LaunchAgents

LaunchAgents are a type of job definition used by macOS launchd to run programs or scripts automatically in a user’s context. They enable per-user automation and background tasks, complementing LaunchDaemons, which run with elevated privileges for system-wide services.

A LaunchAgent is a property list (plist) file that must be well formed and placed in specific locations. The common locations are per-user: ~/Library/LaunchAgents, and system-wide: /Library/LaunchAgents. LaunchDaemons, in contrast, live in /Library/LaunchDaemons and run as root. When a user logs in or when a system policy loads the agent, launchd reads the plist and starts the configured program.

The plist specifies at least a Label to identify the job and either a Program (the executable path) or ProgramArguments (an array of the program and its arguments). Optional keys control behavior, such as RunAtLoad (start when the plist is loaded), StartInterval (time between runs in seconds), and StartCalendarInterval (specific times or dates). KeepAlive can cause the job to respawn if it exits, while StandardOutPath and StandardErrorPath redirect logs. Other common keys include WorkingDirectory and EnvironmentVariables.

Management and usage often involve the launchctl command. Users can load or unload a LaunchAgent with appropriate permissions, and list active jobs with launchctl list. For per-user agents, simply placing the plist in the user’s LaunchAgents directory will typically load at login; system-wide agents may require additional steps or policy configurations.

Security and best practices emphasize using minimal privileges, placing system-wide agents in the correct directory with appropriate ownership, and directing output to log files. Avoid interactive prompts and test changes to ensure stability and expected behavior.