class SSHClient (object):
"""
A high-level representation of a session with an SSH server. This class
wraps L{Transport}, L{Channel}, and L{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).
@since: 1.6
"""
def __init__(self):
"""
Create a new SSHClient.
"""
self._system_host_keys = HostKeys()
self._host_keys = HostKeys()
self._host_keys_filename = None
self._log_channel = None
self._policy = RejectPolicy()
self._transport = None
self._agent = None
def load_system_host_keys(self, filename=None):
"""
Load host keys from a system (read-only) file. Host keys read with
this method will not be saved back by L{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 C{filename} is left as C{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.
@param filename: the filename to read, or C{None}
@type filename: str
@raise IOError: if a filename was provided and the file could not be
read
"""
if filename is None:
# try the user's .ssh key file, and mask exceptions
filename = os.path.expanduser('~/.ssh/known_hosts')
try:
self._system_host_keys.load(filename)
except IOError:
pass
return
self._system_host_keys.load(filename)
def load_host_keys(self, filename):
"""
Load host keys from a local host-key file. Host keys read with this
method will be checked I{after} keys loaded via L{load_system_host_keys},
but will be saved back by L{save_host_keys} (so they can be modified).
The missing host key policy L{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.
@param filename: the filename to read
@type filename: str
@raise IOError: if the filename could not be read
"""
self._host_keys_filename = filename
self._host_keys.load(filename)
def save_host_keys(self, filename):
"""
Save the host keys back to a file. Only the host keys loaded with
L{load_host_keys} (plus any added directly) will be saved -- not any
host keys loaded with L{load_system_host_keys}.
@param filename: the filename to save to
@type filename: str
@raise IOError: if the file could not be written
"""
f = open(filename, 'w')
f.write('# SSH host keys collected by ssh\n')
for hostname, keys in self._host_keys.items():
for keytype, key in keys.items():
f.write('%s %s %s\n' % (hostname, keytype, key.get_base64()))
f.close()
def get_host_keys(self):
"""
Get the local L{HostKeys} object. This can be used to examine the
local host keys or change them.
@return: the local host keys
@rtype: L{HostKeys}
"""
return self._host_keys
def set_log_channel(self, name):
"""
Set the channel for logging. The default is C{"ssh.transport"}
but it can be set to anything you want.
@param name: new channel name for logging
@type name: str
"""
self._log_channel = name
def set_missing_host_key_policy(self, policy):
"""
Set the policy to use when connecting to a server that doesn't have a
host key in either the system or local L{HostKeys} objects. The
default policy is to reject all unknown servers (using L{RejectPolicy}).
You may substitute L{AutoAddPolicy} or write your own policy class.
@param policy: the policy to use when receiving a host key from a
previously-unknown server
@type policy: L{MissingHostKeyPolicy}
"""
self._policy = policy
def connect(self, hostname, port=SSH_PORT, username=None, password=None, pkey=None,
key_filename=None, timeout=None, allow_agent=True, look_for_keys=True,
compress=False):
"""
Connect to an SSH server and authenticate to it. The server's host key
is checked against the system host keys (see L{load_system_host_keys})
and any local host keys (L{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 L{set_missing_host_key_policy}). The default policy is
to reject the key and raise an L{SSHException}.
Authentication is attempted in the following order of priority:
- The C{pkey} or C{key_filename} passed in (if any)
- Any key we can find through an SSH agent
- Any "id_rsa" or "id_dsa" key discoverable in C{~/.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.
