Managing two GitHub accounts on the same Mac is very common. For example, you may have:

Account 1: Personal GitHub account
Account 2: Company / DevOps / Cotocus GitHub account

The problem starts when both accounts use GitHub SSH URLs like this:

git@github.com:username/repository.git

GitHub needs to know which SSH key should be used for which account. The cleanest solution is to configure multiple SSH identities using the ~/.ssh/config file.

In this tutorial, we will configure:

github.com  → Personal GitHub account
devops      → Company / DevOps / Cotocus GitHub account

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Current SSH Key Setup

In this example, the Mac already has two SSH key pairs:

cd ~/.ssh
ls -1

Output:

cotocusin
cotocusin.pub
id_ed25519
id_ed25519.pub
known_hosts
known_hosts.old

Meaning:

id_ed25519       → private key for default/personal GitHub account
id_ed25519.pub   → public key for default/personal GitHub account

cotocusin        → private key for DevOps/Cotocus GitHub account
cotocusin.pub    → public key for DevOps/Cotocus GitHub account

Your SSH directory is:

/Users/rajesh/.ssh

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1. Understand the Problem

By default, GitHub SSH URLs look like this:

git@github.com:username/repo.git

When you run:

git clone git@github.com:username/repo.git

your Mac connects to:

github.com

Then SSH tries to decide which private key to use.

But if you have two GitHub accounts, SSH may choose the wrong key. This can cause errors like:

Permission denied (publickey).

or:

ERROR: Repository not found.

or GitHub may authenticate you as the wrong account.

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2. Best Solution

Use SSH aliases.

We will configure:

Host github.com
    Uses ~/.ssh/id_ed25519

Host devops
    Uses ~/.ssh/cotocusin

After this setup:

git@github.com:personal-user/repo.git

will use:

~/.ssh/id_ed25519

And:

git@devops:Cotocus-QA-Teams/.github.git

will use:

~/.ssh/cotocusin

The word devops is only a local nickname on your Mac. GitHub does not see it. SSH converts it internally to github.com.

---

3. Add Public Keys to Correct GitHub Accounts

First, print your personal public key:

cat ~/.ssh/id_ed25519.pub

Copy the output and add it to your personal GitHub account.

GitHub path:

GitHub → Settings → SSH and GPG keys → New SSH key

Now print your DevOps/Cotocus public key:

cat ~/.ssh/cotocusin.pub

Copy the output and add it to your DevOps/Cotocus GitHub account.

Important rule:

One SSH public key can be added to only one GitHub account.

So do not add the same .pub key to both accounts.

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4. Fix SSH File Permissions

SSH is strict about permissions. Run:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 600 ~/.ssh/cotocusin
chmod 644 ~/.ssh/id_ed25519.pub
chmod 644 ~/.ssh/cotocusin.pub

Also later we will set permission for SSH config:

chmod 600 ~/.ssh/config

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5. Create or Edit SSH Config File

Open SSH config:

nano ~/.ssh/config

Add this configuration:

# Default GitHub account
Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519
    IdentitiesOnly yes
    AddKeysToAgent yes
    UseKeychain yes

# DevOps / Cotocus GitHub account
Host devops
    HostName github.com
    User git
    IdentityFile ~/.ssh/cotocusin
    IdentitiesOnly yes
    AddKeysToAgent yes
    UseKeychain yes

Save the file:

CTRL + O
Enter
CTRL + X

Now fix permission:

chmod 600 ~/.ssh/config

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6. Explanation of SSH Config

Default GitHub account

Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519

This means when you use:

git@github.com:username/repo.git

SSH will use this key:

~/.ssh/id_ed25519

DevOps account

Host devops
    HostName github.com
    User git
    IdentityFile ~/.ssh/cotocusin

This means when you use:

git@devops:Cotocus-QA-Teams/.github.git

SSH will actually connect to:

github.com

but it will use this private key:

~/.ssh/cotocusin

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7. Add Keys to SSH Agent

Run:

ssh-add --apple-use-keychain ~/.ssh/id_ed25519
ssh-add --apple-use-keychain ~/.ssh/cotocusin

Check loaded keys:

ssh-add -l

You should see both keys listed.

On older macOS versions, this command may also work:

ssh-add -K ~/.ssh/id_ed25519
ssh-add -K ~/.ssh/cotocusin

For modern macOS, prefer:

ssh-add --apple-use-keychain

---

8. Test Both GitHub Accounts

Test default GitHub account:

ssh -T git@github.com

Expected output:

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

Now test DevOps/Cotocus account:

ssh -T git@devops

Expected output:

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

This confirms both keys are working correctly.

