While performing Yosemite update this evening get a Circle with line thru it

Mac OS X- Gray screen or prohibitory sign appears during startup

I had the same thing. I could not get my computer to boot up into OS X or in Safe mode. My only option was Recovery mode. I did a "verify disk" check and realized my HD was corrupted. I had to re-install OS X Lion and lost all of my data. I was able to install Yosemite but only after I lost everything.....

I have two Macs , Macbook Air and iMac 27" .

Both had the same problem when trying to upgrade from OSX 10.9.6 to Yosemite. Install started fine and then when it rebooted to continue the install, I got a black screen with a kernal error.

The way i was able to solve the problem was to create a bootable USB memory stick install for Yosemite on another Mac computer, then hold down the option key while booting the crashed install mac with the USB Yosemite install connected. A menu will appear allowing you to run the Yosemite install from the USB. The install completed and I lost no data and the upgrade completed.

You can view instructions to create the USB install here: http://osxdaily.com/2014/10/16/make-os-x-yosemite-boot-install-drive/

I had the same thing happen to me while doing a clean install from a USB stick. After the install failed the boot menu didn't even see either partition on the hard drive and booting from the USB stick again resulted in the circle with line through it. After a PRAM reset I was able to boot off the USB stick and the install resumed and completed successfully.

Apple stinks these guys need to get back to basics. I have upgraded my Macbook Air , iMac and Macbook Pro to Yosemite. It seems to work okay on my iMac and macbook air but on my recently purchased macbook pro which had been very stable it now will not boot up or if it does that b???dy apple logo spins and internet connection keeps dropping out or cannot get connection when I know my internet is working cause my iPhones and iPad and other macs all connecting. I moved to Apple 4 years ago but ready to dump the lot more frustrating than windows systems GET REAL GUYS back to basics.

I cannot see any reason why macbook pro is freezing and drops connection and will then not reconnect.

This sounds like what was happening to my wife's MBP which was upgraded from Mountain Lion to Yosemite. I reformatted the drive and performed a clean install and no longer have any problems with freezing or network connections.

I created an Account just to talk about this mess. I had no DISK. Luckily I had An External Time Capsule. I started it up and eld down COMMAND, letter "R" and rebooted to Utilities. First option I tried was Re-Install Yosemite after 6-8 hours . WRONG. Re-booted again held down Command, with R , this time I decided on the capsule route and re-installed 2 days earlier. And after waiting another 6-8 hours to a total of approximately 12+ Hours.FIXED.

YOSEMITE OS IS THE BIGGEST WASTE, YOU DIDNT DO ANYTHING WRONG WITH YOUR COMPUTER, APPLE DID, SO THEY NEED TO STEP UP AND FIX THIER PROBLEMS BEFORE THEY CELEBRATE.

We are getting the prohibitory signs with 85 macbook pros during Yosmite OSX upgrade in the company, and we are about to lose more.

The next day our company CEO had arranged a meeting with our IT department to discuss about shifting to alternative system.

We are in deep

<Edited by Host>

Thank you,

your solution saved the day.. 21 out of 85 mac books pro are working now.

Apple should hire you for technical support.

Works perfectly.

got my Mac Pro up and running again.

I would be remise if I didn't post my solution to this issue which I toiled with for over 4 days. I too got this got this circle with a line through it after the first install, the second install after a restore from my Time Machine, the third install after I installed clean then tried to migrate my data from time capsule, and finally my fourth install after installing from a USB follow by a migration. Each of this took about 14 hours a piece as I have close to 1TB of data (gotta get rid of some stuff).

Finally I was convinced I could boot in SAFE mode, but even that didn't work but I was able to boot in Verbose mode(command-V). While watching it boot up I noticed an error that lead me to my final solution. I can't remember it exactly but it said something about PGPwde whole drive encryption. After racking my brain I finally remember I had installed PGP tools or something like that. I booted into recovery mode (command-R). Pulled up the console and followed these steps to remove PGP manually.

http://kb.mit.edu/confluence/display/istcontrib/Manually+Removing+PGP+Desktop+fr om+Mac+OS+X

Keep in mind I had to find my data under the Volumes directory of the root drive. So instead of /Library it was /Volumes/<name of your hard drive>/Library. If the drive is not there you might have to mount it, but there are plenty of references on the internet on how to do this.

This did the trick and after a restart Yosemite came right up. Not sure if this is exactly the fix for everyone, but if you book in Verbose mode(Command-V) I would bet you will see whatever culprit is causing the issue.

Hope someone finds this useful.

Haven't been able to install Yosemite on 2 different new15" rMBPs, both stock and the Fall 2014 refresh. Can't upgrade from Mavericks, can't install clean from flash drive or SD card. Ends in kernel panic loops and eventually the prohibitory circle symbol. First rMBP was replaced by Genius Bar earlier this week thinking it was a bad SSD, but the new one does exactly the same thing. Luckily I was able to restore from Time Machine back to Mavericks but wow the QA was garbage on this release.

FWIW Yosemite runs perfect and hasn't crashed once on my 2012 MBA and 2011 iMac. Search around here and you'll find consistent issues with installing Yosemite on newer MBPs. *frustrated*

ArcherClark's advice on removing PGP worked for me - I could see my macbook air hang on PGPwde when booting in verbose mode. Unfortunately, I had deleted (but not uninstalled) pgp from OS X Mavericks, so the remaining bits of it caused Yosemite to hang. I had to do a clean install of Yosemite, then add everything EXCEPT applications (accounts, settings, etc) from my time machine backup using migration assistant. After rebooting, I then installed all of the applications from the time machine backup using migration assistant. Re-booting at this point causes the circle with the line boot failure, but if you don't re-boot you can work with all of your applications. I installed a new copy of PGP at this point and then uninstalled it. Yosemite works now. Thanks ArcherClark!

ArcherClark, you sir, are a veritable GD genius. Worked for me too. Thanks for saving me countless hours.

FINALLY FOUND A SOLUTION THAT WORKS!

I never have made a response on here before but i absolutely had to! I had this error and was so worried about loosing all of my data and am so grateful I found the solution after hours of trying everything. The simple solution is as you boot your computer hold "Command" and "r" at the same time.