I am by no means a computer wizard, so I am kind of lost on your directions. Is there a way that you can dumb it down and list step by step? Because I really need my computer to work. I have been trying to figure out how to fix it for over a week now. Would it just be easier to delete everything and start over? Or would that not fix the problem? All I know is that I was updating to the newest update but had to leave before it finished. When I came back home I kept getting the kernel panic warning and haven't been able to use my computer since.

I had a problem installing El Capitain on a 3 year old MacBook Air. Three times I tried with fresh El Capitain  installs on a reformatted internal drive. Then used El Capitain Migration Assistant to migrate stuff back from a SuperDuper created copy of the original drive. Each time the first startup attempt from the updated internal drive failed with the forbidden icon. This fix from GSfromNL fixed everything! Ensure you do this on the backup drive before you migrate it back!

Thank you so much for giving perfect, foolproof instructions on how to do this!

Char

Thanks for using Apple Support Community.

Prb

Mac Os x El Capitan will not start up after update.

Slt

1-Press and hold the power button for a few seconds until your computer turn off, then release the power button. Wait a few seconds and then press the power button to turn on your computer.

2-I previously wrote an article about how to fix Mac startup problems. Follow the tips in that article.

3-Try starting up in Safe Mode. To do this, turn on your Mac, when you hear the start up sound, press and hold the Shift key until you see the Apple logo. If your Mac can start up, the problem may be that your computer do not have enough space. Did you see any low disk space warnings before this problem? Your Mac should have at least 9 GB of free space. This article explains how to free up space on your Mac.

4-Reset NVRAM. To do that, turn off your Mac, then turn on, when you hear the start up sound, press and hold the Command-Option-P-R keys. Your computer will restart, when you hear the second startup sound release the keys.

5-Reset SMC.

6-Shut down your Mac. Remove all wired, external, non essential peripherals (such as scanners, printers etc), Then try turning on.

7-Repaid Disk. Shut down your Mac. Then turn on your Mac. Press and hold the Command (⌘) and R keys until you see a white screen with an Apple logo. Select Disk Utility then click Continue. Now select the startup volume (usually Macintosh HD) and click Repair Disk.

8-Reinstal OSX

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I Have tried every one of your suggestions multiple times with no success.

what I am especially troubled by is that since I upgraded to El Capitan, and the interminable reboots started, I have been unable to perform a Command Recovery nor boot in Safe mode.

is there a reason other than El Capitan that would cause that problem?

LeeSniper:

Most of these problems are the result of software conflicts on startup with Kernal Extensions (KEXT).

The boot up process fails to even reach the user LOGIN screen.

Moreover, boot-up into SAFE MODE does not help.

The best way to avoid this is to do a clean install of the OS X and then a migration from a backup disk.

However, if a user had already performed the upgrade, one needs to boot up from a different drive and then  manually remove the KEXTs from the non-boot system. A task of manually determining what software is causing the conflict and removing it.

In the past, Apple had run conflict checking software prior to major OS updates.

I did not see this problem until the 10.11.2 update installed much more security software. 

My clean install to a different disk without a migration of computer settings worked for me.

To do a clean install, one needs a backup first.

To LeeSniper and PJ'sPal...

All your suggestions are fine...

But, if not starting up is - ONLY - KEXT related, a clean instal is like shooting with a canon at a mosquito.

Just get rid of old KEXT stuff, remove them from the TWO libraries, System and User.

If anyone, like me, (since Lion...!) never did a clean install, you will be surprised how many old and now obsolete things are residing in these libraries.

As I wrote this in previous posts:

There are TWO ways to solve the Kext problems. One way is to do it with Terminal, the other way is to use Finder, but then you have to be able to start up by means of another bootable disk.

Method 1, by use of Terminal:

From the recovery partition you can get into Terminal, then try the following commands in Terminal to list the kexts on your internal drive, (if asked for your password give it):

Important is :

cd /Volumes/MacHD   Replace MacHD with the exact name of your harddisk.

NOTE: If there is a space in the name of your HD (for instance Mac HD) put in a BACKSLASH before the space like:  Mac\ HD

You should see that you are now on your internal disk... If not: You made a typing error, and you will remain on the recovery partition: Try again!

