# apt-get install git
# curl -sS https://getcomposer.org/installer | php
# mv composer.phar /usr/local/bin/composer
# ln -s /usr/local/bin/composer /usr/bin/composer
#git clone https://github.com/drush-ops/drush.git /usr/local/src/drush
# cd /usr/local/src/drush
# git checkout 7.1.0
# ln -s /usr/local/src/drush/drush /usr/bin/drush
# composer update
# composer install

https://www.linode.com/docs/websites/cms/drush-drupal
https://github.com/drush-ops/drush/issues/1409
http://stackoverflow.com/questions/20106502/php-composer-cant-find-comp…