes128-ctr, aes128-cb and 3des-cbc</item>
      <item>Supports unicode filenames if the emulator and the underlaying OS supports it. See the DESCRIPTION section in <seealso marker="kernel:file">file</seealso> for information about this subject</item>
      <item>Supports unicode in shell and cli</item>
    </list>
 
  </section>
  
  <section>
    <title>DATA TYPES </title>
    <p>Type definitions that are used more than once in
    this module and/or abstractions to indicate the intended use of the data
    type:</p>
    <p><c>boolean() = true | false </c></p>
    <p><c>string() = [byte()]</c></p>
    <p><c>ssh_daemon_ref() - opaque to the user
    returned by ssh:daemon/[1,2,3]</c></p>
    <p><c>ssh_connection_ref() - opaque to the user
    returned by ssh:connect/3</c></p>
    <p><c>ip_address() - inet::ip_address()</c></p>
    <p><c>subsystem_spec() = {subsystem_name(),
    {channel_callback(), channel_init_args()}} </c></p>
    <p><c>subsystem_name() = string() </c></p>
    <p><c>channel_callback() = atom() - Name of the erlang module
    implementing the subsystem using the ssh_channel behavior see</c>
    <seealso marker="ssh_channel">ssh_channel(3)</seealso></p>
    <p><c>channel_init_args() = list()</c></p>
 </section>

 <funcs>
   
   <func>
     <name>close(ConnectionRef) -> ok </name>
      <fsummary>Closes an SSH connection</fsummary>
      <type>
	<v>ConnectionRef = ssh_connection_ref()</v>
      </type>
      <desc><p>Closes an SSH connection.</p>
      </desc>
    </func>
    
    <func>
      <name>connect(Host, Port, Options) -> </name>
      <name>connect(Host, Port, Options, Timeout) -> {ok,
      ssh_connection_ref()} | {error, Reason}</name>
      <fsummary>Connect to an ssh server.</fsummary>
      <type>
        <v>Host = string()</v>
	<v>Port = integer()</v>
	<d>The default is <c><![CDATA[22]]></c>, the assigned well known port
	number for SSH.</d>
	<v>Options = [{Option, Value}]</v>
	<v>Timeout = infinity | integer(milliseconds)</v>
	<d>Negotiation timeout, for connection timeout use the option <c>{connect_timeout, timeout()}</c>.</d>
      </type>
      <desc>
	<p>Connects to an SSH server. No channel is started. This is done
	by calling
	<seealso marker="ssh_connection#session_channel/2">ssh_connection:session_channel/[2, 4]</seealso>.</p>
	<p>Options are:</p>
	<taglist>
	  <tag><c><![CDATA[{inet, inet | inet6}]]></c></tag>
	  <item> IP version to use.</item>
          <tag><c><![CDATA[{user_dir, string()}]]></c></tag>
	  <item>
	    <p>Sets the user directory i.e. the directory containing
	    ssh configuration files for the user such as
	    <c><![CDATA[known_hosts]]></c>, <c><![CDATA[id_rsa,
	    id_dsa]]></c> and
	    <c><![CDATA[authorized_key]]></c>. Defaults to the
	    directory normally referred to as
	    <c><![CDATA[~/.ssh]]></c> </p>
	  </item>
	  <tag><c><![CDATA[{dsa_pass_phrase, string()}]]></c></tag>
	  <item>
	    <p>If the user dsa key is protected by a passphrase it can be
	    supplied with this option.
	    </p>
	  </item>
	  <tag><c><![CDATA[{rsa_pass_phrase, string()}]]></c></tag>
	  <item>
	    <p>If the user rsa key is protected by a passphrase it can be
	    supplied with this option.
