ssh

Interface module for the SSH application.

• SSH requires the crypto and public_key applications.
• Supported SSH version is 2.0
• Supported MAC algorithms: hmac-sha2-256 and hmac-sha1
• Supported encryption algorithms: aes128-ctr, aes128-cb and 3des-cbc
• Supports unicode filenames if the emulator and the underlaying OS supports it. See the DESCRIPTION section in file for information about this subject
• Supports unicode in shell and cli

Type definitions that are used more than once in this module and/or abstractions to indicate the intended use of the data type:

boolean() = true | false

string() = [byte()]

ssh_daemon_ref() - opaque to the user returned by ssh:daemon/[1,2,3]

ssh_connection_ref() - opaque to the user 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(3)

channel_init_args() = list()

Types:

Closes an SSH connection.

Types:

Connects to an SSH server. No channel is started. This is done by calling ssh_connection:session_channel/[2, 4].

Options are:

{inet, inet | inet6}

IP version to use.

{user_dir, string()}

Sets the user directory i.e. 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 that the server will 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. Do note that it may not always be desirable to use those options from a security point of view.

{public_key_alg, 'ssh-rsa' | 'ssh-dss'}

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 'ssh-rsa' first.

{pref_public_key_algs, list()}

List of public key algorithms to try to use, 'ssh-rsa' and 'ssh-dss' available. Will override {public_key_alg, 'ssh-rsa' | 'ssh-dss'}

{connect_timeout, timeout()}

Sets a timeout on the transport layer connection. Defaults to infinity.

{user, string()}

Provides a user name. If this option is not given, ssh reads from the environment (LOGNAME or USER on unix, USERNAME on Windows).

{password, string()}

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.

{key_cb, atom()}

Module implementing the behaviour ssh_client_key_api. Can be used to customize the handling of public keys.

{quiet_mode, atom() = boolean()}

If true, the client will not print out anything on authorization.

{fd, file_descriptor()}

Allow an existing file descriptor to be used (simply passed on to the transport protocol).

{rekey_limit, integer()}

Provide, in bytes, when rekeying should be initiated, defaults to one time each GB and one time per hour.

{idle_time, integer()}

Sets a timeout on connection when no channels are active, default is infinity

Types:

Retrieves information about a connection.

Types:

Starts a server listening for SSH connections on the given port.

Options are:

{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 spec can be retrieved by calling ssh_sftpd:subsystem_spec/1. If the subsystems option is not present the value of [ssh_sftpd:subsystem_spec([])] 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.

{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. Default is to use the erlang shell: {shell, start, []}

{ssh_cli, {channel_callback(), channel_init_args()} | no_cli}

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 shell which is much less work than implementing your own CLI channel. If set to no_cli you will disable CLI channels and only subsystem channels will be allowed.

{user_dir, String}

Sets the user directory i.e. 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 identifies the host keys for ssh. The default is /etc/ssh, note that for security reasons this directory is normally only accessible by the root user.

{auth_methods, string()}

Comma separated string that determines which authentication methodes that the server should support and in what order they will be tried. Defaults to "publickey,keyboard-interactive,password"

{user_passwords, [{string() = User, string() = Password}]}

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.

{password, string()}

Provide a global password that will authenticate any user. From a security perspective this option makes the server very vulnerable.

{pwdfun, fun(User::string(), password::string()) -> boolean()}

Provide a function for password validation. This is called with user and password as strings, and should return true if the password is valid and false otherwise.

{negotiation_timeout, integer()}

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.

{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. So if set to N, and N clients have connected but not started the login process, the N+1 connection attempt will be aborted. If N connections are authenticated and still logged in, no more loggins will be accepted until one of the existing ones log out.

The counter is per listening port, so if two daemons are started, one with {max_sessions,N} and the other with {max_sessions,M} there will be in total N+M connections accepted for the whole ssh application.

Note that if parallel_login is false, only one client at a time may be in the authentication phase.

As default, the 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 a time. If set to true, an unlimited number of login attempts will be allowed simultanously.

If the max_sessions option is set to N and parallel_login is set to true, the max 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 the max_sessions option or a firewall configuration. If set to true, there is no protection against DOS attacks.

{key_cb, atom()}

Module implementing the behaviour ssh_server_key_api. Can be used to customize the handling of public keys.

{fd, file_descriptor()}

Allow an existing file-descriptor to be used (simply passed on to the transport protocol).

{failfun, fun(User::string(), PeerAddress::ip_address(), Reason::term()) -> _}

Provide a fun to implement your own logging when a user fails to authenticate.

{connectfun, fun(User::string(), PeerAddress::ip_address(), Method::string()) ->_}

Provide a fun to implement your own logging when a user authenticates to the server.

{disconnectfun, fun(Reason:term()) -> _}

Provide a fun to implement your own logging when a user disconnects from the server.

Types:

Starts an interactive shell via an SSH server on the given Host. The function waits for user input, and will not return until the remote shell is ended (i.e. exit from the shell).

Types:

Utility function that starts crypto, public_key and the SSH application. Defult type is temporary. See also application(3)

Types:

Stops the SSH application. See also application(3)

Types:

Stops the listener and all connections started by the listener.

Types:

Stops the listener, but leaves existing connections started by the listener up and running.