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

According to this link, below command saves me on macOS Mojave:

sudo chown -R $(whoami) /usr/local/*

I was able to go back to 5.7 for anyone who wants to:

brew uninstall mysql
brew install [email protected]
brew link --force [email protected]
mysql.server start
mysql_secure_installation

After all that, I'm back in 5.7 with all my databases intact. In my case, I knew the data in the databases wasn't crucial, so I didn't attempt to backup the data in advance. Worked fine for me. If you have irreplaceable data in your local databases, you might want to tread carefully. I didn't lose data, but I don't want anyone else to lose data on my advice either. ;)

Normally, I don't mind a MySQL upgrade, but 8.0 looks to have compatibility issues I'd like to vet before going forward, and in the meantime, I'd rather be back on a version that doesn't force me to deal with those issues.

First, backup the content of your data directory: /usr/local/var/mysql by copying it to a safe place.

The error happens because the post-install script check if a file /usr/local/var/mysql/mysql/user.frm exists. For whatever reason you don't have this file. The postinstall script then tries to install a new MySQL 8 database by running mysqld with --initialize-insecure but as the directory already contains some data from MySQL 5.7 the script halts.

Here is the correspoding part of the script in mysql.rb:

  def post_install
    # Make sure the datadir exists
    datadir.mkpath
    unless (datadir/"mysql/user.frm").exist?
      ENV["TMPDIR"] = nil
      system bin/"mysqld", "--initialize-insecure", "--user=#{ENV["USER"]}",
        "--basedir=#{prefix}", "--datadir=#{datadir}", "--tmpdir=/tmp"
    end
  end

There is several possible solutions. If you can still run your MySQL 5.7 database, export everything with mysqldump then install a fresh MySQL 8 database by removing all content in /usr/local/var/mysql and then import everything back again. Another solution, is to use the mysql_upgrade tool.

P.S.: Personally, I use the formula [email protected] and I will in the future switch to MariaDB.

The installation or re-installation, brew install mysql, created the default data directory, and the post installation does not handle it...

1. Simply move the existing data directory (this moves it to a sibling directory, named with the process id of the shell):

   $ mv /usr/local/var/mysql /usr/local/var/mysql-$$
   

   or might need super user privileges...

   $ sudo mv /usr/local/var/mysql /usr/local/var/mysql-$$
   

2. Then run:

   $ brew postinstall mysql