Unable to partition SSD I am trying to partition my HD to install Ubuntu. I have reviewed other questions with similar issues but haven't been able to find a problem with the same symptoms.

Machine is is a Mid 2012 13-inch MacBook Air, El Capitan 10.11.4, with 70GB free space. I am using Disk Utility to create a 50GB partition. 

This is the Disk Utility intent:



And this is the log when the operation fails:



Any assistance would be greatly appreciated.
Answering my own question: this worked.


Reboot the Mac into Single User Mode by holding Command+S during boot
At command prompt type /sbin/fsck -fy
When fsck is complete, type “exit” or “reboot” to reboot
Boot the Mac as usual, verify the disk again in Disk Utility, and partition as usual