| 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.
The Daemons and Services Programming Guide can be found at the following URL:
https://developer.apple.com/library/content/documentation/MacOSX/Conceptual/BPSystemStartup/Chapters/Introduction.html
| 25 November, 2013 | Darwin |