"No hostkey for ... found" in pysftp code even though cnopts.hostkeys is set to None

Question

Background

To SFTP across to another server I use the following command in the UNIX command line:

sftp -i /some_dir/another_dir/key -oPort=12345 user@12.123.456.789

What I want to achieve

I want to convert this to command to be used with PySFTP.

What I have tried

import pysftp
cnopts = pysftp.CnOpts()
cnopts.hostkeys = None

# source: https://pysftp.readthedocs.io/en/release_0.2.7/pysftp.html
srv = pysftp.Connection("user@12.123.456.789", port="12345",  
                         private_key_pass="/some_dir/another_dir/key")

Errors encountered

File "./aws_sql_dumper.py", line 14, in <module>
    srv = pysftp.Connection("user@12.123.456.789", port="12345",  private_key_pass="/some_dir/another_dir/key")
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 132, in __init__
    self._tconnect['hostkey'] = self._cnopts.get_hostkey(host)
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 71, in get_hostkey
    raise SSHException("No hostkey for host %s found." % host)
paramiko.ssh_exception.SSHException: No hostkey for host user@12.123.456.789 found.
Exception ignored in: <bound method Connection.__del__ of <pysftp.Connection object at 0x7f6067c7ea20>>
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 1013, in __del__
    self.close()
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 784, in close
    if self._sftp_live:
AttributeError: 'Connection' object has no attribute '_sftp_live'

Research done

I've read up on the following:

Question

I think I am doing something fundamental wrong. How can I adopt the SFTP command used in UNIX command line to be accepted/interpretted by pysftp?

Changes

I changed a few things around

import pysftp
cnopts = pysftp.CnOpts()
cnopts.hostkeys.load('/home/some_dir/.ssh/known_hosts')

# source: https://pysftp.readthedocs.io/en/release_0.2.7/pysftp.html
srv = pysftp.Connection("user@12.123.456.789", port="12345",  
                         private_key="/some_dir/another_dir/key", cnopts=cnopts)

Output after change

Traceback (most recent call last):
  File "./aws_sql_dumper.py", line 17, in <module>
    srv = pysftp.Connection("user@12.123.456.789", port="12345",  private_key="/some_dir/another_dir/key", cnopts=cnopts)
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 132, in __init__
    self._tconnect['hostkey'] = self._cnopts.get_hostkey(host)
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 71, in get_hostkey
    raise SSHException("No hostkey for host %s found." % host)
paramiko.ssh_exception.SSHException: No hostkey for host user@12.123.456.789" found.
Exception ignored in: <bound method Connection.__del__ of <pysftp.Connection object at 0x7f8120dc6438>>
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 1013, in __del__
    self.close()
  File "/usr/local/lib/python3.4/dist-packages/pysftp/__init__.py", line 784, in close
    if self._sftp_live:
AttributeError: 'Connection' object has no attribute '_sftp_live

Martin Prikryl · Answer 1 · 2020-10-31T09:53:19.770

0

You never use the cnopts variable. You need to pass it to cnopts parameter of Connection class.

Once you resolve this, you will have a problem with the private key, as you pass it to private_key_pass parameter ("private key passphrase") instead of to private_key.

srv = pysftp.Connection("user@12.123.456.789", port="12345",  
                         private_key="/some_dir/another_dir/key", cnopts=cnopts)

Though you should not do cnopts.hostkeys = None, as you lose security by doing so. The right solution is to verify the host key. Check my answer to the same question for correct solutions.

edited Oct 31 '20 at 09:53

answered Mar 14 '19 at 07:10

Martin Prikryl

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I'm still having some difficulty (I've updated the question) I read your answer and did so, but still to no avail. What else should I be doing? Or is there an alternative simpler library you could recommend? – 3kstc Mar 15 '19 at 00:39
So what did you do exactly? How did you update the `known_hosts`? What does the `known_hosts` contains? Show us. – Martin Prikryl Mar 15 '19 at 05:57
Is there a way I can bypass `known_hosts` (I've become so confused with the known hosts - the more I read the more confused I've become) and just use the key (`/some_dir/another_dir/key`) and the user alongside the IP address `user` [`@`] `12.123.456.789` – 3kstc Mar 18 '19 at 01:21
@3kstc What is `/some_dir/another_dir/key`? Actually your are probably confused :) As I assume that `key` is your key for authentication, what has nothing to do with host keys/known hosts. Read my article [Understanding SSH key pairs](https://winscp.net/eng/docs/ssh_keys) - So if you actually put your *authentication key* to `known_hosts`, then it's clear why it does not match the *host key*. – Martin Prikryl Mar 18 '19 at 06:22

score 0 · Accepted Answer · answered Mar 27 '19 at 08:49

After much trial and error, converting the following SFTP command put into the terminal:

sftp -i /some_dir/another_dir/key -oPort=12345 user@12.123.456.789

can be translated* into:

paramiko.SSHClient().connect(hostname='12.123.456.789', username='user', port=12345,
                             key_filename='/some_dir/another_dir/key')

The whole condensed code is:

#!/usr/bin/python3

import paramiko

try:
    client = paramiko.SSHClient()
    client.load_system_host_keys()
    client.set_missing_host_key_policy(paramiko.WarningPolicy)
    client.connect(hostname='12.123.456.789', username='user', port=12345, 
                   key_filename='/some_dir/another_dir/key')

    # -------------------------- [ just for testing ] --------------------------
    stdin, stdout, stderr = client.exec_command('ls -la')   # THIS IS FOR TESTING
    print(stdout.read())                                    # AND PRINTING OUT

finally:
    client.close()

score 0 · Answer 3 · answered Aug 07 '21 at 02:13

I was facing the similar issue (Host key issue) and found a good solution. In am trying to connect from a windows box(source) to Linux box(Destination). In my windows machine we have already installed CYGWIN where i logged in and did the below

1. Logged in using my ID
2. Ran the command ssh-keygen -b 2048 -t rsa
3. under my cygwin home dir (~/.ssh) folder was created with pub and private key.
4. Physically this folder would be in c:\cygwin\home\/.ssh
5. Copy this folder and paste in the c:\user\\.ssh (windows home dir)
6. also open the pub key in the folder and paste that in the destination server ~\.ssh\authroized_keys. This is for password less login.

After this pysftp was able to connect without password less. Host key would be detected without any issues

-Prasanna.K

"No hostkey for ... found" in pysftp code even though cnopts.hostkeys is set to None

3 Answers3

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