jturntdev/krypton/krypton-vps-codex-app

Krypton VPS Codex App

Overview

Turn a Linux VPS into the machine that does the work while the operator's Mac only displays and controls it. The target result is a working Codex App SSH project where commands, edits, builds, tests, tmux/cmux sessions, dev servers, and agent runs happen on the VPS.

Do not describe this as installing Codex App on the VPS. Codex App stays on the operator's Mac or Windows machine; the VPS needs the Codex CLI and repo toolchain so the app can start the remote Codex app server through SSH.

Use the current OpenAI Codex docs for Codex App specifics when facts may have changed. The durable setup facts this skill relies on are:

• Codex App can add projects from an SSH host.
• Codex reads concrete SSH aliases from ~/.ssh/config.
• Remote project threads run commands and edit files on the remote host.
• The remote host provides the repo files, credentials, tools, skills, MCP

setup, browser/computer-use setup, and sandbox/approval behavior.

• The remote codex command must be available on the remote user's login-shell

PATH.

Responsibility Split

Codex can prepare commands, inspect SSH config, audit the VPS, bootstrap tools over SSH when it has access, clone the repo, run checks, and explain failures.

The operator must provide or complete these human steps:

• Buy or provision the VPS if it does not exist yet.
• Create or choose the SSH key pair used for the VPS.
• Add an SSH public key in the VPS provider UI or otherwise grant SSH access.
• Approve any edit to ~/.ssh/config, or add the SSH alias manually.
• Choose how the VPS may access their GitHub repo.
• Decide whether local-only config files should be recreated, copied, or skipped.
• Keep private keys, provider passwords, API keys, and Codex auth files secret.
• Complete Codex App Settings > Connections and choose the remote project folder.
• Complete browser/device authentication when the flow requires user login.

First Response

Start by repeating the setup goal in plain English:

You want the VPS to be the actual development machine. Codex App on the Mac
connects to it over SSH, and the repo, tools, agent sessions, builds, tests,
and dev servers run there.

Then ask this setup-state question first:

Do you already have a VPS with SSH access, or are we starting before the VPS is
created?

If the VPS does not exist yet, give a short purchase/bootstrap checklist: Ubuntu 24.04 LTS unless the repo needs something else, enough CPU/RAM/swap for builds and agent runs, SSH-key access, a non-root daily user, no public dev ports, and GitHub as source of truth. Then ask for the VPS IP, initial username, and public-key path once the VPS is ready.

If the VPS exists, ask for only the missing inputs needed for the next step:

• SSH alias or VPS IP.
• Remote username.
• Repo URL and desired remote path.
• Whether the repo is public or private.
• Which GitHub access path they want: GitHub CLI login, SSH key on their GitHub

account, read-only deploy key, or no GitHub setup yet.

• Whether they have local-only config files such as .env, ignored config,

MCP files, package registry auth, or provider credentials that the VPS needs.

• Stack commands if they are not obvious from the repo.
• Whether Codex should only audit or may bootstrap missing tools over SSH.
• Whether the operator wants setup, audit, troubleshooting, or public post-ready

instructions.

If the user already gave enough, proceed without more questions.

Setup Workflow

1. Host And Security Preflight

Treat this as a development host, not production.

• Use a non-root Linux user for daily work.
• If the first login is root, use it only for bootstrap and move the Codex

SSH alias to a non-root user before day-to-day work.

• Use SSH keys, not passwords.
• Keep GitHub as source of truth for code.
• Keep production deploy targets separate and protected.
• Do not expose dev servers, Codex app-server, Docker sockets, databases, or

private dashboards to the public internet.

• Prefer SSH port forwarding for local browser testing.
• On headless Linux VPS hosts, do not promise Browser or Computer Use unless a

supported browser/desktop stack is explicitly installed and verified. Prefer running the server on the VPS and inspecting it through a local SSH tunnel.

• Never print, paste, or commit ~/.codex/auth.json, API keys, deploy keys,

SSH private keys, or provider tokens.

2. Mac SSH Config

Create or provide a concrete SSH alias on the Mac that runs Codex App. Do not edit ~/.ssh/config silently; show the snippet and ask before writing unless the user already asked Codex to make the edit.

Host krypton-vps
  HostName 203.0.113.10
  User dev
  IdentityFile ~/.ssh/id_ed25519
  IdentitiesOnly yes
  ServerAliveInterval 30
  ServerAliveCountMax 3

Verify from the Mac:

ssh krypton-vps

3. VPS Tooling

On the VPS, install the repo's real toolchain. For a typical Ubuntu 24.04 agent box this means:

• git
• gh
• curl
• jq
• python3
• ripgrep (rg)
• build-essential
• tmux
• unzip
• cmux when the workflow uses it
• node
• corepack
• pnpm
• Docker and Compose when the repo needs containers
• Codex CLI, installed through the current official path
• Claude Code only if the operator uses it and has its auth flow ready

Do not guess a repo's install commands. Read README.md, package manager files, and repo docs first.

4. Codex On The VPS

The remote shell must find codex:

command -v codex
codex --version

For headless login, prefer:

codex login --device-auth

If device auth is unavailable, use the official fallback options. If copying ~/.codex/auth.json, treat it like a password and never expose its contents.

