git.md

Contents

• GitHub Authentication and Authorization
• Configuration

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GitHub Authentication and Authorization

Terminology

• Authentication: "supply or confirm credentials that are unique to you to prove that you are exactly who you declare to be"
• Authorization: determine what a user is allowed to access or do.

Basic respository access from command line

• SSH remotes: autheticate with GitHub CLI or setup an SSH public/private keypair
  • To setup an SSH public/private keypair (see ssh.md for more details):
    1. Generate keypair: ssh-keygen -t ed25519 -C <GitHub email>
       • This produces 2 files: id_ed25519 and id_ed25519.pub
    2. Add the public key in id_ed25519.pub to your GitHub account.
• HTTPS remotes: authenticate with GitHub CLI, use a credential helper like Git Credential Manager, or use a personal access token
  • How does the Git Credential Manager work, if it does not use a personal access token?

References and resources

• https://docs.github.com/en/authentication/keeping-your-account-and-data-secure

Configuration

Configuration scopes and files [docs]

• system: $(prefix)/etc/gitconfig
  • $(prefix) refers to where git is installed. For example, %(prefix)/bin/ refers to the directory in which the Git executable itself lives. Therefore, if git is installed at /usr/bin/git, then $(prefix) is /usr.
    • This is set during compilation. See the INSTALL file: https://github.com/git/git/blob/master/INSTALL.
• global (user-specific): $XDG_CONFIG_HOME/git/config and ~/.gitconfig

  • When the XDG_CONFIG_HOME environment variable is not set or empty, $HOME/.config/ is used as $XDG_CONFIG_HOME... If both files exist, both files are read in the order given above.

• local (respository-specific): $GIT_DIR/config
  • $GIT_DIR refers to the .git folder
• worktree: $GIT_DIR/config.worktree

  • only searched when extensions.worktreeConfig is present in $GIT_DIR/config

• command: GIT_CONFIG_{COUNT,KEY,VALUE} environment variables and the -c option

Show configurations by scope: git config --list --show-scope

Errors

git gc

1. On macOS, running git gc yields an error message

   warning: unable to unlink '.git/objects/07/f47bd76ded355e641fd0367026047da28ef3d5': Operation not permitted

   • Problem: the git object files may have the user immutable flag uchg set, which can be shown by using ls -l -O <file> on macOS.
   • Solution: Run the following command to unset the uchg flag on the files that git gc is attempting to remove, then rerun git gc.
     • git gc 2>&1 1> /dev/null | grep -F 'warning: unable to unlink' | sed -e "s/warning: unable to unlink '//" -e "s/': Operation not permitted//" | xargs chflags -v nouchg