virtualmin is running fine.
I created a domain for drupal installation.
Drupal site is installed successfully. But I found that after installation of drupal, all files or folder under /default folder under /sites of drupal root folder cannot be modified , deleted.
I checked the file owner is same as the domain default admin user. Even though the domain admin user ssh to the server, files are still unable to modified, deleted.
system return permission deined.