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NAME
ssh - Main API of the ssh application
DESCRIPTION
Interface module for the ssh application.
See ssh(7) for details of supported version, algorithms and unicode support.
OPTIONS
The exact behaviour of some functions can be adjusted with the use of options which are documented
together with the functions. Generally could each option be used at most one time in each function call.
If given two or more times, the effect is not predictable unless explicitly documented.
The options are of different kinds:
Limits:
which alters limits in the system, for example number of simultaneous login attempts.
Timeouts:
which give some defined behaviour if too long time elapses before a given event or action, for
example time to wait for an answer.
Callbacks:
which gives the caller of the function the possibility to execute own code on some events, for
example calling an own logging function or to perform an own login function
Behaviour:
which changes the systems behaviour.
DATA TYPES
Type definitions that are used more than once in this module, or abstractions to indicate the intended
use of the data type, or both:
boolean() =:
true | false
string() =:
[byte()]
ssh_daemon_ref() =:
opaque() - as returned by ssh:daemon/[1,2,3]
ssh_connection_ref() =:
opaque() - as returned by ssh:connect/3
ip_address() =:
inet::ip_address
subsystem_spec() =:
{subsystem_name(), {channel_callback(), channel_init_args()}}
subsystem_name() =:
string()
channel_callback() =:
atom() - Name of the Erlang module implementing the subsystem using the ssh_channel behavior, see
ssh_channel(3erl)
key_cb() =:
atom() | {atom(), list()}
atom() - Name of the erlang module implementing the behaviours ssh_client_key_api or
ssh_client_key_api as the case maybe.
list() - List of options that can be passed to the callback module.
channel_init_args() =:
list()
algs_list() =:
list( alg_entry() )
alg_entry() =:
{kex, simple_algs()} | {public_key, simple_algs()} | {cipher, double_algs()} | {mac, double_algs()} |
{compression, double_algs()}
simple_algs() =:
list( atom() )
double_algs() =:
[{client2serverlist,simple_algs()},{server2client,simple_algs()}] | simple_algs()
EXPORTS
close(ConnectionRef) -> ok
Types:
ConnectionRef = ssh_connection_ref()
Closes an SSH connection.
connect(Host, Port, Options) ->
connect(Host, Port, Options, Timeout) -> {ok, ssh_connection_ref()} | {error, Reason}
Types:
Host = string()
Port = integer()
22 is default, the assigned well-known port number for SSH.
Options = [{Option, Value}]
Timeout = infinity | integer()
Negotiation time-out in milli-seconds. The default value is infinity. For connection time-
out, use option {connect_timeout, timeout()}.
Connects to an SSH server. No channel is started. This is done by calling
ssh_connection:session_channel/[2, 4].
Options:
{inet, inet | inet6}:
IP version to use.
{user_dir, string()}:
Sets the user directory, that is, the directory containing ssh configuration files for the
user, such as known_hosts, id_rsa, id_dsa, and authorized_key. Defaults to the directory
normally referred to as ~/.ssh.
{dsa_pass_phrase, string()}:
If the user DSA key is protected by a passphrase, it can be supplied with this option.
{rsa_pass_phrase, string()}:
If the user RSA key is protected by a passphrase, it can be supplied with this option.
{silently_accept_hosts, boolean()}:
When true, hosts are added to the file known_hosts without asking the user. Defaults to false.
{user_interaction, boolean()}:
If false, disables the client to connect to the server if any user interaction is needed, such
as accepting the server to be added to the known_hosts 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. However, those optins are not always desirable to use from
a security point of view.
{disconnectfun, fun(Reason:term()) -> _}:
Provides a fun to implement your own logging when a server disconnects the client.
{unexpectedfun, fun(Message:term(), Peer) -> report | skip }:
Provides a fun to implement your own logging or other action when an unexpected message
arrives. If the fun returns report the usual info report is issued but if skip is returned no
report is generated.
Peer is in the format of {Host,Port}.
{public_key_alg, 'ssh-rsa' | 'ssh-dss'}:
Note:
This option will be removed in OTP 20, but is kept for compatibility. It is ignored if the
preferred pref_public_key_algs option is used.
Sets the preferred public key algorithm to use for user authentication. If the preferred
algorithm fails, the other algorithm is tried. If {public_key_alg, 'ssh-rsa'} is set, it is
translated to {pref_public_key_algs, ['ssh-rsa','ssh-dss']}. If it is {public_key_alg, 'ssh-
dss'}, it is translated to {pref_public_key_algs, ['ssh-dss','ssh-rsa']}.
{pref_public_key_algs, list()}:
List of user (client) public key algorithms to try to use.
The default value is ['ssh-rsa','ssh-dss','ecdsa-sha2-nistp256','ecdsa-sha2-nistp384','ecdsa-
sha2-nistp521']
If there is no public key of a specified type available, the corresponding entry is ignored.
