macOS High SierraでDocker Toolboxがインストールできなくて困った話。

Docker Toolboxのインストーラを起動して実行するとなぜかOverviewで止まる。。。。。

調べてみるとどうやらよく起こる現象らしい。
仕方ないのでbrew cask installでインストールを試す。

$ brew cask install docker-toolbox
==> Satisfying dependencies
==> Installing Cask dependencies: virtualbox
==> Caveats
To install and/or use virtualbox you may need to enable their kernel extension in

  System Preferences → Security & Privacy → General

For more information refer to vendor documentation or the Apple Technical Note:

  https://developer.apple.com/library/content/technotes/tn2459/_index.html

==> Satisfying dependencies
==> Downloading https://download.virtualbox.org/virtualbox/5.2.18/VirtualBox-5.2.18-124319-OSX.dmg
Already downloaded: ~/Library/Caches/Homebrew/Cask/virtualbox--5.2.18,124319.dmg
==> Verifying checksum for Cask virtualbox
==> Installing Cask virtualbox
==> Running installer for virtualbox; your password may be necessary.
==> Package installers may write to any location; options such as --appdir are ignored.
Password:
Sorry, try again.
Password:
installer: Package name is Oracle VM VirtualBox
installer: Installing at base path /
installer: The install failed (エラーによってインストールできませんでした。ソフトウェアの製造元に問い合わせてください。)
==> Purging files for version 5.2.18,124319 of Cask virtualbox
Error: Failure while executing; `/usr/bin/sudo -E -- env LOGNAME=hogehoge USER=hogehoge USERNAME=hogehoge /usr/sbin/installer -pkg /usr/local/Caskroom/virtualbox/5.2.18,124319/VirtualBox.pkg -target /` exited with 1. Here's the output:
Sorry, try again.
installer: Package name is Oracle VM VirtualBox
installer: Installing at base path /
installer: The install failed (エラーによってインストールできませんでした。ソフトウェアの製造元に問い合わせてください。)

Follow the instructions here:
  https://github.com/Homebrew/homebrew-cask#reporting-bugs
/usr/local/Homebrew/Library/Homebrew/system_command.rb:101:in `assert_success'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:46:in `run!'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:23:in `run'
/usr/local/Homebrew/Library/Homebrew/system_command.rb:27:in `run!'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb:58:in `block in run_installer'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb:64:in `with_choices_file'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb:50:in `run_installer'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/artifact/pkg.rb:31:in `install_phase'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:196:in `block in install_artifacts'
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/set.rb:674:in `each'
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/2.3.0/set.rb:674:in `each'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:188:in `install_artifacts'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:90:in `install'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:297:in `block in cask_dependencies'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:296:in `each'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:296:in `cask_dependencies'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:223:in `satisfy_dependencies'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:54:in `fetch'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/installer.rb:85:in `install'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli/install.rb:20:in `block in run'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli/install.rb:14:in `each'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli/install.rb:14:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli/abstract_command.rb:33:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli.rb:90:in `run_command'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli.rb:156:in `run'
/usr/local/Homebrew/Library/Homebrew/cask/lib/hbc/cli.rb:121:in `run'
/usr/local/Homebrew/Library/Homebrew/cmd/cask.rb:7:in `cask'
/usr/local/Homebrew/Library/Homebrew/brew.rb:87:in `<main>'

まさかのvirtualboxがインストールできない。
そして解決策がよくわからない。。。。。
よくよく調べた結果、Macの設定「セキュリティとプライバシー」でOracleのソフトインストールを許可する必要があった。

思ったより変なことに時間を使ったのでメモ。