Develop Reference

Command output is corrupted when executed using Python Paramiko exec_command

I'm a software tester, trying to verify that the log on a remote QNX (a BSD variant) machine will contain the correct entries after specific actions are taken. I am able to list the contents of the directory in which the log resides, and use that information in the command to read (really want to use tail -n XX <file>) the file. So far, I always get a "(No such file or directory)" when trying to read the file.
We are using Froglogic Squish for automated testing, because the Windows UI (that interacts with the server piece on QNX) is built using Qt extensions for standard Windows elements. Squish uses Python 2.7, so I am using Python 2.7.
I am using paramiko for the SSH connection to the QNX server. This has worked great for sending commands to the simulator piece that also runs on the QNX server.
So, here's the code. Some descriptive names have been changed to avoid upsetting my employer.
import sys
import time
import select
sys.path.append(r"C:\Python27\Lib\site-packages")
sys.path.append(r"C:\Python27\Lib\site-packages\pip\_vendor")
import paramiko
# Import SSH configuration variables
ssh_host = 'vvv.xxx.yyy.zzz'
thelog_dir = "/logs/the/"
ssh_user = 'un'
ssh_pw = 'pw'
def execute_Command(fullCmd):
outptLines = []
#
# Try to connect to the host.
# Retry a few times if it fails.
#
i = 1
while True:
try:
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect(ssh_host, 22, ssh_user, ssh_pw)
break
except paramiko.AuthenticationException:
log ("Authentication failed when connecting to %s" % ssh_host)
return 1
except:
log ("Could not SSH to %s, waiting for it to start" % ssh_host)
i += 1
time.sleep(2)
# If we could not connect within time limit
if i == 30:
log ("Could not connect to %s. Giving up" % ssh_host)
return 1
# Send the command (non-blocking?)
stdin, stdout, stderr = ssh.exec_command(fullCmd, get_pty=True)
for line in iter(stdout.readline, ""):
outptLines.append(line)
#
# Disconnect from the host
#
ssh.close()
return outptLines
def get_Latest_Log():
fullCmd = "ls -1 %s | grep the_2" %thelog_dir
files = execute_Command(fullCmd)
theFile = files[-1]
return theFile
def main():
numLines = 20
theLog = get_Latest_Log()
print("\n\nThe latest log is %s\n\n" %theLog)
fullCmd = "cd /logs/the; tail -n 20 /logs/the/%s" %theLog
#fullCmd = "tail -n 20 /logs/the/%s" %theLog
print fullCmd
logLines = execute_Command(fullCmd)
for line in logLines:
print line
if __name__ == "__main__":
# execute only if run as a script
main()
I have tried to read the file using both tail and cat. I have also tried to get and open the file using Paramiko's SFTP client.
In all cases, the response of trying to read the file fails -- despite the fact that listing the contents of the directory works fine. (?!) And BTW, the log file is supposed to be readable by 'world'. Permissions are -rw-rw-r--.
The output I get is:
"C:\Users\xsat086\Documents\paramikoTest>python SSH_THE_MsgChk.py
The latest log is the_20210628_115455_205.log
cd /logs/the; tail -n 20 /logs/the/the_20210628_115455_205.log
(No such file or directory)the/the_20210628_115455_205.log"
The file name is correct. If I copy and paste the tail command into an interactive SSH session with the QNX server, it works fine.
Is it something to do with the 'non-interactive' nature of this method of sending commands? I read that some implementations of SSH are built upon a command that offers a very limited environment. I don't see how that would impact this tail command.
Or am I doing something stupid in this code?

I cannot really explain completely, why you get the results you get.
But in general a corrupted output is a result of enabling and not handling terminal emulation. You enable the terminal emulation using get_pty=True. Remove it. You should not use the terminal emulation, when automating command execution.
Related question:
Is there a simple way to get rid of junk values that come when you SSH using Python's Paramiko library and fetch output from CLI of a remote machine?

How do i send a signal FROM container TO host on some event?