{preferred_algorithms, algs_list()}:
List of algorithms to use in the algorithm negotiation. The default algs_list() can be
obtained from default_algorithms/0.
If an alg_entry() is missing in the algs_list(), the default value is used for that entry.
Here is an example of this option:
{preferred_algorithms,
[{public_key,['ssh-rsa','ssh-dss']},
{cipher,[{client2server,['aes128-ctr']},
{server2client,['aes128-cbc','3des-cbc']}]},
{mac,['hmac-sha2-256','hmac-sha1']},
{compression,[none,zlib]}
}
The example specifies different algorithms in the two directions (client2server and
server2client), for cipher but specifies the same algorithms for mac and compression in both
directions. The kex (key exchange) is implicit but public_key is set explicitly.
Warning:
Changing the values can make a connection less secure. Do not change unless you know exactly
what you are doing. If you do not understand the values then you are not supposed to change
them.
{dh_gex_limits,{Min=integer(),I=integer(),Max=integer()}}:
Sets the three diffie-hellman-group-exchange parameters that guides the connected server in
choosing a group. See RFC 4419 for the function of thoose. The default value is {1024, 6144,
8192}.
{connect_timeout, timeout()}:
Sets a time-out on the transport layer connection. For gen_tcp the time is in milli-seconds
and the default value is infinity.
{user, string()}:
Provides a username. If this option is not given, ssh reads from the environment (LOGNAME or
USER on UNIX, USERNAME on Windows).
{password, string()}:
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.
{key_cb, key_cb()}:
Module implementing the behaviour ssh_client_key_api. Can be used to customize the handling of
public keys. If callback options are provided along with the module name, they are made
available to the callback module via the options passed to it under the key 'key_cb_private'.
{quiet_mode, atom() = boolean()}:
If true, the client does not print anything on authorization.
{id_string, random | string()}:
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.
The value random 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.
{fd, file_descriptor()}:
Allows an existing file descriptor to be used (by passing it on to the transport protocol).
{rekey_limit, integer()}:
Provides, in bytes, when rekeying is to be initiated. Defaults to once per each GB and once
per hour.
{idle_time, integer()}:
Sets a time-out on a connection when no channels are active. Defaults to infinity.
{ssh_msg_debug_fun, fun(ConnectionRef::ssh_connection_ref(), AlwaysDisplay::boolean(),
Msg::binary(), LanguageTag::binary()) -> _}:
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 ConnectionRef is the reference
to the connection on which the message arrived. The return value from the fun is not checked.
The default behaviour is ignore the message. To get a printout for each message with
AlwaysDisplay = true, use for example {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG:
~p~n", [M]) end}
connection_info(ConnectionRef, [Option]) ->[{Option, Value}]
Types:
Option = client_version | server_version | user | peer | sockname
Value = [option_value()]
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()}
Retrieves information about a connection.
daemon(Port) ->
daemon(Port, Options) ->
daemon(HostAddress, Port, Options) -> {ok, ssh_daemon_ref()} | {error, atom()}
Types:
Port = integer()
HostAddress = ip_address() | any
Options = [{Option, Value}]
Option = atom()
Value = term()
Starts a server listening for SSH connections on the given port.
Options:
{inet, inet | inet6}:
IP version to use when the host address is specified as any.
{subsystems, [subsystem_spec()]}:
Provides specifications for handling of subsystems. The "sftp" subsystem specification is
retrieved by calling ssh_sftpd:subsystem_spec/1. If the subsystems option is not present, the
value of [ssh_sftpd:subsystem_spec([])] is used. The option can be set to the empty list if
you do not want the daemon to run any subsystems.
{shell, {Module, Function, Args} | fun(string() = User) - > pid() | fun(string() = User,
ip_address() = PeerAddr) -> pid()}:
Defines the read-eval-print loop used when a shell is requested by the client. The default is
to use the Erlang shell: {shell, start, []}
{ssh_cli, {channel_callback(), channel_init_args()} | no_cli}:
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 shell. This means less work than implementing an own CLI channel. If set to no_cli, the
CLI channels are disabled and only subsystem channels are allowed.
{user_dir, string()}:
Sets the user directory. That is, the directory containing ssh configuration files for the
user, such as known_hosts, id_rsa, id_dsa, and authorized_key. Defaults to the directory
normally referred to as ~/.ssh.
{system_dir, string()}:
Sets the system directory, containing the host key files that identify the host keys for ssh.
Defaults to /etc/ssh. For security reasons, this directory is normally accessible only to the
root user.
