Mac OS X 10.5.5: system becomes stuck in a continuous reboot

As has been the case with several other iterative Mac OS X updates, some users have reported an issue in which the system continuously and autonomously restarts after the Mac OS X 10.5.5 update.

Apple Discussions poster Big D! writes:

"I recently ran the 10.5.5 system update on my iBook G4. However, when my laptop rebooted after the install it got to the gray screen with he spinning wheel, then it sat there for a while then it rebooted itself, now it's doing that in an endless loop. I can't boot into safe mode, or single user mode."

This issue can also occur when users attempt to manually modify system files (for instance, creating or editing launch daemons). When users perform these modifications, they most often simply modify permissions on files and folders to allow access. However, it is very possible that a simple permissions change could cause the continuous reboot issue.

When computers are stuck at boot, the initial recommended steps are to try booting into safe mode and performing simple procedures such as resetting the PRAM and PMU. However, in many cases the system does not properly load into Safe Mode before resetting or hanging. Some users have had success getting to single-user mode, but even then they may not have a clue as to what specifically is causing the problem. While minor edits can be reversed in single-user mode, an improperly applied update may be too complex of a problem to be fixable in this situation.

Given that this problem can be caused by changing permissions on a few system files, users have tried booting from the Mac OS X DVD and running a permissions fix. While this may work, its success dependent on files being in the permissions database so OS X can check them and fix them if necessary. If files are not in this database, then this fix will not work.

Unfortunately, unless the specific files causing the problem can be found, users will have to roll back to a previous system state, either with a Time Machine backup, or by reinstalling Mac OS X

Fixes

Revert to a recent system backup With Time Machine, users will be able to boot off the Leopard DVD and from the "Utilities" menu, select the "Restore System From Backup..." option. This will allow users to select the most recent functional backup from the Time Machine drive and restore the computer.

Perform an Archive and Install If users do not have a recent backup of the system, it is recommended that users perform a reinstallation of OS X using the "Archive and Install" method, outlined in this Apple support article (http://support.apple.com/kb/HT1710).

Preventive Measures To ensure the probability of these issues is at a minimum, especially for users who are just applying official patches from Apple, it is recommended to follow these steps.

• Before the update run Disk Utility and perform both a permissions fix and a hard drive repair
• Download standalone updates from Apple's download page
• Reboot the system into Safe Mode by holding shift at bootup
• Apply the updates when in Safe Mode
• Reboot the computer

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