I'm using Paramiko to execute bash scripts on a remote server. In some of these scripts, there are ssh connections to other servers. If I use bash only, no Python, my DSA key is forwarded and used by the bash script on the first remote server to connect to the second remote server. When I use Paramiko it's not the case.
Bash example:
Jean@mydesktop:~ & ssh root@firstserver
root@firstserver:~ # ssh root@secondserver hostname
secondserver.mydomain.org
Using Paramiko:
#!/usr/bin/python3
# -*- coding: utf-8 -*-
import paramiko
class SSHSession:
def __init__(self, server_address, user='root', port=22):
self.connected = False
self.server_address = server_address
self.user = user
self.port = port
def connect(self, clear_channel=True):
try:
if self.server_address == None:
raise ValueError('No hostname')
except:
raise ValueError('No hostname')
else:
try:
self.ssh_client = paramiko.SSHClient()
self.ssh_client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
self.ssh_client.connect(self.server_address, username=self.user)
#self.transport = self.ssh_client.get_transport()
#self.channel = self.transport.open_forward_agent_channel()
self.channel = self.ssh_client.invoke_shell()
except:
self.connected = False
return False
else:
self.connected = True
return True
def exec_command(self, command, newline='\r'):
if not self.connected:
raise Exception('Not connected')
else:
timeout = 31536000 # 365 days in seconds
self.channel.settimeout(timeout)
line_buffer = ''
channel_buffer = ''
end_string = 'CLIENT_EXPECT_CMD_OK'
print('[SEND ] >>', command)
self.channel.send(command + ' ; echo ' + end_string + newline)
while True:
channel_buffer = self.channel.recv(1).decode('UTF-8')
if len(channel_buffer) == 0:
raise Exception('connection lost with server: ' + self.server_address)
break
channel_buffer = channel_buffer.replace('\r', '')
if channel_buffer != '\n':
line_buffer += channel_buffer
else:
if line_buffer == end_string:
break
print('[RECEIVE] <<', line_buffer)
line_buffer = ''
def disconnect(self):
self.ssh_client.close()
def __enter__(self):
self.connect()
return self
def __exit__(self, _type, value, traceback):
self.disconnect()
if __name__ == "__main__":
server_address = 'firstserver'
ssh_user = 'root'
with SSHSession(server_address) as ssh_session:
ssh_session.exec_command('hostname')
ssh_session.exec_command('ssh root@secondserver hostname')
Output is :
[SEND ] >> hostname
[RECEIVE] << [root@firstserver ~]# hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << firstserver.mydomain.fr
[SEND ] >> ssh root@secondserver hostname
[RECEIVE] << [root@firstserver ~]# ssh root@secondserver hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << Permission denied (publickey,gssapi-keyex,gssapi-with-mic).
I tried:
self.transport = self.ssh_client.get_transport()
self.channel = self.transport.open_forward_agent_channel()
instead of :
self.channel = self.ssh_client.invoke_shell()
but then I get an error :
paramiko.ssh_exception.ChannelException: Administratively prohibited
Does someone knows if this is possible ? I found discutions suggesting that is it, but yet I don't find how to do this.
Ok it works now. I found these helpful posts :
Add paramiko ssh agent forwarding (optional) #4100
open_forward_agent_channel vs. open_session #89
The final code is :
#!/usr/bin/python3
# -*- coding: utf-8 -*-
import paramiko
class SSHSession:
def __init__(self, server_address, user='root', port=22):
self.connected = False
self.server_address = server_address
self.user = user
self.port = port
def connect(self):
try:
self.ssh_client = paramiko.SSHClient()
self.ssh_client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
self.ssh_client.connect(self.server_address, username=self.user)
self.transport = self.ssh_client.get_transport()
self.agent_channel = self.transport.open_session()
self.agent_handler = paramiko.agent.AgentRequestHandler(self.agent_channel)
self.channel = self.ssh_client.invoke_shell()
except:
self.connected = False
else:
self.connected = True
return self.connected
def exec_command(self, command, newline='\r'):
if not self.connected:
raise Exception('Not connected')
else:
timeout = 31536000 # 365 days in seconds
self.channel.settimeout(timeout)
line_buffer = ''
channel_buffer = ''
end_string = 'CLIENT_EXPECT_CMD_OK'
print('[SEND ] >>', command)
self.channel.send(command + ' ; echo ' + end_string + newline)
while True:
channel_buffer = self.channel.recv(1).decode('UTF-8')
if len(channel_buffer) == 0:
raise Exception('connection lost with server: ' + self.server_address)
break
channel_buffer = channel_buffer.replace('\r', '')
if channel_buffer != '\n':
line_buffer += channel_buffer
else:
if line_buffer == end_string:
break
print('[RECEIVE] <<', line_buffer)
line_buffer = ''
def disconnect(self):
self.ssh_client.close()
def __enter__(self):
self.connect()
return self
def __exit__(self, _type, value, traceback):
self.disconnect()
if __name__ == "__main__":
server_address = 'firstserver'
ssh_user = 'root'
with SSHSession(server_address) as ssh_session:
ssh_session.exec_command('hostname')
ssh_session.exec_command('ssh root@secondserver hostname')
Output is :
[SEND ] >> hostname
[RECEIVE] << [root@firstserver ~]# hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << firstserver.mydomain.fr
[SEND ] >> ssh root@secondserver hostname
[RECEIVE] << [root@firstserver ~]# ssh root@secondserver hostname ; echo CLIENT_EXPECT_CMD_OK
[RECEIVE] << secondserver.mydomain.fr
The important part of the code to enable agent forwarding is :
self.agent_channel = self.transport.open_session()
self.agent_handler = paramiko.agent.AgentRequestHandler(self.agent_channel)
You should set the key_filename when connecting:
key_filename (str or list(str)) - the filename, or list of filenames, of optional private key(s) to try for authentication
来源：https://stackoverflow.com/questions/23007143/dsa-key-forwarding-using-paramiko