http://www.bin-co.com/perl/tutorial/modules.php

~$> uname -a 
Linux yt-laptop 3.0.0-19-generic #33-Ubuntu SMP Thu Apr 19 19:05:57 UTC 2012 i686 athlon i386 GNU/Linux

~$ sudo ls -lad /var/www/guestbook.html
-rw-r--r-- 1 www-data www-data 4986 May  7 11:02 /var/www/guestbook.html

~$ find -name 'guests.txt' -exec ls -lad {} \;
-rw-r--r-- 1 root root 43 May  7 10:55 ./guests.txt
~$ cat ./guests.txt 
 came from .E-mail address is .Comments : 

~$ tail /var/log/apache2/error.log
[Tue May 08 20:38:55 2012] [notice] Apache/2.2.20 (Ubuntu) PHP/5.3.6-13ubuntu3.7 with Suhosin-Patch mod_perl/2.0.5 Perl/v5.12.4 configured -- resuming normal operations
[Tue May 08 21:05:59 2012] [error] Can't open guests.txt: No such file or directory\n
[Tue May 08 21:09:51 2012] [error] Can't open guests.txt: No such file or directory\n
[Tue May 08 21:09:54 2012] [error] Can't open guests.txt: No such file or directory\n
[Tue May 08 21:09:57 2012] [error] Can't open guests.txt: No such file or directory\n

Internal Server Error 
The server encountered an internal error or misconfiguration and was unable to complete your request.
 Please contact the server administrator,  webmaster@localhost and inform them of the time the error occurred, and anything you might have done that may have caused the error.
 More information about this error may be available in the server error log.
  Apache/2.2.20 (Ubuntu) Server at localhost Port 80