This causes launchd to behave like inetd , passing each daemon a single socket that is already connected to the incoming client. This key specifies whether your daemon launches on-demand or must always be running. It is recommended that you design your daemon to be launched on-demand. The following simple example launches a daemon named hello , passing world as a single argument, and instructs launchd to keep the job running:. In this example, there are three keys in the top level dictionary.
The first is Label , which uniquely identifies the job. The second is ProgramArguments which has a value of an array of strings which represent the tokenized arguments and the program to run. The third and final key is KeepAlive which indicates that this job needs to be running at all times, rather than the default launch-on-demand behavior, so launchd should always try to keep this job running. You can also include other keys in your configuration property list file.
If you need to pass a port number that is not listed in the well-known ports list, the format is the same, except the string contains a number instead of a name. For example:. The following example enables core dumps, sets standard out and error to go to a log file, and instructs launchd to temporarily increase the debug level of its logging while acting on behalf of your job remember to adjust your syslog.
Alternately, you can specify a calendar-based interval. The following example starts the job on the 7th day of every month at Like the Unix cron subsystem, any missing key of the StartCalendarInterval dictionary is treated as a wildcard—in this case, the month is omitted, so the job is run every month. An additional file system trigger is the notion of a queue directory. The launchd daemon starts your job whenever the given directories are non-empty, and it keeps your job running as long as those directories are not empty:.
The launchd daemon emulates the older inetd -style daemon semantics if you provide the inetdCompatibility key:.
Permissions and Security
Processes that are managed by launchd must follow certain requirements so that they interact properly with launchd. This includes launch daemons and launch agents. To support launchd , you must obey the following guidelines when writing your daemon code:. You must provide a property list with some basic launch-on-demand criteria for your daemon. See Creating a launchd Property List File.
Launching Custom Daemons Using launchd
You must not daemonize your process. This includes calling the daemon function, calling fork followed by exec , or calling fork followed by exit. If you do, launchd thinks your process has died. Daemons and agents that are installed globally must be owned by the root user. Agents installed for the current user must be owned by that user. All daemons and agents must not be group writable or world writable. That is, they must have file mode set to or To support launchd , it is recommended that you obey the following guidelines when writing your daemon code:.
Wait until your daemon is fully initialized before attempting to process requests. Your daemon should always provide a reasonable response rather than an error when processing requests. Register the sockets and file descriptors used by your daemon in your launchd configuration property list file. If your daemon advertises a socket, check in with launchd as part of your daemon initialization. For an example implementation of the check-in process, see SampleD.
During check-in, get the launch dictionary from launchd , extract and store its contents, and then discard the dictionary. Accessing the data structure used for the dictionary is very slow, so storing the whole dictionary locally and accessing it frequently could hurt performance. In addition to the preceding list, the following is a list of things it is recommended you avoid in your code:.
Do not set the user or group ID for your daemon. Do not set the working directory. Do not call chroot to change the root directory. Although many of the preceding behaviors may be standard tasks for daemons to perform, they are not recommended when running under launchd.
The reason is that launchd configures the operating environment for the daemons that it manages. Changing this environment could interfere with the normal operation of your daemon. If you do not expect your daemon to handle many requests, you might want to shut it down after a predetermined amount of idle time, rather than continue running.
Although a well-written daemon does not consume any CPU resources when idle, it still consumes memory and could be paged out during periods of intense memory use. The timing of when to shut down is different for each daemon and depends on several factors, including:. If your daemon does not receive frequent requests and can be launched and shut down quickly, you might prefer to shut it down rather than wait for it to be paged out to disk.
Paging memory to disk, and subsequently reading it back, incurs two disk operations. If you do not need the data stored in memory, your daemon can shut down and avoid the step of writing memory to disk. While launchd takes care of dependencies between daemons, in some cases, your daemon may depend on other system functionality that cannot be addressed in this manner.
This section describes many of these special cases and how to handle them. If your daemon depends on the network being available, this cannot be handled with dependencies because network interfaces can come and go at any time in OS X. To solve this problem, you should use the network reachability functionality or the dynamic store functionality in the System Configuration framework. If your daemon depends on the availability of a mounted volume whether local or remote , you can determine the status of that volume using the Disk Arbitration framework.
This is documented in Disk Arbitration Framework Reference.
Mac OS X: launch daemons vs launch agents
If your daemon has a dependency on a non- launchd daemon, you must take additional care to ensure that your daemon works correctly if that non- launchd daemon has not started when your daemon is started. The best way to do this is to include a loop at start time that checks to see if the non- launchd daemon is running, and if not, sleeps for several seconds before checking again.
Be sure to set up handlers for SIGTERM prior to this loop to ensure that you are able to properly shut down if the daemon you rely on never becomes available. In general, a daemon should not care whether a user is logged in, and user agents should be used to provide per-user functionality.
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However, in some cases, this may be useful. If your daemon requires that a certain kernel extension be loaded prior to executing, you have two options: The daemon may manually request that an extension be loaded. Mac Security. Behind the scenes, macOS starts the launchd process.
This is responsible for starting, stopping, and managing every other process, including the system and individual user accounts. The process is highly optimized and takes only a few moments. This shows that launchd is the primary parent process when the system starts. It is also the last process to exit when the system shuts down. The core responsibility of launchd is to launch other processes or jobs on a scheduled or on-demand basis. These come in two types: LaunchDaemons and LaunchAgents.
LaunchDaemons typically run as root, regardless of whether a user is logged in or not. They cannot display information using the graphical user interface and affect the entire system. For example, the locationd process detects the geographical location of the Mac, while bluetoothd process manages Bluetooth. The list of daemons lives in the following locations:.
LaunchAgents start when a user logs in. Unlike daemons, they can access the user interface and display information. The list of agents lives in the following locations:. Read More. The preference files follow the standard reverse domain naming system.
It begins with the company name, followed by an application identifier, and ends with the property list file extension. For example, at. Unlike those in the System folder, the public LaunchDaemon and LaunchAgent folders are open to both legitimate and illegitimate apps.
You can monitor these folders automatically with Folder Actions. Open the AppleScript Editor app by searching for it in Spotlight. Then select Attach Script to Folder in that same menu. Click OK to open a Finder window. Now select the user LaunchDaemon folder listed above and click Choose. Here are several key Mac details you should check right now. Read More and presents it in an easy-to-read report.
LaunchDaemons vs LaunchAgents
It also has additional help options when dealing with adware, suspicious daemons and agents, unsigned files, and more. Open EtreCheck and click Scan. This including major and minor issues, hardware specification, software compatibility issues, the status of LaunchDaemons and LaunchAgents, and more. Lingon X is another tool that lets you start an app, a script, or run a command automatically on a schedule.