【Tech】 SSH keys setup for GitHub

Setup for the first Github

This is the standard procedure for generating SSH and connect to GitHub:

check current SSH:

ls -al ~/.ssh

generate new:

ssh-keygen -t rsa -b 4096 -C "theimmortalfish@gmail.com"

(-t for type, -b for number of bits, -C for comment)

then press Enter, then set passphrase.

set SSH-agent:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa

add SSH to GitHub:

pbcopy < ~/.ssh/id_rsa.pub

put it into GitHub settings

test SSH:

ssh -T git@github.com

Setup for the second Github

generate a second SSH key

Same steps untli the “then press Enter“, we’ll instead give it another name like “id_rsa_fish”:

Fishs-MacBook-Pro:.ssh Fish$ ssh-keygen -t rsa -b 4096 -C "theimmortalfish@gmail.com"
Generating public/private rsa key pair.
Enter file in which to save the key (/Users/Fish/.ssh/id_rsa): id_rsa_fish
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in id_rsa_fish.
Your public key has been saved in id_rsa_fish.pub.
The key fingerprint is:
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx theimmortalfish@gmail.com
The key's randomart image is:
+--[ RSA 4096]----+
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
|       xxxxx     |
+-----------------+
Fishs-MacBook-Pro:.ssh Fish$ ls -al ~/.ssh/
total 40
drwx------   7 Fish  staff   238 May 14 12:43 .
drwxr-xr-x+ 45 Fish  staff  1530 May 13 23:01 ..
-rw-------   1 Fish  staff  1766 Jul 28  2014 id_rsa
-rw-r--r--   1 Fish  staff   402 Jul 28  2014 id_rsa.pub
-rw-------   1 Fish  staff  3326 May 14 12:43 id_rsa_fish
-rw-r--r--   1 Fish  staff   751 May 14 12:43 id_rsa_fish.pub
-rw-r--r--   1 Fish  staff  2828 May 13 22:47 known_hosts

Again, we’ll do

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_rsa_fish

And also, add public key to the second GitHub account.

SSH configuration

Now this is the key step: go to .ssh folder and create a config file:

touch config

And put in the following configuration:

Host github-old
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa

Host github.com
  HostName github.com
  User git
  IdentityFile ~/.ssh/id_rsa_fish

Depending on your preference, change one of the host from “github.com” to some other names. In my case, I give the name “github-old” to my first SSH, and the second one would just stay the same (cuz I use the second GitHub more frequently).

The next step is the most important!

configure ssh-agent

Now restart your ssh-agent:

killall ssh-agent; eval `ssh-agent -s`

Now if you give it a try, you notice something fishy:

ssh -T git@github.com

ssh -T git@github-old

You notice that only the default SSH key (id_rsa) is being used. You are essentially querying the same GitHub account.

This is wrong. Because we have not added both SSH keys to ssh-agent yet. Immediately, do this:

ssh-add ~/.ssh/id_rsa_fish

ssh-add ~/.ssh/id_rsa

Now if you test connection again, you shall see no problem.

Last step, change remote url

The last step is to make changes to the git repository so that your computer works with both GitHub account.

Whenever we clone or “remote add origin”, we shall replace “github-old” with “github.com” in the remote url.

Example: go to your first GitHub account and create a new repo called “hello”. Then,

mkdir hello
cd hello
git init
git remote add origin git@github-old:old-name/hello.git
touch testing-file.txt
git add .
git commit -m 'first commit'
git push origin master

You should see it works fine. Notice how we changed the remote url from “github.com” to “github-old”, which matches our host configuration in the .ssh folder.

Your second GitHub shall work just like a normal GitHub account. 3 hours of hard work, all done!

Thanks to Jeffrey Way from tutsplus.com for the nice tutorial.