#The Problem

When you have multiple GitHub accounts (personal and work) but only one SSH key pair on your machine, you run into trouble. For example, early on you may have generated an SSH key pair to pull company projects and added it to your company GitHub account. Later, when you want to pull repositories back under your personal account and try to add the same SSH key to your personal GitHub account, you get this message: Key is already in use.

#Cause and Solution

GitHub checks whether an SSH key already exists under some GitHub account, and if it does, it won't add it again. So we can generate multiple SSH keys locally and add each one to a different GitHub account.

#1. Generate Multiple SSH Keys

Open a terminal (Mac/Linux) or Git Bash (Windows). Run the following command, replacing [email protected] with your GitHub email address and key_name with a name you want to give this key:

ssh-keygen -t ed25519 -C "[email protected]" -f ~/.ssh/key_name

For example:

ssh-keygen -t ed25519 -C "[email protected]" -f ~/.ssh/github_work
ssh-keygen -t ed25519 -C "[email protected]" -f ~/.ssh/github_personal

#2. Configure the SSH Config File

Run the following command to create or edit the ~/.ssh/config file:

nano ~/.ssh/config

Add the following content, creating one Host entry for each key:

Host github-work
  HostName github.com
  User git
  IdentityFile ~/.ssh/github_work

Host github-personal
  HostName github.com
  User git
  IdentityFile ~/.ssh/github_personal

Save and close the file.

#3. Add the SSH Keys to the SSH Agent

Start the SSH agent:

eval "$(ssh-agent -s)"

Add your SSH keys to the SSH agent:

ssh-add ~/.ssh/github_work
ssh-add ~/.ssh/github_personal

#4. Add the SSH Keys to Your GitHub Accounts

For each GitHub account:

Copy the public key content: cat ~/.ssh/github_work.pub

or

cat ~/.ssh/github_personal.pub

Log in to the corresponding GitHub account.

Click your avatar in the upper right corner and select "Settings."

In the left menu, click "SSH and GPG keys."

Click "New SSH key" or "Add SSH key."

In the "Title" field, enter a descriptive name for your key.

Paste the copied public key content into the "Key" field.

Click "Add SSH key."

#5. Test the Connection

Test each SSH connection:

ssh -T github-work

ssh -T github-personal

If it succeeds, you will see a welcome message.

You can then pull code using the newly added GitHub SSH key.