Systemd

A simple Swift library to interface with systemd on Linux.

Compatibility

This library is designed to be API-compatible on non-Linux platforms (like macOS), so if an application uses this package it will still compile and run on non-Linux platforms. However, systemd-specific calls will have no effect. For example, SystemdHelpers.isSystemdService will always return false on Windows or macOS.

To use this library in Linux, however, the systemd libraries are required. These can be installed with the following commands on different distributions:

• Debian/Ubuntu: sudo apt install libsystemd-dev
• RHEL/Fedora: sudo dnf install systemd-devel
• SUSE/OpenSUSE: sudo zypper install systemd-devel

For other distributions, look in the package repositories for a systemd dev package and install it.

NOTE: This library is NOT compatible with Musl as it appears that systemd libraries are still not fully ported to Musl yet. Please open a ticket if this changes so that support can be added for Musl, once this configuration is supported.

Installation

Add the following dependency to your Package.swift file:

.package(url: "https://github.com/xtremekforever/swift-systemd.git", from: "0.1.0")

Then, add it to your target dependencies section like this:

.product(name: "Systemd", package: "swift-systemd")

Usage

Take this example systemd service file:

[Unit]
Description=My Systemd Service

[Service]
Type=notify
WorkingDirectory=/usr/local/bin
ExecStart=/usr/local/bin/MyService
WatchdogSec=30

[Install]
WantedBy=multi-user.target

First, add import Systemd to the app use the modules provided by this library.

To see if the app is running under systemd, use the SystemdHelpers interface:

if SystemdHelpers.isSystemdService {
    print("This app is running as a systemd service!")

    // do things like modify logging format (if using swift-log) or whatever else is needed.
}

To send signals to systemd about the state of the app, use the SystemdNotifier interface:

let notifier = SystemdNotifier()

// Call after starting up app (sends READY=1)
notifier.notify(ServiceState.Ready)

// Call before exiting app (sends STOPPING=1)
notifier.notify(ServiceState.Stopping)

Systemd Lifecycle

This repo also contains a separate SystemdLifecycle product that can be used by projects that employ the swift-service-lifecycle library to run and manage application services. It is a simple service that sends the READY=1 and STOPPING=1 signals above from the service run() method.

It can be used by adding the SystemdLifecycle target dependencies section like this:

.product(name: "SystemdLifecycle", package: "swift-systemd")

Then, once the product is imported with import SystemdLifecycle, it can be added to a ServiceGroup:

let serviceGroup = ServiceGroup(
    configuration: .init(
        services: [
            .init(service: SystemdService())
        ]
    )
)
try await serviceGroup.run()

SystemdService does not have any dependencies on other services, so it can be constructed and started at any point in the application's service lifecycle.