upon on turning on my MacBook, after putting in my login password, my MacBook doesn't log in. Instead, I get a progress bar that eventually turns to a circle/slash prohibited symbol. Would like to know why this happened and how to fix it.
Yes, OS X Yosemit. Grey screen, with prohibitory sign after attempting to log in.
This just happened to me and I'd like to share my fix which was ultimately very simple - if the following applies to you:
I have a 2010 Macbook Pro with a replaced drive - Samsung 840 Pro SSD. I use a program called Trim Enabler by Cindori. Turns out that to be able to use this program it has to reset some settings within Yosemite that are stored in NVRAM/PRAM. So if you are pounding away trying to fix some problems with your Mac & default to the old "Reset Your PRAM!" then you will inadvertently reset the kext-signing setting and will be greeted with the gray screen circle slash.
I'm including the info below for further details.
To fix - I just created a boot drive of Yosemite on a USB stick and reinstalled - didn't lose any files etc. - everything seems back to normal - got the notice that I have to activate my Trim again - and the warning about the kext-signing - I was very relieved it wasn't a hardware, or even a software issue for that matter.
I couldn't find any info about this in any of the boards - or on any websites. I'm definitely not a programmer or solid tech so maybe I didn't know what to ask in Google. In any case - I hope this helps someone!
Details from Cindori:
About Trim in Yosemite
In OS X 10.10 (Yosemite), Apple has introduced a new security requirement called kext signing. (A kext is a kernel extension, or a driver, in Mac OS X)
Kext signing basically works by checking if all the drivers in the system are unaltered by a third party, or approved by Apple. If they have been modified, Yosemite will no longer load the driver. This is a means of enforcing security, but also a way for Apple to control what hardware that third party developers can release OS X support for.
Since Trim Enabler works by unlocking the Trim driver for 3rd party SSD’s, this security setting prevents Trim Enabler to enable Trim on Yosemite.
To continue to use Trim Enabler and continue to get Trim for your third party SSD, you first need to disable the kext signing security setting.
It is important to note that the kext-signing setting is global, if you disable it you should be careful to only install system drivers from sources that you trust.
Trim Enabler support
Trim Enabler 3.3 will disable the kext-signing setting automatically for you, by giving a choice when you flip the switch.
By clicking Proceed, your computer will reboot with kext-signing disabled. You can then flip the switch again to enable Trim.
When you flip the switch back to Off, Trim Enabler will ask you if you want to restore the kext-signing setting back to normal.
Important issues
The kext-signing setting is stored in your Mac’s NVRAM/PRAM, a sort of flash memory inside your Mac. This memory can be reset either by accident or by intention (usually by troubleshooting issues with your hardware), causing kext-signing setting to re-activate.
If you try to boot a Trim-enabled system with the kext-signing setting re-activated, you will be met by a gray screen with a stop sign:
This is your system telling you that a driver has been modified, and is not allowed to load.
To avoid this situation, you can make sure to disable Trim before performing any hardware maintenance or PRAM reset on your Mac.
Prohibited sign at login. How do I fix this?
