Mac os x boot caches updating
Once you hear the startup tone hold down the Shift key on your keyboard.When the grey Apple logo appears, release the Shift key.The new mac OS Sierra update is now available to download and install for OS X 10.11 El Capitan users, but if you've just decked out your Mac with the latest operating system and noticed that things don't work the way they should, or encounter any other issues, then we have a list of fixes for the most common problems.As more of us upgrade to mac OS Sierra, more problems are being discovered, so we will be constantly updating this guide as new problems - and solutions - are found.Once in safe mode delete any unnecessary files, or move them to an external hard drive, to free up some disk space.Then restart your Mac and try to install mac OS Sierra again.
To do this, turn off your Mac and wait 10 seconds, the press the power button.
Boot your Mac into Safe mode, then try installing mac OS Sierra again.
It might also be worth switching from a Wi-Fi connection to a wired connection before you download and install.
To force-quit an item, click it in the Activity Monitor list, then click the X at the left of the toolbar, then confirm you want to force-quit. Open the Finder window, select 'Go' from the top menu and select 'Go to Folder'.
In the text box that appears type /Library/Caches Remove the data from inside every folder.