Install and Use Codex CLI on Linux: 2026 Guide

AI-assisted programming does not have to happen in a browser or IDE. The OpenAI Codex CLI brings a coding agent directly into the Linux terminal. It can analyze a project, edit files, diagnose errors, run tests, and review Git changes.

Instead of copying code between a terminal and a chatbot, Codex works in the local repository. This guide explains how to install Codex CLI on Linux, authenticate, configure it safely, and use it productively.

What is OpenAI Codex CLI?

Codex CLI is an AI coding agent for the terminal. Start it in a project and describe your goal in natural language. It can inspect source and structure, edit files, implement features, run shell commands and tests, inspect diffs, review code, and connect external tools through MCP. codex exec supports automation.

“Analyze this error, find the affected code, implement the smallest reasonable fix, and then run the existing tests.”

Install Codex CLI on Linux

OpenAI documents a standalone installer for Linux:

curl -fsSL https://chatgpt.com/codex/install.sh | sh
codex --version
codex --help

Run the installer again to update. Review downloaded installers before executing them, especially on managed systems. See the official Codex CLI documentation for the current command.

Sign in with ChatGPT or an API key

codex login
codex login status
codex logout

ChatGPT sign-in associates use with your account or workspace. Alternatively, pass an API key through standard input:

printenv OPENAI_API_KEY | codex login --with-api-key

Never commit API keys. API-key use is billed separately through the API.

Your first Codex session

cd ~/projects/my-web-app
codex

Analyze this project. Explain languages, frameworks,
structure, entry points, startup, and tests.
Do not change anything yet.

Orientation is safer and more useful than starting with an open-ended request such as “fix everything.”

Ten structured AI prompts for Linux administrators (Read article)

Understand first, then change

Ask Codex to explain the cause, affected files, proposed solution, and possible side effects before implementation. For larger work, use the plan feature or /plan where supported by your current version.

AGENTS.md: persistent project rules

AGENTS.md contains instructions Codex reads before working. Use /init to create a starting point, then document architecture, restrictions, test commands, style, and completion criteria.

# Project rules

## Rules
- No new dependencies without justification.
- Never write credentials to files.
- Plan before large changes.

## Tests
- Backend: pytest
- Frontend: npm test

## Completion
1. Run tests.
2. Review the Git diff.
3. Explain the changes.

Personal instructions can live under ~/.codex/; repositories and subdirectories can contain more specific files. Instructions closer to the working directory can take precedence. See the official AGENTS.md guide.

Configure permissions safely

Codex separates sandbox access from approvals. Common modes include read-only, workspace-write, and danger-full-access. Workspace access is sufficient for many tasks:

codex exec --sandbox workspace-write "Perform the defined task."

Use /status to inspect the session and /permissions to manage rights. Apply least privilege.

Be careful with --yolo

--yolo aliases --dangerously-bypass-approvals-and-sandbox. It disables safeguards. Reserve it for externally isolated environments, never as the default on systems containing SSH keys, cloud credentials, .env files, or production access.

Review AI-generated commands and security risks (Read article)

Essential slash commands

• /status: inspect session configuration.
• /model: choose an available model and supported reasoning settings.
• /permissions: manage rights.
• /diff: inspect current Git changes.
• /review: review selected changes without automatically editing the tree.
• /compact: summarize a long context.
• /init: prepare AGENTS.md.
• /mcp: show MCP connections.
• /exit or /quit: end the session.

Commands can change by version; consult /help and the current slash-command reference.

Target files and run shell commands

Use @ to search for workspace files and include them in the prompt. Prefix a local command with an exclamation mark, such as !git status or !pytest. Sandbox and approval rules still apply.

Review code before committing

A robust flow is implementation → tests → /diff → /review → human review → commit. For bug fixes, explicitly request reproduction, root cause, a small fix, affected edge cases, tests, and a final inspection.

Use Codex for larger refactors

Define the goal, interfaces that must remain stable, prohibited dependencies, test stages, and measurable completion criteria. Plan first, implement in small steps, and test after meaningful changes.

Use current information with web search

codex --search

Live web search helps with framework versions, APIs, security advisories, and current documentation. Verify sources and prefer primary documentation.

