設定預設首頁檔名：the DirectoryIndex page - 所在路徑及檔案"/etc/apache2/mods-available/dir.conf " @ ubuntu server 14

The DirectoryIndex is the default page served by the server when a user requests an index of a
directory by specifying a forward slash (/) at the end of the directory name.
For example, when a user requests the page http://www.example.com/this_directory/, he or she
will get either the DirectoryIndex page if it exists, a server-generated directory list if it does not and
the Indexes option is specified, or a Permission Denied page if neither is true. The server will try
to find one of the files listed in the DirectoryIndex directive and will return the first one it finds.
If it does not find any of these files and if Options Indexes is set for that directory, the server will
generate and return a list, in HTML format, of the subdirectories and files in the directory. The
default value, found in /etc/apache2/mods-available/dir.conf is "index.html index.cgi index.pl
index.php index.xhtml index.htm". Thus, if Apache2 finds a file in a requested directory matching
any of these names, the first will be displayed.

以上內容摘取自"Ubuntu14serverguide.pdf"