Then, but be VERY careful with these commands and use correct Uppercase and lowercase...! (you can copy and paste)

sudo ls -1 /Library/Extensions/ ; sudo find /System/Library/Extensions -ctime +1d -depth 2 ; sudo find /Library/Extensions -ctime +1d -depth 2

This will give you all the kexts to sort out, if you found them:

Make different locations for the not supported kexts with these commands:

sudo md ~/System/Library/KextNotSupported

sudo md ~/Library/KextNotSupported

Move all suspects to the different location with these commands:

sudo cp ~/System/Library/Extensions/EXACT KEXT NAMES  /System/Library/KextNotSupported

sudo cp ~/Library/Extensions/EXACT KEXT NAMES /Library/KextNotSupported

Delete them in original location:

sudo rm ~/System/Library/Extensions/EXACT KEXT NAMES

sudo rm ~/Library/Extensions/EXACT KEXT NAMES

Repeat for every suspected kext.

Note: replace EXACT KEXT NAMES with, for instance, EtimaAsync.kext and, again, use the EXACT Uppercase and lowercase...

Method 2, by using the Finder:

Boot from another disk or thumb drive.

Go with Finder to your internal disk,

go to  Library -> Extensions and look for old suspected kexts. If you found them, make a new folder and move them there: Important: Delete them from the Extensions folder.

Repeat this with System -> Library -> Extensions

Hope this helps!

Dear GSfromNL:

I have a MAC PRO with PCIE expansion slots and a variety of cards that I can install/uninstall for expansion.

I did a clean install with Yosemite about a year or so ago.

I did not do a clean install of El Capitan 10.11.1 and had no problems with it until upgrading to 10.11.2.

The system security improvements did not flag something it could not work with. 

Something I added, after the clean install of Yosemite, inserted a KEXT I believe is causing the problem.

My guess is an antivirus application but I have not yet really determined the issue because it could be others.

The problem is that we may not know exactly what KEXT is causing the problem.

One would assume Apple did not see this as an issue either until now or these users would not experience the problem.

We have to guess one by one and then try and reboot - a process that may take hours to complete.

Conflict Catcher used to do this for us in the old days.

My point is that the hours spent trying to fix things now and guessing at the problem, would have been better spent doing a clean install from a blank drive and migrating data/applications/users automatically overnight.

From my SSD with El Capitan that still  does not boot.

Here are my library extensions:

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/ACS6x.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/ArcMSR.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/ATTOCelerityFC8.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/ATTOExpressSASHBA2.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/ATTOExpressSASRAID2.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/BJUSBLoad.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/CalDigitHDProDrv.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/CIJUSBLoad.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/HighPointIOP.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/HighPointRR.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/hp_io_enabler_compound.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/LittleSnitch.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/PromiseSTEX.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/SoftRAID.kext/

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/SophosNetworkInterceptor.kext /

file:///Volumes/ALG-MacPro2-APD/Library/Extensions/SophosOnAccessInterceptor.kex t/

The CallDigit, hp_io_enabler; and ATTOxxxx for my PCIE card are dated August 2013.

The BJUSBLoad, HighPointxxx, PromiseSTEX; and ACS6x are dated in 2014.

LittleSnitch; Sophos; and SoftRAID are dated in 2015.

If I were to guess, the 2013 and 2014 KEXTs are possibly a problem.

However, I would not rule out SoftRAID or Sophos with 2015 dates. 

If I really wanted to know which was the culprit, I would go through 7 or 9 reboots of my system and may still not find out which is the culprit.

All the SYSTEM/LIBRARY extensions (too many to show) are all dated in 2015.

Of course the date may not be accurate.

Assuming we can drop all the Apple ones, there are significantly more KEXTs here.

To determine exactly which one is the issue, may take months.

I could do it, but I really don't have the time any more. 

What if there is some other problem and it is not a KEXT? 

Maybe Apple's own SSD drive needed some driver for support - the reason why all these MacBooks and my Mac Pro will not boot.

Regardless, I should have followed my own rule of doing clean installs of OS X.

Because this was just a version update, I thought I could get away with the Application Store update process. 

I was wrong.

To finally boot up, I ended up doing a clean install (without computer extensions) on a magnetic hard drive to boot into 10.11.2.

Jotted it down again: No offense, please try:

Getting yourMac to boot:

1) Start the machine while holding down the Option-Apple-P-R keys

2) Wait until you hear the 3rd startup chime, then release the keys.

3) If that doesn't work try an SMC reset here: https://support.apple.com/en-us/HT201295

Now for the fix after you get the machine to boot:

1) Open Terminal in /Applications/Utilities  (-> make sure you are on your internal HD,... otherwise change it to your HD))

2) Enter "system_profiler SPExtensionsDataType > ~/Desktop/kextList.txt" without the quotes and hit return(this will take a while to run).

