Q: El Capitan update won't boot

I solved this on my 13 inch  Mid 2011 MacBook Air and my 17inch  Mid 2009 MacBook Pro - after reinstalling the OS 4 or 5 times on the Air and fighting with the Pro 3 times after each reboot it was the same - login and the progress bar stuck at ZERO for hours at end so, I decided to turn off FILEVAULT.  The machine says it needs to restart to make changes and it does.  Now it will take a few hours to decrypt the drive, but until Apple fixes this I am running unencrypted.

my FILVAULT is always off ... so it dos not help at all on my mid 2011 Macbook Air

No file vault for me and still crashes.

Try this sudo rm -rf /System/Library/Extensions/EltimaAsync.kext  - I have now rebooted the Mid 2011 MacBook Air 7 times and it works each and every time. 

You will need to type in your pass in Terminal once you paste that in.

For all Paralells User ( Sorry in german  ):Parallels Desktop 11 für Mac und Parallels Mac Management für Microsoft SCCM jetzt mit vollständiger Unterstützung von OS X El Capitan

Lol! Brainlight you must be loving the angst of mac users who upgraded to El Captain! Thanks, but no thanks!

What do you subordinate to me? What nonsense..., your comment!!!!      The only one what I love is a perfect OS as well as it was almost always possible in the past. Remain so please objective!!!!

What do you subordinate to me? What nonsense..., your comment!!!!      The only one what I love is a perfect OS as well as it was almost always possible in the past. Remain so please objective!!!!

I've got the same problem too and in the end I returned to Yosemite yesterday. Thank god I've had a backup.

Before that: when restart or shut dow computer - only apple logo and empty progress bar appeared.

Clean install didn't work neither, after migration of data same problem again.

Here's another little "Apple Trap".

Update to El Capitan.

Run Photos.

It'll request to migrate your photo library.

IF it runs, it will import them.

When the entire OSX Crashes, and you try to re-run your Yosemite Photos, it'll say the photo file only works with a newer version, and YOUR YOSEMITE PHOTO LIBRARY CAN'T BE READ ANYMORE.

If you don't have a clean backup of your Yosemite Photos File saved, you could lose everything.

BACKUP CRITICAL FILES BEFORE UPDATING TO El CAPITAN and then make another backup somewhere else to be safe....BEFORE UPDATING OR RUNNING 10.10.11

Don't ask me how I know. I do keep multiple back-ups in my Mac Pro, fortunately.

Thank's

amStig01

Try this sudo rm -rf /System/Library/Extensions/EltimaAsync.kext

This realy helped me to solve this problem

I have installed El Capitan on my iMac and it works perfectly. Hooray.

I have installed on my MacBook Air (mid 2011, 4gb memory, 120gb storage with 77gb free) and it works perfectly; HOWEVER when I restart or turn off my MacBook Air it just hangs. Disk repair and reinstall El Capitan works OK but does not fix the problem.

Can anyone help please.

Plus one on this issue. I upgraded a 2013 imac to el capitan last night. Ran fine all day today, but suddenly went into complete lock up, with all open apps becoming unresponsive. I did a hard shut down, and have been unable to initiate anything since. I can't even get single user mode to drop me into a shell; hangs right after logging an issue with a syncmate kext; never get a prompt. I then tried going into local recovery with command - R, and get presented with apple logo and 90% progress. After a few hours of that, I hard rebooted again, this time trying option key to get a different start up disk option. I see REcovery 10.11, and my time machine disk, but neither will proceed past initial disk and wifi selection; stuck on just apple logo. I'd really like to avoid doing an internet recovery. Seems like a growing, significant problem. Definitely a major pain

was that when you first rebooted after the upgrade or had you restarted more than once already?

Reboot after install worked perfectly and continues to work unless I turn the MacBook off or try a restart, in which case it fails to reboot.

Have tried several times to reinstall but the problem remains