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<chapter>
  <header>
    <copyright>
      <year>2012</year>
      <year>2017</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>Getting Started</title>
    <prepared></prepared>
    <docno></docno>
    <approved></approved>
    <date></date>
    <rev></rev>
    <file>using_ssh.xml</file>
  </header>

  <section>
    <title>General Information</title>
    <p>The following examples use the utility function
    <seealso marker="ssh#start-0"> ssh:start/0</seealso> to start
    all needed applications (<c>crypto</c>, <c>public_key</c>, and <c>ssh</c>).
    All examples are run in an Erlang shell, or in a bash shell, using <em>openssh</em>
    to illustrate how the <c>ssh</c> application can be used. The
    examples are run as the user <c>otptest</c> on a local network where the
    user is authorized to log in over <c>ssh</c> to the host <em>tarlop</em>.
    </p>
    <p>If nothing else is stated, it is presumed that the <c>otptest</c> user
    has an entry in the <em>authorized_keys</em> file of <em>tarlop</em>
    (allowed to log in over <c>ssh</c> without entering a password).
    Also, <em>tarlop</em> is a known host in the <c>known_hosts</c>
    file of the user <c>otptest</c>. This means that host-verification
    can be done without user-interaction.
    </p>
  </section>

  <section>
    <title>Using the Erlang ssh Terminal Client</title>

    <p>The user <c>otptest</c>, which has bash as default shell, uses the
    <c>ssh:shell/1</c> client to connect to the <em>openssh</em> daemon running on a
    host called <em>tarlop</em>:</p>

    <code type="erl" >
      1>  ssh:start().
      ok
      2> {ok, S} = ssh:shell("tarlop").
      otptest@tarlop:> pwd
      /home/otptest
      otptest@tarlop:> exit
      logout
      3>
    </code>
  </section>

  <section>
    <marker id="Running an Erlang ssh Daemon"></marker>
    <title>Running an Erlang ssh Daemon</title>

    <p>The <c>system_dir</c> option must be a directory containing a host
    key file and it defaults to <c>/etc/ssh</c>. For details, see Section
    Configuration Files in <seealso
    marker="SSH_app">ssh(6)</seealso>.
    </p>

    <note><p>Normally, the <c>/etc/ssh</c> directory is only readable by root.</p>
    </note>

    <p>The option <c>user_dir</c> defaults to directory <c>users ~/.ssh</c>.</p>

    <p><em>Step 1.</em> To run the example without root privileges,
    generate new keys and host keys:</p>

    <code>
      $bash> ssh-keygen -t rsa -f /tmp/ssh_daemon/ssh_host_rsa_key
      [...]
      $bash> ssh-keygen -t rsa -f /tmp/otptest_user/.ssh/id_rsa
      [...]
    </code>

    <p><em>Step 2.</em> Create the file <c>/tmp/otptest_user/.ssh/authorized_keys</c>
    and add the content of <c>/tmp/otptest_user/.ssh/id_rsa.pub</c>.</p>

    <p><em>Step 3.</em> Start the Erlang <c>ssh</c> daemon:</p>

    <code type="erl">
      1> ssh:start().
      ok
      2> {ok, Sshd} = ssh:daemon(8989, [{system_dir, "/tmp/ssh_daemon"},
                                        {user_dir, "/tmp/otptest_user/.ssh"}]).
      {ok,&lt;0.54.0>}
      3>
    </code>

    <p><em>Step 4.</em> Use the <em>openssh</em> client from a shell to connect
    to the Erlang <c>ssh</c> daemon:</p>

    <code>
      $bash> ssh tarlop -p 8989  -i /tmp/otptest_user/.ssh/id_rsa\
             -o UserKnownHostsFile=/tmp/otptest_user/.ssh/known_hosts
      The authenticity of host 'tarlop' can't be established.
      RSA key fingerprint is 14:81:80:50:b1:1f:57:dd:93:a8:2d:2f:dd:90:ae:a8.
      Are you sure you want to continue connecting (yes/no)? yes
      Warning: Permanently added 'tarlop' (RSA) to the list of known hosts.
      Eshell V5.10  (abort with ^G)
      1>
    </code>

    <p>There are two ways of shutting down an <c>ssh</c> daemon,
    see <em>Step 5a</em> and <em>Step 5b</em>.</p>

    <p><em>Step 5a.</em> Shut down the Erlang <c>ssh</c> daemon so that it
    stops the listener but leaves existing connections, started by the listener,
    operational:</p>

    <code type="erl">
      3> ssh:stop_listener(Sshd).
      ok
      4>
    </code>

    <p><em>Step 5b.</em> Shut down the Erlang <c>ssh</c> daemon so that it
    stops the listener and all connections started by the listener:</p>

