oscarychen/ssh_for_git.md

## ssh_for_git.md

      
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              ssh_for_git.md
            
          
    Setting up SSH for Git

General set-up for Git/Github account

Generally from a development machine, you would want to set up a ssh key that allows you to access your entire Github account, and access all of the repos under that account, here is how you can do that.
Generate a ssh key to be used from your machine to access your entire Github account:
ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
When prompted "Enter file in which to save the key", you can specify something like: /Users/<username>/.ssh/github
This should result in a private and public key pair being created:
/Users/<username>/.ssh/github
/Users/<username>/.ssh/github.pub

Next, modify or create a configuration file for ssh at /Users/<username>/.ssh/config, which should contain the following:
Host github.com
  HostName github.com
  AddKeysToAgent yes
  UseKeychain yes
  User <github username>
  IdentityFile ~/.ssh/github

If you did not specify a passphrase when creating the ssh key, you can remove the UseKeyChain setting.
Next, start ssh-agent and add the key to ssh agent:
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/github

Next, navigate to Github -> Settings -> SSH and GPG Keys -> New SSH key, and copy the content of the public key from /Users/<username>/.ssh/github.pub
Now, you can clone the repo using ssh instead of https. Ie, instead of:
git clone https://github.com/<username>/<repo-name>.git
You can clone using:
git clone git@github.com:<username>/<repo-name>.git
If you are working with a repo previously cloned using https, you can either re-clone it, or modify the remote origin address to the ssh address:
nano .git/config
SSH key also allows installation from a private git repo using pip, ie:
pip install git+ssh://git@github.com/oscarychen/my_repo.git
If you used a password phrase when creating the ssh key pair, you may need to add the key to the ssh key agent everytime you start up a new bash instance. You may want to automate this by adding the following inside .bash_profile or .bashrc:
if [ -z "$SSH_AUTH_SOCK" ] ; then
  eval `ssh-agent -s`
  ssh-add ~/.ssh/github
fi

Repo-specific deployment key set up

Sometimes from a virtual machine where you are deploying a web app, you would only want this machine to have access to specific project repositories. Here is how you can set them up with deployment keys to specific repos.
Same as the example above, but let's generate the key pair at a different path:
/Users/<username>/.ssh/my_web_app
/Users/<username>/.ssh/my_web_app.pub

Next, modify or create a configuration file for ssh at /Users/<username>/.ssh/config, which should contain the following:
Host github.com-my-web-app
  HostName github.com
  User <github username>
  IdentityFile ~/.ssh/my_web_app

Next, add deployment key to your Github repository: Repo Settings -> Deploy Keys -> Add deploy key, copy and paste the content of the public key from /Users/<username>/.ssh/my_web_app.pub
When cloning the repo, use the ssh repo cloning link but specifying the host as named exactly in the ssh config, for example:
git clone git@github.com-my-web-app:oscarychen/my_web_app.git
Now you can repeat the same process for another deployment repo, the ssh config would look like the following for two different repos:
Host github.com-my-web-app
  HostName github.com
  User <github username>
  IdentityFile ~/.ssh/my_web_app

Host github.com-my-web-app-2
  HostName github.com
  User <github username>
  IdentityFile ~/.ssh/my_web_app_2

sometimes you have to update the config file permission:
chomod 600 ~/.ssh/config
Creating signed commits

Download and install GPG Suite (Mac OS): https://gpgtools.org
or Gpg4win (Windows): https://www.gpg4win.org
Create a Secrete/Public key pair.
Copy the public key and paste to Github: Settings -> SSH and GPG keys -> New GPG key
Configure Git to use your GPG key:
gpg --list-secret-keys --keyid-format LONG

and you shoud see the key id printed after rsa2048/:
sec rsa2048/7FFFC09ACAC05FD0 2017-06-02 [SC] [expires: 2019-06-02]
Run this command with the GPG key from previous step:
git config --global user.signingkey 7FFFC09ACAC05FD0

Now when making a commit, you can add a -S flag to indicate to git to sign the commit, ie:
git commit -S -m"commit message"

To automatically sign commits when they are made (omitting the -S flag), in the git repository:
git config commit.gpgsign true