Server implementation — Paramiko documentation

# Server implementation

`ServerInterface` is an interface to override for server support.

class paramiko.server.ServerInterface

  This class defines an interface for controlling the behavior of Paramiko in server mode.

  Methods on this class are called from Paramiko’s primary thread, so you shouldn’t do too much work in them. (Certainly nothing that blocks or sleeps.)

  check_channel_request(kind, chanid)

    Determine if a channel request of a given type will be granted, and return `OPEN_SUCCEEDED` or an error code. This method is called in server mode when the client requests a channel, after authentication is complete.

    If you allow channel requests (and an ssh server that didn’t would be useless), you should also override some of the channel request methods below, which are used to determine which services will be allowed on a given channel:

    > - `check_channel_pty_request`

    > - `check_channel_shell_request`

    > - `check_channel_subsystem_request`

    > - `check_channel_window_change_request`

    > - `check_channel_x11_request`

    > - `check_channel_forward_agent_request`

    The `chanid` parameter is a small number that uniquely identifies the channel within a `Transport`. A `Channel` object is not created unless this method returns `OPEN_SUCCEEDED` – once a `Channel` object is created, you can call `Channel.get_id` to retrieve the channel ID.

    The return value should either be `OPEN_SUCCEEDED` (or `0`) to allow the channel request, or one of the following error codes to reject it:

    > - `OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED`

    > - `OPEN_FAILED_CONNECT_FAILED`

    > - `OPEN_FAILED_UNKNOWN_CHANNEL_TYPE`

    > - `OPEN_FAILED_RESOURCE_SHORTAGE`

    The default implementation always returns `OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED`.

    Parameters

      - kind (str) – the kind of channel the client would like to open (usually `"session"`).

      - chanid (int) – ID of the channel

    Returns

      an `int` success or failure code (listed above)

  get_allowed_auths(username)

    Return a list of authentication methods supported by the server. This list is sent to clients attempting to authenticate, to inform them of authentication methods that might be successful.

    The “list” is actually a string of comma-separated names of types of authentication. Possible values are `"password"`, `"publickey"`, and `"none"`.

    The default implementation always returns `"password"`.

    Parameters

      username (str) – the username requesting authentication.

    Returns

      a comma-separated `str` of authentication types

  check_auth_none(username)

    Determine if a client may open channels with no (further) authentication.

    Return `AUTH_FAILED` if the client must authenticate, or `AUTH_SUCCESSFUL` if it’s okay for the client to not authenticate.

    The default implementation always returns `AUTH_FAILED`.

    Parameters

      username (str) – the username of the client.

    Returns

      `AUTH_FAILED` if the authentication fails; `AUTH_SUCCESSFUL` if it succeeds.

    Return type

      int

  check_auth_password(username, password)

    Determine if a given username and password supplied by the client is acceptable for use in authentication.

    Return `AUTH_FAILED` if the password is not accepted, `AUTH_SUCCESSFUL` if the password is accepted and completes the authentication, or `AUTH_PARTIALLY_SUCCESSFUL` if your authentication is stateful, and this key is accepted for authentication, but more authentication is required. (In this latter case, `get_allowed_auths` will be called to report to the client what options it has for continuing the authentication.)

    The default implementation always returns `AUTH_FAILED`.

    Parameters

      - username (str) – the username of the authenticating client.

      - password (str) – the password given by the client.

    Returns

      `AUTH_FAILED` if the authentication fails; `AUTH_SUCCESSFUL` if it succeeds; `AUTH_PARTIALLY_SUCCESSFUL` if the password auth is successful, but authentication must continue.

    Return type

      int

  check_auth_publickey(username, key)

    Determine if a given key supplied by the client is acceptable for use in authentication. You should override this method in server mode to check the username and key and decide if you would accept a signature made using this key.

    Return `AUTH_FAILED` if the key is not accepted, `AUTH_SUCCESSFUL` if the key is accepted and completes the authentication, or `AUTH_PARTIALLY_SUCCESSFUL` if your authentication is stateful, and this password is accepted for authentication, but more authentication is required. (In this latter case, `get_allowed_auths` will be called to report to the client what options it has for continuing the authentication.)