I have a mariadb running in a container. On 'docker run', an import script (from a db dump) is run by mariadb, which creates users, builds schema, etc.
As the size of that dump script grows, the time to do the import increases. At this point it's about 8-10 seconds, but i expect amount of data to increase substantially, and the import time will be more difficult to predict.
I'd like to be able to send a signal from the container to the host, to let it know that the data has been loaded, and that db is ready to be used. So far i have found info on how to send signal from one container to another container, but there's no information on how to send signal from container to the host. Also, i need to be able to do this programmatically, as creating container is part part of a larger pipeline.
Ideally, i'd like to be able to do something like this:
client = docker.from_env()
db_c = client.containers.run('my_db_image', ....)
# check for signal from db_c container
# do other things
Thank you!

AFAIK you cannot send signals from the container to a process running on the host but there are other ways to know when the import has finished. I think the easiest is to start the container in detached mode and wait until a specific line gets logged. The following script for example waits until the line done is logged:
import os
import docker
client = docker.from_env()
container = client.containers.run('ubuntu:latest', 'bash -c "for i in {1..10}; do sleep 1; echo working; done; echo done"', detach=True)
print('container started')
for line in container.logs(stream=True):
print line.strip()
if line.strip() == 'done':
break
print('continue....')
If the output of the import script goes to stdout it could contain a simple print at the end:
select 'The import has finished' AS '';
Wait for this string in the python script.
Another approach is to use some other form of inter-process communication. An example using named pipes:
import os
import docker
import errno
client = docker.from_env()
FIFO = '/tmp/apipe'
# create the pipe
try:
os.mkfifo(FIFO)
except OSError as oe:
if oe.errno != errno.EEXIST:
raise
# start the container sharing the pipe
container = client.containers.run('ubuntu:latest', 'bash -c "sleep 5; echo done > /tmp/apipe"', volumes={FIFO: {'bind': FIFO, 'mode': 'rw'}}, detach=True)
print("container started")
with open(FIFO) as fifo:
print("FIFO opened")
while True:
data = fifo.read()
if len(data) == 0:
print("Writer closed")
break
print('Read: "{0}"'.format(data))
print("continue...")
The host shares the named pipe with the container. In the python script the read call to the FIFO is blocked until some data is available in the pipe.
In the container the import script writes to the pipe notifying the program that the data has been loaded. The mysql system command, \! command to execute an external command might come in handy in this situation. You could simply add to the end of the script:
\! echo done > /tmp/apipe
In a similar way you could use IPC sockets (aka Unix sockets) or shared memory but things get a bit more complicated.
Yet another solution is to add a health-check to the container. The health status can be polled on the host by inspecting the container. See How to wait until docker start is finished?
Edited:
The above approaches assume the container is initialized and accepting connections. If the script is executed as part of the initialization process (Initializing a fresh instance), which seems to be the case here, the database is not ready and accepting connections when the import completes. For the initialization the server is temporarily started with the
--skip_networking (allowing only local clients) and only after the initialization completes it is restarted and becomes available remotely.

you can add this code to check if the db is ready to accept the connections:
import MySQLdb
import time
db = MySQLdb.connect(host='MYHost', user='MYNAME', passwd='PASS', db='MYDB')
if not db:
while True:
db = MySQLdb.connect(host='MYHost', user='MYNAME', passwd='PASS', db='MYDB')
if db:
break
print("Still waiting for the DB")
time.sleep(10)

How to connect to windows 2012 machine from Centos using Python3

My requirement is ability to run a PowerShell script on a Windows 2012 server remotely, this has to be triggered from a Linux server using Python script.
Need suggestions on best way to handle this and also sample code (if possible).
Below are the steps I intend to achieve but i see it's not working as expected.
PowerShell scripts to be executed are already placed in Windows server (2012).
Python3 program running on Linux (CentOS) does SSH to Windows server (2012) using netmiko module.
sends the command (PowerShell command to execute script in remote Windows server) over the SSH connection.
I was able to connect to the remote Windows server using Python. But I don't see this method working as expected.
Need an effective and efficient way to achieve this.
from netmiko import ConnectHandler
device = ConnectHandler(device_type="terminal_server",
ip="X.X.X.x",
username="username",
password="password")
hostname = device.find_prompt()
output = device.send_command("ipconfig")
print (hostname)
print (output)
device.disconnect()

