Two GitHub accounts, one computer · step 4 of 6

macOS: SSH keys and Keychain

macOS's ssh-agent remembers the passphrase in Keychain — one flag and reboots stop being a problem.

1. Generate two SSH keys

In Terminal:

ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_user1 -C "user1@example.com"
ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519_user2 -C "user2@example.com"

Set a passphrase for each key — on macOS, “don’t ask every time” is built in and more convenient than on Windows (see step 6).

2. Add the public keys to GitHub

cat ~/.ssh/id_ed25519_user1.pub | pbcopy

Paste it under Settings → SSH and GPG keys on the user1 account. Repeat for user2.

3. Wire the keys into .gitconfig-userX

[core]
    sshCommand = "ssh -i ~/.ssh/id_ed25519_user1 -o IdentitiesOnly=yes"

Paths starting with ~ generally work fine in core.sshCommand on macOS/Linux (unlike Windows, where it’s safer to give the full path).

4. Switch the repository remote to SSH

git remote set-url origin git@github.com:user1/repo-name.git
git remote -v

5. Test the connection

ssh -T -i ~/.ssh/id_ed25519_user1 -o IdentitiesOnly=yes git@github.com

You should see Hi user1! You've successfully authenticated....

6. Skip typing the passphrase on every push

macOS has built-in ssh-agent integration with Keychain. Add an entry to ~/.ssh/config:

Host github.com-user1
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519_user1
    UseKeychain yes
    AddKeysToAgent yes

Host github.com-user2
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519_user2
    UseKeychain yes
    AddKeysToAgent yes

UseKeychain yes plus AddKeysToAgent yes means that after entering the passphrase once during the first ssh-add, it’s stored in Keychain and survives a reboot — unlike on Windows.

Add the keys once:

ssh-add --apple-use-keychain ~/.ssh/id_ed25519_user1
ssh-add --apple-use-keychain ~/.ssh/id_ed25519_user2

Check:

ssh-add -l

If you use Host github.com-userX aliases from ~/.ssh/config together with core.sshCommand in gitconfig, pick one mechanism so they don’t fight each other. core.sshCommand alone (step 1 of the tutorial), without aliases in ~/.ssh/config, is easier to maintain. If you prefer aliases instead, in .gitconfig-userX skip core.sshCommand and just point the remote at git@github.com-user1:user1/repo.git.

Note: Apple’s Git vs Homebrew Git

macOS ships with Apple’s Git (Xcode Command Line Tools) by default. If you’ve also installed Git via Homebrew, check which one is active:

which git
git --version

includeIf behaves identically in both, but it’s worth knowing which install you’re using when something doesn’t behave as expected.