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:
The
chanid
parameter is a small number that uniquely identifies the channel within aTransport
. AChannel
object is not created unless this method returnsOPEN_SUCCEEDED
– once aChannel
object is created, you can callChannel.get_id
to retrieve the channel ID.The return value should either be
OPEN_SUCCEEDED
(or0
) 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
.
- 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"
.
- check_auth_none(username)¶
Determine if a client may open channels with no (further) authentication.
Return
AUTH_FAILED
if the client must authenticate, orAUTH_SUCCESSFUL
if it’s okay for the client to not authenticate.The default implementation always returns
AUTH_FAILED
.
- 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, orAUTH_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
- 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
- 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, orAUTH_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
- 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
- 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 anInteractiveQuery
object containing the prompts and instructions for the user. The response will be sent via a call tocheck_auth_interactive_response
.The default implementation always returns
AUTH_FAILED
.- Parameters
- 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, orAUTH_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
- Returns
AUTH_FAILED
if the user is not authenticated otherwiseAUTH_SUCCESSFUL
- Return type
- Note
Kerberos credential delegation is not supported.
- See
- 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
- 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
- Returns
AUTH_FAILED
if the user is not authenticated otherwiseAUTH_SUCCESSFUL
- Return type
- Note
Kerberos credential delegation is not supported.
- See
- 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
- 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
- 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 of0
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.
- 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.
- 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 inmsg
.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
.
- 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
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
.
- 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
- 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 issftp
.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 returnsTrue
. Otherwise it returnsFalse
.Note
Because the default implementation uses the
Transport
to identify valid subsystems, you probably won’t need to override this method.
- 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
- 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, usingTransport.open_x11_channel
.The default implementation always returns
False
.- Parameters
- 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
- Returns
True
if the AgentForward was loaded;False
if not
If
True
is returned, the server should create anAgentServerProxy
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 aTransport
. AChannel
object is not created unless this method returnsOPEN_SUCCEEDED
– once aChannel
object is created, you can callChannel.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
(or0
) 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
.
- 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
.
- 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.
- 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.
- __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 callingstart_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 classMP3Handler
will be created, andstart_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 thechannel
andname
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
andchannel
are unique; this handler corresponds to exactly oneChannel
on oneTransport
.Note
It is the responsibility of this method to exit if the underlying
Transport
is closed. This can be done by checkingTransport.is_active
or noticing an EOF on theChannel
. If this method loops forever without checking for this case, your Python interpreter may refuse to exit because this thread will still be running.
- finish_subsystem()¶
Perform any cleanup at the end of a subsystem. The default implementation just closes the channel.
New in version 1.1.