How to Execute Shell Commands in a Remote Machine in Python

[Capy987]

Have you ever wanted to quickly execute certain commands in your Linux machine remotely? or do you want to routinely execute some lines of code in your server to automate stuff? In this tutorial, you will learn how you can write a simple Python script to remotely execute shell commands on your Linux machine.


We will be using the paramiko library; let's install it:

Code
pip3 install paramiko
Defining some connection credentials:

import paramiko
Code
hostname = "192.168.1.101"
username = "test"
password = "abc123"
In the above code, I've defined the hostname, username, and password, this is my local Linux box, you need to edit these variables for your case, or you may want to make command-line argument parsing using the argparse module as we usually do in such tasks.

Note that, it isn't safe to connect to SSH using credentials like that. You can configure your SSH listener daemon to only accept public authentication keys, instead of using a password. However, for demonstration purposes, we will be using a password.

Executing Shell Commands

Now let's create a list of commands you wish to execute on that remote machine:

Code
commands = [
"pwd",
"id",
"uname -a",
"df -h"
]
In this case, simple commands output useful information about the operating system.

The below code is responsible for initiating the SSH client and connecting to the server:

Code
# initialize the SSH client
client = paramiko.SSHClient()
# add to known hosts
client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
try:
client.connect(hostname=hostname, username=username, password=password)
except:
print("[!] Cannot connect to the SSH Server")
exit()
Now let's iterate over the commands we just defined and execute them one by one:

Code
# execute the commands
for command in commands:
print("="*50, command, "="*50)
stdin, stdout, stderr = client.exec_command(command)
print(stdout.read().decode())
err = stderr.read().decode()
if err:
print(err)
Here are the results:

Code
================================================== pwd ==================================================
/home/test

================================================== id ==================================================
uid=1000(test) gid=0(root) groups=0(root),27(sudo)

================================================== uname -a ==================================================
Linux rockikz 4.17.0-kali1-amd64 #1 SMP Debian 4.17.8-1kali1 (2018-07-24) x86_64 GNU/Linux

================================================== df -h ==================================================
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 392M 6.2M 386M 2% /run
/dev/sda1 452G 410G 19G 96% /
tmpfs 2.0G 0 2.0G 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 2.0G 0 2.0G 0% /sys/fs/cgroup
tmpfs 392M 12K 392M 1% /run/user/131
tmpfs 392M 0 392M 0% /run/user/1000
Awesome, these commands were successfully executed on my Linux machine!

Executing Scripts

Now that you know how you can execute commands one by one, let's dive a little bit deeper and execute entire shell (.sh) scripts.

Consider this script (named "script.sh"):

Code
cd Desktop
mkdir test_folder
cd test_folder
echo "$PATH" > path.txt
After the SSH connection, instead of iterating for commands, now we read the content of this script and execute it:

Code
# read the BASH script content from the file
bash_script = open("script.sh").read()
# execute the BASH script
stdin, stdout, stderr = client.exec_command(bash_script)
# read the standard output and print it
print(stdout.read().decode())
# print errors if there are any
err = stderr.read().decode()
if err:
print(err)
# close the connection
client.close()
exec_command() method executes the script using the default shell (BASH, SH, or any other) and returns standard input, standard output, and standard error, respectively. We will read from stdout and stderr if there are any, and then we close the SSH connection.

After the execution of the above code, a new file test_folder was created in Desktop and got a text file inside that which contained the global $PATH variable:

Results after executing the Script in Python

Conclusion

As you can see, this is useful for many scenarios. For example, you may want to manage your servers only by executing Python scripts remotely; you can do anything you want!

And by the way, If you want to run more complex jobs on a remote server, you might want to look into Ansible instead.

You can also use Fabric library as it is a high-level Python library designed just to execute shell commands remotely over SSH. It builds on top of Invoke and Paramiko.

Feel free to edit the code as you wish; for example, you may want to parse command-line arguments with argparse.

If you're into cyber security, then I highly encourage you to take our Ethical Hacking with Python EBook, where we build 20+ hacking tools and scripts from scratch using Python!

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