How to Check SSH Connection to Remote Hosts in Linux Using Bash Scripts

Learn how to create a simple Bash script to check SSH connectivity to multiple remote hosts in Linux, ensuring you can quickly determine their accessibility.
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How to Check SSH Connection to Remote Hosts in Linux Using Bash Scripts

Maintaining the ability to connect to remote servers is crucial for system administrators and developers alike. One common challenge is verifying if a server is accessible through SSH (Secure Shell). In this guide, we'll walk you through a straightforward solution: creating a Bash script to check the SSH connection status of multiple remote hosts listed in a file.

The Challenge

You want to check SSH connectivity for a list of remote hosts. Specifically, you want to be able to see which servers are accessible via SSH and which are not. The original script you provided only logged into the first host and did not yield the expected results. Let's break this down and enhance the script to fulfill your requirements.

Requirements

Suppose you have a host file that looks like this:

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You want your script to return output like:

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The Solution: A Revised Bash Script

Here's how to create an efficient Bash script that checks SSH connectivity for each server listed in your HOST file.

Step-by-Step Guide

Open your terminal. This is where you’ll create and edit your Bash script.

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Edit the script using a text editor of your choice and paste the following code:

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Breakdown of the Script

# !/bin/bash: This line specifies that the script should be run in the Bash shell.

for server in $(cat /home/user1/HOST): This command reads each line from the HOST file and iterates through each server.

ssh $server "true": This command attempts to establish an SSH connection to the server. The command true is simply a placeholder that indicates a successful connection if no errors are returned.

-o StrictHostKeyChecking=no: This option prevents SSH from prompting you to confirm the authenticity of the host, which is helpful for automation.

-o ConnectTimeout=2: This option sets a timeout of 2 seconds for the connection attempt, so if the host is not responding, it won’t wait indefinitely.

The if statement evaluates the success of the SSH command and provides appropriate output.

Testing Your Script

To run your script, simply execute the following command in your terminal:

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You'll get a list showing which servers are reachable via SSH and which are not. This feedback will help you quickly assess the health of your server connections.

Conclusion

By using this simple Bash script, you can effectively check the SSH connectivity of multiple remote Linux hosts easily and efficiently. This technique can save you time and streamline your remote server management tasks.

Feel free to modify the script as needed to suit your environment or to add additional logging or error-handling features! Happy scripting!