	    </p>
	  </item>
          <tag><c><![CDATA[{silently_accept_hosts, boolean()}]]></c></tag>
	  <item>
	    <p>When true hosts are added to the
	    file <c><![CDATA[known_hosts]]></c> without asking the user.
	    Defaults to false.
	    </p>
	  </item>
	  <tag><c><![CDATA[{user_interaction, boolean()}]]></c></tag>
	  <item>
	    <p>If false disables the client to connect to the server
	    if any user interaction is needed such as accepting that
	    the server will be added to the <c>known_hosts</c> file or
	    supplying a password. Defaults to true.
	    Even if user interaction is allowed it can be
	    suppressed by other options such as silently_accept_hosts and
	    password. Do note that it may not always be desirable to use
	    those options from a security point of view.</p>
	  </item>
	  <tag><c><![CDATA[{public_key_alg, 'ssh-rsa' | 'ssh-dss'}]]></c></tag>
	  <item>
            <p>Sets the preferred public key algorithm to use for user
	    authentication. If the the preferred algorithm fails for
	    some reason, the other algorithm is tried. The  default is
	    to try <c><![CDATA['ssh-rsa']]></c> first.</p>
	  </item>
	  <tag><c><![CDATA[{pref_public_key_algs, list()}]]></c></tag>
	  <item>
            <p>List of public key algorithms to try to use, 'ssh-rsa' and 'ssh-dss' available. 
	    Will override <c><![CDATA[{public_key_alg, 'ssh-rsa' | 'ssh-dss'}]]></c></p>
	  </item>
	  <tag><c><![CDATA[{connect_timeout, timeout()}]]></c></tag>
	  <item>
	    <p>Sets a timeout on the transport layer
	    connection. Defaults to <c>infinity</c>.</p>
	  </item>
	  <tag><c><![CDATA[{user, string()}]]></c></tag>
          <item>
	    <p>Provides a user name. If this option is not given, ssh
	    reads from the environment (<c><![CDATA[LOGNAME]]></c> or
	    <c><![CDATA[USER]]></c> on unix,
	    <c><![CDATA[USERNAME]]></c> on Windows).</p>
          </item>
	  <tag><c><![CDATA[{password, string()}]]></c></tag>
          <item>
	    <p>Provide a password for password authentication.  If
	    this option is not given, the user will be asked for a
	    password if the password authentication method is
	    attempted.</p>
          </item>
	  <tag><c><![CDATA[{key_cb, atom()}]]></c></tag>
	  <item>
	    <p>Module implementing the behaviour <seealso marker="ssh_client_key_api">ssh_client_key_api</seealso>.
	    Can be used to customize the handling of public keys.
	    </p>
	  </item>
	  <tag><c><![CDATA[{quiet_mode, atom() = boolean()}]]></c></tag>
	  <item>
	    <p>If true, the client will not print out anything on authorization.</p>
	  </item>
	  <tag><c><![CDATA[{fd, file_descriptor()}]]></c></tag>
	  <item>
	    <p>Allow an existing file descriptor to be used
	  (simply passed on to the transport protocol).</p></item>
	  <tag><c><![CDATA[{rekey_limit, integer()}]]></c></tag>
	  <item>
	    <p>Provide, in bytes, when rekeying should be initiated, 
	    defaults to one time each GB and one time per hour.</p>
	  </item>
	  <tag><c><![CDATA[{idle_time, integer()}]]></c></tag>
	  <item>
 	  <p>Sets a timeout on connection when no channels are active, default is infinity</p></item>
	</taglist>
      </desc>   
    </func>