    Note that you don’t have to actually verify any key signtature here. If you’re willing to accept the key, Paramiko will do the work of verifying the client’s signature.

    The default implementation always returns `AUTH_FAILED`.

    Parameters

      - username (str) – the username of the authenticating client

      - key (PKey) – the key object provided by the client

    Returns

      `AUTH_FAILED` if the client can’t authenticate with this key; `AUTH_SUCCESSFUL` if it can; `AUTH_PARTIALLY_SUCCESSFUL` if it can authenticate with this key but must continue with authentication

    Return type

      int

  check_auth_interactive(username, submethods)

    Begin an interactive authentication challenge, if supported. You should override this method in server mode if you want to support the `"keyboard-interactive"` auth type, which requires you to send a series of questions for the client to answer.

    Return `AUTH_FAILED` if this auth method isn’t supported. Otherwise, you should return an `InteractiveQuery` object containing the prompts and instructions for the user. The response will be sent via a call to `check_auth_interactive_response`.

    The default implementation always returns `AUTH_FAILED`.

    Parameters

      - username (str) – the username of the authenticating client

      - submethods (str) – a comma-separated list of methods preferred by the client (usually empty)

    Returns

      `AUTH_FAILED` if this auth method isn’t supported; otherwise an object containing queries for the user

    Return type

      int or `InteractiveQuery`

  check_auth_interactive_response(responses)

    Continue or finish an interactive authentication challenge, if supported. You should override this method in server mode if you want to support the `"keyboard-interactive"` auth type.

    Return `AUTH_FAILED` if the responses are not accepted, `AUTH_SUCCESSFUL` if the responses are accepted and complete the authentication, or `AUTH_PARTIALLY_SUCCESSFUL` if your authentication is stateful, and this set of responses is accepted for authentication, but more authentication is required. (In this latter case, `get_allowed_auths` will be called to report to the client what options it has for continuing the authentication.)

    If you wish to continue interactive authentication with more questions, you may return an `InteractiveQuery` object, which should cause the client to respond with more answers, calling this method again. This cycle can continue indefinitely.

    The default implementation always returns `AUTH_FAILED`.

    Parameters

      responses – list of `str` responses from the client

    Returns

      `AUTH_FAILED` if the authentication fails; `AUTH_SUCCESSFUL` if it succeeds; `AUTH_PARTIALLY_SUCCESSFUL` if the interactive auth is successful, but authentication must continue; otherwise an object containing queries for the user

    Return type

      int or `InteractiveQuery`

  check_auth_gssapi_with_mic(username, gss_authenticated=2, cc_file=None)

    Authenticate the given user to the server if he is a valid krb5 principal.

    Parameters

      - username (str) – The username of the authenticating client

      - gss_authenticated (int) – The result of the krb5 authentication

      - cc_filename (str) – The krb5 client credentials cache filename

    Returns

      `AUTH_FAILED` if the user is not authenticated otherwise `AUTH_SUCCESSFUL`

    Return type

      int

    Note

      Kerberos credential delegation is not supported.

    See

      `ssh_gss`

    Note

      : We are just checking in L{AuthHandler} that the given user is a valid krb5 principal! We don’t check if the krb5 principal is allowed to log in on the server, because there is no way to do that in python. So if you develop your own SSH server with paramiko for a certain platform like Linux, you should call C{krb5_kuserok()} in your local kerberos library to make sure that the krb5_principal has an account on the server and is allowed to log in as a user.

    See

      http://www.unix.com/man-page/all/3/krb5_kuserok/

  check_auth_gssapi_keyex(username, gss_authenticated=2, cc_file=None)

    Authenticate the given user to the server if he is a valid krb5 principal and GSS-API Key Exchange was performed. If GSS-API Key Exchange was not performed, this authentication method won’t be available.

