launchd(8)                   System Manager's Manual                  launchd(8)

     launchd – System wide and per-user daemon/agent manager

     launchd manages processes, both for the system as a whole and for
     individual users.

     The primary and preferred interface to launchd is via the launchctl(1) tool
     which (among other options) allows the user or administrator to load and
     unload jobs. Where possible, it is preferable for jobs to launch on demand
     based on criteria specified in their respective configuration files.

     launchd also manages XPC services that are bundled within applications and
     frameworks on the system.

     During boot launchd is invoked by the kernel to run as the first process on
     the system and to further bootstrap the rest of the system.

     You cannot invoke launchd directly.

     On Darwin operating systems, the canonical way to launch a daemon is
     through launchd as opposed to traditional POSIX and POSIX-like mechanisms
     or mechanisms provided in earlier versions of OS X. These alternate methods
     should be considered deprecated and not suitable for new projects.

     In the launchd lexicon, a daemon is, by definition, a system-wide service
     of which there is one instance for all clients. An agent is a service that
     runs on a per-user basis.  Daemons should not attempt to display UI or
     interact directly with a user's login session. Any and all work that
     involves interacting with a user should be done through agents.

     XPC services which are marked with a ServiceType of System are functionally
     equivalent to daemons and run in the same environment, sharing the same
     Mach bootstrap namespace. XPC services which are marked with a ServiceType
     of User are equivalent to agents with the LimitLoadToSessionType key
     specifying the Background session and run in the same environment, sharing
     the same Mach bootstrap namespace. See launchd.plist(5) for more
     information about user sessions.

     On Darwin platforms, a user environment includes a specific Mach bootstrap
     subset, audit session and other characteristics not recognized by POSIX.
     Therefore, making the appropriate setuid(2) and setgid(2) system calls is
     not sufficient to completely assume the identity for a given user. Running
     a service as a launchd agent or a per-user XPC service is the only way to
     run a process with a complete identity of that user.

     ~/Library/LaunchAgents         Per-user agents provided by the user.
     /Library/LaunchAgents          Per-user agents provided by the
     /Library/LaunchDaemons         System-wide daemons provided by the
     /System/Library/LaunchAgents   Per-user agents provided by Apple.
     /System/Library/LaunchDaemons  System-wide daemons provided by Apple.

     launchctl(1), launchd.plist(5),

     The Daemons and Services Programming Guide can be found at the following

Darwin                          25 November, 2013                         Darwin