Pressing Ctrl-Shift as you are clicking on any app or search result will open it with Administrator privileges. So if you click Start, then type MMC, hold down Ctrl-Shift when you click on it. Run a desktop app as admin from the Search window In the taskbar search field, type in the name of the program that needs to run with administrator permissions. Then, click or tap on the “Run as administrator” option displayed on the right side of the Search window. Press Run as administrator.
If you are developing daemons to run on OS X, it is highly recommended that you design your daemons to be
launchd compliant. Using launchd provides better performance and flexibility for daemons. It also improves the ability of administrators to manage the daemons running on a given system.
If you are running per-user background processes for OS X,
launchd is also the preferred way to start these processes. These per-user processes are referred to as user agents. A user agent is essentially identical to a daemon, but is specific to a given logged-in user and executes only while that user is logged in.
Unless otherwise noted, for the purposes of this chapter, the terms “daemon” and “agent” can be used interchangeably. Thus, the term “daemon” is used generically in this section to encompass both system-level daemons and user agents except where otherwise noted.
There are four ways to launch daemons using
launchd . The preferred method is on-demand launching, but launchd can launch daemons that run continuously, and can replace inetd for launching inetd -style daemons. In addition, launchd can start jobs at timed intervals.
Although
launchd supports non-launch-on-demand daemons, this use is not recommended. The launchd daemon was designed to remove the need for dependency ordering among daemons. If you do not make your daemon be launched on demand, you will have to handle these dependencies in another way, such as by using the legacy startup item mechanism.
Launching Custom Daemons Using launchd
With the introduction of
launchd in OS X v10.4, an effort was made to improve the steps needed to launch and maintain daemons. What launchd provides is a harness for launching your daemon as needed. To client programs, the port representing your daemon’s service is always available and ready to handle requests. In reality, the daemon may or may not be running. When a client sends a request to the port, launchd may have to launch the daemon so that it can handle the request. Once launched, the daemon can continue running or shut itself down to free up the memory and resources it holds. If a daemon shuts itself down, launchd once again relaunches it as needed to process requests.
In addition to the launch-on-demand feature,
launchd provides the following benefits to daemon developers:
The launchd Startup Process
After the system is booted and the kernel is running,
launchd is run to finish the system initialization. As part of that initialization, it goes through the following steps:
The process for per-user agents is similar. When a user logs in, a per-user
launchd is started. It does the following:
Because
launchd registers the sockets and file descriptors used by all daemons before it launches any of them, daemons can be launched in any order. If a request comes in for a daemon that is not yet running, the requesting process is suspended until the target daemon finishes launching and responds.
If a daemon does not receive any requests over a specific period of time, it can choose to shut itself down and release the resources it holds. When this happens,
launchd monitors the shutdown and makes a note to launch the daemon again when future requests arrive.
Important: If your daemon shuts down too quickly after being launched,
launchd may think it has crashed. Daemons that continue this behavior may be suspended and not launched again when future requests arrive. To avoid this behavior, do not shut down for at least 10 seconds after launch.
Creating a launchd Property List File
To run under
launchd , you must provide a configuration property list file for your daemon. This file contains information about your daemon, including the list of sockets or file descriptors it uses to process requests. Specifying this information in a property list file lets launchd register the corresponding file descriptors and launch your daemon only after a request arrives for your daemon’s services. Table 5-1 lists the required and recommended keys for all daemons.
The property list file is structured the same for both daemons and agents. You indicate whether it describes a daemon or agent by the directory you place it in. Property list files describing daemons are installed in
/Library/LaunchDaemons , and those describing agents are installed in /Library/LaunchAgents or in the LaunchAgents subdirectory of an individual user’s Library directory. (The appropriate location for executables that you launch from your job is /usr/local/libexec .)
For more information: For a complete listing of the keys, see the
launchd.plist manual page.
For sample configuration property lists, look at the files in
/System/Library/LaunchDaemons/ . These files are used to configure many daemons that run on OS X.