{auth_methods, string()}:
Comma-separated string that determines which authentication methods that the server is to
support and in what order they are tried. Defaults to "publickey,keyboard-
interactive,password"
{auth_method_kb_interactive_data, PromptTexts}
where:
PromptTexts = kb_int_tuple() | fun(Peer::{IP::tuple(),Port::integer()}, User::string(),
Service::string()) -> kb_int_tuple()
kb_int_tuple() = {Name::string(), Instruction::string(), Prompt::string(), Echo::boolean()}:
Sets the text strings that the daemon sends to the client for presentation to the user when
using keyboar-interactive authentication. If the fun/3 is used, it is called when the actual
authentication occurs and may therefore return dynamic data like time, remote ip etc.
The parameter Echo guides the client about need to hide the password.
The default value is: {auth_method_kb_interactive_data, {"SSH server", "Enter password for
\""++User++"\"", "password: ", false}>
{user_passwords, [{string() = User, string() = Password}]}:
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.
{password, string()}:
Provides a global password that authenticates any user. From a security perspective this
option makes the server very vulnerable.
{preferred_algorithms, algs_list()}:
List of algorithms to use in the algorithm negotiation. The default algs_list() can be
obtained from default_algorithms/0.
If an alg_entry() is missing in the algs_list(), the default value is used for that entry.
Here is an example of this option:
{preferred_algorithms,
[{public_key,['ssh-rsa','ssh-dss']},
{cipher,[{client2server,['aes128-ctr']},
{server2client,['aes128-cbc','3des-cbc']}]},
{mac,['hmac-sha2-256','hmac-sha1']},
{compression,[none,zlib]}
}
The example specifies different algorithms in the two directions (client2server and
server2client), for cipher but specifies the same algorithms for mac and compression in both
directions. The kex (key exchange) is implicit but public_key is set explicitly.
Warning:
Changing the values can make a connection less secure. Do not change unless you know exactly
what you are doing. If you do not understand the values then you are not supposed to change
them.
{dh_gex_groups, [{Size=integer(),G=integer(),P=integer()}] | {file,filename()}
{ssh_moduli_file,filename()} }:
Defines the groups the server may choose among when diffie-hellman-group-exchange is
negotiated. See RFC 4419 for details. The three variants of this option are:
{Size=integer(),G=integer(),P=integer()}:
The groups are given explicitly in this list. There may be several elements with the same
Size. In such a case, the server will choose one randomly in the negotiated Size.
{file,filename()}:
The file must have one or more three-tuples {Size=integer(),G=integer(),P=integer()}
terminated by a dot. The file is read when the daemon starts.
{ssh_moduli_file,filename()}:
The file must be in ssh-keygen moduli file format. The file is read when the daemon starts.
The default list is fetched from the public_key application.
{dh_gex_limits,{Min=integer(),Max=integer()}}:
Limits what a client can ask for in diffie-hellman-group-exchange. The limits will be {MaxUsed
= min(MaxClient,Max), MinUsed = max(MinClient,Min)} where MaxClient and MinClient are the
values proposed by a connecting client.
The default value is {0,infinity}.
If MaxUsed < MinUsed in a key exchange, it will fail with a disconnect.
See RFC 4419 for the function of the Max and Min values.
{pwdfun, fun(User::string(), Password::string(), PeerAddress::{ip_adress(),port_number()},
State::any()) -> boolean() | disconnect | {boolean(),any()} }:
Provides a function for password validation. This could used for calling an external system or
if passwords should be stored as a hash. The fun returns:
* true if the user and password is valid and
* false otherwise.
This fun can also be used to make delays in authentication tries for example by calling
timer:sleep/1. To facilitate counting of failed tries the State variable could be used. This
state is per connection only. The first time the pwdfun is called for a connection, the State
variable has the value undefined. The pwdfun can return - in addition to the values above - a
new state as:
* {true, NewState:any()} if the user and password is valid or
* {false, NewState:any()} if the user or password is invalid
A third usage is to block login attempts from a missbehaving peer. The State described above
can be used for this. In addition to the responses above, the following return value is
introduced:
* disconnect if the connection should be closed immediately after sending a SSH_MSG_DISCONNECT
message.
{pwdfun, fun(User::string(), Password::string()) -> boolean()}:
Provides a function for password validation. This function is called with user and password as
strings, and returns true if the password is valid and false otherwise.
This option ({pwdfun,fun/2}) is the same as a subset of the previous ({pwdfun,fun/4}). It is
kept for compatibility.
{negotiation_timeout, integer()}:
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.
{max_sessions, pos_integer()}:
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 N, and N clients have
connected but not started the login process, connection attempt N+1 is aborted. If N
connections are authenticated and still logged in, no more logins are accepted until one of
the existing ones log out.
The counter is per listening port. Thus, if two daemons are started, one with {max_sessions,N}
and the other with {max_sessions,M}, in total N+M connections are accepted for the whole ssh
application.
