python ssh script for linux ssh command

Question

My Linux script is as below to ssh to host & search patch update which has kernel update

 for host in `cat patch.csv`
    do 
      echo "Host $host" >> /tmp/patching
      ssh -o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no" $host  'sudo yum check-update | grep "kernel.x86"'>>/tmp/patching
    done

Now i am trying to write a python script equivalent to this & its showing error(not able to conenct to ssh). I tried to use subprocess comamnd which is not working - its not able to pick up hostname & public key error.

import subprocess
import os
def read_file():
    # Read and print the entire file line by line
    with open('patch.csv', 'r') as reader:
        with open('server_names.txt', 'w') as writer:
            for host in reader:
                writer.write(host)
                p = subprocess.Popen(["ssh -o 'UserKnownHostsFile=/dev/null' -o 'StrictHostKeyChecking=no' host 'sudo yum check-update | grep kernel.x86'"], shell=True, stdout=subprocess.PIPE)
                output, err = p.communicate()
                print(host)
    print("file read done")

read_file()

For what it's worth, your original script has a number of shell scripting gotchas. Probably see what shellcheck.net has to say about it for a start. (Though replacing most of it with Python might make that moot.) — tripleee
– tripleee, Commented Sep 24, 2020 at 16:12

lucasgrvarela · Accepted Answer · 2020-09-24 00:03:55Z

1

You can use paramiko to solve that problem to ssh to another host using python, we use it on an internal project, works very well.

http://www.paramiko.org/
$ pip install paramiko

You can use password or passphrase as input if it's required by the host, so authentication can be automated.

http://docs.paramiko.org/en/stable/api/client.html#paramiko.client.SSHClient.connect

connect(hostname, port=22, username=None, password=None, pkey=None, key_filename=None, timeout=None, allow_agent=True, look_for_keys=True, compress=False, sock=None, gss_auth=False, gss_kex=False, gss_deleg_creds=True, gss_host=None, banner_timeout=None, auth_timeout=None, gss_trust_dns=True, passphrase=None, disabled_algorithms=None)
Connect to an SSH server and authenticate to it. The server’s host key is checked against the system host keys (see load_system_host_keys) and any local host keys (load_host_keys). If the server’s hostname is not found in either set of host keys, the missing host key policy is used (see set_missing_host_key_policy). The default policy is to reject the key and raise an SSHException.

Code sample adapted from https://gist.github.com/mlafeldt/841944

import paramiko

hostname = host
password = pass123
command = 'sudo yum check-update | grep kernel.x86'
username = "admin"
port = 22

try:
    client = paramiko.SSHClient()
    client.load_system_host_keys()
    client.set_missing_host_key_policy(paramiko.WarningPolicy)
    client.connect(hostname, port=port, username=username, password=password)
    stdin, stdout, stderr = client.exec_command(command)
    print stdout.read()
finally:
    client.close()

answered Sep 24, 2020 at 0:03

lucasgrvarela

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1 Comment

dbNovice Over a year ago

I got some idea from your given code @lucasgvarela & came up with this which actually worked. Is there a way I can do multiple action after ssh is completed? like want to run few mysql query after ssh & check the output of the queries & do something based on that?

dbNovice · Accepted Answer · 2020-09-24 16:06:40Z

0

I got some idea from your given code @lucasgvarela & came up with this using some other posts in stackoverflow which actually worked.

import subprocess
import sys    
# Ports are handled in ~/.ssh/config since we use OpenSSH
COMMAND="uname -a"
COMMAND2="UserKnownHostsFile=/dev/null"
COMMAND3="StrictHostKeyChecking=no"

with open('patch.csv', 'r') as reader:
    with open('server_names.txt', 'w') as writer:
        for HOST in reader:
            print(HOST)
            HOST=HOST.strip()
            ssh = subprocess.Popen(["ssh","-o",COMMAND2,"-o",COMMAND3, "%s" % HOST, COMMAND],
                                shell=False,
                                stdout=subprocess.PIPE,
                                stderr=subprocess.PIPE)
            result = ssh.stdout.readlines()
            if result == []:
                error = ssh.stderr.readlines()
            # print >>sys.stderr, "ERROR: %s" % error
                writer.write(f'The Host failed is {HOST} & the error is {error}')
                print(error)
            else:
                print (result)

answered Sep 24, 2020 at 16:06

dbNovice

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2 Comments

tripleee Over a year ago

"%s" % HOST is just a really clumsy way to write HOST (or, I suppose, str(HOST) if you are not sure it's already a string).

tripleee Over a year ago

You really should avoid Popen when your use case is perfectly well (or actually better) handled by subprocess.run(). But then why not use Paramiko, which is designed for this specific use case, and handles several corner cases where a regular subprocess doesn't work very well?

Singuan Iap · Accepted Answer · 2022-07-29 12:30:46Z

0

You can use "sshscript" package. For the above shell script, it might be able to convert to python script of sshscript-syntax like this:

# filename: test.spy
with open('patch.csv') as fd:
  for host in fd:
    host = host.strip()
    account = f'user@{host}'
    $$echo "Host @{host}" >>  /tmp/patching
    $$ssh -o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no" @{account}  'sudo yum check-update | grep "kernel.x86"'>>/tmp/patching

Executing command on console:

$ sshscript test.spy

The link to documents of the sshscript package: https://iapyeh.github.io/sshscript/index

answered Jul 29, 2022 at 12:30

Singuan Iap

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