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Asked: 2024-09-24T10:29:25+05:30 In:

How can I turn off strict host key checking for SSH connections in Ubuntu?

I’ve been diving deep into using SSH to manage some of my remote servers on Ubuntu, and I ran into this situation that’s driving me a bit nuts. Every time I try to connect to a new server, I get this warning about the host key not being found, and then I have to manually verify whether it’s okay to proceed. It’s a bit of a hassle, especially when I’m trying to automate some deployments or manage multiple servers.

I’ve read somewhere that there’s a way to disable the strict host key checking feature in SSH, which sounds like exactly what I need. But honestly, I’m a bit worried about the potential security implications of doing this. I understand that the purpose of host key checking is to protect against man-in-the-middle attacks, but I feel like there must be a way to handle this without having to deal with these prompts every single time.

Can someone explain how to turn off strict host key checking? Is it just a matter of editing some configuration file, or do I need to set an option every time I run the SSH command? I’ve seen some snippets online that suggest using something like `StrictHostKeyChecking=no`, but it’s not really clear where that goes or if there are better practices around this.

Also, if there are any safer alternatives or methods to manage known hosts, I’m all ears. I really want to streamline my workflow without compromising security too much. Should I be cautious about using this in a production environment?

Any insights, tips, or personal experiences in dealing with this would be super helpful! I’m all about learning from others to avoid any major pitfalls. Thanks in advance!

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    2 Answers

    1. So, I totally get where you’re coming from! Dealing with SSH and those pesky host key warnings can be a real pain, especially when you’re trying to automate stuff or manage a bunch of servers.

      To turn off strict host key checking, you can indeed use the option StrictHostKeyChecking=no. But here’s the thing: it’s usually better to set this in your SSH config file to avoid adding the option every single time you run a command. You can find the config file at ~/.ssh/config. Just open it up (create it if it doesn’t exist) and add something like this:

      Host *
    StrictHostKeyChecking no
    UserKnownHostsFile /dev/null
    LogLevel QUIET

      This configuration will apply to all hosts (due to Host *), but just be aware that setting UserKnownHostsFile to /dev/null means you won’t have any record of the hosts you connect to, which can be risky!

      As for the security side, turning off strict host key checking does open you up to man-in-the-middle attacks, which is definitely something to be cautious about—especially in production environments. If possible, it might be worth considering adding the host keys of your trusted servers to your known hosts file instead. This way, you’re not constantly prompted, but still maintaining a level of security.

      Honestly, I would look into something like using a configuration management tool (Ansible, Chef, etc.) that can help manage SSH keys and host verification more securely and efficiently. Automating the addition of known hosts can be less painful.

      Overall, just exercise caution if you choose to go the StrictHostKeyChecking=no route, especially when it comes to production. Hope this helps!



    2. Disabling Strict Host Key Checking in SSH

      To disable strict host key checking in SSH, you can set the StrictHostKeyChecking=no option. This can be done in two ways: via the command line or by modifying the SSH configuration file. For a one-time connection, you can use the command ssh -o StrictHostKeyChecking=no user@hostname. This will suppress the warning and allow you to connect without prompting. However, if you want to make this option permanent, you can edit your SSH configuration file located at /etc/ssh/ssh_config or ~/.ssh/config. Simply add the following lines to the file:

      Host *
    StrictHostKeyChecking no

      While this setting can streamline your workflow significantly, disabling strict host key checking does expose you to security risks, particularly man-in-the-middle attacks. A more secure alternative would be to manage your known hosts properly. You can prepopulate your known hosts file with the necessary public keys from the servers you’ll be connecting to, thereby maintaining security while avoiding prompts. If you’re deploying in a production environment, it’s recommended to handle host keys carefully, potentially setting StrictHostKeyChecking=accept-new, which will accept the key on the first connection but still alert you to any changes in known host keys. This approach gives a balance between convenience and security, allowing you to streamline your workflow while mitigating risks.


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