Client¶

SSH client & key policies

class paramiko.client.SSHClient¶

A high-level representation of a session with an SSH server. This class wraps Transport, Channel, and SFTPClient to take care of most aspects of authenticating and opening channels. A typical use case is:

client = SSHClient()
client.load_system_host_keys()
client.connect('ssh.example.com')
stdin, stdout, stderr = client.exec_command('ls -l')

You may pass in explicit overrides for authentication and server host key checking. The default mechanism is to try to use local key files or an SSH agent (if one is running).

Instances of this class may be used as context managers.

New in version 1.6.

__init__()¶: Create a new SSHClient.

load_system_host_keys(filename=None)¶

Load host keys from a system (read-only) file. Host keys read with this method will not be saved back by save_host_keys.

This method can be called multiple times. Each new set of host keys will be merged with the existing set (new replacing old if there are conflicts).

If filename is left as None, an attempt will be made to read keys from the user’s local “known hosts” file, as used by OpenSSH, and no exception will be raised if the file can’t be read. This is probably only useful on posix.

Parameters: filename (str) – the filename to read, or None
Raises: IOError – if a filename was provided and the file could not be read

load_host_keys(filename)¶

Load host keys from a local host-key file. Host keys read with this method will be checked after keys loaded via load_system_host_keys, but will be saved back by save_host_keys (so they can be modified). The missing host key policy AutoAddPolicy adds keys to this set and saves them, when connecting to a previously-unknown server.

This method can be called multiple times. Each new set of host keys will be merged with the existing set (new replacing old if there are conflicts). When automatically saving, the last hostname is used.

Parameters: filename (str) – the filename to read
Raises: IOError – if the filename could not be read

save_host_keys(filename)¶

Save the host keys back to a file. Only the host keys loaded with load_host_keys (plus any added directly) will be saved – not any host keys loaded with load_system_host_keys.

Parameters: filename (str) – the filename to save to
Raises: IOError – if the file could not be written

get_host_keys()¶

Get the local HostKeys object. This can be used to examine the local host keys or change them.

Returns: the local host keys as a HostKeys object.

set_log_channel(name)¶

Set the channel for logging. The default is "paramiko.transport" but it can be set to anything you want.

Parameters: name (str) – new channel name for logging

set_missing_host_key_policy(policy)¶

Set policy to use when connecting to servers without a known host key.

Specifically:

A policy is a “policy class” (or instance thereof), namely some subclass of MissingHostKeyPolicy such as RejectPolicy (the default), AutoAddPolicy, WarningPolicy, or a user-created subclass.
A host key is known when it appears in the client object’s cached host keys structures (those manipulated by load_system_host_keys and/or load_host_keys).

Parameters: policy (MissingHostKeyPolicy) – the policy to use when receiving a host key from a previously-unknown server

connect(hostname, port=22, username=None, password=None, pkey=None, key_filename=None, timeout=None, allow_agent=True, look_for_keys=True, compress=False, sock=None, gss_auth=False, gss_kex=False, gss_deleg_creds=True, gss_host=None, banner_timeout=None, auth_timeout=None, channel_timeout=None, gss_trust_dns=True, passphrase=None, disabled_algorithms=None, transport_factory=None, auth_strategy=None)¶

Connect to an SSH server and authenticate to it. The server’s host key is checked against the system host keys (see load_system_host_keys) and any local host keys (load_host_keys). If the server’s hostname is not found in either set of host keys, the missing host key policy is used (see set_missing_host_key_policy). The default policy is to reject the key and raise an SSHException.

Authentication is attempted in the following order of priority:

The pkey or key_filename passed in (if any)

key_filename may contain OpenSSH public certificate paths as well as regular private-key paths; when files ending in -cert.pub are found, they are assumed to match a private key, and both components will be loaded. (The private key itself does not need to be listed in key_filename for this to occur - just the certificate.)

Any key we can find through an SSH agent

Any “id_rsa”, “id_dsa” or “id_ecdsa” key discoverable in ~/.ssh/

When OpenSSH-style public certificates exist that match an existing such private key (so e.g. one has id_rsa and id_rsa-cert.pub) the certificate will be loaded alongside the private key and used for authentication.

Plain username/password auth, if a password was given

If a private key requires a password to unlock it, and a password is passed in, that password will be used to attempt to unlock the key.

Parameters

hostname (str) – the server to connect to
port (int) – the server port to connect to
username (str) – the username to authenticate as (defaults to the current local username)
password (str) – Used for password authentication; is also used for private key decryption if passphrase is not given.
passphrase (str) – Used for decrypting private keys.
pkey (PKey) – an optional private key to use for authentication
key_filename (str) – the filename, or list of filenames, of optional private key(s) and/or certs to try for authentication
timeout (float) – an optional timeout (in seconds) for the TCP connect
allow_agent (bool) – set to False to disable connecting to the SSH agent
look_for_keys (bool) – set to False to disable searching for discoverable private key files in ~/.ssh/
compress (bool) – set to True to turn on compression
sock (socket) – an open socket or socket-like object (such as a Channel) to use for communication to the target host
gss_auth (bool) – True if you want to use GSS-API authentication
gss_kex (bool) – Perform GSS-API Key Exchange and user authentication
gss_deleg_creds (bool) – Delegate GSS-API client credentials or not
gss_host (str) – The targets name in the kerberos database. default: hostname
gss_trust_dns (bool) – Indicates whether or not the DNS is trusted to securely canonicalize the name of the host being connected to (default True).
banner_timeout (float) – an optional timeout (in seconds) to wait for the SSH banner to be presented.
auth_timeout (float) – an optional timeout (in seconds) to wait for an authentication response.
channel_timeout (float) – an optional timeout (in seconds) to wait for a channel open response.
disabled_algorithms (dict) – an optional dict passed directly to Transport and its keyword argument of the same name.
transport_factory – an optional callable which is handed a subset of the constructor arguments (primarily those related to the socket, GSS functionality, and algorithm selection) and generates a Transport instance to be used by this client. Defaults to Transport.__init__.
auth_strategy –
an optional instance of AuthStrategy, triggering use of this newer authentication mechanism instead of SSHClient’s legacy auth method.