    Parameters

      - username (str) – The username of the authenticating client

      - gss_authenticated (int) – The result of the krb5 authentication

      - cc_filename (str) – The krb5 client credentials cache filename

    Returns

      `AUTH_FAILED` if the user is not authenticated otherwise `AUTH_SUCCESSFUL`

    Return type

      int

    Note

      Kerberos credential delegation is not supported.

    See

      `ssh_gss` `kex_gss`

    Note

      : We are just checking in L{AuthHandler} that the given user is a valid krb5 principal! We don’t check if the krb5 principal is allowed to log in on the server, because there is no way to do that in python. So if you develop your own SSH server with paramiko for a certain platform like Linux, you should call C{krb5_kuserok()} in your local kerberos library to make sure that the krb5_principal has an account on the server and is allowed to log in as a user.

    See

      http://www.unix.com/man-page/all/3/krb5_kuserok/

  enable_auth_gssapi()

    Overwrite this function in your SSH server to enable GSSAPI authentication. The default implementation always returns false.

    Returns bool

      Whether GSSAPI authentication is enabled.

    See

      `ssh_gss`

  check_port_forward_request(address, port)

    Handle a request for port forwarding. The client is asking that connections to the given address and port be forwarded back across this ssh connection. An address of `"0.0.0.0"` indicates a global address (any address associated with this server) and a port of `0` indicates that no specific port is requested (usually the OS will pick a port).

    The default implementation always returns `False`, rejecting the port forwarding request. If the request is accepted, you should return the port opened for listening.

    Parameters

      - address (str) – the requested address

      - port (int) – the requested port

    Returns

      the port number (`int`) that was opened for listening, or `False` to reject

  cancel_port_forward_request(address, port)

    The client would like to cancel a previous port-forwarding request. If the given address and port is being forwarded across this ssh connection, the port should be closed.

    Parameters

      - address (str) – the forwarded address

      - port (int) – the forwarded port

  check_global_request(kind, msg)

    Handle a global request of the given `kind`. This method is called in server mode and client mode, whenever the remote host makes a global request. If there are any arguments to the request, they will be in `msg`.

    There aren’t any useful global requests defined, aside from port forwarding, so usually this type of request is an extension to the protocol.

    If the request was successful and you would like to return contextual data to the remote host, return a tuple. Items in the tuple will be sent back with the successful result. (Note that the items in the tuple can only be strings, ints, or bools.)

    The default implementation always returns `False`, indicating that it does not support any global requests.

    Note

    Port forwarding requests are handled separately, in `check_port_forward_request`.

    Parameters

      - kind (str) – the kind of global request being made.

      - msg (Message) – any extra arguments to the request.

    Returns

      `True` or a `tuple` of data if the request was granted; `False` otherwise.

  check_channel_pty_request(channel, term, width, height, pixelwidth, pixelheight, modes)

    Determine if a pseudo-terminal of the given dimensions (usually requested for shell access) can be provided on the given channel.

    The default implementation always returns `False`.

    Parameters

      - channel (Channel) – the `Channel` the pty request arrived on.

      - term (str) – type of terminal requested (for example, `"vt100"`).

      - width (int) – width of screen in characters.

      - height (int) – height of screen in characters.

      - pixelwidth (int) – width of screen in pixels, if known (may be `0` if unknown).

      - pixelheight (int) – height of screen in pixels, if known (may be `0` if unknown).

    Returns

      `True` if the pseudo-terminal has been allocated; `False` otherwise.

  check_channel_shell_request(channel)

    Determine if a shell will be provided to the client on the given channel. If this method returns `True`, the channel should be connected to the stdin/stdout of a shell (or something that acts like a shell).

    The default implementation always returns `False`.

    Parameters

      channel (Channel) – the `Channel` the request arrived on.

    Returns

      `True` if this channel is now hooked up to a shell; `False` if a shell can’t or won’t be provided.

  check_channel_exec_request(channel, command)

    Determine if a shell command will be executed for the client. If this method returns `True`, the channel should be connected to the stdin, stdout, and stderr of the shell command.

