MacOS Can't start MySQL Server

I suggest to use Terminal commands.

Start MySQL

sudo /usr/local/mysql/support-files/mysql.server start

Stop MySQL

sudo /usr/local/mysql/support-files/mysql.server stop

Restart MySQL

sudo /usr/local/mysql/support-files/mysql.server restart

In my case, I had inadvertently transferred ownership of entire /usr/local directory to myself, which resulted in snatching-away of write permission of /usr/local/mysql-5.7.20-macos10.12-x86_64/data directory from the daemon user called "_mysql".

Restoring the ownership fixed the issue.

After a discussion with Richard, the following solves the issue:

my.cnf:

[client]

port = 3306
socket = /tmp/mysql.sock


[mysqld]

port = 3306
socket = /tmp/mysql.sock
datadir = /usr/local/mysql-5.7.17-macos10.12-x86_64/data
tmpdir = /tmp

Essentially, although we'd added the relevant stanza's to the my.cnf file, we'd still missed the section heading. Adding the [mysqld] section allowed mysql to start.