Will not boot into Safe Mode

Thanks Badger!

you're awesome

Thank you laughing_badger

For me too this was very instructive

alright, so if I understand, the following sequence should also work:

cd /sbin

sudo mv fsck_hfs fsck_hfs_orig

sudo cp -p /usr/bin/true fsck_hfs

nvram boot-args="-x -v"

reboot, log in

sudo nvram boot-args=""

reboot

cd /sbin

sudo mv fsck_hfs_orig fsck_hfs

Just in case: changing the boot-args is not strictly necessary to make your computer go through the safe boot process.

You could omit the 'nvram boot-args="-x -v"' command, restart your Mac and hold down any shift key until the safe boot process starts.

Note that with the 'fsck_hfs' command taken out of the picture, the safe boot process can finish very quickly, and you may not even see the grey progress bar which is normally a sign that a safe boot is underway.

Olaf Barthel wrote:

Note that with the 'fsck_hfs' command taken out of the picture, the safe boot process can finish very quickly, and you may not even see the grey progress bar which is normally a sign that a safe boot is underway.

This is useful to know because, yes, the boot process finishes very quickly and there is no really obvious way to know you're in safe mode.

I tried again with a new DIMM. If I have the 8 RAM slots in my MacPro 5.1 populated I can't start in safe mode because the boot process gets stuck at "checking extranded attributes file". If I remove on of the DIMM, I can safe boot without problems.

I can't understand it.

If your Mac is set up to require that you enter a password before you can use it, there will be a message in the top right corner of the login screen (in red) to notify you that safe boot is in effect.

I do not know if there is any similar hint message visible if your Mac is set up to log you in automatically.

Truth be told, I triggered safe boot three times in a row before I noticed the message and realized that the first attempt was successful after all.

My guess is that there is a bug in the code for fsck_hfs that is only triggered with large amounts of memory available, and in the specific memory layout that occurs in safe boot. The next step would be to get a debuggable version of the code and have the safe boot process drop into the debugger before it does the disk check. More work than I have the time to go into at present, sadly.

Many thanks badger on the great workaround for fsck. Works like a charm. You'd think a "safe" boot should be safer.

(Sadly, it didn't end up curing my mdimport / lsboxd bug that I have been trying to cure by doing a safe boot to begin with, but it was good to know how to get it to work.)

Fwiw, if it makes things easier for anyone, to make "true", all you need is this one line of code:

int main(){}

If you save that as true.c, compile it like this:

clang -o true true.c

(Clang knows to have the program return 0 by default. The import and the arguments to main aren't needed.)

It is simple enough if you have the software development tools installed 😉

Simpler still is just copying the existing "true" command from "/usr/bin/true", like so:

sudo cp -pn /usr/bin/true fsck_hfs

The "-pn" options make sure that the access rights to the command are preserved and that no existing file is overwritten (you need to move the original "fsck_hfs" command out of the way before you can plug in the dummy replacement).

In January I wrote:

> I may have a workaround but it's too early to disclose.

About the OS X Mountain Lion v10.8.3 Update does not mention safe boot, but safe boot began working for me whilst I tested a pre-release build of the update.

To any user of OS X 10.8.2 who can not boot in safe mode, please:

1) update to 10.8.3

2) let us know whether 10.8.3 resolves the bug for you.

If not resolved by 10.8.3, I'll offer my workaround.

Hello Graham,

unfortunately the released v.10.8.3 didn't solve this safe boot issue

Hi Graham, No progress for me either on 10.8.3. Stalls at the same step.

Hi Graham,

Seem here, installed 10.8.3, but safe boot still stalls.

This is my first post in this thread, but I'm experiencing the same problem. I just updated to 10.8.3, tried a Safe Mode boot, and it failed the same way: the progress bar got to a little over 25 percent and just stopped. The gear kept spinning, but the progress bar wouldn't move.

I have a stock late-2012 21.5-inch iMac, 2.9 GHz Intel Core i5, that has 8 GB of factory-installed 1600 MHz DDR3 RAM.

I just got this computer at the end of January of this year. I've been on the phone for hours with two different Mac techs over the past two days trying to solve this. Neither seemed to have a clue about this thread and the fact that the issue isn't just isolated to my computer. I've been put through:

• Zapping PRAM
• Booting to the backup volume and using Disk Utility to verify the disk and verify and repair permissions
• Booting in "verbose" mode (though doing nothing else or telling anybody what it said)
• Reinstalling Mountain Lion
• Running Apple Hardware Test (holding down "D" key at startup), basic and extended

Neither Disk Utility nor the Apple Hardware Test found anything wrong.

Now one of the techs wants me to wipe my hard drive and do a clean install, then an incremental backup from Time Machine—which could take the rest of my life. Ha! Not a chance. I've already seen in some related threads where others have gone through a clean install and gotten nowhere.

Apple needs to speak up about this issue, and clue their techs in. There can't possibly be this many people experiencing the same problem without it being something very fundamental to the OS.

UPDATE: I apologize for posting about an iMac in a MacBook Pro forum. I found this thread with a Google search, and didn't realize where I was until I had posted. Given that this is about the exact same issue on a Mac, though—unable to boot in Safe Mode—I hope it has some relevance. I believe this is independent of the specific type of Mac involved.

Message was edited by: Marie Avante