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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>
<prepared></prepared>
<docno></docno>
<date>2007-10-06</date>
<rev></rev>
</header>
<module>ssh</module>
<modulesummary>Main API of the ssh application</modulesummary>
<description>
<p>Interface module for the <c>ssh</c> application.</p>
</description>
<section>
<title>SSH</title>
<list type="bulleted">
<item>For application dependencies see <seealso marker="SSH_app"> ssh(6)</seealso> </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>Supported key exchange algorithms: diffie-hellman-group1-sha1.</item>
<item>Supports unicode filenames if the emulator and the underlaying OS support it.
See section DESCRIPTION in the
<seealso marker="kernel:file">file</seealso> manual page in <c>kernel</c>
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, or abstractions to indicate the intended use of the data
type, or both:</p>
<taglist>
<tag><c>boolean() =</c></tag>
<item><p><c>true | false</c></p></item>
<tag><c>string() =</c></tag>
<item><p><c>[byte()]</c></p></item>
<tag><c>ssh_daemon_ref() =</c></tag>
<item><p>opaque() -
as returned by <c>ssh:daemon/[1,2,3]</c></p></item>
<tag><c>ssh_connection_ref() =</c></tag>
<item><p>opaque() - as returned by <c>ssh:connect/3</c></p></item>
<tag><c>ip_address() =</c></tag>
<item><p><c>inet::ip_address</c></p></item>
<tag><c>subsystem_spec() =</c></tag>
<item><p><c>{subsystem_name(),
{channel_callback(), channel_init_args()}}</c></p></item>
<tag><c>subsystem_name() =</c></tag>
<item><p><c>string()</c></p></item>
<tag><c>channel_callback() =</c></tag>
<item><p><c>atom()</c> - Name of the Erlang module
implementing the subsystem using the <c>ssh_channel</c> behavior, see
<seealso marker="ssh_channel">ssh_channel(3)</seealso></p></item>
<tag><c>channel_init_args() =</c></tag>
<item><p><c>list()</c></p></item>
</taglist>
</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>Connects to an SSH server.</fsummary>
<type>
<v>Host = string()</v>
<v>Port = integer()</v>
<d><c><![CDATA[22]]></c> is default, the assigned well-known port
number for SSH.</d>
<v>Options = [{Option, Value}]</v>
<v>Timeout = infinity | integer()</v>
<d>Negotiation time-out in milli-seconds. The default value is <c>infinity</c>.
For connection time-out, use 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:</p>
<taglist>
<tag><c><![CDATA[{inet, inet | inet6}]]></c></tag>
<item>
<p>IP version to use.</p>
</item>
<tag><c><![CDATA[{user_dir, string()}]]></c></tag>
<item>
<p>Sets the user directory, that is, the directory containing
<c>ssh</c> 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 <c>true</c>, hosts are added to the
file <c><![CDATA[known_hosts]]></c> without asking the user.
Defaults to <c>false</c>.
</p>
</item>
<tag><c><![CDATA[{user_interaction, boolean()}]]></c></tag>
<item>
<p>If <c>false</c>, disables the client to connect to the server
if any user interaction is needed, such as accepting
the server to be added to the <c>known_hosts</c> file, or
supplying a password. Defaults to <c>true</c>.
Even if user interaction is allowed it can be
suppressed by other options, such as <c>silently_accept_hosts</c>
and <c>password</c>. However, those optins are not always desirable
to use 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 preferred algorithm fails,
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.
<c>'ssh-rsa'</c> and <c>'ssh-dss'</c> are available.
Overrides <c><![CDATA[{public_key_alg, 'ssh-rsa' | 'ssh-dss'}]]></c></p>
</item>
<tag><c><![CDATA[{connect_timeout, timeout()}]]></c></tag>
<item>
<p>Sets a time-out on the transport layer
connection. For <c>gen_tcp</c> the time is in milli-seconds and the default value is
<c>infinity</c>.</p>
</item>
<tag><c><![CDATA[{user, string()}]]></c></tag>
<item>
<p>Provides a username. If this option is not given, <c>ssh</c>
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>Provides a password for password authentication.
