Well, atleast it solved the 50% boot screen on our macbook pro 2012 with the 10.10.3 update (was a pain with 10.10.1). Yet to test the mac minis but will update here if it works.

10.10.3 seems to have potentially fixed the problem on the small handful we've tested it on.

We're slowly increasing the update scope each night, and there’s nothing out of the ordinary so far.

We'll be smacking this on 700+ machines soon, so time will tell...

@Abdiaziz No I have not tested a clean 10.10.3 image yet. Creating the AutoDMG image is on my list for today/tomorrow :-)
My iMacs are late 2013 imaged with 10.10.2 then upgraded using the AppStore/Software Update.

Roughly 200+ machines in my environment updated via App Store and have reported it has sped up log in, and no more reports of getting stuck at 50%. All Macs are bound to AD with mobile accounts created and UNC path unchecked.

For the few people reporting that they are still having the boot up problem. Have you tested the latest supplemental update? Has it cleared up any of your problems?

Isn't the supplement update is meant for video issue for movie capturing? I assume it's not really an update for the boot screen issue. But then still have to see others response on this.
Though 10.10.3 actually solved my boot screen issue.

A few of my users are experiencing a black screen after updating to 10.10.3 via software update. Though the issue doesn't seem to appear when computers are re-imaged to 10.10.3. Anyone else seeing this?

I have seen the black screen as well. Had three MacBook Airs so far come in with that issue. I ended up replacing the logic boards on them, they were under warranty. I tried various things to reset them to no avail. I'd like to know why this is happening also myself.

The core issue for this is resolved in 10.10.3. I would like to suggest we open a new thread for new issues, even if the symptom appears to be somewhat like this one. Anyone know how to flag a moderator to lock a thread?

@chris.hotte I don't think it has. I contacted AppleCare and they acknowledged that it hasn't been completely fixed in 10.10.3. I have also forwarded the information to my Apple Senior Engineer for my University.
I think there may have been several issues causing the same "visible effect" but no, it is not fixed for everyone.

Okay.

We have just less than 3000 10.10.3 workstations with Active Directory Enabled. I have no more reports of this particular boot issue. New random ones surfaced as a result of the upgrade. But that's the point I'm making, and I would not speak of them here in order to keep the thread on topic.

@chris.hotte That's awesome. I have a lab of 37 iMacs and 160 mixed MacBook Pros and Airs that have been testing Yosemite and have had nothing but problems. The rest of our labs are still on Mavericks. I would love to be in your position with all our labs on Yosemite but at this point, I don't know if that is going to happen.

In the interests of frustrated googlers arriving here with non AD related issues exhibiting the same symptom (boot progress bar stopping at 50%), I recommend making sure you have no unsigned kernel extensions as per this earlier post:

https://jamfnation.jamfsoftware.com/discussion.html?id=12589#responseChild73238

Many thanks mpebley for the lead!

My issues stemmed from using Migration Assistant to migrate applications from a late 2012 Macbook Pro - in hindsight it's now obvious that it would have imported a host of unsigned drivers.

That said, I still can't quite believe that Apple did not test for and close off the possibility of injecting breaking drivers through the use of one of their core consumer migration tools.

This vulnerability has to be a massive sleeper tech support issue for them.

I have a very small network, but it has been crippled by the Yosemite Installation issue.

Described the problem in the Apple forums:

Yosemite will not start after installation over Mavericks. After installation, narrow progress bar runs with Apple logo above it, the system load process stalls and the logo changes to a circle with a diagonal bar across it similar to a "do not enter sign." Nothing happens after that .

Booting into SAFE MODE yeilds the exact same result. Holding down the OPTION key shows a Yosemite system installed on the proper partition, but choosing it and starting the system again yields the same result.

Holding COMMAND & S to boot into single user mode to run a fsck -fy scan stalls with a message that says it is waiting for the root system. The result is the same after a few seconds; the screen reverts to the light gray with the circle and the diagonal bar.

The attache picture shows the exact spot in the boot into single user mode that the process stalls.
I can boot into the RECOVERY Mode, run Disk Utilities, but disk and file structure is fine. I repaired permissions, but restarting from there yields the same result.

Resetting PRAM doesn't help, and reinstalling Yosemite doesn't help either.

I have a massive number of design applications and the serial numbers are stored in secure notes in my key chain.

I arrived at this predicament after having my certificates corrupted by the April 16th Security Update and after speaking with a senior Apple tech who related that upgrading to Yosemite would solve that problem by installing all new certificates.

So, after meticulous backups to a Time Capsule, disk utility scans and permission repairs, I attempted the Yosemite upgrade. The above is what happened, and the Time Machine backup to the Time Capsule is not available because after the upgrade my regular password credentials were no longer recognized.

I certainly do not have the skills that I've seen displayed here, but I am hoping that someone can give me a not too technical fix with some instructions on how to implement it.

I also work for a law firm and manage their Windows network, but we have a new case that needs research and I do that at my home Mac office.

Please help, and thanks in advance for any assistance.

Vincent

Bumping this thread in case anyone has found that 10.10.4 has addressed this issue?

Hi @yr_joelbruner

This issue was addressed in 10.10.3 for most of the sites we've been working with.

Are you talking about the 50% boot hang? The last thread before yours refers to a prohibitory sign which is a different problem.

@davidacland Yes the 50% boot bug...
Have been very cautious; clearing boot caches from single user mode doesn't scale well :]

It seems to have been working ok from 10.10.3 on the sites we've deployed it. That being said, we've only deployed it where we've had no choice. 10.10 has been a bit of a disaster from our perspective.

@yr_joelbruner I don't know what was special about my environment but the 10.10.3 update did NOT fix the boot issues, HOWEVER a clean 10.10.3 install did. Don't know why but that was my experience. Fortunately, I was able to just make a clean image and redeploy after I figured that out. Haven't had any problems since.

@jrippy did you deploy the combo update or the other one?

@nessts I did not deploy the combo update. I had a Casper Policy simply run Apple Software Update. I thought about the combo update just to see if it worked, but for the environment (thankfully all lab machines), it was easier just to go ahead and generate the new image and redeploy.

In my opinion never run the regular update, I think many others will echo that sentiment. I always push the combo update out. Of course that takes more effort because you have to deploy it somewhat manually, and there were problems getting reboots to work etc, but it solved the 50% boot thing, in my environment.

We generally weigh in the combo vs delta update depending on the size difference. Low numbered combo updates are generally smaller. Best to always test them thoroughly before a full deployment to production. We test a few rows of machines for a week if possible - to see what surfaces and then to a site, then to all sites. Well... that's what we should do. :)

Has anyone seen this pop up again (regress) with the 10.10.4 or 10.10.5 updates?
I'm running into again and I'm not sure which update caused it. The previous fixes are again temporary at best.

Yes, we're seeing it happen a bit again (though not quite as much as before) since we started updating clients to 10.10.5. I fear this particular bug has resurfaced again. It was fixed as of 10.10.3 but now we are seeing it again. Ugh..nothing like reintroducing previously fixed bugs, eh? Thanks Apple!