Notice that if parallel_login is false, only one client at a time can be in the authentication
phase.
By default, this option is not set. This means that the number is not limited.
{max_channels, pos_integer()}:
The maximum number of channels with active remote subsystem that are accepted for each
connection to this daemon
By default, this option is not set. This means that the number is not limited.
{parallel_login, boolean()}:
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.
If the max_sessions option is set to N and parallel_login is set to true, the maximum number
of simultaneous login attempts at any time is limited to N-K, where K is the number of
authenticated connections present at this daemon.
Warning:
Do not enable parallel_logins without protecting the server by other means, for example, by the
max_sessions option or a firewall configuration. If set to true, there is no protection against
DOS attacks.
{minimal_remote_max_packet_size, non_negative_integer()}:
The least maximum packet size that the daemon will accept in channel open requests from the
client. The default value is 0.
{id_string, random | string()}:
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.
The value random 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.
{key_cb, key_cb()}:
Module implementing the behaviour ssh_server_key_api. Can be used to customize the handling of
public keys. If callback options are provided along with the module name, they are made
available to the callback module via the options passed to it under the key 'key_cb_private'.
{profile, atom()}:
Used together with ip-address and port to uniquely identify a ssh daemon. This can be useful
in a virtualized environment, where there can be more that one server that has the same ip-
address and port. If this property is not explicitly set, it is assumed that the the ip-
address and port uniquely identifies the SSH daemon.
{fd, file_descriptor()}:
Allows an existing file-descriptor to be used (passed on to the transport protocol).
{failfun, fun(User::string(), PeerAddress::ip_address(), Reason::term()) -> _}:
Provides a fun to implement your own logging when a user fails to authenticate.
{connectfun, fun(User::string(), PeerAddress::ip_address(), Method::string()) ->_}:
Provides a fun to implement your own logging when a user authenticates to the server.
{disconnectfun, fun(Reason:term()) -> _}:
Provides a fun to implement your own logging when a user disconnects from the server.
{unexpectedfun, fun(Message:term(), Peer) -> report | skip }:
Provides a fun to implement your own logging or other action when an unexpected message
arrives. If the fun returns report the usual info report is issued but if skip is returned no
report is generated.
Peer is in the format of {Host,Port}.
{ssh_msg_debug_fun, fun(ConnectionRef::ssh_connection_ref(), AlwaysDisplay::boolean(),
Msg::binary(), LanguageTag::binary()) -> _}:
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 ConnectionRef is the reference
to the connection on which the message arrived. The return value from the fun is not checked.
The default behaviour is ignore the message. To get a printout for each message with
AlwaysDisplay = true, use for example {ssh_msg_debug_fun, fun(_,true,M,_)-> io:format("DEBUG:
~p~n", [M]) end}
default_algorithms() -> algs_list()
Returns a key-value list, where the keys are the different types of algorithms and the values are
the algorithms themselves. An example:
20> ssh:default_algorithms().
[{kex,['diffie-hellman-group1-sha1']},
{public_key,['ssh-rsa','ssh-dss']},
{cipher,[{client2server,['aes128-ctr','aes128-cbc','3des-cbc']},
{server2client,['aes128-ctr','aes128-cbc','3des-cbc']}]},
{mac,[{client2server,['hmac-sha2-256','hmac-sha1']},
{server2client,['hmac-sha2-256','hmac-sha1']}]},
{compression,[{client2server,[none,zlib]},
{server2client,[none,zlib]}]}]
21>
shell(Host) ->
shell(Host, Option) ->
shell(Host, Port, Option) -> _
Types:
Host = string()
Port = integer()
Options - see ssh:connect/3
Starts an interactive shell over an SSH server on the given Host. The function waits for user
input, and does not return until the remote shell is ended (that is, exit from the shell).
start() ->
start(Type) -> ok | {error, Reason}
Types:
Type = permanent | transient | temporary
Reason = term()
Utility function that starts the applications crypto, public_key, and ssh. Default type is
temporary. For more information, see the application(3erl) manual page in kernel.
stop() -> ok | {error, Reason}
Types:
Reason = term()
Stops the ssh application. For more information, see the application(3erl) manual page in kernel.
stop_daemon(DaemonRef) ->
stop_daemon(Address, Port) -> ok
Types:
DaemonRef = ssh_daemon_ref()
Address = ip_address()
Port = integer()
Stops the listener and all connections started by the listener.
stop_listener(DaemonRef) ->
stop_listener(Address, Port) -> ok
Types:
DaemonRef = ssh_daemon_ref()
Address = ip_address()
Port = integer()
Stops the listener, but leaves existing connections started by the listener operational.
Ericsson AB ssh 4.2.2 ssh(3erl)