whyxno

An embarrassing amount of ‘senior’ developers I work or have worked with do not know how ssh works in the slightest. I’ve shown how to manage two separate github accounts using ssh so many times to slack jawed devs I’m writing this page so I can send it to people instead of having to demonstrate it again. If I have sent you this link then I am talking about you.

You have two github accounts - we’ll call them personal and work

1. Generate keys

First, generate an ssh key for each and add the public key to their respective github accounts. Give them a meaningful name like personal_key and work_key

If you don’t know how to generate an ssh key google it.

2. Edit ssh config file

Edit (or create) the ssh config file (~/.ssh/config):

# Default github account: work (make this whatever you use the most)
Host github.com
   HostName github.com
   IdentityFile ~/.ssh/work_key
   IdentitiesOnly yes
   
# Other github account: personal
Host personal-github.com
   HostName github.com
   IdentityFile ~/.ssh/personal_key
   IdentitiesOnly yes

Let me explain these properties quickly;

• Host: This property defines a host alias or label for the configuration block that follows. It specifies that the settings below apply when you connect to github.com. The Host directive allows you to group settings for a specific destination (in this case, github.com). When you run a command like ssh [email protected] , ssh will look for a matching Host entry and apply the associated settings. The Host can be anything you want it to be.

• Hostname: This specifies the actual hostname or IP address of the server to connect to. In this case, it’s set to github.com, it explicitly tells SSH to resolve and connect to github.com.

• IdentityFile: This line tells ssh which private key file to use for authentication when connecting to the hostname

• IdentitiesOnly yes: This setting instructs ssh to only use the identity (private key) specified by IdentityFile (and no others) for authentication, even if other keys are loaded into an ssh agent. Typically ssh will cycle through all keys until it finds one that works but sometimes it can get stuck on a key that isn’t authenticated. You can see this if you run any ssh command with the verbose flag e.g ssh -T [email protected] -v

3. Add keys to ssh agent

Add ssh private keys to your agent (this is just a background process the manages ssh keys)

$ eval "$(ssh-agent -s)" #start the ssh agent if it isn't running
$ ssh-add ~/.ssh/work_key
$ ssh-add ~/.ssh/personal_key

4. Test your connection

$ ssh-keyscan github.com >> ~/.ssh/known_hosts
$ ssh -T [email protected]
$ ssh -T [email protected]

If everything is working you should see something like this;

Hi work! You've successfully authenticated, but GitHub does not provide shell access.

Hi personal! You've successfully authenticated, but GitHub does not provide shell access.

5. Usage

Now to use it - you just need to use the correct hostname for the project you are working with. We set the default to be github.com so any clones or standard github commands will work with your default. If you want to use your personal account then you need to change the hostname within the command, for example;

[email protected]:org/repo.git => user is personal
[email protected]:org/repo.git          => user is default (work)

Hopefully you can figure out the rest on your own. Just sub the correct hostname in. Good luck.