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Install and Config

Git reads settings from three files layered by scope, and the first commit needs only an identity set at the global level. Interviewers ask about config to check that a candidate knows the system, global and local order and can set a per-directory identity, because a wrong committer email is a common and annoying mistake.

Track: Core · Interview weight: Med

Must-Know Facts

Fact Value Verify with
System scope /etc/gitconfig, all users; git config --system git config --show-scope --list
Global scope ~/.gitconfig, one user; git config --global git config --global --list
Local scope .git/config, one repository; git config --local git config --local --list
Precedence Local overrides global overrides system git config --show-origin <key>
Identity user.name and user.email, stamped into every commit git config user.email
Default branch init.defaultBranch, main on current Git git config init.defaultBranch
Editor core.editor, for commit messages and rebases git config core.editor
Alias git config --global alias.<name> "<command>" git config --get-regexp alias
Per-directory includeIf "gitdir:~/work/" includes another config file git config --show-origin user.email
Read one value git config --get <key> the value

Installing Git

Git ships as a single package on every platform. Confirm the version after installing, because a few features named in these notes (git switch, git restore, SHA-256 repositories) depend on a recent build.

brew install git          # macOS with Homebrew
sudo apt install git      # Debian and Ubuntu
sudo dnf install git      # RHEL, Rocky and Fedora
git --version

winget install --id Git.Git
git --version

Output:

git version 2.50.1 (Apple Git-155)

The Three Config Scopes

Settings live in three files, and a lookup returns the value from the most specific scope that has it. System applies to every user, global to one user, and local to a single repository.

git config --global user.name "Amina Yusuf"
git config --global user.email "amina@example.com"
git config --global init.defaultBranch main
git config --global core.editor "vim"
git config --global pull.rebase true

None of those print output; each writes a line into ~/.gitconfig. Listing the file with the origin of each value confirms where a setting came from.

git config --list --show-origin --global

Output:

file:/home/amina/.gitconfig user.name=Amina Yusuf
file:/home/amina/.gitconfig user.email=amina@example.com
file:/home/amina/.gitconfig init.defaultbranch=main
file:/home/amina/.gitconfig core.editor=vim
file:/home/amina/.gitconfig pull.rebase=true

Keys are stored lowercased in the section (init.defaultbranch), which is why config keys are case-insensitive in the section and name but case-sensitive in the value.

System scope needs root, and a local override hides a global identity

git config --system writes /etc/gitconfig and needs sudo, so most user settings go in global. A user.email set locally in one repository silently overrides the global one, which is the usual reason commits on a single project carry the wrong address.

Precedence and Reading a Value

A local setting in .git/config overrides the same key set globally, so a repository can carry a different committer email than the user default.

git config --local user.email "amina@work.example.com"
git config user.email

Output:

amina@work.example.com

git config --show-scope --get-all <key> shows every scope that defines a key, which is the fastest way to explain a surprising value.

git config --show-scope --get-all user.email

Output:

global  amina@example.com
local   amina@work.example.com

The lookup returns the local value because local is more specific than global. git config --get <key> reads the single effective value for scripts.

Per-Directory Identity with includeIf

includeIf pulls in another config file only when the repository path matches, which sets a work email for everything under ~/work/ without editing each repository.

cat >> ~/.gitconfig <<'EOF'
[includeIf "gitdir:~/work/"]
    path = ~/work/.gitconfig-work
EOF
git config --get includeIf.gitdir:~/work/.path

Output:

~/work/.gitconfig-work

The included file holds the overriding user.email. The gitdir: pattern must end with a slash to match a directory tree, and the include is evaluated by the path of the repository Git is operating in.

Aliases shorten a long command to a single word

git config --global alias.lg "log --oneline --graph --decorate" makes git lg run the full command. An alias starting with ! runs a shell command instead of a Git subcommand, which is how aliases call external scripts.

Common Errors

Author identity unknown and Please tell me who you are

Cause: user.name or user.email is unset in every scope, so Git cannot stamp a committer onto the commit.

Fix: set them globally with git config --global user.email "you@example.com" (and user.name), or locally for one repository.

error: key does not contain a section: name

Cause: a git config key was given without a section, such as git config name instead of git config user.name.

Fix: use the full section.key form, for example git config user.name.

Interview Checkpoints

L1: What are the three config scopes and their order of precedence?

Say first: system (/etc/gitconfig, all users), global (~/.gitconfig, one user) and local (.git/config, one repository); local overrides global, which overrides system.

Proof: git config --show-origin user.email names the file the effective value came from.

Follow-up: How do you give one repository a different committer email from your default?

L1: Where does Git get the name and email it puts on a commit?

Say first: from user.name and user.email, resolved through the scope precedence, with the local repository value winning if set.

Proof: git config user.email prints the effective value; git config --show-scope --get-all user.email shows every scope that defines it.

Follow-up: What does Git do if neither is set anywhere?

L2: Set your identity globally but override the email for all repositories under ~/work.

Say first: set the global identity, then add an includeIf "gitdir:~/work/" block pointing at a work config file that redefines user.email.

Proof:

git config --global user.email "amina@example.com"
git config --show-origin user.email   # from ~/work run inside a work repo

Follow-up: Why must the gitdir: pattern end with a slash?

L2: Create an alias so git lg shows a decorated one-line graph.

Say first: git config --global alias.lg "log --oneline --graph --decorate".

Proof: git config --get-regexp alias lists the alias; git lg runs the expansion.

Follow-up: How would you make an alias that runs a shell command rather than a Git subcommand?

L3: A colleague's commits show the wrong email on one project only. Where do you look?

Say first: a local override in that repository's .git/config is winning over their global identity.

Proof: git config --show-scope --get-all user.email lists both scopes; the local line is the culprit.

Follow-up: How would you fix the commits that already carry the wrong email?

L4: How does Git decide which config file a value comes from?

Say first: it reads system, then global (with any includeIf files spliced in where they match), then local, later files overriding earlier keys, so the last write to a key in precedence order wins.

Proof: git config --list --show-origin prints every value with its source file in read order.

Don't say: "Local and global are merged and the alphabetically first wins."

Captured on macOS 26 with git 2.50.1 (throwaway local repositories), 2026-09.