If you’re trying to add an SSH key to GitHub and get the error:

“Key is already in use”,
don’t worry—you’re not alone. This is a common issue, especially if you work on multiple machines, have multiple GitHub accounts, or have previously added the key but forgot about it.

In this guide, we’ll walk you through why this error happens and how to resolve it step by step. By the end, you’ll be able to connect to GitHub over SSH without any issues.

❓ Why You’re Seeing “Key is already in use”

GitHub gives this error when the SSH key you're trying to add is already present in their system. That happens in one of two cases:

1. The key has already been added to another GitHub account.
   → GitHub doesn’t allow one SSH key to be used across multiple accounts.
2. The key has already been added to the same account.
   → You might’ve added it before, and GitHub just won’t accept it twice.

✅ How to Fix the Issue

🔍 Step 1: Check the SSH Key You’re Using

In your terminal, run:

cat ~/.ssh/id_rsa.pub

Or if you use a custom-named key:

cat ~/.ssh/id_ed25519.pub

→ Copy the output and check if it already exists on GitHub:
Go to GitHub → Settings → SSH and GPG keys to verify.

If the key is there, you don’t need to add it again.

🔄 Step 2: Generate a New SSH Key (Recommended)

If you want to use a new key for this machine or account, create one like this:

ssh-keygen -t ed25519 -C "your_email@example.com"

When prompted for the file location, enter a new name such as:

~/.ssh/id_ed25519_codetuthub

Then add the new key to the SSH agent:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519_codetuthub

Finally, copy the new public key:

cat ~/.ssh/id_ed25519_codetuthub.pub

→ Add it to your GitHub account.

⚙️ Step 3: Use SSH Config to Point to the Right Key

If you manage multiple SSH keys, create or update the config file:

nano ~/.ssh/config

Add this content:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_codetuthub

This tells SSH to use the correct key when connecting to GitHub.

🧼 Step 4: Remove Old Key (If Needed)

If the key is already used on another account and you no longer need it there:

• Log into the other GitHub account
• Go to Settings → SSH and GPG keys
• Remove the old key
• Then try adding it to your new account

☕ Wrapping Up

The “Key is already in use” error is nothing to panic about. It’s just GitHub’s way of preventing SSH key conflicts. Once you understand how keys are tied to accounts, the fix is straightforward—either remove the old one or create a fresh new key.

If this article helped you, feel free to bookmark it or share it with your team. And if you still run into issues, drop a comment and let’s figure it out together.