通过SSH读取远程服务器日志时Python subprocess连接异常断开

问题描述 #

我尝试通过SSH连接服务器的特定端口并读取日志，但用Python subprocess执行相关命令时，SSH连接在认证完成后立即关闭。我使用的命令为：sshpass -p xxxx ssh -tt -v root@xxx.xxx.xxx.xx -p 2200 | tee -i -a remoteserver.log。调试日志如下：

debug1: Authentication succeeded (password).
debug1: channel 0: new [client-session]
debug1: Entering interactive session.
debug1: pledge: network
debug1: tty_make_modes: no fd or tio
debug1: Sending environment.
debug1: Sending env LANG = en_US
debug1: client_input_channel_req: channel 0 rtype exit-status reply 0
debug1: channel 0: free: client-session, nchannels 1
debug1: fd 0 clearing O_NONBLOCK
debug1: fd 1 clearing O_NONBLOCK
debug1: fd 2 clearing O_NONBLOCK
Connection to xxx.xxx.xxx.x closed.
Transferred: sent 1808, received 1440 bytes, in 0.0 seconds
Bytes per second: sent 36560.7, received 29119.1
debug1: Exit status 0

注：该命令在终端直接执行时运行正常。有人遇到过类似问题吗？

解决办法 #

这种情况核心是Python subprocess默认的环境和终端交互环境不匹配——终端里有完整的tty支持，能维持SSH的交互式会话，但subprocess默认的流处理会导致SSH在认证后没有输入源，直接退出。试试以下几种方案：

1. 给subprocess模拟终端环境
   用Popen时显式指定流参数，同时开启终端模拟：

   import subprocess
   
   cmd = "sshpass -p xxxx ssh -tt -v root@xxx.xxx.xxx.xx -p 2200 | tee -i -a remoteserver.log"
   # 开启shell支持管道，绑定标准流并模拟新会话
   proc = subprocess.Popen(
       cmd,
       shell=True,
       stdin=subprocess.PIPE,
       stdout=subprocess.PIPE,
       stderr=subprocess.STDOUT,
       start_new_session=True
   )
   # 保持进程运行，读取输出
   output, _ = proc.communicate()
   print(output.decode())
   

2. 把tee逻辑移到Python里，去掉管道依赖
   直接捕获SSH输出并写入日志文件，避免管道带来的流同步问题：

   import subprocess
   
   ssh_cmd = "sshpass -p xxxx ssh -tt -v root@xxx.xxx.xxx.xx -p 2200"
   proc = subprocess.Popen(
       ssh_cmd,
       shell=True,
       stdout=subprocess.PIPE,
       stderr=subprocess.STDOUT,
       universal_newlines=True
   )
   
   # 实时写入日志并打印
   with open("remoteserver.log", "a") as log_file:
       for line in proc.stdout:
           print(line.strip())
           log_file.write(line)
   

3. 用pexpect处理交互式会话
   如果上述方法还是不行，试试专门处理终端交互的pexpect库，它能更好地模拟终端环境：

   import pexpect
   
   ssh_cmd = "sshpass -p xxxx ssh -tt -v root@xxx.xxx.xxx.xx -p 2200"
   child = pexpect.spawn(ssh_cmd)
   
   with open("remoteserver.log", "a") as log_file:
       while True:
           try:
               line = child.readline()
               if not line:
                   break
               content = line.decode()
               print(content.strip())
               log_file.write(content)
           except pexpect.EOF:
               break
   

内容的提问来源于stack exchange，提问作者mrutyunjay