GitHub SSH Key Management

Generate an SSH Key for GitHub

ssh-keygen -t ed25519 -C "your_email@example.com" -f ~/.ssh/id_ed25519_github

• -C is a comment (any label, not functionally required)
• -f specifies the filename to save the key
• Press Enter twice to skip setting a passphrase (or set one for security)

Add the Public Key to GitHub

cat ~/.ssh/id_ed25519_github.pub

1. Copy the output
2. Go to GitHub → Settings → SSH and GPG keys
3. Click "New SSH key", give it a name, and paste the public key

Configure SSH to Use the Right Key

Edit (or create) the ~/.ssh/config file:

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_ed25519_github
  IdentitiesOnly yes

The IdentitiesOnly yes tells SSH to use only this key instead of offering every key in your agent.

without it, it will try:

• Keys from ssh-agent
• Default files in ~/.ssh/
  • ~/.ssh/id_rsa
  • ~/.ssh/id_ecdsa
  • ~/.ssh/id_ed25519
  • ~/.ssh/id_dsa
  • Any others added in recent OpenSSH versions
• Keys listed in your ~/.ssh/config for the current Host (Host github.com)

with it, SSH uses only the key you specified — no default keys, no ssh-agent keys, no surprises.

Test SSH Connection to GitHub

ssh -Tssh using specific key

this is assume I configed the ssh key correctly (using ssh-add(ssh-agent) or editing ~/.ssh/config)

ssh -T git@github.com

Expected result:

Hi <your-username>! You've successfully authenticated, but GitHub does not provide shell access.

Use case:

• You're testing if a specific key works
• You haven’t set up a config file or SSH agent
• You want a one-off manual override

  ssh -i ~/.ssh/id_ed25519_github git@github.com
  

Expected result:

PTY allocation request failed on channel 0
Hi <your-username>! You've successfully authenticated, but GitHub does not provide shell access.
Connection to github.com closed.

Use SSH with Git

git clone git@github.com:your-username/your-repo.git

Use default commit message template (specific repository)

echo "SF:" > .mycommitmsg.txt
git config --local commit.template .mycommitmsg.txt

Notes

• GitHub uses git@github.com for all SSH connections.
• SSH authentication is done via public key fingerprint, not username.
• GitHub matches the SSH key to your account during the handshake.
• You can manage multiple SSH keys by configuring ~/.ssh/config for each host.