Nothing much is done for 'terminal_server" device type. You have to do manual passing at the moment.
Below is extracted from COMMON_ISSUES.md
Does Netmiko support connecting via a terminal server?
There is a 'terminal_server' device_type that basically does nothing post SSH connect. This means you have to manually handle the interaction with the terminal server to connect to the end device. After you are fully connected to the end network device, you can then 'redispatch' and Netmiko will behave normally
from __future__ import unicode_literals, print_function
import time
from netmiko import ConnectHandler, redispatch
net_connect = ConnectHandler(
device_type='terminal_server', # Notice 'terminal_server' here
ip='10.10.10.10',
username='admin',
password='admin123',
secret='secret123')
# Manually handle interaction in the Terminal Server
# (fictional example, but hopefully you see the pattern)
# Send Enter a Couple of Times
net_connect.write_channel("\r\n")
time.sleep(1)
net_connect.write_channel("\r\n")
time.sleep(1)
output = net_connect.read_channel()
print(output) # Should hopefully see the terminal server prompt
# Login to end device from terminal server
net_connect.write_channel("connect 1\r\n")
time.sleep(1)
# Manually handle the Username and Password
max_loops = 10
i = 1
while i <= max_loops:
output = net_connect.read_channel()
if 'Username' in output:
net_connect.write_channel(net_connect.username + '\r\n')
time.sleep(1)
output = net_connect.read_channel()
# Search for password pattern / send password
if 'Password' in output:
net_connect.write_channel(net_connect.password + '\r\n')
time.sleep(.5)
output = net_connect.read_channel()
# Did we successfully login
if '>' in output or '#' in output:
break
net_connect.write_channel('\r\n')
time.sleep(.5)
i += 1
# We are now logged into the end device
# Dynamically reset the class back to the proper Netmiko class
redispatch(net_connect, device_type='cisco_ios')
# Now just do your normal Netmiko operations
new_output = net_connect.send_command("show ip int brief")

Persistent ssh session to Cisco router

I have search on this site and multiple other locations but I have been unable to resolve my problem of connecting and maintaining ssh session after one command. Below is my current code:
#!/opt/local/bin/python
import os
import pexpect
import paramiko
import hashlib
import StringIO
while True:
cisco_cmd = raw_input("Enter cisco router cmd:")
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('192.168.221.235', username='nuts', password='cisco', timeout = 30)
stdin, stdout, stderr = ssh.exec_command(cisco_cmd)
print stdout.read()
ssh.close()
if cisco_cmd == 'exit': break
I can run multiple commands but for every commands a new ssh session is created.
The above program does not work when I need to configuration mode because ssh session
is not reused.Any assistance in resolving this matter is greatly appreciated.

I used Exscript instead of paramiko and I am now able to get persistent session on IOS device.
#!/opt/local/bin/python
import hashlib
import Exscript
from Exscript.util.interact import read_login
from Exscript.protocols import SSH2
account = read_login() # Prompt the user for his name and password
conn = SSH2() # We choose to use SSH2
conn.connect('192.168.221.235') # Open the SSH connection
conn.login(account) # Authenticate on the remote host
conn.execute('conf t') # Execute the "uname -a" command
conn.execute('interface Serial1/0')
conn.execute('ip address 114.168.221.202 255.255.255.0')
conn.execute('no shutdown')
conn.execute('end')
conn.execute('sh run int Serial1/0')
print conn.response
conn.execute('show ip route')
print conn.response
conn.send('exit\r') # Send the "exit" command
conn.close() # Wait for the connection to close

You need to create, connect and close connection outside the while loop.

Your loop does that
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('192.168.221.235', username='nuts', password='cisco', timeout = 30)
while True:
cisco_cmd = raw_input("Enter cisco router cmd:")
stdin, stdout, stderr = ssh.exec_command(cisco_cmd)
print stdout.read()
if cisco_cmd == 'exit': break
ssh.close()
Move the initialisation and setup outside the loop.
EDIT: Moved close()

The above program does not work when I
need to configuration mode because ssh
session is not reused
Your ssh session will be reused once you move the connect and close outside of the loop, but each exec_command() happens in a new shell (through a new channel), and are unrelated. You will need to format your commands so that they don't require any state from the shell.
If I remember correctly, some Cisco devices only allow a single exec, and then close the connection. In that case, you will need to use invoke_shell(), and work interactively using the pexpect module (which you already have imported, but aren't using).

