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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
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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 to the user,
returned by <c>ssh:daemon/[1,2,3]</c></p></item>
<tag><c>ssh_connection_ref()</c></tag>
<item><p>Opaque to the user,
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>
</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>
</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>
