Context

Let’s say you have two accounts (or more) in a git hosted service:

• A public GitHub account 👨‍💻
• Another private account 🕵️‍️ (could be GitHub, Gitlab, BitBucket, …)

Also, you want to have a separate SSH key for each of your account. Because like with password you prefer not to use one for all of your services.

So here is how you would do it.

SSH configuration

Generate the SSH keys

If it’s not done already, you can learn how to create and register the SSH key in → Get started with GitHub.
The process should be similar for any other online service.

Some caveat for it to work:

• Make sure you create the keys with different name
  • the public one 👨‍💻 can be named the default name id_rsa
  • the other one 🕵️‍️ can be named id_rsa_private
• Make sure that each SSH key is registered in the correct account online
  • Give them some meaningful name, and add each to the relevant remote git repository

Now that the SSH keys are created, you will need to do a bit of configuration to make it work.

Set up SSH config

To start using different ssh key depending on the repository. Create a new file in the ssh folder as ~/.ssh/config. This will allow you to override the checking mechanism to specify which ssh key to use based on the host, even if it’s the same host name.

#public account
Host github.com
        HostName github.com
        User git
        IdentityFile ~/.ssh/id_rsa

#special account
Host github.com-private
        HostName github.com
        User git
        IdentityFile ~/.ssh/id_rsa_private

You have noticed the Host is not exactly the same even though both are GitHub accounts in this case. We have two Hosts:

• The normal GitHub host: Host github.com
• With a hyphen after: Host github.com-private

It is small drawback, as the ssh key can’t be contextually by the folder it’s called from. Confused as to how it works? It will make sense in the usage part, as long as the HostName is still github.com, the host doesn’t matter much.

Local Git configuration

Since you have two accounts, you also want your user to be correct, it’d be annoying to commit with the wrong user. Make sure you have your repositories separated in different folders depending on the account:

.
└── repositories
     ├── private
     │    ├── .gitconfig
     │    ├── repo_1
     │    └── repo_2
     └── public
          └── my_repo

On your Home, not shown in the above folder structure, you have the master config file for git. In this file: ~/.gitconfig, you will put the default [user] information, here the public one:

[user]
        name = public.me
        email = public.me@mail.com

[includeIf "gitdir:~/repositories/private/"]
        path = ~/repositories/private/.gitconfig

Everything under the tag [includeIf "gitdir:~/repositories/private/"] will be included when in the specified git directory. That way we can add some configuration for our other account with its repositories in the private folder. You would have in ~/repositories/private/.gitconfig this configuration:

[user]
    name = private.me
    email = private.me@mail.com

That way, the committing user will be by default private.me in the private folder instead of public.me everywhere else. You can stack as many includeIf in your home .gitconfig for your many accounts.

Usage

For our setup to work, we still need to clone the repository locally. Note that you need to use the ssh git address.

If you remember the host for the private SSH key being Host github.com-private that will be of use now.
To clone a private repository, or any repository with your private account 🕵️
Add -private to the github.com host:

git clone git@github.com-private:account/repository.git

In the other hand, if you want to use your default public account to clone a public repository.
You can use the normal url without the -private in the end to clone with your public account 👨‍💻

git clone git@github.com:account/repository.git

By modifying the host with the -private you are telling the SSH agent which key to use. Keep in mind that if you see an error it might be because you are trying to clone a private repository with an account that does not have access to it.

You should be now all set up! If you are working with upstream repositories check this article
→ How to use git with an upstream repository