Tux-Dock

A lightweight C++ Docker TUI

Tux-Dock is a modern C++17 Docker terminal frontend built with FTXUI. It gives you a guided, keyboard-first TUI for common Docker operations without memorizing long CLI flags.

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Table of Contents

• Features
• Why tuxreaperd?
• Web workload guide
  • Signal conventions
  • Required PHP-FPM configuration
  • Starting services inside the container
  • Verification: long-running PHP request
  • Troubleshooting
• Build Requirements
• Build & Run
• Menu Overview
• Design Overview
  • Responsibilities
• Testing
• About / Version
• License

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Features

• Interactive Docker workflows through a single-screen TUI with modal steps.
• Picker-based selection (arrow keys + Enter) for containers/images instead of numeric menus.
• Busy-operation modals with a spinner and input blocking while Docker work completes.
• Rich container display with state and forwarded ports.
• Interactive shell handoff with clean terminal clear before/after shell transitions.
• Image operations: pull/list/delete with full docker hub image support.
• Docker Engine API access through /var/run/docker.sock for structured list and lifecycle operations.
• Direct fork/exec process execution for CLI-backed streaming and interactive commands.
• Persistent container listings that retain exited containers.
• Robust stop handling with state polling, timeout retry, and idempotent stop responses.
• tuxreaperd micro init system: a tiny statically-linked C daemon mounted into created containers as PID 1, acting as a subreaper so orphaned processes never linger as zombies, broadcasting lifecycle signals (SIGTERM, SIGQUIT, SIGINT, SIGHUP, SIGUSR1, SIGUSR2) to the whole process tree via kill(-1, sig), and propagating exit status. Includes architecture-specific O_DIRECTORY handling for x86_64 and aarch64, Apache-aware SIGTERM→SIGWINCH, nginx-aware SIGTERM→SIGQUIT, and PHP-FPM-aware SIGTERM→SIGQUIT remapping (with prefix matching for versioned binaries) for graceful shutdown, plus a 60-second container stop timeout so descendants have time to finish. Note: PHP-FPM graceful shutdown also requires process_control_timeout to be set in the PHP-FPM pool config (e.g., process_control_timeout = 60s). Processes don't fear tuxreaperd!
• About screen in-app with project/version/repository info.

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Why tuxreaperd?

Most container inits are generic: they spawn one child, forward signals, and reap zombies. That is enough for simple apps, but it breaks down for classic web engines that violate standard UNIX signal conventions:

• Apache HTTPD uses SIGWINCH for graceful shutdown.
• Nginx uses SIGQUIT for graceful shutdown.
• PHP-FPM uses SIGQUIT for graceful shutdown.

tuxreaperd encodes those quirks directly. It scans /proc/<pid>/exe during signal broadcast and translates SIGTERM into the correct graceful-shutdown signal for each daemon, then waits up to 60 seconds for worker descendants to drain.

Feature / Scenario	tini	dumb-init	mini-init-asm	tuxreaperd (~4.7 KB)
Automatic per-binary signal translation	No	Manual --rewrite only	No	Yes (Apache / nginx / PHP-FPM)
Zero-config web graceful stops	No	No	No	Yes
Post-exit descendant draining	No	No	No	Yes, 60-second bounded drain
Multi-pass /proc signal sweeps	No	No	No	Two-pass sweep
Freestanding / no libc	No	No (unless musl)	Yes	Yes
Restart-on-crash	No	No	Yes (EP_RESTART_ENABLED)	No
Configurable grace → SIGKILL timeout	No	No	Yes (EP_GRACE_SECONDS)	No (fixed 60s drain)

Static binary size comparison (KB):

tuxreaperd       |## 4.7
dumb-init (musl) |######## 20
tini             |######### 23
mini-init-asm    |################ 41

dumb-init (glibc static) is ~700+ KB and omitted from the chart for scale.

mini-init-asm and dumb-init are excellent generic inits with useful extras like restart-on-crash or configurable kill timeouts, but they treat workloads as black boxes. tuxreaperd trades that generic flexibility for deep, zero-configuration automation of the three web-engine families that actually need signal translation.

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Web workload guide

tuxreaperd is built for containerized web engines that violate standard UNIX signal conventions. This guide covers Apache HTTPD, nginx, and PHP-FPM.

Signal conventions

Engine	Graceful shutdown signal	Fast shutdown signal
Apache HTTPD	SIGWINCH	SIGTERM
Nginx	SIGQUIT	SIGTERM / SIGINT
PHP-FPM	SIGQUIT	SIGTERM

When docker stop sends SIGTERM to PID 1, tuxreaperd inspects /proc/<pid>/exe and automatically translates the signal:

• Apache processes receive SIGWINCH.
• Nginx processes receive SIGQUIT.
• PHP-FPM processes (matched by the /usr/sbin/php-fpm prefix) receive SIGQUIT.

Required PHP-FPM configuration

PHP-FPM has a known quirk: on SIGQUIT its master process exits immediately unless process_control_timeout is configured. Without it, the FastCGI socket closes and nginx drops in-flight requests.

Add this to your PHP-FPM pool config (e.g., /etc/php/8.4/fpm/pool.d/www.conf):

[global]
process_control_timeout = 60s

Then restart PHP-FPM.