If this option is not given, the user is 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 <c>true</c>, the client does not print anything on authorization.</p>
</item>
<tag><c><![CDATA[{id_string, random | string()}]]></c></tag>
<item>
<p>The string that the client presents to a connected server initially. The default value is "Erlang/VSN" where VSN is the ssh application version number.
</p>
<p>The value <c>random</c> will cause a random string to be created at each connection attempt. This is to make it a bit more difficult for a malicious peer to find the ssh software brand and version.
</p>
</item>
<tag><c><![CDATA[{fd, file_descriptor()}]]></c></tag>
<item>
<p>Allows an existing file descriptor to be used
(by passing it on to the transport protocol).</p></item>
<tag><c><![CDATA[{rekey_limit, integer()}]]></c></tag>
<item>
<p>Provides, in bytes, when rekeying is to be initiated.
Defaults to once per each GB and once per hour.</p>
</item>
<tag><c><![CDATA[{idle_time, integer()}]]></c></tag>
<item>
<p>Sets a time-out on a connection when no channels are active.
Defaults to <c>infinity</c>.</p></item>
<tag><c><![CDATA[{ssh_msg_debug_fun, fun(ConnectionRef::ssh_connection_ref(), AlwaysDisplay::boolean(), Msg::binary(), LanguageTag::binary()) -> _}]]></c></tag>
<item>
<p>Provide a fun to implement your own logging of the SSH message SSH_MSG_DEBUG. The last three parameters are from the message, see RFC4253, section 11.3. The <c>ConnectionRef</c> is the reference to the connection on which the message arrived. The return value from the fun is not checked.</p>
<p>The default behaviour is ignore the message.
To get a printout for each message with <c>AlwaysDisplay = true</c>, use for example <c>{ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG: ~p~n", [M]) end}</c></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:</p>
<taglist>
<tag><c><![CDATA[{inet, inet | inet6}]]></c></tag>
<item><p>IP version to use when the host address is specified as <c>any</c>.</p></item>
<tag><c><![CDATA[{subsystems, [subsystem_spec()]}]]></c></tag>
<item>
<p>Provides specifications for handling of subsystems. The
"sftp" subsystem specification is retrieved by calling
<c>ssh_sftpd:subsystem_spec/1</c>. If the subsystems option is
not present, the value of
<c>[ssh_sftpd:subsystem_spec([])]</c> is used.
The option can be set to the empty list if
you do not want the daemon to run any subsystems.</p>
</item>
<tag><c><![CDATA[{shell, {Module, Function, Args} |
fun(string() = User) - > pid() | fun(string() = User,
ip_address() = PeerAddr) -> pid()}]]></c></tag>
<item>
<p>Defines the read-eval-print loop used when a shell is
requested by the client. The default is to use the Erlang shell:
<c><![CDATA[{shell, start, []}]]></c></p>
</item>
<tag><c><![CDATA[{ssh_cli, {channel_callback(),
channel_init_args()} | no_cli}]]></c></tag>
<item>
<p>Provides your own CLI implementation, that is, a channel callback
module that implements a shell and command execution. The shell
read-eval-print loop can be customized, using the
option <c>shell</c>. This means less work than implementing
an own CLI channel. If set to <c>no_cli</c>, the CLI channels
are disabled and only subsystem channels are allowed.</p>
</item>
<tag><c><![CDATA[{user_dir, String}]]></c></tag>
<item>
<p>Sets the user directory. That is, the directory containing
<c>ssh</c> 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 identify the host keys for <c>ssh</c>. Defaults to
<c><![CDATA[/etc/ssh]]></c>. For security reasons,
this directory is normally accessible only to the root user.</p>
</item>
<tag><c><![CDATA[{auth_methods, string()}]]></c></tag>
<item>
<p>Comma-separated string that determines which
authentication methods that the server is to support and
in what order they are 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>Provides passwords for password authentication. The passwords
are used when someone tries to connect to the server and
public key user-authentication fails. The option provides
a list of valid usernames and the corresponding passwords.
