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My macbook is currently a brick. I added a /etc/launchctl.conf file that must be malformed. The OS now crashes even when attempting to start in safe mode:

"launchd System bootstrapper has crashed: Seg fault"

I tried booting from a 10.6 boot CD but it just spun and spun. I have been able to boot an Ubuntu Live CD and mount the mac partition, but the hfsplus partition is always mounted read-only.

There must be an Apple utility I can use to get to a live terminal and delete this single file that is preventing my laptop from booting? If I can get the OSX install CD to boot will there be a utility that can help me?

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One thing that I might try is using the OSX boot disk to run diskutil, which I think can disable journaling. Then from what I have read Linux should be able to mount the drive as writable. –  Jeremy Mullin May 19 '11 at 19:27
    
Single user mode was the solution. I had tried Safe Mode earlier and when that didn't work I gave up on boot tricks thinking it was the lowest level I could boot in to. Thanks again Michael! –  Jeremy Mullin May 19 '11 at 19:47

3 Answers 3

up vote 7 down vote accepted

You can boot into single user mode by holding Command + s at startup.

Single user mode starts you directly at the console, bypassing core Mac OS X startup processes. You should be able to remove or alter the offending file from there.

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Thanks, that got me close, then "mount -o update /" to make the mount writable was the final step! –  Jeremy Mullin May 19 '11 at 19:37

Don't forget there's always Target Disk Mode, too. Start the Mac and hold down T until a Firewire icon appears - you now have the world's most expensive external hard drive. :) Plug into another Mac (or a Windows PC, maybe?) and you can access the hard drive on the machine in Target Disk Mode.

(Note that this doesn't work on Macs without Firewire. Mac Book Air users, you're bang out of luck.)

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Cool! I imagine at least some drivers have to load for this to work, though? –  Jeremy Mullin May 19 '11 at 20:17
    
Not sure about drivers, but the OS doesn't load so your changes to /etc/launchctl.conf won't get the chance to break anything. –  Simon Whitaker May 19 '11 at 20:22

Start in single-user mode (like that other guy said). It'll say "If you wish to make modifications to files:" and give you two lines of commands. Type the second one, or type the first one for a File System Check, then press Enter. Then, if you want to delete a file (let's call it "brokenfile"), type (without quotes): "rm brokenfile", then press Enter.

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