    <func>
      <name>connection_info(ConnectionRef, [Option]) ->[{Option,
      Value}] </name>
      <fsummary> Retrieves information about a connection. </fsummary>
      <type>
        <v>Option = client_version | server_version | user | peer | sockname </v>
	<v>Value = [option_value()] </v>
	<v>option_value() = {{Major::integer(), Minor::integer()}, VersionString::string()} | User::string() |
	Peer::{inet:hostname(), {inet::ip_adress(), inet::port_number()}} |
	Sockname::{inet::ip_adress(), inet::port_number()} () </v>
      </type>
      <desc>
        <p> Retrieves information about a connection. 
	</p>
      </desc>
    </func>
    
    <func>
      <name>daemon(Port) -> </name>
      <name>daemon(Port, Options) -> </name>
      <name>daemon(HostAddress, Port, Options) -> {ok,
      ssh_daemon_ref()} | {error, atom()}</name>
      <fsummary>Starts a server listening for SSH connections 
      on the given port.</fsummary>
      <type>
        <v>Port = integer()</v>
	<v>HostAddress = ip_address() | any</v>
	<v>Options = [{Option, Value}]</v>
        <v>Option = atom()</v>
	<v>Value = term()</v>
      </type>
      <desc>
        <p>Starts a server listening for SSH connections on the given
        port.</p>
	<p>Options are:</p>
        <taglist>
	  <tag><c><![CDATA[{inet, inet | inet6}]]></c></tag>
	  <item> IP version to use when the host address is specified as <c>any</c>. </item>
	  <tag><c><![CDATA[{subsystems, [subsystem_spec()]]]></c></tag>
	  <item>
	    Provides specifications for handling of subsystems. The
	    "sftp" subsystem spec can be retrieved by calling
	    ssh_sftpd:subsystem_spec/1. If the subsystems option in
	    not present the value of
	    <c>[ssh_sftpd:subsystem_spec([])]</c> will be used.  It is
	    of course possible to set the option to the empty list if
	    you do not want the daemon to run any subsystems at all.
	  </item>
	  <tag><c><![CDATA[{shell, {Module, Function, Args} |
	  fun(string() = User) - > pid() | fun(string() = User,
	  ip_address() = PeerAddr) -> pid()}]]></c></tag>
	  <item>
	    Defines the read-eval-print loop used when a shell is
	    requested by the client. Default is to use the erlang shell:
	    <c><![CDATA[{shell, start, []}]]></c>
	  </item>
	  <tag><c><![CDATA[{ssh_cli, {channel_callback(),
	  channel_init_args()} | no_cli}]]></c></tag>
	  <item>
	    Provides your own CLI implementation, i.e. a channel callback
	    module that implements a shell and command execution. Note
	    that you may customize the shell read-eval-print loop using the
	    option <c>shell</c> which is much less work than implementing
	    your own CLI channel. If set to  <c>no_cli</c> you will disable
	    CLI channels and only subsystem channels will be allowed.
	  </item>
	  <tag><c><![CDATA[{user_dir, String}]]></c></tag>
	  <item>
	    <p>Sets the user directory i.e. the directory containing
	    ssh configuration files for the user such as
	    <c><![CDATA[known_hosts]]></c>, <c><![CDATA[id_rsa,
	    id_dsa]]></c> and
	    <c><![CDATA[authorized_key]]></c>. Defaults to the
	    directory normally referred to as
	    <c><![CDATA[~/.ssh]]></c> </p>
	  </item>
          <tag><c><![CDATA[{system_dir, string()}]]></c></tag>
          <item>
            <p>Sets the system directory, containing the host key files
            that identifies the host keys for ssh. The default is
            <c><![CDATA[/etc/ssh]]></c>, note that for security reasons
            this directory is normally only accessible by the root user.</p>
	  </item>
	  <tag><c><![CDATA[{auth_methods, string()}]]></c></tag>
	  <item>
	    <p>Comma separated string that determines which
	    authentication methodes that the server should support and
	    in what order they will be tried. Defaults to
	    <c><![CDATA["publickey,keyboard-interactive,password"]]></c></p>
          </item>
	  <tag><c><![CDATA[{user_passwords, [{string() = User,
	  string() = Password}]}]]></c></tag>
	  <item>
            <p>Provide passwords for password authentication.They will
	    be used when someone tries to connect to the server and
	    public key user authentication fails. The option provides
	    a list of valid user names and the corresponding password.
	    </p>
          </item>
          <tag><c><![CDATA[{password, string()}]]></c></tag>
          <item>
            <p>Provide a global password that will authenticate any
              user. From a security perspective this option makes
	      the server very vulnerable.</p>
	  </item>
	  <tag><c><![CDATA[{pwdfun, fun(User::string(), password::string()) -> boolean()}]]></c></tag>
	  <item>
	    <p>Provide a function for password validation. This is called
	      with user and password as strings, and should return
	      <c><![CDATA[true]]></c> if the password is valid and
	      <c><![CDATA[false]]></c> otherwise.</p>
	  </item>

	  <tag><c><![CDATA[{negotiation_timeout, integer()}]]></c></tag>
	  <item>
	    <p>Max time in milliseconds for the authentication negotiation.  The default value is 2 minutes. If the client fails to login within this time, the connection is closed.
	    </p>
	  </item>

	  <tag><c><![CDATA[{max_sessions, pos_integer()}]]></c></tag>
	  <item>
	    <p>The maximum number of simultaneous sessions that are accepted at any time for this daemon.  This includes sessions that are being authorized.  So if set to <c>N</c>, and <c>N</c> clients have connected but not started the login process, the <c>N+1</c> connection attempt will be aborted.  If <c>N</c> connections are authenticated and still logged in, no more loggins will be accepted until one of the existing ones log out.
	    </p>
	    <p>The counter is per listening port, so if two daemons are started, one with <c>{max_sessions,N}</c> and the other with <c>{max_sessions,M}</c> there will be in total <c>N+M</c> connections accepted for the whole ssh application.
	    </p>
	    <p>Note that if <c>parallel_login</c> is <c>false</c>, only one client at a time may be in the authentication phase.
	    </p>
	    <p>As default, the option is not set. This means that the number is not limited.
	    </p>
	  </item>