@param hostname: the server to connect to
@type hostname: str
@param port: the server port to connect to
@type port: int
@param username: the username to authenticate as (defaults to the
current local username)
@type username: str
@param password: a password to use for authentication or for unlocking
a private key
@type password: str
@param pkey: an optional private key to use for authentication
@type pkey: L{PKey}
@param key_filename: the filename, or list of filenames, of optional
private key(s) to try for authentication
@type key_filename: str or list(str)
@param timeout: an optional timeout (in seconds) for the TCP connect
@type timeout: float
@param allow_agent: set to False to disable connecting to the SSH agent
@type allow_agent: bool
@param look_for_keys: set to False to disable searching for discoverable
private key files in C{~/.ssh/}
@type look_for_keys: bool
@param compress: set to True to turn on compression
@type compress: bool
@raise BadHostKeyException: if the server's host key could not be
verified
@raise AuthenticationException: if authentication failed
@raise SSHException: if there was any other error connecting or
establishing an SSH session
@raise socket.error: if a socket error occurred while connecting
"""
for (family, socktype, proto, canonname, sockaddr) in socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM):
if socktype == socket.SOCK_STREAM:
af = family
addr = sockaddr
break
else:
# some OS like AIX don't indicate SOCK_STREAM support, so just guess. :(
af, _, _, _, addr = socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM)
sock = socket.socket(af, socket.SOCK_STREAM)
if timeout is not None:
try:
sock.settimeout(timeout)
except:
pass
sock.connect(addr)
t = self._transport = Transport(sock)
t.use_compression(compress=compress)
if self._log_channel is not None:
t.set_log_channel(self._log_channel)
t.start_client()
ResourceManager.register(self, t)
server_key = t.get_remote_server_key()
keytype = server_key.get_name()
if port == SSH_PORT:
server_hostkey_name = hostname
else:
server_hostkey_name = "[%s]:%d" % (hostname, port)
our_server_key = self._system_host_keys.get(server_hostkey_name, {}).get(keytype, None)
if our_server_key is None:
our_server_key = self._host_keys.get(server_hostkey_name, {}).get(keytype, None)
if our_server_key is None:
# will raise exception if the key is rejected; let that fall out
self._policy.missing_host_key(self, server_hostkey_name, server_key)
# if the callback returns, assume the key is ok
our_server_key = server_key
if server_key != our_server_key:
raise BadHostKeyException(hostname, server_key, our_server_key)
if username is None:
username = getpass.getuser()
if key_filename is None:
key_filenames = []
elif isinstance(key_filename, str):
key_filenames = [ key_filename ]
else:
key_filenames = key_filename
self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys)
def close(self):
"""
Close this SSHClient and its underlying L{Transport}.
"""
if self._transport is None:
return
self._transport.close()
self._transport = None
if self._agent != None:
self._agent.close()
self._agent = None
def exec_command(self, command, bufsize=-1):
"""
Execute a command on the SSH server. A new L{Channel} is opened and
the requested command is executed. The command's input and output
streams are returned as python C{file}-like objects representing
stdin, stdout, and stderr.
@param command: the command to execute
@type command: str
@param bufsize: interpreted the same way as by the built-in C{file()} function in python
@type bufsize: int
@return: the stdin, stdout, and stderr of the executing command
@rtype: tuple(L{ChannelFile}, L{ChannelFile}, L{ChannelFile})
@raise SSHException: if the server fails to execute the command
"""
chan = self._transport.open_session()
chan.exec_command(command)
stdin = chan.makefile('wb', bufsize)
stdout = chan.makefile('rb', bufsize)
stderr = chan.makefile_stderr('rb', bufsize)
return stdin, stdout, stderr
def invoke_shell(self, term='vt100', width=80, height=24):
"""
Start an interactive shell session on the SSH server. A new L{Channel}
is opened and connected to a pseudo-terminal using the requested
terminal type and size.
@param term: the terminal type to emulate (for example, C{"vt100"})
@type term: str
@param width: the width (in characters) of the terminal window
@type width: int
@param height: the height (in characters) of the terminal window
@type height: int
@return: a new channel connected to the remote shell
@rtype: L{Channel}
@raise SSHException: if the server fails to invoke a shell
"""
chan = self._transport.open_session()
chan.get_pty(term, width, height)
chan.invoke_shell()
return chan
def open_sftp(self):
"""
Open an SFTP session on the SSH server.
@return: a new SFTP session object
@rtype: L{SFTPClient}
"""
return self._transport.open_sftp_client()
def get_transport(self):
"""
Return the underlying L{Transport} object for this SSH connection.
This can be used to perform lower-level tasks, like opening specific
kinds of channels.
@return: the Transport for this connection
@rtype: L{Transport}
"""
return self._transport
def _auth(self, username, password, pkey, key_filenames, allow_agent, look_for_keys):
"""
Try, in order:
- The key passed in, if one was passed in.
- Any key we can find through an SSH agent (if allowed).
- Any "id_rsa" or "id_dsa" key discoverable in ~/.ssh/ (if allowed).
- Plain username/password auth, if a password was given.
(The password might be needed to unlock a private key.)