</p>
</item>
<tag><c><![CDATA[{password, string()}]]></c></tag>
<item>
<p>Provides a global password that authenticates 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>Provides a function for password validation. This function is called
with user and password as strings, and returns
<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>Maximum time in milliseconds for the authentication negotiation.
Defaults to 120000 (2 minutes). If the client fails to log in 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.
Thus, if set to <c>N</c>, and <c>N</c> clients have connected but not started
the login process, connection attempt <c>N+1</c> is aborted.
If <c>N</c> connections are authenticated and still logged in, no more logins
are accepted until one of the existing ones log out.
</p>
<p>The counter is per listening port. Thus, if two daemons are started, one with
<c>{max_sessions,N}</c> and the other with <c>{max_sessions,M}</c>, in total
<c>N+M</c> connections are accepted for the whole <c>ssh</c> application.
</p>
<p>Notice that if <c>parallel_login</c> is <c>false</c>, only one client
at a time can be in the authentication phase.
</p>
<p>By default, this 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 at a time.
If set to true, an unlimited number of login attempts are allowed simultaneously.
</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 maximum 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, by 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[{minimal_remote_max_packet_size, non_negative_integer()}]]></c></tag>
<item>
<p>The least maximum packet size that the daemon will accept in channel open requests from the client. The default value is 0.
</p>
</item>
<tag><c><![CDATA[{id_string, random | string()}]]></c></tag>
<item>
<p>The string the daemon will present to a connecting peer initially. The default value is "Erlang/VSN" where VSN is the ssh application version number.
</p>
<p>The value <c>random</c> will cause a random string to be created at each connection attempt. This is to make it a bit more difficult for a malicious peer to find the ssh software brand and version.
</p>
</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>Allows an existing file-descriptor to be used
(passed on to the transport protocol).</p></item>
<tag><c><![CDATA[{failfun, fun(User::string(),
PeerAddress::ip_address(), Reason::term()) -> _}]]></c></tag>
<item>
<p>Provides 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>Provides 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>Provides a fun to implement your own logging when a user disconnects from the server.</p>
</item>
<tag><c><![CDATA[{ssh_msg_debug_fun, fun(ConnectionRef::ssh_connection_ref(), AlwaysDisplay::boolean(), Msg::binary(), LanguageTag::binary()) -> _}]]></c></tag>
<item>
<p>Provide a fun to implement your own logging of the SSH message SSH_MSG_DEBUG. The last three parameters are from the message, see RFC4253, section 11.3. The <c>ConnectionRef</c> is the reference to the connection on which the message arrived. The return value from the fun is not checked.</p>
<p>The default behaviour is ignore the message.
To get a printout for each message with <c>AlwaysDisplay = true</c>, use for example <c>{ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG: ~p~n", [M]) end}</c></p>
</item>
</taglist>
</desc>
</func>
<func>
<name>shell(Host) -> </name>
<name>shell(Host, Option) -> </name>
<name>shell(Host, Port, Option) -> _</name>
<fsummary>Starts an interactive shell over an SSH server.</fsummary>
<type>
<v>Host = string()</v>
<v>Port = integer()</v>
<v>Options - see ssh:connect/3</v>
</type>
<desc>
<p>Starts an interactive shell over an SSH server on the
given <c>Host</c>. The function waits for user input,
and does not return until the remote shell is ended (that is,
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 the applications <c>crypto</c>, <c>public_key</c>,
and <c>ssh</c>. Default type is <c>temporary</c>.
For more information, see the <seealso marker="kernel:application">application(3)</seealso>
manual page in <c>kernel</c>.</p>
</desc>
</func>
<func>
<name>stop() -> ok | {error, Reason}</name>
<fsummary>Stops the <c>ssh</c> application.</fsummary>
<type>
<v>Reason = term()</v>
</type>
<desc>
<p>Stops the <c>ssh</c> application.
For more information, see the <seealso marker="kernel:application">application(3)</seealso>
manual page in <c>kernel</c>.</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 operational.</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 operational.</p>
</desc>
</func>
</funcs>
</erlref>
