Can't catch multiple exceptions from python3/paramiko

Question

In python3, I'm using multiprocessing.Pool to run paramiko in parallel to connect to every ssh device on a subnet. I get a series of errors which I can't seem to trap.

I have put a variety of try/except statements here and none of them catch this error. I've even wrapped the Pool setup and statements with try/except but nothing changed there. All the paramiko stuff is in the try_login function, so it should be coming from there, but all of it is in a try/except, and there's even a generic except which should get everything.

I've also tried combining exceptions that cause this output.

#!/usr/bin/env python3

import paramiko
import socket
import ipaddress

network_address = '192.168.50.0/24'
username = ''
password = ''
timeout = 3
num_threads = 30

def trylogin(ipaddress):
    global username, password
    try:
        ssh = paramiko.SSHClient()
        ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        ssh.connect(ipaddress, username=username, password=password, timeout=timeout)
        (stdin, stdout, stderr) = ssh.exec_command('cat /var/serial_number')
        imei = stdout.readline()
        if imei != '': print("[+] {}: Success! Found ".format(ipaddress))
        return [ipaddress, imei]
    except paramiko.AuthenticationException:
        print("[-] {}: Authentication Exception!".format(ipaddress))
    except paramiko.SSHException:
        print("[-] {}: SSH Exception!".format(ipaddress))
    except (paramiko.ssh_exception.SSHException, OSError, EOFError):
        pass
    except EOFError:
        pass
    except OSError:
        pass
    except paramiko.ssh_exception.NoValidConnectionsError:
        pass
    except paramiko.ssh_exception.SSHException:
        pass
    except Exception as e:
        print('caught a new fish')
        print(e)
        pass
    finally:
        try:
            ssh.close()
        except:
            pass
    return

network = ipaddress.ip_network(network_address)
for ipaddr in network.hosts():
    print('Checking {}'.format(str(ipaddr)))
    trylogin(str(ipaddr))

What happens when this runs is that most of what's supposed to happen does. But I get an error showing two exceptions which I thought were handled. First an OSError, then a paramiko.ssh_exception.SSHException. I don't understand why I can't trap these.

$ ./find_ssh.py
[-] 192.168.50.1 trying...
[-] 192.168.50.2 trying...
[-] 192.168.50.3 trying...
[-] 192.168.50.4 trying...
[-] 192.168.50.5 trying...
[-] 192.168.50.6 trying...
[-] 192.168.50.7 trying...
[-] 192.168.50.8 trying...
[-] 192.168.50.9 trying...
[-] 192.168.50.10 trying...
[-] 192.168.50.10: Authentication Exception!
[-] 192.168.50.11 trying...
[-] 192.168.50.12 trying...
[-] 192.168.50.13 trying...
[-] 192.168.50.14 trying...
[-] 192.168.50.14: SSH Exception!
[-] 192.168.50.15 trying...
Exception: Error reading SSH protocol banner[Errno 9] Bad file descriptor
Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/paramiko/transport.py", line 2211, in _check_banner
    buf = self.packetizer.readline(timeout)
  File "/usr/local/lib/python3.5/dist-packages/paramiko/packet.py", line 380, in readline
    buf += self._read_timeout(timeout)
  File "/usr/local/lib/python3.5/dist-packages/paramiko/packet.py", line 607, in _read_timeout
    x = self.__socket.recv(128)
OSError: [Errno 9] Bad file descriptor

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.5/dist-packages/paramiko/transport.py", line 2039, in run
    self._check_banner()
  File "/usr/local/lib/python3.5/dist-packages/paramiko/transport.py", line 2216, in _check_banner
    "Error reading SSH protocol banner" + str(e)
paramiko.ssh_exception.SSHException: Error reading SSH protocol banner[Errno 9] Bad file descriptor

[-] 192.168.50.16 trying...
[-] 192.168.50.17 trying...
[-] 192.168.50.18 trying...
[-] 192.168.50.19 trying...
[-] 192.168.50.20 trying...

EDIT: revised to remove multiprocessing calls. It's slower but clearer.

Try not using map (this is not causing the error), but instead (and don't use list comprehensions either) use a good-old for loop, and add prints between trylogin calls, and you'll see that things will become much simpler. It's best to stay away of complex things when simpler ones aren't clear :) — CristiFati
– CristiFati, Commented Jul 25, 2019 at 0:34
While good advice, it doesn't buy me any more. I did do this, but no new errors. I've added a bit of logging to determine which device is causing the problem, which is 192.168.50.15. When I manually ssh -vvv to that device, I don't see any different behavior than for a device which doesn't have an error. — Jim
– Jim, Commented Jul 25, 2019 at 14:36

Jim · Accepted Answer · 2019-07-25 18:39:10Z

1

This is an ugly workaround more than it's an answer, but it makes the error disappear which is useful.

Add the line:

paramiko.util.log_to_file("main_paramiko_log.txt", level = "INFO")

The effect of this is that a file is created which contains the outputs from paramiko. It is straightforward to change the level from INFO to WARN or ERR. This particular error series is now printed to the logfile as an error, and no longer is printed to the screen.

Apparently uncaught errors are common in paramiko, there are a variety of related issues posted on their github, which I didn't realize before posting this.

answered Jul 25, 2019 at 18:39

Jim

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1 Comment

Jhoubert Rincon Over a year ago

Many thanks Jim, i have the same problem and this solution it worked for me i've tried many things and nothing work, really this line does not solve the problem only hide it, for the moment it's perfect for me.

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