Reset OS X Lion?

Question

macOS

The Mac began to slow down a lot, there are no extra programs, a rather modest set of available ones. I sin on OS X Lion (because the hardware is normal, iMac 2011). There is plenty of free disk space - 700 gigabytes. In autorun, the very minimum. How can I reset the operating system to the state “software set as when buying, but personal data is saved (My files, Downloads, Documents, etc)”? Thank you.

Answer 1

First, boot from the system recovery disk, enter disk utility and restore the rights. Then you can see in the console and system monitoring what exactly slows down the system - how much it eats up processor time, or memory ...
If you still decide to reset the system to its original state, you will have to reinstall from scratch. Copy personal data to external media and reinstall the system. To make sure there are no traces of the old system left, erase a large partition in disk utility before installing.

Answer 2

Filter all errors - enter error in the search bar - read what the system writes.

Answer 3

System brakes are the first sign that the screw has begun to crumble. Check immediately!