Writing a “Hello World!” launchd Job
The following simple example launches a daemon named
hello , passing world as a single argument, and instructs launchd to keep the job running:
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In this example, there are three keys in the top level dictionary. The first is
Label , which uniquely identifies the job. when. 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.
Listening on Sockets
You can also include other keys in your configuration property list file. For example, if your daemon monitors a well-known port (one of the ports listed in
/etc/services ), add a Sockets entry as follows:
The string for
SockServiceName typically comes from the leftmost column in /etc/services . The SockType is one of dgram (UDP) or stream (TCP/IP). 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:
Debugging launchd Jobs
There are some options that are useful for debugging your launchd job.
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.conf accordingly):
Running a Job Periodically
The following example creates a job that is run every five minutes (300 seconds):
Alternately, you can specify a calendar-based interval. The following example starts the job on the 7th day of every month at 13:45 (1:45 pm). 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.
Monitoring a Directory
The following example starts the job whenever any of the paths being watched have changed:
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:
Emulating inetd
The launchd daemon emulates the older
inetd -style daemon semantics if you provide the inetdCompatibility key:
Behavior for Processes Managed by launchd
Processes that are managed by
launchd must follow certain requirements so that they interact properly with launchd . This includes launch daemons and launch agents.
Required Behaviors
To support
launchd , you must obey the following guidelines when writing your daemon code:
Recommended Behaviors
To support
launchd , it is recommended that you obey the following guidelines when writing your daemon code: Outline app for mac.
In addition to the preceding list, the following is a list of things it is recommended you avoid in your code:
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.
Deciding When to Shut Down
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.
Special Dependencies
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.
Network Availability
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. This is documented in System Configuration Programming Guidelines and System Configuration Framework Reference. For more information about network reachability, see Determining Reachability and Getting Connected in System Configuration Programming Guidelines.
Disk or Server Availability
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.
Non-launchd Daemons
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.
User Logins
In general, a daemon should not care whether a user is logged in, and user agents should be used to provide per-user functionality. However, in some cases, this may be useful.
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To determine what user is logged in at the console, you can use the System Configuration framework, as described in Technical Q&A QA1133.
Kernel Extensions
If your daemon requires that a certain kernel extension be loaded prior to executing, you have two options: load it yourself, or wait for it to be loaded. Uninstall apps on mac os.
The daemon may manually request that an extension be loaded. To do this, run
kextload with the appropriate arguments using exec or variants thereof. I/O Kit kernel extensions should not be loaded with kextload ; the I/O Kit will load them automatically when they are needed.
Note: The
kextload executable must be run as root in order to load extensions into the kernel. For security reasons, it is not a setuid executable. This means that your daemon must either be running as the root user or must include a helper binary that is setuid root in order to use kextload to load a kernel extension.
Alternatively, our daemon may wait for a kernel service to be available. To do this, you should first register for service change notification. This is further documented in I/O Kit Framework Reference.
After registering for these notifications, you should check to see if the service is already available. By doing this after registering for notifications, you avoid waiting forever if the service becomes available between checking for availability and registering for the notification.
Note: In order for your kernel extension to be detected in a useful way, it must publish a node in the I/O registry to advertise the availability of its service. For I/O Kit drivers, this is usually handled by the I/O Kit family.
For other kernel extensions, you must explicitly register the service by publishing a nub, which must be an instance of
IOService .
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For more information about I/O Kit services and matching, see IOKit Fundamentals, I/O Kit Framework Reference (user space reference), and Kernel Framework Reference (kernel space reference).
For More Information
The manual pages for
launchd and launchd.plist are the two best sources for information about launchd .
In addition, you can find a source daemon accompanying the
launchd source code (available from http://www.macosforge.org/). This daemon is also provided from the Mac Developer Library as the SampleD sample code project.
The Daemons and Agents technical note provides additional information about how
launchd daemons and agents work under the hood.
Finally, many Apple-provided daemons support launchd . Their property list files can be found in /System/Library/LaunchDaemons . Some of these daemons are also available as open source from http://www.opensource.apple.com/ or http://www.macosforge.org/.
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