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[solved] Install and Configure OpenAI GPT-5 Codex CLI and choose the best model on Ubuntu and Linux Mint

Introduction

The landscape of AI-powered development tools has evolved dramatically with the introduction of OpenAI's GPT-5 Codex CLI. This revolutionary coding assistant brings the power of GPT-5's advanced reasoning capabilities directly to your Ubuntu or Linux Mint terminal, transforming how developers write, debug, and maintain code. Whether you're a beginner developer looking to accelerate your learning curve or an experienced system administrator seeking to automate complex coding tasks, GPT-5 Codex CLI offers unprecedented AI assistance right from your command line.

In this comprehensive guide, we'll walk you through the complete process of installing, configuring, and optimizing OpenAI GPT-5 Codex CLI on Ubuntu and Linux Mint systems. From initial setup to advanced configuration options, you'll learn everything needed to harness this powerful AI coding agent for your development workflow.

What is OpenAI GPT-5 Codex CLI?

OpenAI GPT-5 Codex CLI is a lightweight, open-source command-line tool that integrates GPT-5's coding capabilities directly into your terminal environment. Unlike web-based coding assistants, Codex CLI runs locally on your machine while leveraging OpenAI's cloud-based models for intelligent code generation, debugging, and analysis.

The tool acts as an intelligent coding partner that can read, modify, and execute code within your local development environment. It supports multimodal inputs, allowing you to share screenshots, wireframes, and diagrams to help the AI understand your coding requirements better. With the recent GPT-5-Codex upgrade released in September 2025, the tool has become significantly more capable at handling complex, long-running coding tasks.

Key Features and Capabilities

GPT-5 Codex CLI offers several compelling features that make it an essential tool for modern developers:

Intelligent Code Generation: The AI can create complete functions, classes, and even entire applications based on natural language descriptions. It understands context from your existing codebase and maintains consistency with your coding style and architectural patterns.

Advanced Debugging: Codex can analyze error messages, examine stack traces, and suggest precise fixes for bugs. It can even execute code in a sandboxed environment to test potential solutions before applying them to your working directory.

Refactoring and Optimization: The tool excels at improving existing code by suggesting optimizations, converting between different programming paradigms, and updating deprecated functions or libraries.

Multi-Language Support: From Python and JavaScript to Rust and Go, Codex CLI supports virtually every major programming language and can work seamlessly across polyglot codebases.

Step-by-Step Installation Process

Installing GPT-5 Codex CLI on Ubuntu or Linux Mint involves downloading the appropriate binary, configuring it in your system PATH, and setting up authentication with OpenAI's services.

Download the Latest Binary

Navigate to the official OpenAI Codex releases page to download the latest version:

Go to OpenAI Codex Releases

For most Ubuntu and Linux Mint installations (x86_64 architecture), download the codex-x86_64-unknown-linux-gnu binary. If you're using an ARM-based system, select the codex-aarch64-unknown-linux-musl version instead.

You can download directly from the terminal using wget:

cd ~/Downloads
wget https://github.com/openai/codex/releases/latest/download/codex-x86_64-unknown-linux-gnu.tar.gz
tar -xzf codex-x86_64-unknown-linux-gnu.tar.gz

Install the Binary by copying it into a a binary directory that's in your $PATH environment variable

Open Terminal and check the $PATH variable in order to see viable paths to move/copy the codex binary into:

echo $PATH

Search for a path like

/home/youruser/.local/bin

Move or copy the codex binary to that folder:

mv codex-x86_64-unknown-linux-gnu ~/.local/bin/
chmod 755 ~/.local/bin/codex-x86_64-unknown-linux-gnu

Configure the Alias

To optimize your Codex CLI experience, create an alias with recommended settings that enable GPT-5-Codex model usage, appropriate approval settings, and workspace sandboxing:

echo 'alias codex="codex-x86_64-unknown-linux-gnu --model=\"gpt-5-codex\" --ask-for-approval=\"on-failure\" --sandbox=\"workspace-write\" --search --cd ."' >> ~/.bashrc

This alias configuration provides several important optimizations:

Model Selection (highly recommended to use the special "-codex" model for programming): --model="gpt-5-codex" ensures you're using the latest GPT-5-powered coding model.

Smart Approvals: --ask-for-approval="on-failure" only prompts for approval when commands fail, streamlining your workflow

Secure Sandbox: --sandbox="workspace-write" allows file modifications within your project directory while protecting system files

Enhanced Search: --search enables web search capabilities for finding documentation and solutions

Directory Context: --cd . starts Codex in your current working directory

Apply Configuration Changes

Restart your terminal or reload your shell configuration to enable the new alias:

source ~/.bashrc

 

Authentication and Initial Setup

Before using GPT-5 Codex CLI, you need to authenticate with OpenAI's services. The process is streamlined and secure, requiring only a web browser for the initial setup.

