MariaDB homebrew install errors

Having been unsuccessful with further Googling of the problem I tried manually creating a /usr/local/etc/my.cnf.d and now the mysql_install_db command seems to have worked okay. I'm not sure if this is the appropriate solution or if my.cnf.d not existing is indicative of a deeper problem with the install but, as things seem to be working, I'll mark as resolved.

[Update] As I was a little unsure in my answer whether this was the 'correct' solution I just wanted to confirm that, after a month, everything is still working fine.

None of the solution here helped, I had to do this:

The post-install step did not complete successfully MySQL Mac OS Sierra

in short,

• I made a backup of the folder /usr/local/var/mysql , then removed it
• removed Mariadb brew remove mariadb
• reinstalled Mariadb brew install mariadb
• run brew services start mariadb

After that I could access with mysql -u root

Just open the config file at /usr/local/etc/my.cnf with your editor and comment out the following line:

!includedir /usr/local/etc/my.cnf.d