Yosemite: boot hangs at 50% percent

My iMac late 2013 crash again.

It would appear that it is a faulty hard drive. And because it is enclosed and not user serviceable I was unable to replace it for now (some ifixit research necessary)

In the meantime I am running my iMac with an external WD MyPassport 2TB. It has not crashed, I did not have to turn anything off... it just works.

I found an article which links to problem not to hardware failure but firmware which parks the heads of the internal drive too aggressively conflicting with Yosemite. Apple does not have a firmware upgrade for its hard drives since 2011.

The fix for this is safe boot, login to a user account, restart. Has worked for me on 100+ Mac's of all models.

Many thanks DlavVal, the following command saved my day!

bless --device /dev/disk2s1 --setBoot

Steps:

reboot machine - hold down the magic keys (cmd+alt+P+R) and go to the terminal window in the resulting trouble shooting program that comes up

(Terminal)

mount

bless --device /dev/disk2s1 --setBoot

(although in my case the disk was called /dev/disk1s2)

Restart machine

My Macbook is stuck at 50%, and it just won't start up. Many of these posts talk about restarting it in SafeMode but I'm not sure yet. This is urgent; any advice is appreciated. I'm on OS X Yosemite.

Did you lose any files in this process?

I was having an issue where a few of our machines were having this issue, most of them I could resolve with varying combinations of PRAM resets, safe boot, single user mode, etc.

One though gave me a lot of trouble until I turned auto-login off (in safe mode). Once I did that and rebooted, it came back up. However, most of my hair is now gone.

My problem is bigger, my children erase the recovery partition, so there is no way to recover the OSX.

So when installing original DVD/USB from scratch I have the same problem! The scroll bar stop at 50% installation.

Also I reboot in safe mode, I reset the nvram, reset all no way.

Thank you in advance!.

Nelson MAcbook air 6,2. Please help me!.

We've issue with Macs hanging on boot with number of iMacs in the office.

WHat works for us is bootting them into verbose mode (Cmd+V on boot). After about 2-3 minutes system loggs in.

Now you can reboot it as normal and startup in normal mode without hanging half way through.

Hope this helps you too!

I try that too, verbose, single user mode. Nopes. Downloading to mavericks, previus Lion Snow installation, migration......Guess is a bug with OSX Yosemite installer . Another forums said press N al startup (netboot start) but it don't work. , Macbook6,2 I5, intel graphics. thank U.

perhaps upgrading bios correct the problem, but i'm only guessing and leaning about MAC as never before!

I used:

Our school also uses Active Directory and here's what we have confirmed:

1. The hang occurs only after the power is cut (either by pulling the plug or holding the power button) AND an Active Directory user has logged in since the last boot.

2. Booting to Single User mode (cmd-S), typing exit, powering off and back allows the machine to boot again.

3. The log files don't seem to show much since the machine is hanging during boot and therefore not showing what it's hanging on.

and that finally worked.

I can also confirm its related to AD.

What I did was create mobile accounts for users on macs who requires it, and unbined macs from AD. Workes like a charm, and will remain until fix is ready.

Also the good news is, that from our preliminary tests it looks like issue is resolved to certain extend in public 10.10.3 beta. It still takes a little while to boot up after unclean reboot, but it does boot up 🙂

Dan.

Old Toad, what would we do without you??? Once again, your advice was spot-on and fixed my problem instantly. Here's hoping you never leave the Apple Support Communities -- I can't tell you how many times you've helped me. I should just start searching for your posts from the get go!

Problem: Recent install of Yosemite hangs as described at 50% upon boot. In addition, system hangs occur after the machine has been idle for "some time" causing the need for a re-boot.

Partial Solutions: Performed PRAM zaps as suggested by other users, and then was able to boot in SAFE mode some of the time. Other times, even SAFE mode would not reboot.

Solution: Boot into Recovery mode as suggest by Old Toad, repair disk and permissions. Machine boots smoothly.

Will update if the hangs / need for reboot come back...

I upgraded to Yosemite some weeks ago on a room full of iMacs that were not on AD and all has been well. I later upgraded a room full of iMacs recently on AD and I started getting the hang on 50% boot problem!!!

I think that the boot problem occurs after a hard reset! If the iMacs are on full sleep mode in Energy Saver the students see a blank screen and think the iMac is turned off and so go to turn it and and do hard reset instead! I have turned screen saver to come on after 5 mins. Now they can see they are switched on, they don't try to boot up!

This boot problem on AD may be something to do with multiple profiles on the Macs!

The work around I use is boot in safe mode, repair disk permissions and re boot!

Boot into Single User mode

Type Reboot to exit

Immediately boot into Safe Mode

Restart at login screen

These are the steps that worked for me. I couldn't boot into safe mode until I tried Single User mode first. This is a AD managed machine as well.

I've been following this discussion and tried everything without success, I can in some cases get the machine to start in safe boot, sometimes not.

The build having this issue has never been bound to AD. Tried all possible ways with upgrading to 10.10.3 without success, did a recovery, that is installing a fresh 10.10.3 on top, no show...

Luckily, I have a working older build backed up via DeployStudio, so I will continue using this one, patching and adding features to see if the problem occurs again.

Really frustrating.