	  <tag><c><![CDATA[{parallel_login, boolean()}]]></c></tag>
	  <item>
	    <p>If set to false (the default value), only one login is handled a time.  If set to true, an unlimited number of login attempts will be allowed simultanously.
	    </p>
	    <p>If the <c>max_sessions</c> option is set to <c>N</c> and <c>parallel_login</c> is set to <c>true</c>, the max number of simultaneous login attempts at any time is limited to <c>N-K</c> where <c>K</c> is the number of authenticated connections present at this daemon.
	    </p>
	    <warning>
	      <p>Do not enable <c>parallel_logins</c> without protecting the server by other means, for example the <c>max_sessions</c> option or a firewall configuration. If set to <c>true</c>, there is no protection against DOS attacks.</p>
	    </warning>
	  </item>

	  <tag><c><![CDATA[{key_cb, atom()}]]></c></tag>
	  <item>
	    <p>Module implementing the behaviour <seealso marker="ssh_server_key_api">ssh_server_key_api</seealso>.
	    Can be used to customize the handling of public keys.
	    </p>
	  </item>
	  <tag><c><![CDATA[{fd, file_descriptor()}]]></c></tag>
	  <item>
	    <p>Allow an existing file-descriptor to be used
	  (simply passed on to the transport protocol).</p></item>
	  <tag><c><![CDATA[{failfun, fun(User::string(), PeerAddress::ip_address(), Reason::term()) -> _}]]></c></tag>
	  <item>
	    <p>Provide a fun to implement your own logging when a user fails to authenticate.</p>
	  </item>
	  <tag><c><![CDATA[{connectfun, fun(User::string(), PeerAddress::ip_address(), Method::string()) ->_}]]></c></tag>
	  <item>
	    <p>Provide a fun to implement your own logging when a user authenticates to the server.</p>
	  </item>
	  <tag><c><![CDATA[{disconnectfun, fun(Reason:term()) -> _}]]></c></tag>
	  <item>
	    <p>Provide a fun to implement your own logging when a user disconnects from the server.</p>
	  </item>
        </taglist>
      </desc>
    </func>


    <func>
      <name>shell(Host) -> </name>
      <name>shell(Host, Option) -> </name>
      <name>shell(Host, Port, Option) -> _</name>
      <fsummary> </fsummary>
      <type>
        <v> Host = string()</v>
	<v> Port = integer()</v>
	<v> Options - see ssh:connect/3</v>
      </type>
      <desc>
        <p>Starts an interactive shell via an SSH server on the
	given <c>Host</c>. The function waits for user input,
	and will not return until the remote shell is ended (i.e.
	exit from the shell).
	</p>
      </desc>
    </func>

    <func>
      <name>start() -> </name>
      <name>start(Type) -> ok | {error, Reason}</name>
      <fsummary>Starts the SSH application. </fsummary>
      <type>
        <v>Type =  permanent | transient | temporary</v>
	<v>Reason = term() </v>
      </type>
      <desc>
        <p>Utility function that starts crypto, public_key and the SSH
	application. Defult type is temporary.
	See also <seealso marker="kernel:application">application(3)</seealso>
	</p>
      </desc>
    </func>

    <func>
      <name>stop() -> ok | {error, Reason}</name>
      <fsummary>Stops the SSH application.</fsummary>
      <type>
        <v>Reason = term()</v>
      </type>
      <desc>
        <p>Stops the SSH application. See also
          <seealso marker="kernel:application">application(3)</seealso></p>
      </desc>
    </func>
    
    <func>
      <name>stop_daemon(DaemonRef) -> </name>
      <name>stop_daemon(Address, Port) -> ok </name>
      <fsummary>Stops the listener and all connections started by 
      the listener.</fsummary>
      <type>
	<v>DaemonRef = ssh_daemon_ref()</v>
	<v>Address = ip_address()</v>
	<v>Port = integer()</v>
      </type>
      <desc>
	<p>Stops the listener and all connections started by 
	the listener.</p>
      </desc>
    </func>

    <func>
      <name>stop_listener(DaemonRef) -> </name>
      <name>stop_listener(Address, Port) -> ok </name>
      <fsummary>Stops the listener, but leaves existing connections started
	by the listener up and running.</fsummary>
      <type>
	<v>DaemonRef = ssh_daemon_ref()</v>
        <v>Address = ip_address()</v>
	<v>Port = integer()</v>
      </type>
      <desc>
	<p>Stops the listener, but leaves existing connections started
	by the listener up and running.</p>
      </desc>
    </func>

  </funcs>
  
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