InnoDB duplicate mysql process
I use MAMP Pro and this error tends to annoy me when I change PHP versions:
Check that you do not already have another mysqld process using the same InnoDB data or log files
I used to restart my system but it's far easier.
On MacOS, open Activity Monitor and look for 'mysql' under CPU or memory.
Kill the process.
Save the servers in MAMP Pro.
The problem should be fixed now!