Manage multiple Github accounts with SSH keys

We can access and write data in repositories on Github.com using SSH (Secure Shell Protocol). When we connect via SSH, we authenticate using a private key file on our local machine. For more information about SSH, see Secure Shell on Wikipedia.

Generate new SSH keys

1. Open terminal
2. Paste the text below, substituting the email with your own Github email address.

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

   This will create a new SSH key, using the provided email as a label. When you’re prompted to “Enter a file in which to save the key”, you can press Enter to accept the default file location. Please note that if you created SSH keys previously, ssh-keygen may ask you to rewrite another key, in which case we strongly recommend creating a custom-named SSH key. To do so, type the default file location and replace id_ssh_keyname with your custom key name (such as id_ed25519_userA and id_ed25519_userB).

3. At the prompt, type a secure passphrase.

   > Enter passphrase (empty for no passphrase): [Type a passphrase]
   > Enter same passphrase again: [Type passphrase again]
   

Adding SSH key to the ssh-agent

1. Start the ssh-agent in the background.

   $ eval "$(ssh-agent -s)"
   > Agent pid 59566
   

2. Check the file ~/.ssh/config exists or not. If not, use touch ~/.ssh/config to create it.
3. Configure the file ~/.ssh/config. To demonstrate, suppose we have generated the following two SSH keys

   ~/.ssh/id_ed25519_userA
   ~/.ssh/id_ed25519_userB
   

   They correspond to two different email addresses. Edit the ~/.ssh/config as follows:

   # Default Github account
   Host github.com
      HostName github.com
      User git
      AddKeysToAgent yes
      IdentityFile ~/.ssh/id_ed25519_userA
   # Another Github account
   Host userB.github.com
      HostName github.com
      User git
      AddKeysToAgent yes
      IdentityFile ~/.ssh/id_ed25519_userB
   # repeat for as many keys/identities as you like, and name the `Host` and key files whatever works best for you
   

   Note that the second Host userB.github.com is used to differentiate multiple Github accounts. You can also use github.com-userB as well. However, please make sure you are consistent with the notation since this is relevant when you clone a repository or set the remote origin for a local repository (see the below sections for details).

4. Add the SSH keys to the ssh-agent.

   ssh-add ~/.ssh/id_ed25519_userA
   ssh-add ~/.ssh/id_ed25519_userB
   

5. Add the SSH public key to your account on Github. See “Adding a new SSH key to your GitHub account.”

Clone a repository as different users

By default, we clone a repository in the following way:

git clone git@github.com:owner/repo.git

On cloning, note that we use the host names that we have set in ~/.ssh/config. Since in this case the string between @ and : is github.com, we are cloning the repository repo as userA using the identity file ~/.ssh/id_ed25519_userA.

If you want to clone the repo as userB, you need to modify the clone command to

git clone git@userB.github.com:owner/repo.git

The string between @ and : should match what we have given in the SSH config file.

Setting remote url for existing repositories

To list the Git remote of a repository, use git remote -v. We can set the git URL as follows:

git remote set-url origin git@userB.github.com:owner/repo.git

If you find this command is hard to remember, you can also open .git/config file in the repository by your favorite editor and modify the url item there.

References

1. Generating a new SSH key and adding it to the ssh-agent
2. How to manage multiple GitHub accounts on a single machine with SSH keys