Launch Codex for First Time

Execute the codex command in your terminal:

codex

On first launch, Codex CLI will prompt you to authenticate with OpenAI. The tool will provide a secure link that you need to visit in your web browser. This link connects your local Codex installation with your OpenAI account, allowing the CLI to access GPT-5-Codex services. It's recommended to use an existing OpenAI account. You can also go with the API solution where you "pay-as-you-go". By experience this solution is much more expensive.

Follow these steps for authentication:

Step 1: Click the provided authentication link or copy it to your browser

Step 2: Log in to your OpenAI account (create one if necessary)

Step 3: Grant permission for Codex CLI to access your account

Step 4: Return to your terminal where Codex should now be authenticated

Model Configuration

Once authenticated, configure the specific GPT-5-Codex model variant for optimal performance:

/model

This command opens the model selection interface. Choose gpt-5-codex high for the most capable reasoning level. This setting enables extended thinking time for complex coding tasks and provides the highest quality code generation.

Optimizing Your Development Workflow

With GPT-5 Codex CLI installed and configured, you can now leverage its powerful capabilities to enhance your coding productivity.

Basic Usage Examples

Here are some practical examples to get you started:

Code Generation:

codex "Create a REST API endpoint for user authentication in Python Flask"

Debugging Assistance:

codex "Analyze this error and suggest a fix" --image error_screenshot.png

Code Refactoring:

codex "Refactor this function to use async/await pattern"

Documentation Generation:

codex "Generate comprehensive documentation for this module"

Advanced Configuration Options

For power users, Codex CLI offers extensive customization through configuration files. Create a config file at ~/.codex/config.toml to fine-tune behavior:

[general]
model = "gpt-5-codex"
reasoning_level = "high"
auto_commit = false
verbose_logging = true

[sandbox]
policy = "workspace-write"
network_access = false

 

Troubleshooting Common Issues

While GPT-5 Codex CLI is designed for reliability, you may encounter some common issues during setup or usage.

Authentication Problems

If you experience authentication failures, try these solutions:

Clear Authentication Cache:

rm ~/.codex/auth.json
codex login

Check API Key Permissions: Ensure your OpenAI account has the necessary permissions for Codex CLI access. Some features require specific subscription tiers.

Network Configuration: If you're behind a corporate firewall, you may need to configure proxy settings in ~/.codex/config.toml

[network]
proxy = "http://your-proxy:8080"
timeout = "30s"

 

Advanced Tips and Productivity Hacks

Maximize your productivity with these advanced Codex CLI techniques:

Custom Project Instructions

Create project-specific guidance by adding AGENTS.md files to your repositories:

# Project Coding Standards

## Architecture
- Use microservices pattern
- Implement clean architecture principles
- Follow SOLID design patterns

## Testing
- Minimum 80% code coverage
- Use TDD approach
- Include integration tests

## Documentation
- Document all public APIs
- Include usage examples
- Maintain changelog

Batch Operations

Use Codex for bulk operations across multiple files:

codex "Add comprehensive error handling to all Python files in the src/ directory"

Integration with Git Workflows

Leverage Codex for Git-related tasks:

codex "Generate a detailed commit message for the current staged changes"
codex "Create a pull request description summarizing recent commits"

 

Future Updates and Roadmap

OpenAI continues to enhance Codex CLI with regular updates and new features. Recent improvements include enhanced multimodal capabilities, extended reasoning sessions, and better integration with popular IDEs.

Stay updated with the latest developments by:

Following the GitHub Repository: Star and watch the official repository for updates and community contributions

Conclusion

GPT-5 Codex CLI represents a significant advancement in AI-powered development tools, bringing sophisticated coding assistance directly to your Ubuntu or Linux Mint terminal. By following this comprehensive setup guide, you've configured a powerful AI coding partner that can accelerate your development workflow, improve code quality, and help you tackle complex programming challenges with confidence.

The combination of local execution, advanced reasoning capabilities, and seamless terminal integration makes Codex CLI an invaluable tool for developers at any skill level. Whether you're building web applications, automating system tasks, or exploring new programming languages, GPT-5 Codex CLI provides the intelligent assistance needed to write better code faster.

As AI coding tools continue to evolve, mastering GPT-5 Codex CLI positions you at the forefront of modern software development practices. Start experimenting with simple tasks, gradually incorporating more complex workflows, and discover how this powerful tool can transform your coding experience.

Remember to keep your installation updated, follow security best practices, and engage with the growing community of developers who are pushing the boundaries of what's possible with AI-assisted programming. The future of software development is collaborative, and GPT-5 Codex CLI is your gateway to that exciting frontier.