    The default implementation always returns `False`.

    Parameters

      - channel (Channel) – the `Channel` the request arrived on.

      - command (str) – the command to execute.

    Returns

      `True` if this channel is now hooked up to the stdin, stdout, and stderr of the executing command; `False` if the command will not be executed.

    New in version 1.1.

  check_channel_subsystem_request(channel, name)

    Determine if a requested subsystem will be provided to the client on the given channel. If this method returns `True`, all future I/O through this channel will be assumed to be connected to the requested subsystem. An example of a subsystem is `sftp`.

    The default implementation checks for a subsystem handler assigned via `Transport.set_subsystem_handler`. If one has been set, the handler is invoked and this method returns `True`. Otherwise it returns `False`.

    Note

    Because the default implementation uses the `Transport` to identify valid subsystems, you probably won’t need to override this method.

    Parameters

      - channel (Channel) – the `Channel` the pty request arrived on.

      - name (str) – name of the requested subsystem.

    Returns

      `True` if this channel is now hooked up to the requested subsystem; `False` if that subsystem can’t or won’t be provided.

  check_channel_window_change_request(channel, width, height, pixelwidth, pixelheight)

    Determine if the pseudo-terminal on the given channel can be resized. This only makes sense if a pty was previously allocated on it.

    The default implementation always returns `False`.

    Parameters

      - channel (Channel) – the `Channel` the pty request arrived on.

      - width (int) – width of screen in characters.

      - height (int) – height of screen in characters.

      - pixelwidth (int) – width of screen in pixels, if known (may be `0` if unknown).

      - pixelheight (int) – height of screen in pixels, if known (may be `0` if unknown).

    Returns

      `True` if the terminal was resized; `False` if not.

  check_channel_x11_request(channel, single_connection, auth_protocol, auth_cookie, screen_number)

    Determine if the client will be provided with an X11 session. If this method returns `True`, X11 applications should be routed through new SSH channels, using `Transport.open_x11_channel`.

    The default implementation always returns `False`.

    Parameters

      - channel (Channel) – the `Channel` the X11 request arrived on

      - single_connection (bool) – `True` if only a single X11 channel should be opened, else `False`.

      - auth_protocol (str) – the protocol used for X11 authentication

      - auth_cookie (str) – the cookie used to authenticate to X11

      - screen_number (int) – the number of the X11 screen to connect to

    Returns

      `True` if the X11 session was opened; `False` if not

  check_channel_forward_agent_request(channel)

    Determine if the client will be provided with an forward agent session. If this method returns `True`, the server will allow SSH Agent forwarding.

    The default implementation always returns `False`.

    Parameters

      channel (Channel) – the `Channel` the request arrived on

    Returns

      `True` if the AgentForward was loaded; `False` if not

    If `True` is returned, the server should create an `AgentServerProxy` to access the agent.

  check_channel_direct_tcpip_request(chanid, origin, destination)

    Determine if a local port forwarding channel will be granted, and return `OPEN_SUCCEEDED` or an error code. This method is called in server mode when the client requests a channel, after authentication is complete.

    The `chanid` parameter is a small number that uniquely identifies the channel within a `Transport`. A `Channel` object is not created unless this method returns `OPEN_SUCCEEDED` – once a `Channel` object is created, you can call `Channel.get_id` to retrieve the channel ID.

    The origin and destination parameters are (ip_address, port) tuples that correspond to both ends of the TCP connection in the forwarding tunnel.

    The return value should either be `OPEN_SUCCEEDED` (or `0`) to allow the channel request, or one of the following error codes to reject it:

    > - `OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED`

    > - `OPEN_FAILED_CONNECT_FAILED`

    > - `OPEN_FAILED_UNKNOWN_CHANNEL_TYPE`

    > - `OPEN_FAILED_RESOURCE_SHORTAGE`

    The default implementation always returns `OPEN_FAILED_ADMINISTRATIVELY_PROHIBITED`.

