How do I do a clean install?
What is the procedure for doing a clean install on my late 2008 unibody Macbook?
MacBook, OS X 10.11
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First of all download a copy of the Mac OS X installer package.
Make a bootable USB flash drive.
Make a full back up of your mac to an external disk.
Boot to your the bootable USB flash drive.
Erase your mac internal drive.
Install OS X El Capitan.
If you do have an operating system on your mac and it is functioning then you can download
El Capitan using this method.
How to get old versions of macOS – Apple Support
Go to Download OS and click on OS X El Capitan 10.11
this downloads InstallMacOSX.dmg to your Downloads folder.
The next section can only be done on a mac that is capable of running El Capitan.
This includes macs that have the potential to run El Capitan but have been upgraded to a newer OS.
A mac that came preinstalled with an OS later than El Capitan will refuse to do the next bit.
When downloaded open to InstallMacOSX.pkg, double-click on
that and an installation window will open, this does not install El Capitan
but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which
you will find in your Applications folder, it should be 6.2GBs in size.
(If the installation window asks which disk you want to install to, you must pick
the disk that you are booted to at the time. Not any internal or external disk that
you want to eventually install El Capitan on, that is for later.)
Create a bootable USB installer disk using the Install OS X El Capitan.app in the Applications
folder and the createinstallmedia command in the Terminal app.
Read the instructions here,
How to create a bootable installer for macOS – Apple Support
Make a full backup of your mac to an external drive.
Restart your mac while pressing and holding the option/ alt key.
In a minute or two you will see the Startup Manager, select the bootable USB flash drive.
Press Return.
Your mac will now boot the USB and you will see a Utilities panel select Disk Utility press Continue.
Highlight the Disk not any indented Volumes the Disk will be called Apple HDD or something similar.
Click on the Erase button.
Give the Disk a name.
Format: Mac OS Extended (Journaled)
Scheme: GUID Partition Map.
Click Erase.
When Done quit Disk Utility.
Click on Install OS X, press Continue.
The installation process should start up, follow the prompts.
After installing the OS you can choose to restore only your personal data
from the back up you made earlier.