systemg

Table of Contents

1. Getting Started
   • 1.1 How It Works
   • 1.2 Installation
   • 1.3 Running a Basic Start Command
   • 1.3 How It Works (docs)
2. Why systemg
   • 2.1 Features
   • 2.2 Comparison
3. Development
   • 3.1 Testing
   • 3.2 Build from Source
   • 3.3 Contributing

systemg - A General-Purpose Program Composer

systemg is a general-purpose program composer that transforms arbitrary programs into coherent systems with explicit lifecycles, dependencies, and health monitoring. Instead of managing individual daemons or containers, it focuses on composition over mechanics—turning a collection of processes into a system you can reason about, evolve, and deploy cleanly.

Built on top of existing OS primitives like systemd and cgroups, systemg inherits their stability while adding higher-level intent: how programs relate, start, roll, and recover together.

Getting Started

How It Works

Curious about the architecture? Read How Systemg Works for a deep dive into userspace vs. kernel-space behavior, socket activation, and runtime helpers.

Installation

Install the system binary:

$ curl --proto '=https' --tlsv1.2 -fsSL https://sh.sysg.dev/ | sh

Install systemg using cargo:

$ cargo install sysg

Or download the pre-built binary from the releases page.

For system deployments, scripts/install-systemg.sh installs /usr/bin/sysg, provisions /etc/systemg, /var/lib/systemg, /var/log/systemg, and drops sample logrotate + systemd assets for socket activation. Review and adapt it to match your distribution policies before running. Pair it with examples/system-mode.yaml and check the new docs/docs/security.md guide for hardening best practices.

Running a Basic Start Command

Start the process manager with the default configuration:

# Start with default configuration file (systemg.yaml)
$ sysg start

# Start with a specific configuration file
$ sysg start --config systemg.yaml

# Start the long-lived supervisor (persists after you log out)
$ sysg start --config systemg.yaml --daemonize

When the supervisor is running it remains active in the background, holding service processes in the same process group so commands like sysg stop, sysg restart, sysg status, and sysg logs can coordinate them even after you disconnect from the shell that started them.

Why systemg

Traditional service managers focus on the mechanics of keeping processes alive. systemg takes a different approach: it's about composing programs into systems. While tools like systemd manage individual units with complex dependency chains, systemg lets you declare how programs work together as a coherent whole—with explicit lifecycles, health checks, and deployment strategies that make the system's behavior predictable and evolvable.

Features

• Program Composition - Declare how programs relate and work together, not just individual service configs.
• Explicit Lifecycles - Define startup sequences, health checks, and recovery behaviors as first-class concepts.
• Dependency Orchestration - Programs start in topological order with health-aware cascading on failures.
• Rolling Deployments - Built-in blue-green swaps with health validation—no external deployment tools needed.
• Environment Inheritance - Consistent environment propagation from .env files across all composed programs.
• Lifecycle Webhooks - Integrate with external systems through event-driven notifications. See Webhooks documentation.
• Cron Scheduling - Short-lived tasks run alongside services with proper overlap detection.
• OS Primitive Integration - Leverages systemd/cgroups when available while maintaining userspace simplicity.
• Single Static Binary - No runtime dependencies, instant startup, predictable memory usage.

Privileged Mode (Optional)

Need to manage system daemons, bind privileged ports, or attach cgroup limits? Run the supervisor in privileged mode:

# Start with elevated privileges and system-wide state directories
$ sudo sysg --sys start --config /etc/systemg/nginx.yaml --daemonize

# Bind as root, then immediately drop to the configured service user
$ sudo sysg --sys --drop-privileges start --service web

# Check status without elevated privileges (falls back to userspace mode)
$ sysg status --service web

In privileged mode systemg relocates state to /var/lib/systemg, writes supervisor logs to /var/log/systemg/supervisor.log, and respects the new service-level fields:

services:
  web:
    command: "./server"
    user: "www-data"
    group: "www-data"
    supplementary_groups: ["www-logs"]
    limits:
      nofile: 65536
      nproc: 4096
      memlock: "unlimited"      # supports K/M/G/T suffixes
      nice: -5
      cpu_affinity: [0, 1]
      cgroup:
        memory_max: "512M"
        cpu_max: "200000 100000"
    capabilities:
      - CAP_NET_BIND_SERVICE
      - CAP_SYS_NICE
    isolation:
      network: true
      pid: true
      mount: true

All privileged operations are opt-in: services that omit these fields continue to run unprivileged, and unit tests skip elevated scenarios automatically when not running as root.

