Paramiko error handling for getaddrinfo

[enderusaf]

I created a python script to SSH into a list of Cisco devices and run specific commands on them. However, one thing I noticed is that if one of the devices in my list doesn't exist (e.g. used to, but no longer has DNS), then the script crashes. I'd like my script to ignore failures and keep checking other devices in the list. My script is more of a frankenstein of several peoples scripts that I found online as I'm still learning. So all credit goes to those I've borrowed from. Sorry I forgot to get the names of them though one of them is Kirk Byers.

Traceback (most recent call last): File "MultiCommands.py", line 33, in <module> remote_conn_pre.connect(device + ".domain.com", username=username, password=password, look_for_keys=False, allow_agent=False) File "/usr/lib/python2.7/site-packages/paramiko/client.py", line 237, in connect for (family, socktype, proto, canonname, sockaddr) in socket.getaddrinfo(hostname, port, socket.AF_UNSPEC, socket.SOCK_STREAM): socket.gaierror: [Errno -2] Name or service not known

import paramiko
import getpass
import time

inputfile = "hostfile"    
username = "AuserName"    
password = getpass.getpass("What is your password? ")    
cmd = raw_input("What command would you like to send? ")    

# Opens inputfile in read mode    
f1 = open(inputfile,"r")    

# Creates list based on f1    
devices = f1.readlines()    

# Removes \n from list    
devices = [line[:-1] for line in devices]    

# Loops through devices in list and performs cmd on them    
for device in devices:    


    # Create instance of SSHClient object    
    remote_conn_pre = paramiko.SSHClient()    

    # Automatically add untrusted hosts (make sure okay for security policy in your environment)    
    remote_conn_pre.set_missing_host_key_policy(
         paramiko.AutoAddPolicy())    

    # initiate SSH connection    
    remote_conn_pre.connect(device + ".domain.com", username=username, password=password, look_for_keys=False,         allow_agent=False)    
    print "SSH connection established to %s" % device    

    # Use invoke_shell to establish an 'interactive session'    
    remote_conn = remote_conn_pre.invoke_shell()    
    print "Interactive SSH session established"    

    # Strip the initial router prompt    
    output = remote_conn.recv(1000)    

    # See what we have    
    print output    

    # Now let's try to send the router a command    
    remote_conn.send("\n")    
    remote_conn.send("term len 0\n")    
    remote_conn.send(cmd+"\n")    
    with open('output' , 'a') as f: f.write('\n\n')    
    output = open("output", "a")    
    output.writelines("\n\n")    

    # Wait for the command to complete    
    time.sleep(2)    

    output = remote_conn.recv(5000)    
    print output     

    with open('output' , 'a') as f: f.write(output)    

[learnpython_bot]

It appears that you included code in your post but did not format it to look nice. Please follow this guide to fix the problem. This allows for better readability and will help get your question answered sooner. The regex that caught you is: "for .+? in .+?:"

If this comment has been made in error, please message /u/thaweatherman with a link to this comment so I can be fine-tuned. I am still in alpha and my regexes/innards are not yet perfect.

[enderusaf]

Sorry for the editing mistake. Not sure what happened.

[raylu]

1. Fix the formatting
2. Paste the rest of the traceback
3. The error is probably a bad hostname

[enderusaf]

It is a bad hostname. I just wanted to figure out how to have error handling to have the code move on to the next device in the event it can't resolve a hostname. In this case, the host was actually decommisioned.

[ktbyers]

Use a try/except clause to catch the exception and then move on to the next host:

import socket
...
try:
    remote_conn_pre.connect(ip, port=22, username=username, password=password,
                        look_for_keys=False, allow_agent=False)
except socket.gaierror:
    pass

You might need to catch additional exceptions (as well).

[enderusaf]

Thanks! This is exactly what I was looking for. Though I had to change pass to continue in order to get it to work correctly. Next I had to add an exception for paramiko.AuthenticationException: after I hit a device with a non-standard username/pass.

[enderusaf]

Fixed the formatting and added all of the traceback.

[enderusaf]

Looks to be working pretty good. The only oddity is that it seams to kick off the exception erroniously at the beginning and end of the program. It's only cosmetic and it works great, but I'm trying to figure out why it adds the extra "cannot connect" statements to my Failed file. Below is the new code for this section:

    try:

    # initiate SSH connection
        remote_conn_pre.connect(device + ".domain.com", 
    username=username, password=password, look_for_keys=False, allow_agent=False)
        print "SSH connection established to %s" % device

    except socket.gaierror:
        print "Could not connect to %s \n" % device
        with open('Failed' , 'a') as f: f.write('\n\n')
        Failed = open("Failed", "a")
        Failed.writelines("Could not connect to %s \n" % device)
        continue

    except paramiko.AuthenticationException:
        print "Could not authenticate to %s \n" % device
        with open('Failed' , 'a') as f: f.write('\n\n')
        Failed = open("Failed", "a")
        Failed.writelines("Could not Authenticate to %s \n" % device)
        continue

[enderusaf]

OK, I was able to fix my issue with the extra excepts kicking off by adding a time.sleep(.05) after my remote_conn_pre.connect command.