Launchctls

launchd is a system for bootstrapping daemons and agents on macOS and other Darwin-based operating systems. It was introduced in Mac OS X 10.4 Tiger and has largely replaced older mechanisms like init scripts and cron. Launchd is responsible for starting, stopping, and managing processes on the system, acting as a central control point for system services and user-specific applications.

The core components of launchd are property list (.plist) files. These files, written in XML, define jobs that launchd will manage. A job can be a daemon, which runs in the background for the entire system, or a agent, which runs on behalf of a specific user. These .plist files specify the executable to run, arguments, environment variables, and various conditions under which the job should be started or stopped. Launchd monitors these conditions and acts accordingly.

Key functionalities of launchd include on-demand execution, where jobs are started only when needed, such as when a network connection is requested or a file is accessed. It also handles automatic restarts of failed jobs, ensuring system stability. Launchd manages the transition between system states, like waking from sleep or logging in a user. The command-line utility launchctl is used to interact with launchd, allowing users and administrators to load, unload, start, stop, and query the status of jobs. This provides a powerful and flexible way to manage system processes and custom services.