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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.

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, gss_trust_dns=True, passphrase=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 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 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.

  • 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.
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.

Changed in version 2.3: Added the gss_trust_dns argument.

Changed in version 2.4: Added the passphrase argument.

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.

  • 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.

the stdin, stdout, and stderr of the executing command, as a 3-tuple
SSHException -- if the server fails to execute the command

Changed in version 1.10: Added the get_pty kwarg.


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

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.

the Transport for this connection
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.

  • 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
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.

filename (str) -- the filename to read
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.

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

Open an SFTP session on the SSH server.

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.

filename (str) -- the filename to save to
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.

name (str) -- new channel name for logging

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


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.