Anatomy of a Startup Item

Unlike many other bundled structures, a startup item does not appear as an opaque file in the Finder. A startup item is a directory whose executable and configuration property list reside in the top-level directory. The name of the startup item executable must match the name of the startup item itself. The name of the configuration property list is always StartupParameters.plist. Depending on your needs, you may also include other files in your startup item bundle directory.

MyStartupItem/

    |

    |- MyStartupItem

    \- StartupParameters.plist

To create your startup item:

1. Create the startup item directory. The directory name should correspond to the behavior you’re providing.

   Example: MyDBServer

2. Add your executable to the directory. The name of your executable should be exactly the same as the directory name. For more information, see Creating the Startup Item Executable.

3. Create a property list with the name StartupParameters.plist and add it to the directory. For information on the keys to include in this property list, see Specifying the Startup Item Properties .

   Example: MyDBServer/StartupParameters.plist

4. Create an installer to place your startup item in the /Library/StartupItems directory of the target system. (Your installer may need to create this directory first.)

   Your installer script should set the permissions of the startup item directory to prevent non-root users from modifying the startup item or its contents. For more information, see Startup Item Permissions.

Creating the Startup Item Executable

The startup item executable can be a binary executable file or an executable shell script. Shell scripts are more commonly used because they are easier to create and modify.

If you are implementing your startup item executable as a shell script, OS X provides some code to simplify the process of creating your script. The file /etc/rc.common defines routines for processing command-line arguments and for gathering system settings. In your shell script, source the rc.common file and call the RunService routine, passing it the first command-line argument, as shown in the following example:

#!/bin/sh

. /etc/rc.common

# The start subroutine

StartService() {

    # Insert your start command below.  For example:

    mydaemon -e -i -e -i -o

    # End example.

}

# The stop subroutine

StopService() {

    # Insert your stop command(s) below.  For example:

    killall -TERM mydaemon

    sleep 10

    killall -9 mydaemon

    # End example.

}

# The restart subroutine

RestartService() {

    # Insert your start command below.  For example:

    killall -HUP mydaemon

    # End example.

}

RunService "$1"

The RunService routine looks for StartService, StopService, and RestartService functions in your shell script and calls them to start, stop, or restart your services as needed. You must provide implementations for all three routines, although the implementations can be empty for routines whose commands your service does not support.

If your startup-item executable contains code that might take a long time to finish, consider spawning off a background process to run that code. Performing lengthy startup tasks directly from your scripts delays system startup. Your startup item script should execute as quickly as possible and then exit.

For more information about writing shell scripts, see Shell Scripting Primer.

Specifying the Startup Item Properties

The configuration property list of a startup item provides descriptive information about the startup item, lists the services it provides, and lists its dependencies on other services. OS X uses the service and dependency information to determine the launch order for startup items. This property list is stored in ASCII format (as opposed to XML) and can be created using the Property List Editor application.

Table A-1 lists the key-value pairs you can include in your startup item’s StartupParameters.plist file. Each of the listed arrays contains string values. You can use the Property List Editor application that comes with the Xcode Tools to create this property list. When saving your property-list file, be sure to save it as an ASCII property-list file.

For example, here is an old-style plist:

{

  Description     = "Software Update service";

  Provides        = ("SoftwareUpdateServer");

  Requires        = ("Network");

  Uses            = ("Network");

  OrderPreference = "Late";

  Messages =

  {

    start = "Starting Software Update service";

    stop  = "Stopping Software Update service";

  };

}

And here is an XML plist example:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist SYSTEM "file://localhost/System/Library/DTDs/PropertyList.dtd">

<plist version="0.9">

    <dict>

        <key>Description</key>

        <string>Apple Serial Terminal Support</string>

        <key>OrderPreference</key>

        <string>Late</string>

        <key>Provides</key>

        <array>

                <string>Serial Terminal Support</string>

        </array>

        <key>Uses</key>

        <array>

                <string>SystemLog</string>

        </array>

    </dict>

</plist>

The service names you specify in the Requires and Uses arrays may not always correspond directly to the name of the startup item that provides that service. The Provides property specifies the actual name of the service provided by a startup item, and while this name usually matches the name of the startup item, it is not required to do so. For example, if the startup item launches multiple services, only one of those services can have the same name as the startup item.

