Nagios: Could not read object configuration data!
If you are using Debian lenny/sid and Nagios complains after apt-get install nagios3 with the message: “Error: Could not read object configuration data!” than one solution could be to add the user www-data to the group www-data. Command:
adduser www-data www-data Don’t forget to reload the apache process.
For some strange reason this user was not in his default group and so the CGI could not read the file /var/cache/nagios3/objects.