System Services on macOS

If you’re coming from Linux, you’ll search for systemctl and find nothing. macOS uses launchd, a fundamentally different approach to service management that Apple introduced in 2005. Understanding launchd is essential for managing background processes, scheduling tasks, and running services on macOS.

What Is launchd?

launchd is macOS’s unified service management framework. It replaces:

• init (process 1)
• cron (scheduled tasks)
• inetd (network services)
• xinetd (extended inetd)
• rc.d scripts (startup scripts)

launchd is always PID 1:

$ ps aux | head -2
USER   PID  %CPU %MEM      VSZ    RSS   TT  STAT STARTED      TIME COMMAND
root     1   0.1  0.1 410148544  18624   ??  Ss   10:00AM   0:05.23 /sbin/launchd

Key Concepts

Jobs vs Services

In launchd terminology:

• Job: Any task managed by launchd (one-time or recurring)
• Daemon: A background process running as root
• Agent: A background process running as a user

Property Lists (plists)

launchd jobs are configured via property list files:

# System-wide daemons
/Library/LaunchDaemons/

# System-wide agents
/Library/LaunchAgents/

# Per-user agents
~/Library/LaunchAgents/

# Apple's daemons (don't modify)
/System/Library/LaunchDaemons/

# Apple's agents (don't modify)
/System/Library/LaunchAgents/

launchctl

launchctl is the command-line interface to launchd:

# List all services
$ launchctl list

# Load/start a service
$ launchctl load /Library/LaunchDaemons/com.example.daemon.plist

# Unload/stop a service
$ launchctl unload /Library/LaunchDaemons/com.example.daemon.plist

What You’ll Learn in This Part

launchd: The Heart of macOS provides a comprehensive overview of launchd architecture, how it boots the system, and its role in process management.

Understanding Property Lists (plists) explains the XML and binary formats used for launchd configuration and how to create and edit them.

Creating Launch Agents and Daemons walks through creating your own background services step by step.

launchctl Command Reference is a comprehensive guide to the launchctl command and all its subcommands.

Process Management: CLI vs GUI covers managing processes from both Terminal and Activity Monitor.

Background Task Scheduling explains how to schedule recurring tasks using launchd (the macOS way) and cron (the traditional Unix way).

XPC Services and IPC introduces Apple’s modern inter-process communication framework.

Comparing launchd to systemd and init helps Linux users understand how macOS’s approach differs from what they know.

Quick Example

Here’s a simple launch agent that runs a script every hour:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.example.hourly</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/myscript.sh</string>
    </array>
    <key>StartInterval</key>
    <integer>3600</integer>
</dict>
</plist>

Save as ~/Library/LaunchAgents/com.example.hourly.plist and load:

$ launchctl load ~/Library/LaunchAgents/com.example.hourly.plist

The following chapters explain this and much more in detail.