Why is ssh connecting but giving no output?

burvil · Oct-02-2018, 11:44 PM

I have the code below that runs without errors, but doesn't seem to give any output after establishing the connection, nor after running exec_command to execute the command. Any thoughts on why that is?

        
          
          
              
               #####################################################
# IN: hostname to connect to, username to connect as, string of command(s) to run
# OUT: array of information to parse for OS; returns nothing if not able to connect
 
def SSHConnect(hostname, username, command):
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    output = []
 
    try:
        Log("info",  inspect.getframeinfo(inspect.currentframe()).function, "Connecting to " + hostname + " by ssh as user " + username + " t
        result = ssh.connect(hostname, username=username, password=GetCreds(username), auth_timeout=30, look_for_keys=True)
        print("SSH result is " + str(result))
        (sdtin, stdout, stderr) = ssh.exec_command(command)
        Log("info", "stdout is " + str(stdout) + ", stderr is " + str(stderr))
        output = stdout.readlines()
        if (stderr):
            Log("err", inspect.getframeinfo(inspect.currentframe()).function, "Errors generated - " + str(stderr))
        ssh.close()
    except (socket.error,paramiko.AuthenticationException,paramiko.SSHException) as message:
        Log("err",  inspect.getframeinfo(inspect.currentframe()).function, "Error in connecting - " + message)
        pass
 
    finally:
        Log("debug",  inspect.getframeinfo(inspect.currentframe()).function, "Output - " + str(output))
        return output

            

        
      

It runs without errors, and accepts the password, but the output contains nothing. In contrast, I can ssh to it from the bash prompt and the desired command (hostname), using the same password.

Output:$ rm -f /tmp/ssh.log ; ./ssh-test.py; cat /tmp/ssh.log
Starting, using ssh-test.cfg and writing to logfile /tmp/ssh.log
SSHConnect - Connecting to hostname-here by ssh as user username-here to run command(s) hostname
GetCreds - Found credentials for user username-here
SSH result is None
<module> - Finished.  Duration is 0.092745 seconds.
2018-10-02 16:20:15,773 - <module> - INFO - Started ./ssh-test.py at 0.15
2018-10-02 16:20:15,773 - <module> - INFO - Using config file ssh-test.cfg
2018-10-02 16:20:15,798 - Log - INFO - SSHConnect - Connecting to ga-devarcmsdc19.ds.dtveng.net by ssh as user d401771 to run command(s) hostname
2018-10-02 16:20:15,798 - Log - DEBUG - GetCreds - Getting creds for user username-here
2018-10-02 16:20:15,798 - Log - INFO - GetCreds - Found credentials for user username-here
2018-10-02 16:20:16,168 - _log - DEBUG - starting thread (client mode): 0xb9e0510L
2018-10-02 16:20:16,168 - _log - DEBUG - Local version/idstring: SSH-2.0-paramiko_2.4.1
2018-10-02 16:20:16,188 - _log - DEBUG - Remote version/idstring: SSH-2.0-OpenSSH_7.4
2018-10-02 16:20:16,188 - _log - INFO - Connected (version 2.0, client OpenSSH_7.4)
2018-10-02 16:20:16,192 - _log - DEBUG - kex algos:[u'gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==', u'gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==', u'gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==', u'curve25519-sha256', u'curve25519-sha256@libssh.org', u'ecdh-sha2-nistp256', u'ecdh-sha2-nistp384', u'ecdh-sha2-nistp521', u'diffie-hellman-group-exchange-sha256', u'diffie-hellman-group16-sha512', u'diffie-hellman-group18-sha512', u'diffie-hellman-group14-sha256', u'diffie-hellman-group14-sha1'] server key:[u'ssh-rsa', u'rsa-sha2-512', u'rsa-sha2-256', u'ecdsa-sha2-nistp256', u'ssh-ed25519'] client encrypt:[u'chacha20-poly1305@openssh.com', u'aes128-ctr', u'aes192-ctr', u'aes256-ctr', u'aes128-gcm@openssh.com', u'aes256-gcm@openssh.com'] server encrypt:[u'chacha20-poly1305@openssh.com', u'aes128-ctr', u'aes192-ctr', u'aes256-ctr', u'aes128-gcm@openssh.com', u'aes256-gcm@openssh.com'] client mac:[u'umac-64-etm@openssh.com', u'umac-128-etm@openssh.com', u'hmac-sha2-256-etm@openssh.com', u'hmac-sha2-512-etm@openssh.com', u'hmac-sha1-etm@openssh.com', u'umac-64@openssh.com', u'umac-128@openssh.com', u'hmac-sha2-256', u'hmac-sha2-512', u'hmac-sha1'] server mac:[u'umac-64-etm@openssh.com', u'umac-128-etm@openssh.com', u'hmac-sha2-256-etm@openssh.com', u'hmac-sha2-512-etm@openssh.com', u'hmac-sha1-etm@openssh.com', u'umac-64@openssh.com', u'umac-128@openssh.com', u'hmac-sha2-256', u'hmac-sha2-512', u'hmac-sha1'] client compress:[u'none', u'zlib@openssh.com'] server compress:[u'none', u'zlib@openssh.com'] client lang:[u''] server lang:[u''] kex follows?False
2018-10-02 16:20:16,192 - _log - DEBUG - Kex agreed: ecdh-sha2-nistp256
2018-10-02 16:20:16,192 - _log - DEBUG - HostKey agreed: ssh-ed25519
2018-10-02 16:20:16,192 - _log - DEBUG - Cipher agreed: aes128-ctr
2018-10-02 16:20:16,192 - _log - DEBUG - MAC agreed: hmac-sha2-256
2018-10-02 16:20:16,192 - _log - DEBUG - Compression agreed: none
2018-10-02 16:20:16,248 - _log - DEBUG - kex engine KexNistp256 specified hash_algo <built-in function openssl_sha256>
2018-10-02 16:20:16,249 - _log - DEBUG - Switch to new keys ...
2018-10-02 16:20:16,273 - _log - DEBUG - Adding ssh-ed25519 host key for ga-devarcmsdc19.ds.dtveng.net: c9d6111e7dac37c8c1312116d0d0af62
2018-10-02 16:20:16,274 - _log - DEBUG - Trying discovered key f5c702e13542e4ad0dcc614d8f15deeb in /Users/bc143k/.ssh/id_rsa
2018-10-02 16:20:16,304 - _log - DEBUG - userauth is OK
2018-10-02 16:20:16,363 - _log - INFO - Auth banner: S
Kernel 3.10.0-862.11.6.el7.x86_64 on an x86_64