3) There should now be a kextList.txt file on your desktop, open it and press both the "Apple(Command)" and "F" keys to bring up the find.

4) In the find field insert "Obtained from: Not Signed" Copy the destination to the .kext file to a list for use later. (Click next to cycle through all of them.) Example: /System/Library/Extensions/JMicronATA.kext 

5) Browse your drive to /System/Library/Extensions and remove any of the unsigned kext files.

6) Reboot and you should be all set.

Hi GSfromNL:

Thank you the further information.

I previously zapped the PRAM.

I also tried the SMC reset and no luck.

I previously tried the safe boot with El Capitan on my SSD. 

It fails and stalls at the same spot with safe boot - getting past the hardware chimes and the software progress bar.

It never gets to the LOGIN screen.

The Mac Pro is booting EL Capitan 10.11.2  now from a different drive with the same hardware, so it is not likely the NVRAM and/or SMC controller in hardware that is causing problems.

I have not analyzed the KEXTs if they are signed and can pass the SIP or not.

It would be interesting if I could turn off SIP on the SSD but I can't get to the terminal command when booting from the SSD.
If there were keystrokes to immediately could go into terminal mode, memories of the old golden days of computers, that would be useful but it does not.

If it booted up to LOGIN with SIP off, that would tell me that SIP is offended by some software.

I have been in contact with Apple customer service and I sent them my system diagnosis files from boot up from my SSD and my bootable hard drive.

They wanted to see if they could improve the next 10.11.3  release. 

I hope that I have been able to help them with it.

When I get through the holidays and my end of year due dates, I will spend some time to try and figure out what KEXT may be the problem.

This is just not the time to be debugging software.

Just for the notice, I tried every single way mentioned here and in other places / forums online, even after deleting the kexts, after a few days the OS was freezing, shuts down after putting it up from sleep mode. I had kept it on (no sleep mode) for days so that I get my work done and it still froze or I would find it shut down at some point.

I really advise in this case to make a clean install after backing up. And do not update to the 10.11.2 version, because that is when the problems occurred..

I tried this method on a client's Mac and he had no unsigned kexts. We solved the problem by downloading the complete El Capitan installer and running it over his current install.

Hi @Tsofa and @GSfromNL

You together saved my day.

I put together what I did finally, and try to make it more generic.

I had a MacBookPro15 Retina running on 10.8.5 and then updated to 10.11.2 El Capitan without a clean install because I wanted to keep my Quark9.5.4.1 Install alive (the installers do not run on newer Systems anymore). You can manage that but I tried the in place upgrade after having proper backups.

I had a nice running machine after the upgrade but it fails when having a first reboot after 3 days.

After some booting progress the bar stopped at around 75% and I got a black screen with a white stop sign.

Restarting using a pressed Cmd-S or Cmd-V key combination displayed the boot terminal.

The last line ended with "Still wating for root device" before displaying the Stop Sign.

(I add these details all for people to make it easier to find this)

1. Boot your system into the Recovery System by pressing Alt during boot or R
   (with alt you need to manually select your boot partition. If you have a working partition you maybe can avoid the harder terminal stuff I describe now)
2. Open the Terminal from the Utilities menu at the top
3. We need to start Safari via Terminal to have the browser AND another terminal (you cannot open two Applications in Recovery Mode via the GUI) type (no copy paste at this state, sorry):
         /Applications/Safari.app/Contents/MacOS/Safari
   and hit return
4. Confirm all upcoming error messages and wait for Safari to show up. The process binds to the first terminal and blocks it, that is ok for now.
5. Type the URL of this post into Safari by hand and keep the browser window small but handy for reading and copying.
6. Click again into the Terminal Window
7. Create a new Terminal by typing Cmd-N
8. List all partitions of your system:
   type:
   ls /Volumes/
   and hit return.
9. Note down your boot partitions name if not "Macintosh\ HD" (take care of the spaces and special characters if you use diacritical characters. You need to quote them using the backslash I use or by putting your path into quotes.)
10. We create a list of all key extensions of our system and write them to a text file on your desktop using the following terminal command:
    Enter the indented line by replacing [Macintosh\HD] with your boot partitions name and [userid] with your short username. Recovery Mode cannot use the ~ trick to get the current user as GSfromNL suggested.
         system_profiler SPExtensionsDataType > /Volumes/[Macintosh\ HD]/Users/[userid]/Desktop/kextList.txt
    and hit return (this will take a short while to run). Thanks GSfromNL!
11. You can browse the file using the command and use exactly the same path to the textfile as in the preceeding command (you can use arrow up to to reedit the line or copy from there):
       less /Volumes/[Macintosh\ HD]/Users/[userid]/Desktop/kextList.txt
12. It is cumbersome to find what we need by viewing the file like this but you get an idea how it looks.
    
