Pushing to multiple github accounts from the same machine

Sometimes one has to use several github accounts from the same machine (maybe one has a specific account for work, in addition of one's default hobby account), and when tryig to push from a local repo, there could be problems as git may not see the alternative account.

There are two areas that need configured deliberately for this setup to work: git config and SSH config.

Git config

Normally, git configuration is defined by default in ~/.gitconfig That's where configuration directive sets with --global go.

That' also wher the email I use for my default github account is set:

[user]
  email = mainaccount@example.com

to add support for an alternate account, you need to choose another location for an alternate configuration file and the following block in the default config file:

[includeIf "gitdir:~/dev/alternate/"]
    path = ~/dev/alternate/.gitconfig

Here I chose ~/dev/alternate/ to have the alternate configuration. Then create ~/dev/alternate/.gitconfig:

[user]
    email = alternate@example.com

To figure whether the above setup works and which config git is using, you can run from a repository inside the alternate location and from outside:

git config user.email

The value shown will be the alternate email and the main one respectively.

Note

Any git repository that pertains to the alternate account must be inside the directory you have used in the includeIf directive.

SSH config

You need to have two sets of SSH keys for each github account. Then you need to have the public key (*.pub) to be added in github.com's SSH Keys settings for each user. Then ensure the default user SSH configuration at ~/.ssh/config has the three blocks below:

IdentitiesOnly yes

Host gh-main
AddKeysToAgent yes
UseKeychain yes
HostName github.com
User git
IdentityFile /Users/username/.ssh/main_github

Host gh-alt
AddKeysToAgent yes
UseKeychain yes
HostName github.com
User git
IdentityFile /Users/username/.ssh/alt_github

Example

To add a remote for the main account use git remote add origin git@gh-main:mainaccount/my-repo.git (or git remote set-url origin git@gh-main:mainaccount/my-repo.git when updating existing remote).

To add a remote for the alternate account use git remote add origin git@gh-alt:altaccount/my-repo-alt.git (or git remote set-url origin git@gh-alt:altaccount/my-repo-alt.git when updating existing remote).

Same with cloning: git clone git@gh-main:mainaccount/some-repo.git or git clone git@gh-alt:altaccount/another-repo.git

Troubleshoooting

To test the ssh connection, you can use:

ssh -T git@host-label1

If they are issues, you can test the specific SSH Key created for a given github account

ssh -F /dev/null -vvv -T -i ~/.ssh/ssh-key-account1 git@host-label1

where the -F /dev/null parameter tells SSH to not read the configuration file and -vvv active 3 levels of debug information.

Warning

That's the command that helped me figure that without the IdentitiesOnly=yes directive, ssh will try all the SSH keys in ~/.ssh/ even if IdentityFile or -i is specified, so that if you happen to have a SSH key used in another github account, it may connect to the wrong one.