Managing ssh keys for multiple GitHub accounts

1. Create ssh keys using the following command:

   ssh-keygen -t rsa -C "xxx@youremail.com"

   ssh-keygen -t rsa -C "yyy@youremail.com"

   Each email corresponds to a different github account. 

   It is also possible to have repository specific deploy keys.

   If a repository does not have its own deploy key, access to it 

   is given by the repo's github account ssh keys. 

2.  Two pairs of ssh keys are created in ~/.ssh dir:

1. ~/.ssh/id_rsa_xxx

   ~/.ssh/id_rsa_yyy

   with names chosen in step 1.

3. Add keys using:
1.   ssh-add ~/.ssh/id_rsa_xxx

    ssh-add ~/.ssh/id_rsa_yyy

   This adds adds your RSA identities to the authentication agent,  

   ssh-agent, a program for storing private keys used for public key 

   authentication.

4.  Use ssh-add -l to list all added keys
5. Associate the keys with the Github accounts according to instructions on:
1.  https://help.github.com/articles/generating-ssh-keys/
6. On your local machine configure GitHub settings. Add configuration to ~/.ssh/config:

1. #xxx account
   Host github.com-xxx
       HostName github.com 
       User git
       IdentityFile ~/.ssh/id_rsa_xxx
   
   #yyy account
   Host github.com-yyy
       HostName github.com
       User git 
       IdentityFile ~/.ssh/id_rsa_yyy

   Hosts github.com-xxx, github.com-yyy are arbitrary names,

   that help distinguish the two accounts 

7.  Test authorization to connect to GitHub:
1. ssh -T git@github.com-xxx
2. ssh -T git@github.com-yyy
8. Clone a repository, using the relevant Host alias:
1. git clone git@github.com-xxx:xxx/repo_aaa.git [aaa_dir]
9.  The general git configuration can be found in ~/.gitconfig. The entries can be either added manually or through git commands:
1.  git config --global ... (user.email, user.name etc)
10.  For repository specific configuration (repository's .git/config): 
1. cd repo_aaa (or aaa_dir)
2. git config user.name "X XXX" 
3. git config user.email "xxx@gmail.com"
4. git remote set-url origin  git@github.com-xxx:xxx/repo_aaa.git
1. This will result in the following setup:
   

   [remote "origin"]
           url = git@github.com-xxx:xxx/repo_aaa.git

   where

   github.com-xxx corresponds to the Host value in step 6

   xxx            corresponds to the github username 

NOTE

• Configuration, that is present only in the global git config file ~/.gitconfig (setup either through the git config --global comand or manually) and not overriden by cloned repository's .git/config setup, will be used.
• Setting up the [remote "origin"] block in the global configuration, results in a bizarre situation, where one can be cloning an empty (well, any) github repo, and the local clone will have an unexpected content (corresponding to the remote origin url, ie a different repo).