SSH & Remote Administration

Fix the maddening SSH host key collision when you rebuild VMs

🧩 The Challenge

Everyone who rebuilds dev VMs on the same IP has seen that terrifying red wall of text screaming about a man-in-the-middle attack. You just want to log in, but instead, you’re stuck manually editing your known_hosts file like it’s 1999.

💡 The Fix

Tell your local SSH client to stop being so paranoid about specific hosts that you know are constantly getting wiped and refreshed. It saves you from deleting lines in a file every single morning.

ssh -o StrictHostKeyChecking=accept-new -o UserKnownHostsFile=/dev/null user@hostname

⚙️ Why It Works

Setting the UserKnownHostsFile to /dev/null means your machine ignores the cache entirely, and accept-new automatically adds fresh keys without prompting. It’s a massive time-saver when you’re spinning up ephemeral boxes in a lab environment.

🚀 Pro-Tip: Don’t do this for production servers unless you enjoy leaving your front door wide open for actual interceptors.

Linux Tips & Tricks | © ngelinux.com | 10/12/2026