2018-10-02 16:20:16,364 - _log - INFO - Authentication (publickey) failed.
2018-10-02 16:20:16,379 - _log - DEBUG - Trying discovered key f7385028aa9a79f265ef275ab994e606 in /Users/bc143k/.ssh/id_dsa
2018-10-02 16:20:16,398 - _log - DEBUG - userauth is OK
2018-10-02 16:20:16,419 - _log - INFO - Authentication (publickey) failed.
2018-10-02 16:20:16,522 - _log - DEBUG - userauth is OK
2018-10-02 16:20:16,603 - _log - INFO - Authentication (password) successful!
2018-10-02 16:20:16,633 - _log - DEBUG - [chan 0] Max packet in: 32768 bytes
2018-10-02 16:20:17,232 - _log - DEBUG - Received global request "hostkeys-00@openssh.com"
2018-10-02 16:20:17,232 - _log - DEBUG - Rejecting "hostkeys-00@openssh.com" global request from server.
2018-10-02 16:20:17,232 - _log - DEBUG - Debug msg: Ignored authorized keys: bad ownership or modes for directory /home/bchang
2018-10-02 16:20:17,232 - _log - DEBUG - Debug msg: Ignored authorized keys: bad ownership or modes for directory /home/bchang
2018-10-02 16:20:17,233 - _log - DEBUG - [chan 0] Max packet out: 32768 bytes
2018-10-02 16:20:17,233 - _log - DEBUG - Secsh channel 0 opened.
2018-10-02 16:20:17,277 - _log - DEBUG - [chan 0] Sesch channel 0 request ok
2018-10-02 16:20:17,277 - Log - DEBUG - SSHConnect - Output - []
2018-10-02 16:20:17,278 - Log - INFO - <module> - Finished.  Duration is 0.092745 seconds.
2018-10-02 16:20:17,302 - _log - DEBUG - EOF in transport thread

Again, I'm confused on why it's not throwing any exceptions, but doesn't appear to give any kind of output. Thoughts?

burvil · (This post was last modified: Oct-04-2018, 10:09 PM by burvil.)

Updated working code below. Primary reason is stdin is spelled wrong above.

        
          
          
              
              #####################################################
# IN: hostname to connect to, username to connect as, string of command(s) to run
# OUT: array of information to parse for OS; returns nothing if not able to connect
 
def SSHConnect(hostname, username, command):
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    output = ""
    (stdin, stdout, stderr) = "", "", ""
 
    try:
        Log("info",  inspect.getframeinfo(inspect.currentframe()).function, "Connecting to " + hostname + " by ssh as user " + username + " to run command(s) " + command)
        #result = ssh.connect(hostname, 22, username=username, password=GetCreds(username), auth_timeout=30, look_for_keys=True)
        ssh.connect(hostname, username=username, 
                password=GetCreds(username), key_filename="full-path-of-pemfile-here") 
        stdin, stdout, stderr = ssh.exec_command(command)
        #Log("debug", inspect.getframeinfo(inspect.currentframe()).function, "stdout is " + str(stdout) + ", stderr is " + str(stderr))
        stdout = stdout.readlines()
        for line in stdout:
            output=output+line
        if output!="":
            Log("debug", inspect.getframeinfo(inspect.currentframe()).function, "Output is " + output)
        else:
            Log("err", inspect.getframeinfo(inspect.currentframe()).function, "There was no output for command " + command )
        ssh.close()
    except (socket.error,paramiko.AuthenticationException,paramiko.SSHException) as message:
        Log("err",  inspect.getframeinfo(inspect.currentframe()).function, "Error in connecting - " + message)
        pass
 
    finally:
        Log("debug",  inspect.getframeinfo(inspect.currentframe()).function, "Output - " + str(output) + ", stdout is " + str(stdout) + ", stderr is " + str(stderr) )
        return output

            

        
      

**j.crater** · Oct-05-2018, 03:50 PM

Thank you for notifying and posting the solution to your issue.

Why is ssh connecting but giving no output?

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