A new version of an application often introduces new configuration settings. Sometimes obsolete configuration settings are removed. Existing configuration settings may also now have additional options, or certain options are no longer valid any more. Because of this, an application upgrade usually installs a fresh set of configuration files, containing a default configuration that's known to work. Keeping the existing files carries the risk of the application failing to function properly due to a configuration that is no longer valid.

A typical application installation script copies over configuration files with default settings. Existing configuration files are backed up or overwritten. With sysconftool, an application will install a configuration file names filename.dist, instead of filename. Then, the application's installation script runs sysconftool. sysconftool copies filename.dist to filename, but also checks if filename from an older version of the application already exist. If filename an older sysconftool-installed configuration file, it's configuration settings replace the defaults in filename.dist, which is then subsequently installed as filename. sysconftool is smart enough to:

• Remove configuration settings that no longer exist.

• Add new configuration settings.

• Do not preserve an older configuration setting if there's a possibility that it is no longer valid in the new version of the application.

sysconftool produces a short report when it runs. The report lists every configuration setting in $filename.dist, and its disposition. The possible dispositions are:

new

This a new configuration setting that wasn't found in the existing $filename.

unchanged

This setting's value was taken from the existing $filename, replacing the default value provided by $filename.dist.

UPDATED

This setting has been previously set in $filename, but the setting's value may no longer be valid in the new version of the application, so its default value is taken from $filename.dist, and it may need to be manually adjusted.

All this logic is based on some additional metadata that must be included in each configuration file, that sysconftool reads. For this to work, both the old and the new version of the application must be sysconftool-ized. sysconftool operates in a fail-safe mode. If the old version did not use sysconftool, $filename is backed up to $filename.bak, and $filename is copied to $filename. This is what would essentially happen anyway without sysconftool. The local configuration needs to be reentered into $filename, so nothing is lost. However, the next upgrade will see sysconftool do its job.