Dependency Handling

Declare service relationships with the depends_on field to coordinate startup order and health checks. Systemg will:

• start services in a topologically sorted order so each dependency is running or has exited successfully before its dependents launch;
• skip dependents whose prerequisites fail to start, surfacing a clear dependency error instead of allowing a partial boot;
• stop running dependents automatically when an upstream service crashes, preventing workloads from running against unhealthy backends.

For example:

version: "1"
services:
  database:
    command: "postgres -D /var/lib/postgres"

  web:
    command: "python app.py"
    depends_on:
      - database

If database fails to come up, web will remain stopped and log the dependency failure until the database is healthy again.

Rolling Deployments

Services can opt into rolling restarts so existing instances keep serving traffic until replacements are healthy. Add a deployment block to configure the behavior:

version: "1"
services:
  api:
    command: "./target/release/api"
    restart_policy: "always"
    deployment:
      strategy: "rolling"          # default is "immediate"
      pre_start: "cargo build --release"
      health_check:
        url: "http://localhost:8080/health"
        timeout: "60s"
        retries: 5
      grace_period: "5s"

• strategy — set to rolling to enable the zero-downtime workflow, or omit to keep the traditional stop/start cycle.
• pre_start — optional shell command executed before the new instance launches (perfect for build or migrate steps).
• health_check — optional HTTP probe the replacement must pass before traffic flips; configure timeout and retry budget per service.
• grace_period — optional delay to keep the old instance alive after the new one passes health checks, giving load balancers time to rebalance.

If any rolling step fails, systemg restores the original instance and surfaces the error so unhealthy builds never replace running services.

Cron Scheduling

Services can be configured to run on a cron schedule for short-lived, recurring tasks. Cron jobs are managed by the supervisor and run independently of regular services:

version: "1"
services:
  backup:
    command: "sh backup-script.sh"
    cron:
      expression: "0 0 * * * *"  # Run every hour at minute 0
      timezone: "America/New_York"  # Optional, defaults to system timezone

Key features:

• Standard cron syntax - Uses 6-field cron expressions (second, minute, hour, day, month, day of week).
• Overlap detection - If a cron job is scheduled to run while a previous execution is still running, the new execution is skipped and an error is logged.
• Execution history - The last 10 executions are tracked with their start time, completion time, and status.
• Service separation - A service cannot have both a command for continuous running and a cron configuration; cron is opt-in via the cron field.

Note: Cron jobs do not support restart policies, as they are designed to be short-lived tasks that complete and exit.

Additional Commands

The sysg command-line interface provides several subcommands for managing processes:

Stop - Stop the process manager or a specific service:

# Stop the supervisor and every managed service
$ sysg stop

# Stop a specific service
$ sysg stop --service myapp

Restart - Restart the process manager:

# Restart all services managed by the supervisor
$ sysg restart

# Restart a specific service
$ sysg restart -s myapp

# Restart with a different configuration
$ sysg restart --config new-config.yaml

Status - Check the status of running services:

# Show status of all services (uses default systemg.yaml)
$ sysg status

# Show status with a specific configuration file
$ sysg status --config myapp.yaml

# Show status of a specific service
$ sysg status --service webserver

# Show all services including orphaned state
$ sysg status --all

Inspect - Inspect a service or cron unit in detail:

# Inspect a specific service or cron unit by name or hash
$ sysg inspect myservice

# Show metrics in JSON format
$ sysg inspect myservice --json

# Display only the most recent data (last 2 minutes)
$ sysg inspect myservice --window 2m

# Render output without ANSI coloring
$ sysg inspect myservice --no-color

Logs - View logs for a specific service:

# View the last 50 lines of stdout logs (default)
$ sysg logs

# View logs for a specific service
$ sysg logs api-service

# View a custom number of log lines
$ sysg logs database --lines 100

# View specific log type (stdout, stderr, or supervisor)
$ sysg logs myservice --kind stderr

Log Level - Override logging verbosity:

# Override logging verbosity for the current run (works with every subcommand; names or 0-5)
$ sysg start --log-level debug
$ sysg start --log-level 4

Comparison

Development

Testing

To run the test suite:

# Run all tests
$ cargo test

# Run specific test
$ cargo test test_service_lifecycle

Build from Source

To build systemg from source:

# Clone the repository
$ git clone https://github.com/ra0x3/systemg.git
$ cd systemg

# Build the project
$ cargo build --release

# The binary will be available at target/release/sysg

Contributing

Contributions to systemg are welcome! Please see the CONTRIBUTING.md file for guidelines.