For troubleshooting, use codex doctor on the VPS. Do not manually expose codex app-server for a normal Codex App SSH project; the app starts the remote app server over SSH.

5. Repo And Project

Before copying code, ask:

Do you want GitHub to be the source of truth for this VPS checkout? That is the
recommended path. It keeps code transfer clean, repeatable, and reviewable.

If yes, ask which GitHub access method the operator wants:

• GitHub CLI login on the VPS: best when the user wants normal development,

private repo access, issues, PRs, and pushes from the VPS.

• SSH key on the user's GitHub account: good when the VPS should behave like one

of the user's dev machines. This key can access every repo that account can access, so do not use it casually on shared hosts.

• Read-only deploy key: best for cloning one private repo with least privilege.

It is not enough if Codex needs to push branches back to GitHub.

• Public HTTPS clone: fine for public repos or read-only public examples.
• rsync/archive from the Mac: fallback for code not in GitHub; do not present

this as the default for active codebases.

Never ask the user to paste a GitHub token into the chat or put a token in a Git remote URL. If token auth is unavoidable, use the official GitHub CLI or provider flow and avoid printing the token.

For private repos with GitHub CLI:

ssh krypton-vps
gh auth login
gh auth status
gh repo clone ORG/REPO ~/src/REPO

For SSH Git access:

ssh krypton-vps
ssh-keygen -t ed25519 -C "krypton-vps" -f ~/.ssh/github-krypton-vps
cat ~/.ssh/github-krypton-vps.pub

The operator adds the printed public key to GitHub. Then verify and clone:

ssh -T git@github.com
mkdir -p ~/src
git clone git@github.com:ORG/REPO.git ~/src/REPO
cd ~/src/REPO

For a read-only deploy key, add the public key under the single GitHub repo's Deploy keys with write access disabled. Use this only when the VPS needs to clone or pull, not push.

After clone, set the normal project path:

mkdir -p ~/src
git clone git@github.com:ORG/REPO.git ~/src/REPO
cd ~/src/REPO

Install dependencies using the repo's own commands. If the repo uses checked-in skills, hooks, MCP config, or local environment actions, keep them in the repo so Codex App sees the same project guidance remotely.

6. Local Config And Secrets

Treat code and local configuration as separate moves.

Ask before touching local config:

Do you want to recreate local config on the VPS from examples, copy selected
ignored files from this machine, or skip local config for now?

Recommended order:

1. Recreate from checked-in examples such as .env.example, README setup, or

project docs.

1. Copy selected ignored files only when the operator confirms the exact files.
2. Skip secrets until the repo can boot far enough to show what is missing.

Safe copy pattern for selected local files:

rsync -av --chmod=F600,D700 .env.local krypton-vps:~/src/REPO/.env.local

Do not bulk-copy the whole home directory, .ssh, .codex, browser profiles, node_modules, build outputs, caches, or private key files. Do not commit copied local config. After copying, verify permissions and keep secrets out of terminal summaries.

Optional stronger CLI proof before the app UI:

ssh krypton-vps 'cd ~/src/REPO && codex exec --ephemeral --sandbox read-only -C "$PWD" "Run pwd, hostname, whoami, command -v codex, codex --version, git status --short, and do not modify files."'

This proves the remote Codex CLI can complete a read-only turn. It does not replace the final Codex App remote-thread proof.

7. Codex App Connection

In Codex App on the Mac:

1. Open Settings.
2. Open Connections.
3. Add or enable the SSH host alias.
4. Choose the remote project folder, for example ~/src/REPO.
5. Start a remote project thread.

This is a user-operated app step unless the current Codex session has explicit desktop/app-control tools and the operator asks to use them. Do not pretend SSH alone completes the Codex App connection.

Proof prompt for the first remote thread:

Run pwd, hostname, command -v codex, codex --version, git status --short, and
do not modify files.

The result should show the VPS hostname, the remote repo path, a working Codex binary, and a clean or understood Git state.

8. Port Forwarding

Use SSH forwarding for local browser proof:

ssh -L 3000:127.0.0.1:3000 krypton-vps

Run the dev server on the VPS bound to localhost or the documented dev-host address. Browse from the Mac at http://127.0.0.1:3000.

9. cmux And tmux

Use tmux for persistence and cmux for managing multiple agent sessions when the operator wants that workflow:

tmux new -s krypton

Keep the rule simple: Mac displays, VPS works, GitHub stores source, production stays separate.

Audit Script

When an SSH alias exists, run:

.codex/skills/krypton/krypton-vps-codex-app/scripts/audit-vps-codex-app.sh \
  --host krypton-vps \
  --repo-url git@github.com:ORG/REPO.git \
  --repo-path ~/src/REPO

The script is read-only. It checks SSH reachability, Linux/Ubuntu details, required command availability, whether codex is on the login-shell PATH, basic auth-cache presence without printing secrets, GitHub repo reachability when --repo-url is supplied, Git repo state, root-user risk, and common agent-workflow tools. It does not prove the Codex App UI connection by itself; finish with a real remote project thread.

Troubleshooting Rules