SCP a tar file using pexpect

I am using ssh to log into a camera, scp a tarball over to it and extract files from the tarbal and then run the script. I am having problems with Pexpect, though. Pexpect times out when the tarball is being copied over. It seem's not to wait until it is done. And then it start's doing the same thing with the untar command, The code I have is below:
ssh_newkey = 'Are you sure you want to continue connecting'
copy = pexpect.spawn('ssh service#10.10.10.10')
i=copy.expect([ssh_newkey,'password:',pexpect.EOF])
if i==0:
copy.sendline('yes')
i=copy.expect([ssh_newkey,'password:',pexpect.EOF])
if i==1:
copy.sendline("service")
print 'Password Accepted'
copy.expect('service#user:')
copy.sendline('su - root')
i=copy.expect('Password:')
copy.sendline('root')
i=copy.expect('#')
copy.sendline('cd /tmp')
i=copy.expect("#")
copy.sendline('scp user#20.20.20.20:/home/user/tarfile.tar.gz .')
i=copy.expect([ssh_newkey,'password:',pexpect.EOF])
if i==0:
copy.sendline('yes')
i=copy.expect([ssh_newkey,'password:',pexpect.EOF])
else:
pass
copy.sendline('userpwd')
i=copy.expect('#')
copy.sendline('tar -zxvf tarfile.tar.gz bin/installer.sh')
i=copy.expect("#")
copy.sendline("setsid /tmp/bin/installer.sh /tmp/tarfile.tar.gz > /dev/null 2>&1 &")
elif i==2:
print "I either got key or connection timeout"
else:
pass
Can anyone help find a solution for this?
Thanks

I'm not sure if this is correct, but I'd try setting the timeout to None:
copy = pexpect.spawn('ssh service#10.10.10.10', timeout=None)
According to the source code, pexpect seems to not check the timeout when it's set to None.
Anyway, the reason I'm answering this even though I'm not sure whether it solves your problem is that I wanted to recommend using paramiko instead. I had good experience using it for communication over SSH in the past.

Is there a reason your using pexpect or even paramiko?
if you setup a public/private key then you can just use as a single example:
command = "scp user#20.20.20.20:/home/user/tarfile.tar.gz"
split_command = shlex.split(command)
subprocess.call(split_command)
Then as per the suggestion above use paramiko to send commands.
you can use the keyfile for that as well:
The following class method will give you a persistent session (although it is untested):
#!/usr/bin/python
# -*- coding: utf-8 -*-
from __future__ import print_function
import os
from paramiko import SSHClient, AutoAddPolicy, AuthenticationException, RSAKey
from subprocess import call
class CommsSuite(object):
def __init__(self):
self.ssh_client = SSHClient()
#--------------------------------------
def _session_send(command):
"""
Use to send commands over ssh in a 'interactive_session'
Verifies session is present
If the interactive_session is not present then print the failed command.
This may be updated to raise an error,
which would probably make more sense.
#param command: the command to send across as a string
::TODO:: consider raise exception here as failed
session will most likely be fatal.
"""
if self.session.send_ready():
self.session.send("%s\n" % command)
else:
print("Session cannot send %s" % command)
#--------------------------------------
def _get_persistent_session(_timeout = 5):
"""
connect to the host and establish an interactive session.
#param _timeout: sets the timout to prevent blocking.
"""
privatekeyfile = os.path.expanduser('~/.ssh/id_rsa')#this must point to your keyfile
private_key = RSAKey.from_private_key_file(privatekeyfile)
self.ssh_client.set_missing_host_key_policy(AutoAddPolicy())
self.ssh_client.connect(hostname,
username = <username>,
pkey = private_key,
timeout = _timeout)
self.transport = self.ssh_client.get_transport()
self.session = self.transport.open_session()
self.session.exec_command("bash -s")
_get_persistent_session()
# build a comma seperated list of commands here as a string "[a,b,c]"
commands = ["tar -zxvf tarfile.tar.gz bin/installer.sh", "setsid /tmp/bin/installer.sh /tmp/tarfile.tar.gz > /dev/null 2>&1"]
# then run the list of commands
if len(commands) > 0:
for command in commands:
_session_send(command)
self.session.close()#close the session when done
CommsSuite()