"""
saved_exception = None
if pkey is not None:
try:
self._log(DEBUG, 'Trying SSH key %s' % hexlify(pkey.get_fingerprint()))
self._transport.auth_publickey(username, pkey)
return
except SSHException as e:
saved_exception = e
for key_filename in key_filenames:
for pkey_class in (RSAKey, DSSKey):
try:
key = pkey_class.from_private_key_file(key_filename, password)
self._log(DEBUG, 'Trying key %s from %s' % (hexlify(key.get_fingerprint()), key_filename))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
if allow_agent:
if self._agent == None:
self._agent = Agent()
for key in self._agent.get_keys():
try:
self._log(DEBUG, 'Trying SSH agent key %s' % hexlify(key.get_fingerprint()))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
keyfiles = []
rsa_key = os.path.expanduser('~/.ssh/id_rsa')
dsa_key = os.path.expanduser('~/.ssh/id_dsa')
if os.path.isfile(rsa_key):
keyfiles.append((RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((DSSKey, dsa_key))
# look in ~/ssh/ for windows users:
rsa_key = os.path.expanduser('~/ssh/id_rsa')
dsa_key = os.path.expanduser('~/ssh/id_dsa')
if os.path.isfile(rsa_key):
keyfiles.append((RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((DSSKey, dsa_key))
if not look_for_keys:
keyfiles = []
for pkey_class, filename in keyfiles:
try:
key = pkey_class.from_private_key_file(filename, password)
self._log(DEBUG, 'Trying discovered key %s in %s' % (hexlify(key.get_fingerprint()), filename))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
except IOError as e:
saved_exception = e
if password is not None:
try:
self._transport.auth_password(username, password)
return
except SSHException as e:
saved_exception = e
# if we got an auth-failed exception earlier, re-raise it
if saved_exception is not None:
raise saved_exception
raise SSHException('No authentication methods available')
def _log(self, level, msg):
self._transport._log(level, msg)
def _auth(self, username, password, pkey, key_filenames, allow_agent, look_for_keys):
"""
Try, in order:
- The key passed in, if one was passed in.
- Any key we can find through an SSH agent (if allowed).
- Any "id_rsa" or "id_dsa" key discoverable in ~/.ssh/ (if allowed).
- Plain username/password auth, if a password was given.
(The password might be needed to unlock a private key.)
"""
saved_exception = None
if pkey is not None:
try:
self._log(DEBUG, 'Trying SSH key %s' % hexlify(pkey.get_fingerprint()))
self._transport.auth_publickey(username, pkey)
return
except SSHException as e:
saved_exception = e
for key_filename in key_filenames:
for pkey_class in (RSAKey, DSSKey):
try:
key = pkey_class.from_private_key_file(key_filename, password)
self._log(DEBUG, 'Trying key %s from %s' % (hexlify(key.get_fingerprint()), key_filename))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
if allow_agent:
if self._agent == None:
self._agent = Agent()
for key in self._agent.get_keys():
try:
self._log(DEBUG, 'Trying SSH agent key %s' % hexlify(key.get_fingerprint()))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
keyfiles = []
rsa_key = os.path.expanduser('~/.ssh/id_rsa')
dsa_key = os.path.expanduser('~/.ssh/id_dsa')
if os.path.isfile(rsa_key):
keyfiles.append((RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((DSSKey, dsa_key))
# look in ~/ssh/ for windows users:
rsa_key = os.path.expanduser('~/ssh/id_rsa')
dsa_key = os.path.expanduser('~/ssh/id_dsa')
if os.path.isfile(rsa_key):
keyfiles.append((RSAKey, rsa_key))
if os.path.isfile(dsa_key):
keyfiles.append((DSSKey, dsa_key))
if not look_for_keys:
keyfiles = []
for pkey_class, filename in keyfiles:
try:
key = pkey_class.from_private_key_file(filename, password)
self._log(DEBUG, 'Trying discovered key %s in %s' % (hexlify(key.get_fingerprint()), filename))
self._transport.auth_publickey(username, key)
return
except SSHException as e:
saved_exception = e
except IOError as e:
saved_exception = e
if password is not None:
try:
self._transport.auth_password(username, password)
return
except SSHException as e:
saved_exception = e
# if we got an auth-failed exception earlier, re-raise it
if saved_exception is not None:
raise saved_exception
raise SSHException('No authentication methods available')