https://coderwall.com/p/7smjkq/multiple-ssh-keys-for-different-accounts-on-github-or-gitlab

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 id_rsa_company id_rsa_home.pub id_rsa_company.pub
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"