brewコマンドでmysqlをインストール

## 概要
Homebrewを利用してmysqlをインストールした時に，少し躓いた部分があったので，正常なインストールの手順と対処法をメモ．

### 環境
- OS
    - 10.9.5
- Mysql(GA版)
    - 5.6.21
- Homebrewインストール済み

## インストール
```zsh
# mysqlのインストール
brew install mysql

==> Downloading https://downloads.sf.net/project/machomebr
Already downloaded: /Library/Caches/Homebrew/mysql-5.6.21.mavericks.bottle.tar.gz
==> Pouring mysql-5.6.21.mavericks.bottle.tar.gz
==> Caveats
A "/etc/my.cnf" from another install may interfere with a Homebrew-built
server starting up correctly.

To connect:
    mysql -uroot

To have launchd start mysql at login:
    ln -sfv /usr/local/opt/mysql/*.plist ~/Library/LaunchAgents
Then to load mysql now:
    launchctl load ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
Or, if you don't want/need launchctl, you can just run:
    mysql.server start
==> Summary
?  /usr/local/Cellar/mysql/5.6.21: 9620 files, 339M
```

### 起動の方法
#### デーモンとして起動

```zsh
# launchctlコマンドを利用
ln -sfv /usr/local/opt/mysql/*.plist ~/Library/LaunchAgents
launchctl load 

#起動
launchctl load ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist

#停止
launchctl unload ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist

```

#### 任意での起動
```zsh
#起動
mysql.server start

#停止
mysql.server stop
```

### 起動後
セキュリティ周りの調整のため，mysql_secure_installationコマンドを実行

```zsh
# コマンドの実行
mysql_secure_installation

NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MySQL
      SERVERS IN PRODUCTION USE!  PLEASE READ EACH STEP CAREFULLY!

In order to log into MySQL to secure it, we'll need the current
password for the root user.  If you've just installed MySQL, and
you haven't set the root password yet, the password will be blank,
so you should just press enter here.

Enter current password for root (enter for none):
OK, successfully used password, moving on...

Setting the root password ensures that nobody can log into the MySQL
root user without the proper authorisation.

You already have a root password set, so you can safely answer 'n'.

Change the root password? [Y/n]
New password:
Re-enter new password:
Password updated successfully!
Reloading privilege tables..
 ... Success!


By default, a MySQL installation has an anonymous user, allowing anyone
to log into MySQL without having to have a user account created for
them.  This is intended only for testing, and to make the installation
go a bit smoother.  You should remove them before moving into a
production environment.

Remove anonymous users? [Y/n]
 ... Success!

Normally, root should only be allowed to connect from 'localhost'.  This
ensures that someone cannot guess at the root password from the network.

Disallow root login remotely? [Y/n]
 ... Success!

By default, MySQL comes with a database named 'test' that anyone can
access.  This is also intended only for testing, and should be removed
before moving into a production environment.

Remove test database and access to it? [Y/n]
 - Dropping test database...
ERROR 1008 (HY000) at line 1: Can't drop database 'test'; database doesn't exist
 ... Failed!  Not critical, keep moving...
 - Removing privileges on test database...
 ... Success!

Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.

Reload privilege tables now? [Y/n]
 ... Success!




All done!  If you've completed all of the above steps, your MySQL
installation should now be secure.

Thanks for using MySQL!


Cleaning up...
```

## トラブル
### rootユーザーが存在しない
rootユーザーでログインしようとしたが，rootユーザーが存在しなかった．
そのため，mysqladminコマンドやmysql_secure_installationコマンドといったものが利用できずに頭を悩ませた．

原因は以前違うバージョンのmysqlをインストールした時の設定ファイルが残っており，初期化した場合に/usr/local/var/mysql内に作成されるはずのmysqlディレクトリが存在しなかったため．
なぜこのディレクトリが存在しなかったのかはわからない・・・

```zsh
#ログインしようとすると・・・
mysql -u root -p

#エラー
Access denied for user 'root'@'localhost' (using password: NO)
```

### 対処法
1. デーモンを一旦停止
2. 以前の設定ファイルを削除
3. もう一度デーモンを起動

```zsh
#コマンド
launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
rm -r /usr/local/var/mysql/
launchctl load -w ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
```

どうやら，以前brewでインストールした時に起動していたデーモンが生き続けていたっぽい・・・．
前のバージョンでは，初期化スクリプトを自動実行しなければユーザーが作られなかったのだろうか，
謎のままである．