Cannot Update iMac, OS X, From 10.11.2 to 10.11.6 I have attempted multiple times to update my iMac from the App Store updates section like I did when I updated to Mavericks, Yosemite, then to El Capitan. It would finish the download and then nothing. No attempt at installing the update. 

Next I found the update in a dmg file at Apple's website. I would run the package contained inside but would get the error during the installation:


  "OS X El Capitan Update can't be installed on this disk. This volume does not meet the requirements for this update."


What must I do to get my Early 2009 iMac updated? 

(I am still learning about Macintosh computers.)
I'm not sure what's going on with the App Store update, but I have a guess about the downloaded update: did you get the "OS X El Capitan 10.11.6 Update" (759.1 MB), or the OS X El Capitan 10.11.6 Combo Update (1.5GB)? If you downloaded the first one, it won't work because it's only capable of updating from 10.11.5 to 10.11.6; since you have 10.11.2, you need the "combo" version, which rolls in all of the earlier 10.11.x updates, and is therefore capable of updating from any earlier version of 10.11 to 10.11.6.

(BTW, this requirement is listed on the download pages for the two updates, but you have to click "System Requirements" to actually see it, and even then it's not very explicit. The first says it requires "OS X El Capitan 10.11.5", but the second just says "OS X El Capitan 10.11".)