Use multiple SSH keys for different GitHub accounts

Written byPhuoc Nguyen

#Creating different keys

Assume that `foo` and `bar` are two GitHub usernames that you would like to use in the same computer. You can follow the official GitHub guide to generate SSH key.

// Generate SSH key for `foo`
$ ssh-keygen -t ed25519 -C "foo@domain.com"

When you're asked to indicate the file to save the key, don't use the default key. Change the name of file to something associate with the account, for example:

Enter a file in which to save the key (/home/you/.ssh/id_ed25519):
`/home/you/.ssh/id_foo`

Repeat the same steps for the `bar` account. Now, we have two private keys, `id_foo` and `id_bar` located at the `~/.ssh` folder.

#Adding keys to SSH agent

// Delete cached keys
$ ssh-add -D

// Start the ssh-agent in the background
$ eval "$(ssh-agent -s)"

// Add your SSH private keys to the ssh-agent
$ ssh-add ~/.ssh/id_foo
$ ssh-add ~/.ssh/id_bar

#Mapping keys to GitHub repos

This step lets SSH know which private key should be used for particular hosts.

$ cd ~/.ssh
$ touch config

Add the following content to the `config` file:

Host github.com-foo
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_foo
  IdentitiesOnly yes

Host github.com-bar
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_bar
  IdentitiesOnly yes

You'll realize that `github.com-foo` and `github.com-bar` look invalid hosts, but actually they are treated as aliases. SSH maps it with the `HostName` option and uses the private key in the `IdentityFile` option.

#Changing GitHub settings

Let's say that the `foo` account accesses a GitHub repose whose URL is `github.com/foo/a-foo-repos`. Go to its cloned folder, and change the `.git/config` file as below.

It's worth noting that the SSH host `github.com-foo` created in the previous step is used:

[remote "origin"]
url = git@github.com-foo:foo/a-foo-repos.git

Apply the similar settings for the `bar` repositories.

#See also

Set Git configuration conditionally

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Phước Nguyễn