If two startup items provide a service with the same name, the system runs only the first startup item it finds with that name. This is one of the reasons why your own startup items should launch only one service. If the name of only one of the services matches the name of another service, the entire startup item might not be executed and neither service would be launched.

The values of the Requires and Uses keys do not guarantee a particular launch order.

In OS X v10.4 and later, most low-level services are started with launchd. By the time your startup item starts executing, launchd is running, and any attempt to access any of the services provided by a launchd daemon will result in that daemon starting. Thus, you can safely assume (or at least pretend) that any of these services are running by the time your startup item is called.

For this reason, with few exceptions, the Requires and Uses keys are largely irrelevant after OS X v10.3 except to support service dependencies between two or more third-party startup items.

Managing Startup Items

During the boot process, the system launches the available startup items, passing a start argument to the startup item executable. After the boot process, the system may run the startup item executable again, this time passing it a restart or stop argument. Your startup item executable should check the supplied argument and act accordingly to start, restart, or stop the corresponding services.

If you want to start, restart, or stop startup items from your own scripts, you can do so using the SystemStarter program. To use SystemStarter, you must execute it with two parameters: the desired action and the name of the service provided by the startup item. For example, to restart the Apache Web server (prior to OS X v10.4), you would execute the following command:

/sbin/SystemStarter restart "Web Server"

Startup items should always respect the arguments passed in by SystemStarter. However, the response to those arguments is dependent on the startup item. The stop and restart options may not make sense in all cases. Your startup item could also support the restart option using the existing code for stopping and starting its service.

Displaying and Localizing a Startup Message

When your startup item starts at boot time, you may (if desired) display a message to the user. To do this, use the ConsoleMessage command. (You can use this command even if the computer is not starting up, but the user will not see it unless the Console application is running.)

For example:

ConsoleMessage "MyDaemon is running.  Better go catch it."

If you want to localize the message displayed when a startup item starts, you must create a series of property list files with localized versions of the strings. Each of these files must be named Localizable.strings, and must be in a localized project directory whose name is based on the name of a language or locale code for the desired language. These folders, in turn, must be in a folder called Resources in the startup item folder.

For example, you might create a tree structure that looks like this:

MyDaemon

    |

    |- MyDaemon

    |- StartupParameters.plist

    \- Resources

            |

            |- English.lproj

            |- French.lproj

            |- German.lproj

            \- zh_CN.lproj

Within each of these localizable strings files, you must include a dictionary whose keys map an English string to a string in another language. For example, the French version of the PrintingServices localization file looks like this:

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<plist version="1.0">

    <dict>

        <key>Starting printing services</key>

        <string>Démarrage des services d’impression</string>

    </dict>

</plist>

Whenever the ConsoleMessage command is passed the string “Starting printing services”, if the user’s language preference is French, the user will instead see “Démarrage des services d’impression” at startup. C’est très bien!

The value of the key field must precisely match the English string printed by your startup item using ConsoleMessage.

See the manual page for locale for more information about locale codes.

Startup Item Permissions

Because startup items run with root authority, you must make sure your startup item directory permissions are set correctly. For security reasons, your startup item directory should be owned by root, the group should be set to wheel, and the permissions for the directory should be 755 (rwxr-xr-x). This means that only the root user can modify the directory contents; other users can examine the directory and view its contents, but cannot modify them. The files inside the directory should have similar permissions and ownership. Thus, the file listing for the Apache startup item directory is as follows:

./Apache:

total 16

drwxr-xr-x    4 root  wheel   136 Feb 14 14:33 .

drwxr-xr-x   21 root  wheel   714 Feb 14 15:03 ..

-rwxr-xr-x    1 root  wheel  1253 Feb 10 19:31 Apache

-rw-r--r--    1 root  wheel   152 Feb 10 19:31 StartupParameters.plist