Installer Fails with Drupal Multi-Site

I set up a typical Drupal 7.20 multisite installation, with my domain in sites/mydomain/

I untarred civicrm-4.2.8-drupal.tar.gz into sites/all/modules/

I ran the CiviCRM installer at https://mydomain/sites/all/modules/civicrm/install/index.php

I entered the database information, changed the file permissions it asked for and hit the install button. After a short time, the installer crashed with the following error:

You need to define CIVICRM_DSN in civicrm.settings.php

After this, running the installer told me CiviCRM was installed but the CiviCRM link did not appear in the Drupal menu. On debugging I noticed that CiviCRM was asking me to make sites/default/ writeable, not sites/mydomain/

The bug seems to be that the installer always creates the civicrm.settings.php file in sites/default/ but tries to read it from the site-specific subdirectory sites/mydomain/ later in the install process.

The workaround is to create a symlink from sites/mydomain/civicrm.settings.php into sites/default/ - that allows the file created by the installer to be read later. Once the install is complete, the civicrm.settings.php file can be moved from sites/default/ to sites/mydomain/