I think it's very likely this is (at least in some cases) related to nvidia drivers.
I first got this problem while trying to fix a problem with ubuntu freezing after initial login described [here](http://askubuntu.com/a/760935/207604). I did "update" > "upgrade" > "upgrade nvidia drivers" as per the answer I've highlighted.
Unfortunately this upgraded the kernel from .36 to .38 as well as upgrading nvidia drivers from 364 (I think) to 370, so I don't know which caused the problem.
For anyone else with this problem: the only solution/work-around I found was to set
I think it's very likely this is (at least in some cases) related to nvidia drivers.
I first got this problem while trying to fix a problem with ubuntu freezing after initial login described [here](http:// askubuntu. com/a/760935/ 207604). I did "update" > "upgrade" > "upgrade nvidia drivers" as per the answer I've highlighted.
Unfortunately this upgraded the kernel from .36 to .38 as well as upgrading nvidia drivers from 364 (I think) to 370, so I don't know which caused the problem.
For anyone else with this problem: the only solution/ work-around I found was to set
GRUB_ CMDLINE_ LINUX=" " CMDLINE_ LINUX_DEFAULT= ""
GRUB_
in "/etc/default/ grub", then "update-grub". Not sure if both are required but that worked and I'm not touching it any more.