Here's the problem: my colleague has a MacBook Pro Retina with El Capitan installed and he's been having issues with regular freezes lately. Everything has worked fine under Mavericks for well over a year, then it was upgraded to El Capitan, worked mostly fine for some time and then started to hang up regularly.
Freezes happen on/during either of the following:
- the boot screen
- the login screen (most often)
- within seconds after logging in
Freezes do not happen in either single user or safe mode.
As stated above, the machine hangs most often at the login screen. I start typing the password and bang, after a few characters it just stops responding - I cannot type anything on the keyboard or move the pointer with the touchpad. Keyboard backlight is on permanently and doesn't turn off.
After booting into safe mode in
/var/log/system.log I've found lots of entries like this:
WindowServer: GPU Driver appears to be hung (over 5 continuous seconds of unreadiness) --- last message repeated 817 times ---
The problem is reproducible on all users. Since we have a Time Machine backup and I could experiment freely, I've tried reinstalling El Capitan (keeping user files). No change. Then I wiped the system drive and did a fresh installation of El Capitan, created a user during the initial setup and crashed into the same problem, before even restoring the backup.
Hardware test (accessible by holding
S during boot) was run twice and did not yield any results.
The disk was encrypted with FileVault before my wiping it clean. Now it's unencrypted and the problem persists, so this doesn't seem to be of relevance.
My questions here are:
- What could be a possible cause of such problems?
- Is there any known solution to these?
- Is it possible to download Mavericks from a reliable source and installing it over El Capitan? That's the last OS X version known to work well on this machine.
- What can I do to debug the causes?
Any suggestions not contained in the questions are also welcome.