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9. Clone Repository Using Personal Account

For your default/personal GitHub account, use normal GitHub SSH URL:

git clone git@github.com:USERNAME/REPO.git

Example:

git clone git@github.com:rajesh/myrepo.git

This will use:

~/.ssh/id_ed25519

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10. Clone Repository Using DevOps/Cotocus Account

For your DevOps/Cotocus GitHub account, use devops instead of github.com.

Example:

git clone git@devops:Cotocus-QA-Teams/.github.git

This will use:

~/.ssh/cotocusin

Notice the difference:

git@github.com:Cotocus-QA-Teams/.github.git

uses the default key.

But:

git@devops:Cotocus-QA-Teams/.github.git

uses the Cotocus/DevOps key.

That small change is the whole magic.

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11. Update Existing Repository Remote URL

If you already cloned a repository using the wrong URL, go inside the repository:

cd your-repo

Check current remote:

git remote -v

You may see:

origin  git@github.com:Cotocus-QA-Teams/.github.git (fetch)
origin  git@github.com:Cotocus-QA-Teams/.github.git (push)

Change it to use the DevOps alias:

git remote set-url origin git@devops:Cotocus-QA-Teams/.github.git

Check again:

git remote -v

Expected output:

origin  git@devops:Cotocus-QA-Teams/.github.git (fetch)
origin  git@devops:Cotocus-QA-Teams/.github.git (push)

Now try:

git pull
git push

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12. Set Git Username and Email Per Repository

SSH decides authentication, but Git commit identity is separate.

Inside your personal repo:

git config user.name "Rajesh"
git config user.email "your-personal-email@example.com"

Inside your DevOps/Cotocus repo:

git config user.name "Rajesh"
git config user.email "common.cotocus@gmail.com"

Check current repo identity:

git config user.name
git config user.email

To check global identity:

git config --global user.name
git config --global user.email

To list all Git config values:

git config --list

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13. Recommended Final Setup

Your final SSH setup should be:

~/.ssh/id_ed25519     → Default GitHub account
~/.ssh/cotocusin      → DevOps/Cotocus GitHub account

Your ~/.ssh/config should be:

# Default GitHub account
Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519
    IdentitiesOnly yes
    AddKeysToAgent yes
    UseKeychain yes

# DevOps / Cotocus GitHub account
Host devops
    HostName github.com
    User git
    IdentityFile ~/.ssh/cotocusin
    IdentitiesOnly yes
    AddKeysToAgent yes
    UseKeychain yes

Use this for default GitHub:

git clone git@github.com:USERNAME/REPO.git

Use this for DevOps/Cotocus GitHub:

git clone git@devops:Cotocus-QA-Teams/.github.git

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14. Common Errors and Fixes

Error 1: Permission denied publickey

Error:

Permission denied (publickey).

Fix:

ssh -T git@github.com
ssh -T git@devops

Also check:

ssh-add -l

If keys are not loaded:

ssh-add --apple-use-keychain ~/.ssh/id_ed25519
ssh-add --apple-use-keychain ~/.ssh/cotocusin

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Error 2: Repository not found

Error:

ERROR: Repository not found.

Possible reasons:

1. You are using the wrong SSH key.
2. Your GitHub account does not have access to the repository.
3. Remote URL is using github.com instead of devops.

Check remote:

git remote -v

For Cotocus repo, it should be:

git@devops:Cotocus-QA-Teams/.github.git

not:

git@github.com:Cotocus-QA-Teams/.github.git

Fix:

git remote set-url origin git@devops:Cotocus-QA-Teams/.github.git

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Error 3: Wrong GitHub username appears

Run:

ssh -T git@github.com
ssh -T git@devops

If git@devops shows the wrong username, your key may be added to the wrong GitHub account.

Check the public key:

cat ~/.ssh/cotocusin.pub

Make sure this key is added to the correct GitHub account.

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Error 4: Bad owner or permissions

Error:

Bad owner or permissions on ~/.ssh/config

Fix:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/config
chmod 600 ~/.ssh/id_ed25519
chmod 600 ~/.ssh/cotocusin

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15. Best Practice

Use short and meaningful aliases.

Good examples:

github.com  → default account
devops      → company account
office      → office account
client      → client account

Avoid confusing names like:

github.com-personal
github.com-cotocusin
github-account-2-long-name

They work, but they are annoying to type daily.

Your chosen setup is clean:

github.com = normal/default GitHub
devops     = company/DevOps GitHub

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Final Summary

Using two GitHub accounts on one Mac is easy when you configure SSH properly.

The key idea is:

Different GitHub account = different SSH key = different SSH Host alias

Final usage:

git clone git@github.com:personal-user/repo.git

for your default GitHub account.

And:

git clone git@devops:Cotocus-QA-Teams/.github.git

for your DevOps/Cotocus account.

This setup keeps both accounts clean, avoids authentication conflicts, and makes daily Git work much smoother.