Warning

This parameter is incompatible with all other authentication-related parameters (such as, but not limited to, password, key_filename and allow_agent) and will trigger an exception if given alongside them.

Returns

AuthResult if auth_strategy is non-None; otherwise, returns None.

Raises

BadHostKeyException – if the server’s host key could not be verified.
AuthenticationException – if authentication failed.
UnableToAuthenticate – if authentication failed (when auth_strategy is non-None; and note that this is a subclass of AuthenticationException).
socket.error – if a socket error (other than connection-refused or host-unreachable) occurred while connecting.
NoValidConnectionsError – if all valid connection targets for the requested hostname (eg IPv4 and IPv6) yielded connection-refused or host-unreachable socket errors.
SSHException – if there was any other error connecting or establishing an SSH session.

Changed in version 1.15: Added the banner_timeout, gss_auth, gss_kex, gss_deleg_creds and gss_host arguments.

Changed in version 2.3: Added the gss_trust_dns argument.

Changed in version 2.4: Added the passphrase argument.

Changed in version 2.6: Added the disabled_algorithms argument.

Changed in version 2.12: Added the transport_factory argument.

Changed in version 3.2: Added the auth_strategy argument.

close()¶

Close this SSHClient and its underlying Transport.

This should be called anytime you are done using the client object.

Warning

Paramiko registers garbage collection hooks that will try to automatically close connections for you, but this is not presently reliable. Failure to explicitly close your client after use may lead to end-of-process hangs!

exec_command(command, bufsize=- 1, timeout=None, get_pty=False, environment=None)¶

Execute a command on the SSH server. A new Channel is opened and the requested command is executed. The command’s input and output streams are returned as Python file-like objects representing stdin, stdout, and stderr.

Parameters

command (str) – the command to execute
bufsize (int) – interpreted the same way as by the built-in file() function in Python
timeout (int) – set command’s channel timeout. See Channel.settimeout
get_pty (bool) – Request a pseudo-terminal from the server (default False). See Channel.get_pty
environment (dict) –
a dict of shell environment variables, to be merged into the default environment that the remote command executes within.

Warning

Servers may silently reject some environment variables; see the warning in Channel.set_environment_variable for details.

Returns

the stdin, stdout, and stderr of the executing command, as a 3-tuple

Raises

SSHException – if the server fails to execute the command

Changed in version 1.10: Added the get_pty kwarg.

invoke_shell(term='vt100', width=80, height=24, width_pixels=0, height_pixels=0, environment=None)¶

Start an interactive shell session on the SSH server. A new Channel is opened and connected to a pseudo-terminal using the requested terminal type and size.

Parameters

term (str) – the terminal type to emulate (for example, "vt100")
width (int) – the width (in characters) of the terminal window
height (int) – the height (in characters) of the terminal window
width_pixels (int) – the width (in pixels) of the terminal window
height_pixels (int) – the height (in pixels) of the terminal window
environment (dict) – the command’s environment

Returns

a new Channel connected to the remote shell

Raises

SSHException – if the server fails to invoke a shell

open_sftp()¶

Open an SFTP session on the SSH server.

Returns: a new SFTPClient session object

get_transport()¶

Return the underlying Transport object for this SSH connection. This can be used to perform lower-level tasks, like opening specific kinds of channels.

Returns: the Transport for this connection

class paramiko.client.MissingHostKeyPolicy¶

Interface for defining the policy that SSHClient should use when the SSH server’s hostname is not in either the system host keys or the application’s keys. Pre-made classes implement policies for automatically adding the key to the application’s HostKeys object (AutoAddPolicy), and for automatically rejecting the key (RejectPolicy).

This function may be used to ask the user to verify the key, for example.

missing_host_key(client, hostname, key)¶: Called when an SSHClient receives a server key for a server that isn’t in either the system or local HostKeys object. To accept the key, simply return. To reject, raised an exception (which will be passed to the calling application).

__weakref__¶: list of weak references to the object (if defined)

class paramiko.client.AutoAddPolicy¶

Policy for automatically adding the hostname and new host key to the local HostKeys object, and saving it. This is used by SSHClient.

missing_host_key(client, hostname, key)¶: Called when an SSHClient receives a server key for a server that isn’t in either the system or local HostKeys object. To accept the key, simply return. To reject, raised an exception (which will be passed to the calling application).

class paramiko.client.RejectPolicy¶

Policy for automatically rejecting the unknown hostname & key. This is used by SSHClient.

missing_host_key(client, hostname, key)¶: Called when an SSHClient receives a server key for a server that isn’t in either the system or local HostKeys object. To accept the key, simply return. To reject, raised an exception (which will be passed to the calling application).

class paramiko.client.WarningPolicy¶

Policy for logging a Python-style warning for an unknown host key, but accepting it. This is used by SSHClient.

missing_host_key(client, hostname, key)¶: Called when an SSHClient receives a server key for a server that isn’t in either the system or local HostKeys object. To accept the key, simply return. To reject, raised an exception (which will be passed to the calling application).

Client¶

Paramiko

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