Minecraft wiki entry for Create_a_Mac_OS_X_startup_daemon, associated text: This will show up a list of all the created users on your computer, along with their UIDs. Again, it doesn't matter what they are, but an empty UID is necessary, again in the daemon range (less than 500). Verify if 300 is unused. You can select a different UID and GID, they need not to be identical, but it's certainly tidier if they are.