Paramiko无法使用exec_command发送所有命令

Question

如果我运行command='ps'或'ls'且类似，则一切正常。但是，当我想从远程主机下载日志到winscp然后是一个问题时，没有错误但没有任何反应。

import sys
import time
import socket
import paramiko
import os
import telnetlib
import time
import subprocess
import os

hostname = 'localhost'
port = 22
command=('log -c')
pliczek='pliczek.txt'

client = paramiko.SSHClient()

def connection(hostname, port):

    try:
        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        sock = socket.socket()
        sock.connect((hostname, port))
        t = paramiko.Transport(sock)
        t.connect()
        t.auth_none('root')
        client._transport = t

    except:
        print ('Error')

def commands(command):

    plik= open(pliczek, 'w+')
    chan =  client.get_transport().open_session()

    stdin, stdout, stderr = client.exec_command(command)
    stdin = client.exec_command(command)
    output = stdout.readlines()
    stdin.close()


    lista=''.join(output)
    print(lista)
    plik.write(lista)

    plik.close()
    print lista

def close_sesion():
    client.close()
    print 'closed'