Python paramiko script, problems reading output during exec_command()

Question

Background: I am using python and paramiko to automate the process I go through everytime I have to hand in a program for a class. We use a command called "handin" to submit source code, but this must be done from a school computer. So when I submit code from home, I have to: sftp into school servers, put the files in a dir, ssh into school computer, use 'handin' command

I can successfully put files onto the school machines. The problem occurs when I try to use exec_command('handin my files') and then read the output to determine the next action.

so I have

try:
   (stdin, stdout, stderr) = client.exec_command(s)
except:
   print 'whoops'
   sys.exit()
print stdout.readlines()

But this causes a deadlock for some reason, the script appears to be doing nothing and I have to eventually kill the entire process (ctrl+c doesnt work). Im not sure if exec_command is not completing correctly (even though it is getting out of the try/catch block) or if im having network problems or what.

Any ideas?

update:

The problem is with interacting with the handin command during execution. After executing the command, handin may or may not still be running. If its the first time submitting it says success, blah blah, and finishes executing. All is well. But if I am re-submitting I have to authorize an overwrite (stdin.write('y')) for each file.

TL/DR:

How do I check if a exec_command() is still running, waiting for input, and readline() from stdout accordingly?

Answer 1

I don't see anything wrong with the code snippit above. The program below is a complete script which logs into a host and runs the ls command to view files. I just tried it and it works for me. Perhaps try this and see if it works for you. If it does not work, I suspect some issue specific to either your ssh server, command you are running, or paramiko installation. If it does work for you, its just a matter of making changes to this to move towards your existing functionality and see where it breaks.

import paramiko
ssh=paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('<ip address here>',username='<username here>',password='<password here>')
stdin,stdout,stderr = ssh.exec_command("ls /")
print stdout.readlines()

If that works for you my next suggestion would be to try replacing the 'ls /' with the actual handin command you are trying to run. Its possible that command is hanging waiting for user input, etc.

Answer 2

The problem might be that the remote command is waiting for input (it expects you to write something to stdin, not knowing that you aren't going to unless you tell so). Try stdin.channel.shutdown_write() (I believe stdin.close() by itself won't do the trick: that will only cause a flush)

Answer 3

To workaround this and get the output of Ifconfig, you may wanna try to use the option get_pty=True

e.g:

import paramiko
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())

def MonitorProcess():
    ssh.connect('10.2.0.230', username='ibmsys1', password='passw0rd', timeout=5)
    stdin, stdout, stderr = ssh.exec_command('/sbin/ifconfig', timeout=3, get_pty=True)
    #stdin, stdout, stderr = ssh.exec_command('/sbin/ifconfig') -> simple exec ex.
    print stdout.read()

MonitorProcess()

Answer 4

This is an old thread but I have seen this issue as well. This is due to a bug in Paramiko which it cannot process large STDOUT from the remote command so it hangs.

Ref: https://github.com/paramiko/paramiko/issues/515

Possible Solution: https://gist.github.com/matjohn2/2c1c4988e17112a34f310667e0ff6e7e