Update Problem

This procedure will delete certain temporary and cache files used by system processes. The files are automatically generated and don't contain any of your data. Occasionally they can become corrupt and cause problems such as yours.

Back up all data before proceeding.

Triple-click anywhere in the line below on this page to select it:

/var/folders/zz

Right-click or control-click the highlighted line and select

Services ▹ Reveal in Finder (or just Reveal)

from the contextual menu.* A folder should open with a subfolder named "zz" selected. Move that subfolder to the Trash. You may be prompted for your administrator login password. Restart the computer and empty the Trash.

*If you don't see the contextual menu item, copy the selected text to the Clipboard by pressing the key combination command-C. In the Finder, select

Go ▹ Go to Folder...

from the menu bar and paste into the box that opens by pressing command-V. You won't see what you pasted because a line break is included. Press return.

Absolutely do not follow those instructions or do anything else unless you have a backup.

I suggest you shut down the computer immediately and don't turn it on again until you have at least one external hard drive (two or more recommended) to dedicate to backup. Each backup drive must have at least enough capacity to hold all the data on the internal drive comfortably, as well as any data that you have on secondary drives. Then follow the instructions in this support article.