This problem is a very common problem that happen at a Yosemite update. Sometimes after updating yosemite, some users may tripped a permission lever unintentionally.
Well actually there’s a Terminal-based process to solve this, there are the instructions
- Select > Restart.
- After the Mac shuts down and makes the startup chime, hold down Command-R to boot into Recovery mode immediately.
- After the Recovery screen shows , select the menu item Utilties > Terminal.
resetpasswordand press Return. Remember: this will not reset your password.
- A dialog will showed up from and you can select your startup volume if it’s not selected by default.
- Choose your username from the Select the User Account dropdown menu.
- In the lower-right corner of the screen, click Reset next to the Reset Home Directory Permissions and ACLs area.
- Last choose File > Quit, and then in the main Recovery window, choose > Restart.
When the system comes back up with the OS X installation, this problem should be gone.