paramiko's ssh channel closed after executing one cmd - Python

Question

I'm using Python's Paramiko to execute commands in a remove server. The code is much simple.

Here's my definition of the SSHConn class:

class SSHConn:

  def __init__(self, hostname, user, pwd, filename=None):
    self.client = paramiko.SSHClient()
    self.client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    self.client.connect(hostname, username=user, password=pwd,
                          key_filename=filename)
    self.transport = self.client.get_transport()
    self.channel = self.transport.open_session()

So I'm running the following code:

local_ssh = ssh.SSHConn(host, user, passwd)

cmds = ('foo', 'bar')
for cmd in cmds:
   local_ssh.channel.exec_command(cmd)
   self.log.info(local_ssh.channel.recv(1024))

However, when I execute the following code snipped I'm getting:

INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_6.6.1p1)
INFO:paramiko.transport:Authentication (publickey) failed.
INFO:paramiko.transport:Authentication (password) successful!
INFO:paramiko.transport:Secsh channel 1 opened.
INFO:testsets.testcase:
ERROR:testsets.testcase:Channel is not open
Traceback (most recent call last):
  File "/root/fds-src/source/test/integration-framework/testsets/testcases/test_100gb_volume.py", line 87, in runTest
    local_ssh.channel.exec_command(cmd)
  File "/usr/lib/python2.7/dist-packages/paramiko/channel.py", line 209, in exec_command
    raise SSHException('Channel is not open')
SSHException: Channel is not open
ERROR:testsets.testcase:Test Case Test100GBVolume failed.
Traceback (most recent call last):
  File "/root/fds-src/source/test/integration-framework/testsets/testcases/test_100gb_volume.py", line 87, in runTest
    local_ssh.channel.exec_command(cmd)
  File "/usr/lib/python2.7/dist-packages/paramiko/channel.py", line 209, in exec_command
    raise SSHException('Channel is not open')
SSHException: Channel is not open

How can I keep the channel open?

parsley72 · Accepted Answer · 2025-06-27 04:06:41Z

9

The channel docs are very clear about this point. You need to open a new channel for each exec_command.

From Paramiko / Channel / exec_command

exec_command(*args, **kwds)

Execute a command on the server. If the server allows it, the channel will then be directly connected to the stdin, stdout, and stderr of the command being executed.

When the command finishes executing, the channel will be closed and can’t be reused. You must open a new channel if you wish to execute another command.

The SSHClient object has an exec_command method that does this for you.

edited Jun 27 at 4:06

parsley72

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answered Mar 5, 2015 at 17:00

tdelaney

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