Supervisord — Process Control System for Unix

Introduction

Supervisor is a process control system for Unix that lets you manage and monitor long-running processes. It automatically starts processes at boot, restarts them on crash, and provides a CLI and web interface for managing process groups. It is widely used to run application servers, workers, and background tasks in production.

What Supervisord Does

• Starts, stops, and restarts managed processes with automatic crash recovery
• Groups related processes for batch control (start/stop a service stack at once)
• Provides a CLI tool (supervisorctl) for interactive process management
• Exposes a web UI and XML-RPC API for remote monitoring
• Logs stdout and stderr from managed processes to rotated log files

Architecture Overview

Supervisord runs as a daemon (the server process) that reads an INI-style configuration file defining programs and their parameters. Each managed program runs as a child process. The daemon monitors child processes via SIGCHLD signals and restarts them according to the configured policy. The supervisorctl client communicates with the daemon over a Unix socket or TCP using XML-RPC.

Self-Hosting & Configuration

• Install via pip: pip install supervisor
• Generate a config template: echo_supervisord_conf > /etc/supervisord.conf
• Define programs in [program:name] sections with command, directory, and user
• Set autorestart=true for automatic crash recovery
• Enable the web UI by configuring [inet_http_server] with a port and credentials

Key Features

• Automatic process restart on crash or exit
• Process groups for managing related services together
• Built-in log rotation for stdout and stderr
• Event listeners for custom notifications on process state changes
• Web dashboard for real-time status monitoring

Comparison with Similar Tools

• systemd — Linux-native init system; Supervisord is cross-platform and simpler to configure
• PM2 — Node.js-focused process manager with clustering; Supervisord is language-agnostic
• Docker — Container-level process management; Supervisord manages processes within a single host or container
• runit — Minimal init scheme; Supervisord offers richer monitoring and a web UI

FAQ

Q: Can Supervisord manage Docker containers? A: Supervisord manages Unix processes, not containers. It is often used inside Docker containers to run multiple processes in a single container when needed.

Q: How does Supervisord handle process dependencies? A: Use priority values to control start order and process_groups to manage related services. For strict dependency ordering, use event listeners or startup scripts.

Q: Does Supervisord work on macOS? A: Yes. Supervisord runs on any Unix-like system including macOS and Linux. It does not support Windows natively.

Q: Can I extend Supervisord with plugins? A: Yes. Supervisord supports event listeners that react to process state changes, and third-party plugins like superlance add advanced monitoring features.

Sources

• GitHub Repository
• Official Documentation