Mac OSX Startup

16 May 2007

Some notes on the startup sequence for Mac OSX 10.4 (Tiger), and troubleshooting the startup process. These will be corrected/expanded as I learn more about the process.



  • POST (Power On Self Test) is done – checks hardware and initialises components; errors (eg RAM) will cause varying numbers of beeps (or flashing LEDs on some systems)
  • on PPC machines Open Firmware is run
  • on Intel machines EFI (Extended Firmware Interface) is run
  • Command-Option-O-F will start PPCs and Intels in Open Firmware Mode prompt. Five commands can be used: mac-boot, shut-down, reset-all, reset-nvram, eject cd


  • BootX loads the kernel (similar to Grub/LILO in Linux, ntldr in Windows) as well as drivers needed to access I/O busses
  • various icons are displayed (Metallic Apple, Circle with Slash, Globe, etc) indicating whether Open Firmware has found BootX or had problems, or is looking for BootX over the network. See KB 58042
  • device drivers are loaded from a previously built cache, or from** System/Library/Extensions** if cache is missing/corrupt


  • the kernel file is mach_kernel
  • the kernel launches I/O kit, which loads drivers for I/O devices
  • the kernel launches launchd – similar to init in Linux


  • launchd manages both system and user daemons, and is configured using plist (xml) files. It also replaces the functionality of **crond **on Linux systems ie it can be used to periodically launch daemons
  • these locations are searched:
    • /System/Library/LaunchAgents
    • /System/Library/LaunchDaemons
    • /Library/LaunchDaemons
    • /Library/LaunchAgents
    • ~/Library/LaunchAgents
  • during Safe Boot (Shift key), only items in /System/Library are started
  • launchd then runs any scripts in **/etc/rc **– one of which is **SystemStarter **, which starts items in **/System/Library/StartupItems **and **/Library/StartupItems **(below)
  • launchd then starts loginwindow

Startup Scripts, Startup Items

  • items here are being replaced by launchd
  • **/System/Library/StartupItems **– when troubleshooting, rename rather than delete things from here
  • */Library/StartupItems **– can use this to for example manually map a drive. When troubleshooting, this should *usually be empty – move items to Desktop rather than deleting


User Environment Setup

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