13. Now we use grep command to filter the lines of the text and get the context of possible errors :
        grep "Loadable:" /Volumes/[Macintosh\ HD]/Users/[userid]/Desktop/kextList.txt
14. You can now scroll again through the result and see if you find a line containing "Loadable: No"
15. If yes you can now find the possible killer kext file by grepping the context like this:
        grep -C10 "Loadable: No" /Volumes/[Macintosh\ HD]/Users/[userid]/Desktop/kextList.txt
    this will fetch a context of 10 lines before and after the found issue.
16. Note down the found path(s) to the faulty kext files
17. We create safe locations outside the System standard boot lookup path to move the files out of the way and keep them just in case we make a mistake. Type into your terminal:
        mkdir /Volumes/[Macintosh\ HD]/System/Library/Extensions/Unsupported
    and:
        mkdir /Volumes/[Macintosh\ HD]/Library/Extensions/Unsupported
18. Move each extension you found into the new locations depending on which base path was listed (/Library/... or /System/Library/...)  type:
        mv /Volumes/[Macintosh\ HD]/Library/Extensions/[myfaulty.kext]  /Volumes/[Macintosh\ HD]/Library/Extensions/Unsupported/
    and / or
    mv /Volumes/[Macintosh\ HD]/System/Library/Extensions/[myfaulty.kext]  /Volumes/[Macintosh\ HD]/System/Library/Extensions/Unsupported/
19. Reboot your system!

I wish you success!

Sorry for the verbose list in detail, but newbees with just finder experience need this, if they want to help themselves.

Remark:

• One could simplify the commands using the cd command first and then go on from there. But I avoided it here. My approach is more explicit and helps if you are lost with the other procedures posted before from others.

Tipps:

• Open a third terminal to keep the grep results in focus when you have multiple kill candidates.
• When you type your individual paths in the terminal, try to hit "tab" after each "/" . The terminal can autocomplete your path if the solution ist obvious.
• Try typing tab multiple times to get alternate suggestions that e.g are possible partition or usernames!
• Be lazy: Arrow-Up and down gives access to your command history

Argh. At the end of the thread GSfromNL and others already described the above. Hope this increases SEO find possibilities...

Hi! and sincere thanks to all of you who have helped with this problem.  The last post was a month ago today, so I hope you'all are still checking in.

Just briefly, this is my first Mac; I inherited it last fall (2015) from a family member but with a clean Yosemite install.  It's a late 2011, 15" , I7, etc. It began having the same problem(s) described in this thread about 4-6 weeks ago, probably when I upgraded initially to El Capitan or the latest version - not sure which.

I'm having one additional twist that I haven't read in any of the other posts: after the startup chime, my login screen is not the smooth pale blue, but rather has pinkish blue horizontal lines. The login box, the shutdown, restart, etc. are all still legible, but it will NOT BOOT from this screen. I've tried 100 times at least, not even in safe or recovery but instead will go to the "smooth" pale blue screen that I assume is what's called the "blue screen of death". After a few seconds here - maybe 15 or 20 seconds - it restarts on it's own back to the "blue lines" login.

Well, magically yesterday the login was smooth (no horizontal pinkish blue lines) and it booted. Guess it was my Valentine Day gift!! While it was up I went thru all the kext files as advised. There are no "Not Signed" and only one "Loadable: No".  The "Loadable: No" is AppleOSXUSBNCM.kext (I think -should have written it down). I was not able to either move or delete it because it's a "required system file" or something like that.

There is one, however, named "Unsupported".  It showed in the text file on my desktop, but I could never find it in Finder. I found the one immediately preceding it, but "Unsupported" did not show in Finder.  It was signed by Apple....something or other.

Sadly, when I did a restart, it's back to the "blue lines" again, so I'm down.  I hope I have made a small contribution here with my unique version of the much larger problem.

Where do I go from here?

Thanks!!