SSH client & key policies

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.

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.


list of weak references to the object (if defined)

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.

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()
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.


Create a new SSHClient.


Close this SSHClient and its underlying Transport.


Failure to do this may, in some situations, cause your Python interpreter to hang at shutdown (often due to race conditions). It’s good practice to close your client objects anytime you’re done using them, instead of relying on garbage collection.

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)

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)
  • Any key we can find through an SSH agent
  • Any “id_rsa”, “id_dsa” or “id_ecdsa” key discoverable in ~/.ssh/
  • 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.

  • 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) – a password to use for authentication or for unlocking a private key
  • pkey (PKey) – an optional private key to use for authentication
  • key_filename (str) – the filename, or list of filenames, of optional private key(s) 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
  • banner_timeout (float) – an optional timeout (in seconds) to wait for the SSH banner to be presented.

BadHostKeyException – if the server’s host key could not be verified


AuthenticationException – if authentication failed


SSHException – if there was any other error connecting or establishing an SSH session


socket.error – if a socket error occurred while connecting

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

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

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.

  • 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

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


SSHException – if the server fails to execute the command


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.

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
invoke_shell(term='vt100', width=80, height=24, width_pixels=0, height_pixels=0)

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.

  • 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

a new Channel connected to the remote shell


SSHException – if the server fails to invoke a shell


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

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

Open an SFTP session on the SSH server.

Returns:a new SFTPClient session object

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

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


  • A policy is an instance of a “policy class”, namely some subclass of MissingHostKeyPolicy such as RejectPolicy (the default), AutoAddPolicy, WarningPolicy, or a user-created subclass.


    This method takes class instances, not classes themselves. Thus it must be called as e.g. .set_missing_host_key_policy(WarningPolicy()) and not .set_missing_host_key_policy(WarningPolicy).

  • 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
class paramiko.client.WarningPolicy

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