Extend Codex CLI with MCP

codex mcp list
codex mcp add openaiDeveloperDocs --url https://developers.openai.com/mcp

MCP connects Codex to additional tools and sources under controlled permissions. OpenAI's public documentation server provides read-only developer documentation.

Model Context Protocol and MCP servers explained (Read article)

Run Codex non-interactively

codex exec "Analyze the repository for obvious errors."
codex exec --sandbox workspace-write "Perform the defined task."

codex exec is designed for scripts and CI. Automation needs clear output requirements, restricted permissions, safe secrets, and reproducible tests. OpenAI also provides an official Codex GitHub Action.

Codex configuration on Linux

Persistent settings live in ~/.codex/config.toml. It can define the model, reasoning, sandbox, approval policy, profiles, and MCP. CLI flags can override settings for one run.

A safe Linux workflow

1. Open the repository and check git status.
2. Create a deliberate Git checkpoint when appropriate.
3. Start Codex and inspect AGENTS.md.
4. Plan complex work first.
5. Define a narrow, verifiable task.
6. Inspect diff and review.
7. Run tests.
8. Commit only after human review.

Create and test shell scripts safely (Read article)

What Codex should not do unchecked

Avoid broad instructions such as “delete every unnecessary file,” “clean up production,” or “fix everything and deploy.” Ask for analysis and a risk-assessed proposal first. Production systems require narrow permissions and human approval.

Ten useful Codex prompts

1. Explain the repository without changes.
2. Identify a bug's root cause.
3. Implement a minimal fix without unrelated refactoring.
4. Review changes for bugs and security issues.
5. Add normal, edge, and failure-case tests.
6. Rank performance bottlenecks by likely impact.
7. Review validation, authentication, authorization, secrets, and injection risks.
8. Update technical documentation from the implementation.
9. Plan a behavior-preserving refactor.
10. Critically inspect your own changes, tests, and diff.

Common mistakes

Starting in the wrong directory

Start Codex in the repository, not broadly in your home directory.

Oversized tasks

“Improve the application” is not verifiable. Limit component, outcome, and allowed changes.

No Git checkpoints

Inspect status and preserve a deliberate starting point.

Excessive permissions

workspace-write is often safer than unrestricted access.

Blind trust

Use Codex → tests → diff → review → human → commit.

Codex CLI vs. ChatGPT

Capability	ChatGPT	Codex CLI
Answer questions	Yes	Yes
Local terminal	No	Yes
Repository analysis	Provided context	Directly local
Files and shell	Interface-dependent	With permissions
Git review	With context	Directly in repository
Automation	Different workflows	codex exec

FAQ: Codex CLI on Linux

Does Codex CLI run on Linux?

Yes. OpenAI provides an official installer.

How do I install Codex on Ubuntu or Debian?

curl -fsSL https://chatgpt.com/codex/install.sh | sh

Do I need an API key?

No. Interactive use supports ChatGPT sign-in; API-key use is billed through the API.

Can Codex edit files and run shell commands?

Yes, within configured sandbox and approval rules.

What is AGENTS.md?

A file containing persistent, hierarchical project instructions.

Can Codex review code?

Yes, including with /review.

Does Codex support MCP?

Yes. Manage connections with codex mcp.

Can Codex run in scripts?

Yes, with codex exec.

Conclusion

Codex CLI turns the Linux terminal into an AI workspace for repository analysis, debugging, implementation, testing, diff inspection, review, and automation. Its real strength comes from clear tasks, a useful AGENTS.md, least-privilege permissions, and consistent human control.

1. Start in the correct repository.
2. Plan complex tasks first.
3. Use AGENTS.md for persistent rules.
4. Apply least privilege.
5. Always inspect tests, diff, and review.

Codex CLI Linux cheat sheet

curl -fsSL https://chatgpt.com/codex/install.sh | sh
codex --version
codex login
codex login status
cd ~/projects/my-project
codex
codex mcp list
codex exec "Analyze this repository"
codex --search
codex logout

/init  /plan  /status  /model  /permissions
/diff  /review  /mcp  /compact  /exit

Sources and currency

Content current as of August 9, 2026 and checked against official OpenAI documentation on August 12, 2026. Sources: Codex CLI, CLI reference, authentication, security and permissions, AGENTS.md, MCP, and non-interactive mode.