Yosemite: boot hangs at 50% percent

Yea I've done the reinstall 4 times and it'll work for a few days or even a week or more but eventually I run into problems again at least on my machine. Now, after reinstalling Yosemite os from recovery mode and a bunch of Time machine backup restores finally the boot doesn't hang at 50 anymore but I have a bunch of i/o errors and the spinning pinwheel of death. again IM not an apple tech so idk how to do the suggestion about going in and entering codes and stuff. I'm not bad at some of this stuff but I'm really not sure what in doing in terminal so I dont mess with it. Maybe that's what it'll take though? And if so apple should help us with a walk-through if that is something that's now necessary with this new os.

as mentioned before I think I need a new drive and I'm honestly hoping this will fix the issue as really nothing else mentioned above has worked...

I work at a School District and had a bunch of 20 inch 2009 iMacs with 10.10.1 installed from an image. Occasionally, 1/3 of them would exhibit the 50% boot (daily) and PRAM reset might work but not all the time. I sent the >>>>> bless --device /dev/disk2s1 --setBoot out via ARD to all it it worked great. All now restart normally. Keep in mind that the "disk2s1" part of the command was found through terminal beforehand... your name may be different.

Thanks for the advice!

Well, after all of that, I've now got a brand new upgraded drive in and everything is running superbly. Aside for the occasional normal spinning wheel as an application opens there are NO issues. I've restarted a few times since this new drive has been the primary installed os (or course with a clean slate of Yosemite installed) and the boot is actually faster than it ever was and didn't hang at all. I checked the Logs as well and actually with the old disc it would hang even trying to click on system log before it would even bring up a word. With this new WD drive in it doesn't even blink. I also tried running one of my more drive intensive programs and so far not even a glitch. I was probably due for a new disk and at least on my end my hanging issues (especially during boot) were most likely caused by bad sectors, yada yada yada...

Best of luck to the rest trying to figure this out. So far for me this looks like the fix. Tried everything else.

I did reinstall the iOS three times and still get stuck at 50%

i can't boot in safe mode either.

I Can't log on my WiFi I can only use Ethernet cable to reinstall the Yosemit.

Anything else I tried would not work

I have a late 2008 MacBookPro...

This worked for me. Thank you!

Ok, since installing the new hard drive and restoring from time machine backup I've had absolutely NO issues at all. The boot loads normally and no spinning pinwheel of deaths! Been checking the logs and haven't seen anything at all out of the ordinary. With the old drive I was seeing I/O errors all over the place when I was even able to open console (sometimes it would freeze). The moral of the story is that the drive was well over 5 years old (was really not big enough for my purposes anyway) and probably had countless bad sectors! Pair this with the intense upgrade to Yosemite as was mentioned above and the drive finally started kicking in the bucket. Fortunately all things consider it's a pretty cheap fix and now my Mac is running better than ever. Of course the second I see it hang on boot I'll be back here to update but until then I'll enjoy my nicely working late 2008 macbook running the latest Yosemite OS smoothly!

This worked... https://www.afp548.com/2015/01/14/when-yosemite-has-fallen-and-it-cant-get-up/

Hi L1C,

I just got it fixed with apple support.

He made me shut off the computer and turn it vack on and the bar would still freeze. Then he asked me if anything else was plugged to the computer through USB. I unplugged my DVD player and printer and everything was fine within seconds!

Hope this helps!!!

Upgraded three systems, 50% hang on one. Power off, wait, power on fixed it. In this case it seemed like it hung on final reboot. Six pages on this topic, plot other threads, suggests an intermittent bug -- not sufficiently tested prior to release?

My Mac mini exhibited exactly this problem - but I am posting because it turned out to be completely different, as did resolution.

I was using torrent app Transmission so in other words a large file was being written to my home-brew Fusion drive in a 2012 Mac mini. Transmission hung, and I restarted - and got the Yosemite hang as above. Symptoms were exactly as above (and I have the Samsung 840 SSD). Unfortunately, I could not boot in Safe Mode at all. I could get into Target Disk mode so took all the stuff off it I needed. I could also get to Recovery Mode OK and from that Disk Utility. Disk Utility could not do anything with the home-brew Fusion but I noticed that it was reporting the SSD was fine; it was the Apple HDD that had errors it couldn't fix, and by extension it could not fix the single logical drive. But, I also couldn't erase the drive (or install a fresh copy of Yosemite), and was wondering if I was going to have to take out the SSD (or at least disconnect it) and start again. (Sidebar: my Mac mini is out of warranty but adding the SSD voided it anyway; to get Apple to look at it in the worst-case scenario the SSD would need to be removed.)

But, I found this advice:

http://www.macworld.com/article/2015664/how-to-split-up-a-fusion-drive.html

Caution - this is destructive - i.e. it erases all data! Note also the bit about Target Disk mode and taking all the stuff off it!

Once I had done this (in Terminal, from cmnd-R Recovery Mode - Terminal is invoked from the menu bar) I went to Disk Utility which had flagged the two drives in red, like they were disassociated parts of a Fusion drive, and it offered to fix it, i.e. recombine them. (This erases them again but at this stage they are already erased so it should be academic.)

From that, I could do a Time Machine restore.

So, the upshot is:

If the advice about TRIM isn't working for you, it might be something else altogether.

Splitting up and recombining the logical Fusion drive worked for me. It is however a completely destructive process but my own experience is that Target Disk Mode works so if you do not have a back-up you are comfortable with check that first. A Time Machine restore is also very slow.

I am wondering about TRIM as I would appear to be front-and-center of the people likely to be affected by it, but Yosemite was until this working just fine for me, and it is again.

I hope this is of help to someone pulling their hair out because the advice above wasn't helping.

Currently facing the same problem. Downloaded Yosemite 10.10.1 and restarted. Comes the installation and it freezes and 50%. It's been 3 days. Still no fix. Resetted PRAM, called Apple Support, rebooted. No fix whatsoever. Might have to reinstall to 10.10.

Did you try the steps from https://www.afp548.com/2015/01/14/when-yosemite-has-fallen-and-it-cant-get-up/?

That seems to resolve the issue. It happens mostly when the MacBook runs out of battery power... and then hangs on power restart.

I had the same problem on a 2008 desktop iMac (no SSD) and solved it by rebooting into Safe mode, resetting the NVRAM, repairing disk permissions and rebooting again normally. Thanks for the solution!

I am close to a solution, I can taste it.

Try changing your background wallpaper to the plain blue that comes with mac. Do not use your own.

I suspect I will have some sceptical people so lets take you on my journey.

I've had random crashes since November last year with my iMac 27" Late 2013.

This is what I have tried in order:

- Restore from time machine. This bought me max 1 day of good but not okay performance

- Restore from internet - this never worked. Kept crashing on Essentials.pkg error

- Finally did a from USB install 4 days ago.

-- STILL had crashes

- I then Found WiFriedX which basically turns off awdl0 interface (Airdrop and Handoff)

- And got rid of custom desktop wallpaper.

-- THIS WORKED FOR 48hrs no crashes

- NOW I AM TRYING MY WALLPAPER THEORY - 3 hours and counting.

-- Re-enabled awdl0 and stopped WiFriedX - ONLY have the plain desktop.

Things seem okay. The true test will be a 24 - 48hour no boot AND a unplug power without shutting down.

11 hours... and going strong