System wide and per-user daemon/agent
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
launchd also manages XPC services that are
bundled within applications and frameworks on the system.
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
On Darwin operating systems, the canonical way to launch a daemon
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.
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
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
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.
- Per-user agents provided by the user.
- Per-user agents provided by the administrator.
- System-wide daemons provided by the administrator.
- Per-user agents provided by Apple.
- System-wide daemons provided by Apple.
The Daemons and Services Programming Guide can be found at the following URL: