Apple releases supplemental update to Yosemite to fix start-up issue
Mac owners will be seeing an emergency update today. The update is being described as a “Supplemental Update to 10.10.3, designed to fix a bug discovered after the 10.10.3 update that was released about a week ago that introduced the new Photos app.
Supplemental updates are rare, so rare that I can not remember one. Most are simply labeled bug fix or security updates. Maybe Apple, which is quickly developing a reputation for releasing software insufficiently tested, is getting tired of tech websites calling them out for their bugs.
The bad news: the update will require a reboot.