Logic with Timeout in Nested SSH with Paramiko

Question

So I am able to ssh into a list of cisco devices stored in a text file. It works great when the device is up and functioning, but it breaks if it times out due to a infinite loop that happens when the Password field never pops up.

The logic of this with the while loops is what is killing my thought process. I know my attempts to fix are vague but this is hard to test as if I get it wrong it locks me out of my account to do this on our network for some time. Any help would be much appreciated.

Current Code:

import paramiko
import time
#*****************************************
#SSH Credentials for logging into routers
bass_host = 'ssh.server.com'
ssh_username = 'username'
ssh_password = 'password'
port = 22
#*****************************************

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

ssh.connect(bass_host, port, ssh_username, ssh_password)
#For Intro Show Commands
router_channel = ssh.invoke_shell()
# Ssh and wait for the password prompt.

hostnames = open('/hostlist.txt', 'r').readlines()
hostnames = map(lambda s: s.strip(), hostnames)


for device in hostnames:
    command = 'ssh ' + device + '\n'
    router_channel.send(command)
    buff = ''


    while not buff.endswith('Password: '):
        resp = router_channel.recv(9999)
        buff += resp

    # Send the password and wait for a prompt.
    router_channel.send('passwordhere\n')
    buff = ''

    while not buff.endswith('#'):
        resp = router_channel.recv(99999)
        buff += resp

    router_channel.send('terminal length 0\n')
    buff = ''

    while not buff.endswith('#'):
        resp = router_channel.recv(99999)
        buff += resp

Area of Concern:

for device in hostnames:
    command = 'ssh ' + device + '\n'
    router_channel.send(command)
    buff = ''


    while not buff.endswith('Password: '):
        resp = router_channel.recv(9999)
        buff += resp

    # Send the password and wait for a prompt.
    router_channel.send('passwordhere\n')
    buff = ''

    while not buff.endswith('#'):
        resp = router_channel.recv(99999)
        buff += resp

    router_channel.send('terminal length 0\n')
    buff = ''

Attempted:

for device in hostnames:
    command = 'ssh ' + device + '\n'
    router_channel.send(command)
    buff = ''
    timeout = time.time() + 8*3


    while not buff.endswith('Password: '):
        resp = router_channel.recv(9999)
        buff += resp
        print 'broke'
        if time.time() > timeout:
          print 'Broke'
          break
          continue 
        else:
          continue 

    # Send the password and wait for a prompt.
    router_channel.send('passwordhere\n')
    buff = ''

    while not buff.endswith('#'):
        resp = router_channel.recv(99999)
        buff += resp

    router_channel.send('terminal length 0\n')
    buff = ''

related: use signals to interrupt long-running command stackoverflow.com/a/13587384/143880 — johntellsall
– johntellsall, Commented Aug 31, 2014 at 20:41

BilliAm · Accepted Answer · 2014-08-31 23:24:51Z

Paramiko commands of setting timeout on a channel was exactly what fixed it.

router_channel.settimeout(23)  


for device in hostnames:
    try:
      command = 'ssh ' + device + '\n'
      router_channel.send(command)
      buff = ''
      timeout = time.time() + 8*3


      while not buff.endswith('Password: '):
          resp = router_channel.recv(9999)
          buff += resp
          print 'broke'
          if time.time() > timeout:
            print 'Broke'
            break
            continue 
          else:
            continue 

      # Send the password and wait for a prompt.
      router_channel.send('passwordhere\n')
      buff = ''

      while not buff.endswith('#'):
          resp = router_channel.recv(99999)
          buff += resp

      router_channel.send('terminal length 0\n')
      buff = ''

except socket.timeout:
    print 'connection failed to ' + jConnectID
    continue

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