As explained below, Mac OSX Yosemite 10.10.3 introduced security changes that caused problems for real-time systems in Antelope 5.4 and below. These problems have been fully addressed for Antelope 5.5, 5.6 and beyond. The FAQ entry below is preserved for instructional purposes.
With the latest Mac OSX Yosemite 10.10.3 update, some of the basic system services have changed in a fundamental way. In particular, the ability to put processes into the background safely, so that the user can log out and expect the background processes to keep on running properly, has changed in 10.10.3 and these changes introduce some fundamental limitations on how background processes can be launched. The real concern for Antelope is the basic real-time executive process, rtexec. With the latest version of Yosemite, rtexec can only be run continuously (surviving user logout) as the root user, which requires that all of the files rtexec uses must also be owned by root; or as a turnkey boot script controlled by Apple's launchctl program. If you launch rtexec as a non-root user, Apple will shut it down when you log out. This limitation comes about due to new security rules in the system utility launchctl which is used by rtexec to turn itself into a background process. These limitations did not appear prior to 10.10.3. Another critical problem introduced in Yosemite is the removal of the SystemStarter(8) system utility altogether. This is the utility that starts up rtexec instances automatically at boot time. For Antelope 5.5 we have re-engineered the turnkey boot implementation to adjust for this, per the man-page install_turnkey_boot_script(8) or com.brtt.rtexec.plist(8). For users running Antelope 5.4 and earlier, you will not be able to start rtexec instances automatically at boot time if you install the latest version of MacOSX Yosemite or upgrade your Yosemite systems with the latest Apple patches.
We recommend strongly that all users running Antelope versions up to Antelope 5.4 on Apple computers DO NOT upgrade to MacOSX Yosemite (OSX 10.10). If you are running a system where you have upgraded to Yosemite, we recommend you downgrade to the most recent version of Mavericks, MacOSX 10.9.5. We have fixes in our Antelope 5.5 release, but those fixes do not remove all of the new limitations. Apple's philosophy appears to be that they do not want to allow daemon processes like rtexec to be runable by non-root users. We can try to get around the roadblocks Apple puts in front of us, but eventually we may not be able to get around those roadblocks and this situation appears to be a moving target with potential system dysfunction each time Apple puts out a patch or a new version of MacOSX. The safest approach for our users is to stay with Mavericks (OSX 10.9) and/or downgrade to Mavericks.
If you "purchased" the Mavericks installer through the App Store (it was a free purchase), then you should be able to see the Mavericks installer as a downloadable item in the App Store Purchases page. The Mavericks installer will be downloaded to your /Applications folder with the name "Install OS X Mavericks.app". Once you have downloaded the Mavericks installer from the App Store it will start up automatically. You can either install from there or quit the app and use the following instructions to make a bootable media copy of the installer, something we strongly recommend.
Unfortunately, Apple no longer makes the Mavericks installer available as a new "purchase". If you did not already purchase the installer, then you will not be able to get it with your Apple ID through the App Store. There claim to be copies of the Mavericks installer on various web sites, but be careful about using any of these. Most of them are just patch installers that require Mavericks to already be installed on your system. The actual Mavericks installer is 5.31Gbytes in size. If you cannot get the authentic installer through the App Store, then we recommend you sign up for the Apple Developer's Program. It costs $99/year and gives you access to developer resources from Apple including old versions of MacOSX, such as Mavericks. You can get a full Mavericks installer through the Apple Developer web portal as long as you are a member of the program.
Apple could decide at any time to remove access to these old installers. The prudent thing to do is to ALWAYS backup all of your MacOSX installers into separate bootable media. This way you will be able to boot recovery systems from the backup media and install full systems from the media. Here at BRTT we always copy the installers onto DVDs or USB thumb drives that we can boot directly. We have separate media for each installer. There are many web sites that describe how to do this. In fact there is an Apple web site that describes how to do this for Mavericks and Yosemite.
If you are interested in running 24/7 real time systems on Mac, you will have to upgrade to the new Antelope 5.6 release unless you are willing to run the systems manually as root and do not need to start the systems automatically at boot. All of the other Antelope processes should run as before.