    <code type="erl">
      3> ssh:stop_daemon(Sshd)
      ok
      4>
    </code>

  </section>

  <section>
    <title>One-Time Execution</title>

    <p>In the following example, the Erlang shell is the client process
    that receives the channel replies.</p>

    <note><p>The number of received messages in this example depends on which OS
    and which shell that is used on the machine running the <c>ssh</c> daemon.
    See also <seealso marker="ssh_connection#exec-4">ssh_connection:exec/4</seealso>.
    </p></note>

    <p>Do a one-time execution of a remote command over <c>ssh</c>:</p>

    <code type="erl" >
      1>  ssh:start().
      ok
      2> {ok, ConnectionRef} = ssh:connect("tarlop", 22, []).
      {ok,&lt;0.57.0>}
      3>{ok, ChannelId} =  ssh_connection:session_channel(ConnectionRef, infinity).
      {ok,0}
      4> success = ssh_connection:exec(ConnectionRef, ChannelId, "pwd", infinity).
      5>  flush().
      Shell got {ssh_cm,&lt;0.57.0>,{data,0,0,&lt;&lt;"/home/otptest\n">>}}
      Shell got {ssh_cm,&lt;0.57.0>,{eof,0}}
      Shell got {ssh_cm,&lt;0.57.0>,{exit_status,0,0}}
      Shell got {ssh_cm,&lt;0.57.0>,{closed,0}}
      ok
      6>
    </code>

    <p>Notice that only the channel is closed. The connection is still up and can
    handle other channels:</p>

    <code type="erl" >
      6> {ok, NewChannelId} =  ssh_connection:session_channel(ConnectionRef, infinity).
        {ok,1}
	...
    </code>
  </section>

  <section>
    <title>SFTP Server</title>

    <p>Start the Erlang <c>ssh</c> daemon with the SFTP subsystem:</p>

    <code type="erl" >
      1> ssh:start().
      ok
      2> ssh:daemon(8989, [{system_dir, "/tmp/ssh_daemon"},
                           {user_dir, "/tmp/otptest_user/.ssh"},
                           {subsystems, [ssh_sftpd:subsystem_spec([{cwd, "/tmp/sftp/example"}])
                                        ]}]).
      {ok,&lt;0.54.0>}
      3>
    </code>

    <p>Run the OpenSSH SFTP client:</p>

    <code type="erl">
      $bash> sftp -oPort=8989 -o IdentityFile=/tmp/otptest_user/.ssh/id_rsa\
             -o UserKnownHostsFile=/tmp/otptest_user/.ssh/known_hosts tarlop
      Connecting to tarlop...
      sftp> pwd
      Remote working directory: /tmp/sftp/example
      sftp>
    </code>
  </section>

  <section>
    <title>SFTP Client</title>

    <p>Fetch a file with the Erlang SFTP client:</p>

    <code type="erl" >
      1> ssh:start().
      ok
      2> {ok, ChannelPid, Connection} = ssh_sftp:start_channel("tarlop", []).
      {ok,&lt;0.57.0>,&lt;0.51.0>}
      3>  ssh_sftp:read_file(ChannelPid, "/home/otptest/test.txt").
      {ok,&lt;&lt;"This is a test file\n">>}
    </code>
  </section>

  <section>
    <title>SFTP Client with TAR Compression and Encryption</title>

    <p>Example of writing and then reading a tar file follows:</p>
    <code type="erl">
      {ok,HandleWrite} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [write]),
      ok = erl_tar:add(HandleWrite, .... ),
      ok = erl_tar:add(HandleWrite, .... ),
      ...
      ok = erl_tar:add(HandleWrite, .... ),
      ok = erl_tar:close(HandleWrite),

      %% And for reading
      {ok,HandleRead} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [read]),
      {ok,NameValueList} = erl_tar:extract(HandleRead,[memory]),
      ok = erl_tar:close(HandleRead),
    </code>

    <p>The previous write and read example can be extended with encryption and decryption as follows:</p>
    <code type="erl">
%% First three parameters depending on which crypto type we select:
Key = &lt;&lt;"This is a 256 bit key. abcdefghi">>,
Ivec0 = crypto:strong_rand_bytes(16),
DataSize = 1024,  % DataSize rem 16 = 0 for aes_cbc

%% Initialization of the CryptoState, in this case it is the Ivector.
InitFun = fun() -> {ok, Ivec0, DataSize} end,

%% How to encrypt:
EncryptFun =
    fun(PlainBin,Ivec) ->
        EncryptedBin = crypto:block_encrypt(aes_cbc256, Key, Ivec, PlainBin),
        {ok, EncryptedBin, crypto:next_iv(aes_cbc,EncryptedBin)}
    end,

%% What to do with the very last block:
CloseFun =
    fun(PlainBin, Ivec) ->
        EncryptedBin = crypto:block_encrypt(aes_cbc256, Key, Ivec,
                                            pad(16,PlainBin) %% Last chunk
                                           ),
       {ok, EncryptedBin}
    end,

