Because FIS’s instance is a multisite, our standard upgrade procedures need slight modification. Once you have reviewed the client manifest and verified that no customizations will break from a standard upgrade, follow these steps to upgrade Drupal modules (including core):
Put all the sites in maintenance mode, then clear all their caches:
$ drush -y @sites vset --exact maintenance_mode 1 $ drush -y @sites cc all
Backup the files and databases for the instance that is to be upgraded. Be sure to keep copies of .htaccess and robots.txt easily accessible. Drupal core upgrades will overwrite these, and you’ll need to replace customizations post-upgrade. Copying them to the conf directory, a sibling of htdocs, is a good idea.
Upgrade the desired modules. In this example, we’re upgrading just core. This step will download the files, which only needs to be done once, then run the database upgrades for the default site only: $ cd /path/to/webroot/sites/default $ drush -y up drupal
Run the database upgrades for all sites: $ drush -y @sites updb
Compare the new .htaccess and robots.txt files with your backups. Restore any customizations that were overwritten.