SSH for Git Quick Reference

mark notes: this blog post was created with the help of an AI assistant.

Every time I set up a new machine, I forget at least one of these steps. So here’s the whole thing in one place.

Generate a key

ssh-keygen -t ed25519 -C "any label you want"

Accept the default location (~/.ssh/id_ed25519). Set a passphrase if you want the extra security. Then grab the public key:

cat ~/.ssh/id_ed25519.pub

Copy that output, go to GitHub User Account Icon (top-right) Menu → Settings → SSH and GPG keys → New SSH key, paste it in, save. Then test the connection:

ssh -T git@github.com
# Expected: Hi markgodiy! You've successfully authenticated...

If you get that response, you’re good.

Day-to-day

Once the key is on GitHub, cloning over SSH just works:

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

From there, git pull and git push work like normal, no credentials prompt.

If you’ve got an existing repo that’s pointing at HTTPS, swap the remote:

git remote set-url origin git@github.com:username/repo.git
git remote -v  # verify

SSH Agent (stop retyping the passphrase)

If you set a passphrase on your key, SSH will ask for it every time unless you’ve got an agent running. This fixes that:

eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

To make it automatic on login, throw this in your ~/.bashrc or ~/.zshrc:

eval "$(ssh-agent -s)" && ssh-add ~/.ssh/id_ed25519

Generating multiple keys

The default key name is id_ed25519, but if you’ve got more than one purpose (personal GitHub, work GitHub, a home server, etc.), you want separate keys. Just give each one a name with -f:

ssh-keygen -t ed25519 -C "personal github" -f ~/.ssh/id_ed25519_personal
ssh-keygen -t ed25519 -C "work github"     -f ~/.ssh/id_ed25519_work
ssh-keygen -t ed25519 -C "home server"     -f ~/.ssh/id_ed25519_homelab

Each command drops two files in ~/.ssh/ — the private key and .pub counterpart. The label after -C is just a comment so you can tell them apart in GitHub’s key list or ssh-add -l. Put anything you want there.

Then add each one to the agent:

ssh-add ~/.ssh/id_ed25519_personal
ssh-add ~/.ssh/id_ed25519_work
ssh-add ~/.ssh/id_ed25519_homelab

Multiple GitHub accounts

This one tripped me up for a while. If you’ve got a personal account and a work account, you can’t just point two keys at the same hostname. The fix is aliases in ~/.ssh/config:

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

Host github-work
    HostName github.com
    User git
    IdentityFile ~/.ssh/id_ed25519_work

Then clone using the alias instead of github.com:

git clone git@github-personal:username/repo.git

SSH resolves the alias and picks the right key automatically.

Key files worth knowing

When things break

# Verbose output -- shows exactly which keys are being tried
ssh -vT git@github.com

# See what's loaded in the agent
ssh-add -l

# Fix permissions (SSH is strict about this)
chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub

The permissions one catches me sometimes after copying keys between machines. SSH silently refuses to use a private key if the permissions are too open, and it doesn’t always tell you why.