Cw = {InitFun,EncryptFun,CloseFun},
{ok,HandleWrite} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [write,{crypto,Cw}]),
ok = erl_tar:add(HandleWrite, .... ),
ok = erl_tar:add(HandleWrite, .... ),
...
ok = erl_tar:add(HandleWrite, .... ),
ok = erl_tar:close(HandleWrite),

%% And for decryption (in this crypto example we could use the same InitFun
%% as for encryption):
DecryptFun =
    fun(EncryptedBin,Ivec) ->
        PlainBin = crypto:block_decrypt(aes_cbc256, Key, Ivec, EncryptedBin),
       {ok, PlainBin, crypto:next_iv(aes_cbc,EncryptedBin)}
    end,

Cr = {InitFun,DecryptFun},
{ok,HandleRead} = ssh_sftp:open_tar(ChannelPid, ?tar_file_name, [read,{crypto,Cw}]),
{ok,NameValueList} = erl_tar:extract(HandleRead,[memory]),
ok = erl_tar:close(HandleRead),
    </code>
  </section>

  <section>
    <title>Creating a Subsystem</title>

    <p>A small <c>ssh</c> subsystem that echoes N bytes can be implemented as shown
    in the following example:</p>

    <code type="erl" >
-module(ssh_echo_server).
-behaviour(ssh_daemon_channel).
-record(state, {
	  n,
	  id,
	  cm
	 }).
-export([init/1, handle_msg/2, handle_ssh_msg/2, terminate/2]).

init([N]) ->
    {ok, #state{n = N}}.

handle_msg({ssh_channel_up, ChannelId, ConnectionManager}, State) ->
    {ok, State#state{id = ChannelId,
		     cm = ConnectionManager}}.

handle_ssh_msg({ssh_cm, CM, {data, ChannelId, 0, Data}}, #state{n = N} = State) ->
    M = N - size(Data),
    case M > 0 of
	true ->
	   ssh_connection:send(CM, ChannelId, Data),
	   {ok, State#state{n = M}};
	false ->
	   &lt;&lt;SendData:N/binary, _/binary>> = Data,
           ssh_connection:send(CM, ChannelId, SendData),
           ssh_connection:send_eof(CM, ChannelId),
	   {stop, ChannelId, State}
    end;
handle_ssh_msg({ssh_cm, _ConnectionManager,
		{data, _ChannelId, 1, Data}}, State) ->
    error_logger:format(standard_error, " ~p~n", [binary_to_list(Data)]),
    {ok, State};

handle_ssh_msg({ssh_cm, _ConnectionManager, {eof, _ChannelId}}, State) ->
    {ok, State};

handle_ssh_msg({ssh_cm, _, {signal, _, _}}, State) ->
    %% Ignore signals according to RFC 4254 section 6.9.
    {ok, State};

handle_ssh_msg({ssh_cm, _, {exit_signal, ChannelId, _, _Error, _}},
	       State) ->
    {stop, ChannelId,  State};

handle_ssh_msg({ssh_cm, _, {exit_status, ChannelId, _Status}}, State) ->
    {stop, ChannelId, State}.

terminate(_Reason, _State) ->
    ok.
 </code>

 <p>The subsystem can be run on the host <em>tarlop</em> with the generated keys,
 as described in Section <seealso marker="#Running an Erlang ssh Daemon">
 Running an Erlang ssh Daemon</seealso>:</p>

 <code type="erl" >
   1> ssh:start().
   ok
   2> ssh:daemon(8989, [{system_dir, "/tmp/ssh_daemon"},
                        {user_dir, "/tmp/otptest_user/.ssh"}
                        {subsystems, [{"echo_n", {ssh_echo_server, [10]}}]}]).
   {ok,&lt;0.54.0>}
   3>
 </code>

 <code type="erl" >
   1> ssh:start().
   ok
   2>{ok, ConnectionRef} = ssh:connect("tarlop", 8989, [{user_dir, "/tmp/otptest_user/.ssh"}]).
    {ok,&lt;0.57.0>}
   3>{ok, ChannelId} = ssh_connection:session_channel(ConnectionRef, infinity).
   4> success = ssh_connection:subsystem(ConnectionRef, ChannelId, "echo_n", infinity).
   5> ok = ssh_connection:send(ConnectionRef, ChannelId, "0123456789", infinity).
   6> flush().
   {ssh_msg, &lt;0.57.0>, {data, 0, 1, "0123456789"}}
   {ssh_msg, &lt;0.57.0>, {eof, 0}}
   {ssh_msg, &lt;0.57.0>, {closed, 0}}
   7> {error, closed} = ssh_connection:send(ConnectionRef, ChannelId, "10", infinity).
 </code>
<p>See also <seealso marker="ssh_channel"> ssh_channel(3)</seealso>.</p>

</section>

</chapter>
