In order to log in to the same server (e.g. GitHub) with two different accounts I use two browsers. For user A I use Firefox. For user B I use Chrome.

For push and pull it was a bit trickier. I think I could have used https access, but that would mean for every interaction I have to type in my password. I wanted to avoid that. So I wanted to use ssh access.

So I will need a separate set of ssh-keypairs for each user and I'll need to set up some configuration that will always use the correct keypair.

ssh allows the use of a configuration file located in ~/.ssh/config that allows us to configure different keypairs (identity files) per host. This is how an entry in that file looks like:

host github.com
   HostName github.com
   IdentityFile ~/.ssh/id_rsa
   User szabgab

This however does not help us as this is based on the target hostname and I'd like to access the same host, and even use the same remote username (git) but use two different Identity files.

The solution

Generate new Identity files:

[core]
    sshCommand = "ssh -i /full/path/to/id_a/id_rsa"

The clone command will use this ssh and finally we remove the entry from the global configuration file.

git config --global core.sshCommand "ssh -i /full/path/to/id_a/id_rsa"
git clone ...
git config --global --unset core.sshCommand

Configure each cloned directory to use its own identity file and its own user and email for the identification of commits.

cd project-dir
git config --local core.sshCommand "ssh -i /full/path/to/id_a/id_rsa"
git config --local user.name "User A"
git config --local user.email A@code-maven.com

This will change the .git/config file in the current directory.

Full steps

Let's assume we have two Bitbucket users: Mary and Joe with usernames "mary" and "joe" respectively. Mary has a private repository called https://bitbucket.org/mart/demo. She configures it to make it writable by Joe as well. (Done on the web interface of BitBucket.)

We create directory to use for this whole project:

cd ~
mkdir demo
cd demo

We create directories for the identity files:

mkdir mary
mkdir joe

We generate two Identity Files:

ssh-keygen -f mary/id_rsa -N ''
ssh-keygen -f joe/id_rsa -N ''

We upload the content of mary/id_rsa.pub to the BitBucket account of Mary and the content of joe/id_rsa.pub to the BitBucket account of Joe.

We clone the repository of Mary with the credentials of Mary to the local directory called "demo_mary" but we also make sure to remove her credentials from the global configuration file.

git config --global core.sshCommand "ssh -i mary/id_rsa"
git clone git@bitbucket.org:mary/demo.git demo_mary
git config --global --unset core.sshCommand

Then we configure this newly cloned repository to use the credentials of Mary:

cd demo_mary
git config --local core.sshCommand "ssh -i mary/id_rsa"
git config --local user.name "Mary"
git config --local user.email mary@code-maven.com

Then we go back to the common directory and do the same for Joe:

We clone the repository of Mary using the credentials of Joe and then remove those credentials from the global configuration file:

cd ..
git config --global core.sshCommand "ssh -i joe/id_rsa"
git clone git@bitbucket.org:mary/demo.git demo_joe
git config --global --unset core.sshCommand

Then we configure this newly cloned repository to use the credentials of Joe:

cd demo_joe
git config --local core.sshCommand "ssh -i joe/id_rsa"
git config --local user.name "Joe"
git config --local user.email joe@code-maven.com

The short solution

GIT_SSH_COMMAND="ssh -i /full/path/to/id_a/id_rsa" git clone ...
cd repo_name
git config --local core.sshCommand "ssh -i /full/path/to/id_a/id_rsa"
git config --local user.name "User A"
git config --local user.email A@code-maven.com