How to know if a paramiko SSH channel is disconnected?

问题:

I'm desinging test cases in which I use paramiko for SSH connections. Test cases usually contain paramiko.exec_command() calls which I have a wrapper for (called run_command()). Here self.ssh is an intance of paramiko.SSHClient(). I use a decorator to check the ssh connection before each call. (self.get_ssh() negotiates the connection)

def check_connections(function):     ''' A decorator to check SSH connections. '''     def deco(self, *args, **kwargs):         if self.ssh is None:             self.ssh = self.get_ssh()         else:             ret = getattr(self.ssh.get_transport(), 'is_active', None)             if ret is None or (ret is not None and not ret()):                 self.ssh = self.get_ssh()         return function(self, *args, **kwargs)     return deco 

@check_connections def run_command(self, command):     ''' Executes command via SSH. '''     stdin, stdout, stderr = self.ssh.exec_command(command)     stdin.flush()     stdin.channel.shutdown_write()     ret = stdout.read()     err = stderr.read()     if ret:         return ret     elif err:         return err     else:         return None 

It works perfectly until my remote node reboots, which can happen sometimes. When it occurs the next run_command() call generates a socket.error exception. The problem is, that the paramiko.Transport object seems to be remain in active state until an exception is thrown:

Python 2.7.3 (default, Mar  7 2013, 14:03:36) [GCC 4.3.4 [gcc-4_3-branch revision 152973]] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import os >>> import paramiko >>> ssh = paramiko.SSHClient() >>> print ssh  >>> print ssh.get_transport() None >>> ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy()) >>> ssh.load_host_keys(os.path.expanduser('~') + '/.ssh/known_hosts') >>> ssh.connect(hostname = '172.31.77.57', username = 'root', password = 'rootroot', timeout = 5.0) >>> print ssh  >>> print ssh.get_transport()  >>> print ssh.get_transport().is_active() True >>> ssh.exec_command('ls') (>>, >>, >>) >>> print ssh  >>> print ssh.get_transport()  >>> print ssh.get_transport().is_active() True >>> ssh.exec_command('reboot') (>>, >>, >>) >>> print ssh  >>> print ssh.get_transport()  >>> print ssh.get_transport().is_active() True >>> ssh.exec_command('ls') No handlers could be found for logger "paramiko.transport" Traceback (most recent call last):   File "", line 1, in    File "/home/pytest/lib/python2.7/site-packages/paramiko/client.py", line 370, in exec_command     chan = self._transport.open_session()   File "/home/pytest/lib/python2.7/site-packages/paramiko/transport.py", line 662, in open_session     return self.open_channel('session')   File "/home/pytest/lib/python2.7/site-packages/paramiko/transport.py", line 764, in open_channel     raise e socket.error: [Errno 104] Connection reset by peer >>> print ssh  >>> print ssh.get_transport()  >>> print ssh.get_transport().is_active() False >>> 

Question: how can I be sure that the connection is really active or not?

回答1:

In python, it's easier to ask for forgiveness than permission.

Wrap each call to ssh.exec_command like so:

try:     ssh.exec_command('ls') except socket.error as e:     # Crap, it's closed. Perhaps reopen and retry? 

回答2:

My solution basically the same as yours, just organized differently:

def connection(self):     if not self.is_connected():         self._ssh = paramiko.SSHClient()         self._ssh.connect(self.server, self.port,                           username = self.username, password = self.password)      return self._ssh  def is_connected(self):     transport = self._ssh.get_transport() if self._ssh else None     return transport and transport.is_active()  def do_something(self):     self.connection().exec_command('ls') 

回答3:

This works:

import paramiko client = paramiko.SSHClient() client.set_missing_host_key_policy(paramiko.AutoAddPolicy())        # Setting the missing host policy to auto add it client.connect('192.168.1.16', port=22, username='admin', password='admin', timeout=3, banner_timeout=2)  channel = client.invoke_shell()                 # Request an interactive shell session on this channel. If the server allows it, the channel will then be directly connected to the stdin, stdout, and stderr of the shell. print channel.closed          # False command = 'reboot' channel.send(command + '\n') # wait a while print channel.closed          # True 

文章来源: How to know if a paramiko SSH channel is disconnected?