https://getcomposer.org/doc/articles/troubleshooting.md#xdebug-impact-on-composer https://github.com/Homebrew/homebrew-php/issues/2536#issuecomment-178798390
Comment out the line enable xdebug in /usr/local/etc/php/5.6/conf.d/ext-xdebug.ini
[xdebug]
;zend_extension="/usr/local/opt/php56-xdebug/xdebug.so"