If you have a dedicated server that runs Debian GNU/Linux or a derivative distribution, such as Ubuntu Server Edition, you should be familiar with apt-get. This is the command you normally use to install, uninstall, and update software packages. A simple installation string looks like this:
# apt-get install packagename
When a package is installed, it also installs default configurations files. When you start using the software, it will create a distinct configuration file that holds your custom information. Furthermore, you can adjust that configuration file manually to suit your individual needs. Unfortunately, there are situations when you might make a mistake, and the software stops working. If you know what you are doing, you can go back and fix the configuration file. That is why it is a good idea to make backups anytime you change something.
If that does not work, or if you forgot to make a backup, another solution is to reconfigure the package. This process will restore the original configuration used when the package was installed. To accomplish this, use dpkg-reconfigure:
# dpkg-reconfigure packagename
This command will restore configuration settings and may ask you for input, depending on the normal installation process. Once completed, the software should function again as expected, but any configuration changes you made will be lost. If it does not work, the problem may be related to something other than basic configuration changes, and you should check to make sure you did not change anything else on the server that may be related.