    Parameters

      - chanid (int) – ID of the channel

      - origin (tuple) – 2-tuple containing the IP address and port of the originator (client side)

      - destination (tuple) – 2-tuple containing the IP address and port of the destination (server side)

    Returns

      an `int` success or failure code (listed above)

  check_channel_env_request(channel, name, value)

    Check whether a given environment variable can be specified for the given channel. This method should return `True` if the server is willing to set the specified environment variable. Note that some environment variables (e.g., PATH) can be exceedingly dangerous, so blindly allowing the client to set the environment is almost certainly not a good idea.

    The default implementation always returns `False`.

    Parameters

      - channel – the `Channel` the env request arrived on

      - name (str) – name

      - value (str) – Channel value

    Returns

      A boolean

  get_banner()

    A pre-login banner to display to the user. The message may span multiple lines separated by crlf pairs. The language should be in rfc3066 style, for example: en-US

    The default implementation always returns `(None, None)`.

    Returns

      A tuple containing the banner and language code.

    New in version 2.3.

  __weakref__

    list of weak references to the object (if defined)

class paramiko.server.InteractiveQuery(name='', instructions='', *prompts)

  A query (set of prompts) for a user during interactive authentication.

  __init__(name='', instructions='', *prompts)

    Create a new interactive query to send to the client. The name and instructions are optional, but are generally displayed to the end user. A list of prompts may be included, or they may be added via the `add_prompt` method.

    Parameters

      - name (str) – name of this query

      - instructions (str) – user instructions (usually short) about this query

      - prompts (str) – one or more authentication prompts

  add_prompt(prompt, echo=True)

    Add a prompt to this query. The prompt should be a (reasonably short) string. Multiple prompts can be added to the same query.

    Parameters

      - prompt (str) – the user prompt

      - echo (bool) – `True` (default) if the user’s response should be echoed; `False` if not (for a password or similar)

  __weakref__

    list of weak references to the object (if defined)

class paramiko.server.SubsystemHandler(channel, name, server)

  Handler for a subsystem in server mode. If you create a subclass of this class and pass it to `Transport.set_subsystem_handler`, an object of this class will be created for each request for this subsystem. Each new object will be executed within its own new thread by calling `start_subsystem`. When that method completes, the channel is closed.

  For example, if you made a subclass `MP3Handler` and registered it as the handler for subsystem `"mp3"`, then whenever a client has successfully authenticated and requests subsystem `"mp3"`, an object of class `MP3Handler` will be created, and `start_subsystem` will be called on it from a new thread.

  __init__(channel, name, server)

    Create a new handler for a channel. This is used by `ServerInterface` to start up a new handler when a channel requests this subsystem. You don’t need to override this method, but if you do, be sure to pass the `channel` and `name` parameters through to the original `__init__` method here.

    Parameters

      - channel (Channel) – the channel associated with this subsystem request.

      - name (str) – name of the requested subsystem.

      - server (ServerInterface) – the server object for the session that started this subsystem

  get_server()

    Return the `ServerInterface` object associated with this channel and subsystem.

  start_subsystem(name, transport, channel)

    Process an ssh subsystem in server mode. This method is called on a new object (and in a new thread) for each subsystem request. It is assumed that all subsystem logic will take place here, and when the subsystem is finished, this method will return. After this method returns, the channel is closed.

    The combination of `transport` and `channel` are unique; this handler corresponds to exactly one `Channel` on one `Transport`.

    Note

    It is the responsibility of this method to exit if the underlying `Transport` is closed. This can be done by checking `Transport.is_active` or noticing an EOF on the `Channel`. If this method loops forever without checking for this case, your Python interpreter may refuse to exit because this thread will still be running.

    Parameters

      - name (str) – name of the requested subsystem.

      - transport (Transport) – the server-mode `Transport`.

      - channel (Channel) – the channel associated with this subsystem request.

  finish_subsystem()

    Perform any cleanup at the end of a subsystem. The default implementation just closes the channel.

    New in version 1.1.