How to Use Paramiko and Python to SSH into a Server

When your Python program needs to run an external password-dependent program, or access a remote server, use Paramiko. Paramiko is a Python module that implements the SSHv2 protocol. Paramiko is not part of Python’s standard library, although it’s widely used. This guide shows you how to use Paramiko in your Python scripts to authenticate to a server using a password and SSH keys.

Before You Begin

1. Familiarize yourself with our Getting Started guide and complete the steps for setting your Linode’s hostname and timezone.

2. This guide will use sudo wherever possible. Complete the sections of our Securing Your Server to create a standard user account, harden SSH access and remove unnecessary network services. Do not follow the Configure a Firewall section yet–this guide includes firewall rules specifically for an OpenVPN server.

3. Update your system:

   sudo apt-get update && sudo apt-get upgrade
   

Install Paramiko

You must install Paramiko on your system before being able to use it in your Python programs. Use the command below to install Paramiko with Pip:

pip install paramiko

Note

If you are not familiar with Pip or do not have it installed on your system, see our How to Manage Python Packages and Virtual Environments on Linux guide.

If your system is configured to use Anaconda, you can use the following command to install Paramiko:

conda install -c anaconda paramiko

A Paramiko SSH Example: Connect to Your Server Using a Password

This section shows you how to authenticate to a remote server with a username and password. To begin, create a new file named first_experiment.py and add the contents of the example file. Ensure that you update the file with your own Linode’s details. Replace the values for YOUR_IP_ADDRESS, YOUR_LIMITED_USER_ACCOUNT, and YOUR_PASSWORD. Use the Find Your Linode’s IP Address guide, if needed.

File: password_login.py

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import paramiko command = "df" # Update the next three lines with your # server's information host = "YOUR_IP_ADDRESS" username = "YOUR_LIMITED_USER_ACCOUNT" password = "YOUR_PASSWORD" client = paramiko.client.SSHClient() client.set_missing_host_key_policy(paramiko.AutoAddPolicy()) client.connect(host, username=username, password=password) _stdin, _stdout,_stderr = client.exec_command("df") print(stdout.read().decode()) client.close()

This file connects to remote server over SSH using the IP address and credentials that you provide. It then uses the df command to generate a report of your server’s free disk space.

Execute the file with the following command:

python password_login.py

You see a similar output:

Filesystem       1K-blocks  Used Available Use% Mounted on
devtmpfs           1921544     0   1921544   0% /dev
tmpfs              1936296     0   1936296   0% /dev/shm
tmpfs              1936296   211308   1724988  11% /run
tmpfs              1936296     0   1936296   0% /sys/fs/cgroup
/dev/mapper/cl-root  46110724 20501872  25608852  45% /
/dev/sda1           999320   187324 743184  21% /boot

The file above provides a high-level example that you can use to incorporate Paramiko into your Python code. While everything Paramiko does can also be done with shell commands, Paramiko gives you all the power of Python. Python gives you access to structuring data, looping, parsing, and other powerful features that go beyond what is available in shell scripting. For example, if you are writing a program to calculate system usage percentages, Python is better at extracting and calculating values from your system’s output.

Second Paramiko Example: Connect to your Server Using SSH Keys

One of Paramiko’s specific strengths is the correct handling of SSH add keys. The introductory example above depended on the use of your limited user account’s password. It is more secure, however, to use SSH keys for server authentication. The example file below, provides a report that alerts you of any logins by users that are not included in your list of expected users. The Python script relies on Paramiko (notice the key_based_connect() function) to use SSHv2 authentication to connect to any of the servers provided in the code’s server_list list.

File: key_based_login.py

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# This is a small tool to report on successful logins # to accounts other than those listed in the variable # expected. Such a report might lead to an investigation # into how and why those other accounts were logging in. import paramiko def examine_last(server, connection): command = "sudo last" expected = ["user1", "reboot", "root", "sys-admin"] _stdin, stdout, _stderr = connection.exec_command("sudo last") lines = stdout.read().decode() connection.close() for line in lines.split("\n"): # Ignore the last line of the last report. if line.startswith("wtmp begins"): break parts = line.split() if parts: account = parts[0] if not account in EXPECTED: print(f"Entry '{line}' is a surprise on {server}.") def key_based_connect(server): host = "192.0.2.0" special_account = "user1" pkey = paramiko.RSAKey.from_private_key_file("./id_rsa") client = paramiko.SSHClient() policy = paramiko.AutoAddPolicy() client.set_missing_host_key_policy(policy) client.connect(host, username=special_account, pkey=pkey) return client def main(): server_list = ["worker1", "worker2", "worker3"] for server in server_list: connection = key_based_connect(server) examine_last(server, connection) main()

Execute the file with the following command:

python key_based_login.py

If a user outside of the Python script’s expected list accesses one of your servers, the Python script returns the following:

Entry user4   pts/0     192.0.2.0  Wed Sep 23 15:13 - 17:28  (02:14)' is a surprise on 192.0.2.0.

Going Further with Paramiko

Paramiko helps you automate repetitive system administration tasks on remote servers. More advanced Paramiko programs send the lines of a script one at a time. It does this rather than transacting all of a command, such as df or last, synchronously to completion. Paramiko is a helpful addition to your system administrator toolchain when working to automate common tasks. You can visit Paramiko’s documentation to learn about its special-purpose methods and variables that go beyond the examples covered in this guide.

More Information

You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

• Paramiko GitHub