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/github and second account for your company/gitlab.

Generate first key

ssh-keygen -t rsa -C "youremail@example.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_gitlab

Next, you’ll be asked to enter a passphrase.

So, you have created SSH key for your home/github account, now you can generate SSH key for your company/gitlab account.

Generate second key

Call SSH key generator again with second mail.

ssh-keygen -t rsa -C "your_another_email@example.com"

Enter name for github

id_rsa_github

After all steps you can check that all keys were created.

$ ls ~/.ssh

You should see a similar files list:

id_rsa_gitlab id_rsa_github id_rsa_gitlab.pub id_rsa_github.pub

Create config file

Now you need a config file for organize these keys. Create a config file under ~/.ssh/

$ vim config

Add following to config file:

#gitlab
Host gitlab.com
  HostName gitlab.com
  PreferredAuthentications publickey
  IdentityFile ~/.ssh/id_rsa_gitlab

#github
Host github.com
  HostName github.com
  PreferredAuthentications publickey
  IdentityFile ~/.ssh/id_rsa_github

Check connection

Next you can check connection

$ ssh -T git@github.com
Hi einverne! You've successfully authenticated, but GitHub does not provide shell access.

$ ssh -T git@gitlab.com
Welcome to GitLab, Ein Verne (einverne)!

Till now, everything seems ok.

Q & A

Q1. Can one single SSH key be used to push to different Git remotes?

Yes, assuming you are using the one id_rsa.pub or otherwise named public key, together with your private key on all of your development workstations, then simply uploading that one public key to multiple Git hosts will allow you the same access as you currently get from the multiple keys. This will also make your production life a bit easier, without having to manage multiple keys and ensuring you connect with the right one each time you communicate with the server. If you use multiple workstations (ie, home and office), you may also choose to use the same public/private key-pair on each of your local workstations. This further reduces the number of different keys you need to keep track of.

Q2. What is the purpose that we have to generate multiple SSH keys for different remote server?

There is no reason that you have to generate multiple keys for multiple remote Git repository servers, as indicated by the answer to your first question. As Jan Hudec has mentioned though, the reason one might choose to use different keys for different Git repositories, would be for an additional layer of security or management control.

Q3. 如果遇到权限问题，可能是新建的 config 文件权限问题

ssh -T git@gitlab.com
Bad owner or permissions on /home/einverne/.ssh/config

比如遇到上述问题，需要修改一下 config 文件权限

chmod 600 ~/.ssh/config
chown $USER ~/.ssh/config

reference

From:stackoverflow