Paramiko channel stucks when reading large ouput

Question

I have a code where i am executing a command on remote Linux machine and reading the output using Paramiko. The code def looks like this:

ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(IPAddress, username=user['username'], password=user['password'])


chan = self.ssh.get_transport().open_session()

chan.settimeout(10800)

try:
    # Execute thecommand
    chan.exec_command(cmd)

    contents = StringIO.StringIO()

    data = chan.recv(1024)

    # Capturing data from chan buffer.
    while data:
        contents.write(data)
        data = chan.recv(1024)

except socket.timeout:
    raise socket.timeout


output = contents.getvalue()

return output,chan.recv_stderr(600),chan.recv_exit_status()

The above code works for small outputs, but it gets stuck for larger outputs.

Is there any buffer related issue in here?

Answer 1

i see no problem related to stdout channel, but i'm not sure about the way you are handling stderr. Can you confirm, its not the stderr capturing thats causing problem? I'll try out your code and let you know.

Update: when a command you execute gives lots of messages in STDERR, your code freezes. I'm not sure why, but recv_stderr(600) might be the reason. So capture error stream the same way you capture standard output. something like,

contents_err = StringIO.StringIO()

data_err = chan.recv_stderr(1024)
while data_err:
    contents_err.write(data_err)
    data_err = chan.recv_stderr(1024)

you may even first try and change recv_stderr(600) to recv_stderr(1024) or higher.