https://coderwall.com/p/7smjkq/multiple-ssh

cheng029

　　Multiple SSH keys for different accounts on Github or Gitlab
　　SSH GIT GITLAB GITHUB
　　Sometimes you need more accounts than one for access to Github or Gitlab and similar tools. For example you can have one account for your projects at home and second account for your company.
　　Case 1: Multiple accounts on Github
　　Create SSH keys with different names
　　$ ssh-keygen -t rsa -C "your_name@home_email.com"
　　When you see this message
　　Generating public/private rsa key pair.
　　Enter file in which to save the key (/home/user_name/.ssh/id_rsa):
　　Enter unique name, for example:
　　id_rsa_home
　　Next, you'll be asked to enter a passphrase.
　　So, you'll have created SSH key for your home account, now you can generate SSH key for your company account.
　　Call SSH key generator again with second mail.
　　$ ssh-keygen -t rsa -C "your_name@company_email.com"
　　Enter name for file
　　id_rsa_company
　　After all steps you can check that all keys were created.
　　$ ls ~/.ssh
　　You should see a similar files list:

　　id_rsa_home>　　Now you need a config file for organise these keys.
　　$ cd ~/.ssh/
　　$ touch config
　　$ nano config
　　Add into config file:
Home account
　　Host home.github.com
　　HostName github.com
　　PreferredAuthentications publickey
　　IdentityFile ~/.ssh/id_rsa_home
Company account
　　Host company.github.com
　　HostName github.com
　　PreferredAuthentications publickey
　　IdentityFile ~/.ssh/id_rsa_company
　　Next you'll delete cached keys
　　$ ssh-add -D
　　If you see a message
　　Could not open a connection to your authentication agent.
　　Then enter:
　　eval ssh-agent -s
　　and try again previous command.
　　Next, you can check that your keys were added:
　　$ ssh-add -l
　　2048 d4:e0:39:e1:bf:6f:e3:26:14:6b:26:73:4e:b4:53:83 /home/user/.ssh/id_rsa_home (RSA)
　　2048 7a:32:06:3f:3d:6c:f4:a1:d4:65:13:64:a4:ed:1d:63 /home/mateusz/.ssh/id_rsa_company (RSA)
　　If you haven't any entries then you should add your keys
　　ssh-add ~/.ssh/id_rsa_company
　　ssh-add ~/.ssh/id_rsa_home
　　Now you can check connection
　　$ ssh -T git@home.github.com
　　Hi home_user! You've successfully authenticated, but GitHub does not provide shell access.
　　$ ssh -T git@work.github.com
　　Hi company_user! You've successfully authenticated, but GitHub does not provide shell access.
　　Note! Check the last paragraph of this tip.
　　Case 2: Account on Github and Gitlab
　　This is very similar case to the previous. I won't describe it step by step, because all steps are the same. I'll add only example config file.
　　For example you have own account for home works and company account on gitlab.
GITLAB
　　Host gitlab.company_url.com
　　HostName gitlab.company_url.com
　　PreferredAuthentications publickey
　　IdentityFile ~/.ssh/id_rsa_company
GITHUB
　　Host github.com
　　HostName github.com
　　PreferredAuthentications publickey
　　IdentityFile ~/.ssh/id_rsa_home
　　The test connections
　　$ ssh -T git@gitlab.company_url.com
　　Welcome to GitLab, CompanyUser!
　　$ ssh -T git@github.com
　　Hi home_user! You've successfully authenticated, but GitHub does not provide shell access.
　　As you probably have seen, prefix on hostname isn't required.
　　You may need to set git config user details for any project.
　　It's required to distinguish your accounts.
　　$ cd ~/home_project
　　$ git config user.name "home_user"
　　$ git config user.email "your_name@home_email.com"