Starting services inside the container

Create the container with tux-dock, which already injects tuxreaperd as PID 1 and sets --stop-timeout=60. Then start your web services as descendants:

# Start PHP-FPM in the background
docker exec my-container /usr/sbin/php-fpm8.4 --nodaemonize &

# Start nginx in the foreground (or background)
docker exec my-container /usr/sbin/nginx -g 'daemon off;'

Make sure the binary paths match the ones tuxreaperd recognizes:

• /usr/sbin/apache2, /usr/sbin/httpd, /usr/local/apache2/bin/httpd
• /usr/sbin/nginx, /usr/local/nginx/sbin/nginx
• /usr/sbin/php-fpm*, /usr/local/sbin/php-fpm*

Verification: long-running PHP request

Create /var/www/html/sleep.php:

<?php
ob_end_clean();
header('Content-Type: text/plain');
header('Cache-Control: no-cache');

echo "Test started at: " . date('H:i:s') . "\n";
echo "Sleeping for 30 seconds...\n";
flush();

sleep(30);

echo "Test finished at: " . date('H:i:s') . "\n";
?>

Start the request, then stop the container:

curl -i http://localhost:8087/sleep.php
# In another terminal:
docker stop my-container

Expected result: the full response body is printed, including the “Test finished at: …” line, with no curl: (18) transfer closed with outstanding read data remaining error.

Troubleshooting

• Connection drops early → Verify process_control_timeout is set in PHP-FPM and restart it.
• Container stops instantly → The container must be recreated to pick up --stop-timeout=60; existing containers keep their original stop timeout.
• PHP-FPM not detected → Confirm the binary path starts with /usr/sbin/php-fpm or /usr/local/sbin/php-fpm.

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Build Requirements

• C++17 or newer compiler (e.g. g++, clang++)
• CMake 3.16+
• Docker Engine installed and running

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Build & Run

# Clone the repo
git clone https://mentalnet.xyz/forgejo-v2/markmental/tuxdock.git
cd tuxdock

# Configure, build, and test (FTXUI and nlohmann/json are fetched automatically)
./compile.sh

# Run it (requires Docker permissions)
sudo ./build/tux-dock

# Build without running tests
./compile.sh --no-test

# Run tests and serve an HTML 3.2 report on port 8095
./compile.sh --web-test-view

# Override the report server port
./compile.sh --web-test-view 9000

# Force the libc-based tuxreaperd implementation
./compile.sh --force-libc-reaper

# Build with verbose tuxreaperd debug output during tests
./compile.sh --debug-reaper

compile.sh builds the tuxreaperd micro init before the main project. On supported hosts (x86_64/amd64/aarch64/arm64) it first tries the freestanding syscall implementation in tuxreaperdasm.c; on other architectures, or if the freestanding build fails, it falls back to the standard POSIX implementation in tuxreaperdgnu.c. Pass --force-libc-reaper to skip the freestanding build and use the libc implementation directly. Pass --debug-reaper to build tuxreaperd with TUXREAPERD_DEBUG and run tests with verbose output, showing the reaper's internal /proc scans, signal broadcasts, and descendant waits.

The web report is generated under /tmp and includes exact CTest output, test summaries, Docker integration output, a text rendition of the TUI flow, and the tuxreaperd zombie-reaping results. It requires nc, netcat, or Nmap's ncat; press Ctrl-C to stop the server. The default port is 8095; pass a port after --web-test-view to override it. --web-test-view --no-test is invalid. Normal test runs include a Docker integration test using debian:forky, so Docker must be available. On systems with 1 GB or less of available memory, the script automatically uses a smaller build configuration and a single build job.

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Menu Overview

Current TUI actions:

1. Pull Docker Image
2. Create Container
3. List All Containers
4. List All Images
5. Start Detached Container Session
6. Delete Docker Image
7. Stop Container
8. Remove Container
9. Attach Shell to Running Container
10. Run Detached Command in Container
11. Run Command in Container (with output)
12. About Tux-Dock
13. Exit

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Design Overview

Tux-Dock is organized around the TUI, Docker manager, Engine API client, and direct process runner:

Responsibilities

• DockerEngineClient

  • Talks directly to Docker over the Unix socket.
  • Parses HTTP responses, including chunked and bodyless responses.

• ProcessRunner

  • Executes direct argument vectors using fork and exec.
  • Supports captured output and inherited terminal I/O.

• DockerManager

  • Maps Engine API JSON into application data.
  • Performs lifecycle operations and robust stop-state confirmation.
  • Preserves cached state when refreshes fail.

• TuxDockApp

  • Renders the FTXUI interface.
  • Manages modal flows (input/select/confirm/message).
  • Handles modal flows, busy operations, blocked input, and interactive shell transitions.
  • Coordinates end-to-end user flows by calling DockerManager methods.

This split keeps Docker behavior isolated while making UI behavior easier to extend.

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Testing

cmake -S . -B build -DBUILD_TESTING=ON
cmake --build build
ctest --test-dir build --output-on-failure

compile.sh runs these tests by default. Pass --no-test to skip them. The suite includes tuxreaperd-zombie-tests, which boots a container with tuxreaperd as PID 1 and verifies orphaned processes are reaped (no zombies), exit status propagates, and SIGTERM is forwarded on docker stop. Docker must be available.

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About / Version

• Version: 0.4.2-beta
• Created by: markmental
• GitHub: https://github.com/MARKMENTAL/tuxdock
• Forgejo: https://mentalnet.xyz/forgejo-v2/markmental/tuxdock

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License

MIT License — free to use, modify, and share.