3.2 Checking Software Dependencies

The software of one package might only work properly if the required package is also installed. If packages with identical or similar functionality use the same system resource, they should not be installed at the same time, because this would cause a package conflict.

When the package manager starts, it examines the system and displays the installed packages. When you select to install and remove packages, the package manager automatically checks the dependencies and selects any other required packages (resolution of dependencies). If you select or deselect conflicting packages, the package manager indicates this and suggests possible solutions to this problem (resolution of conflicts).

Check Dependencies and Autocheck are located under the information window. If you click Check Dependencies, the package manager checks if the current package selection results in any unresolved package dependencies or conflicts. In the event of unresolved dependencies, the required additional packages are selected automatically. For package conflicts, the package manager opens a dialog that shows the conflict and offers various options for solving the problem.

If you activate Autocheck, any change of a package status triggers an automatic check. This is a useful feature, because the consistency of the package selection is monitored permanently. However, this process consumes resources and can slow down the package manager. For this reason, Autocheck is not activated by default. In either case, a consistency check is performed when you confirm your selection with Accept.

For example, sendmail and postfix may not be installed concurrently. Figure 3-1 shows the conflict message prompting you to take a decision. postfix is already installed. Accordingly, you can refrain from installing sendmail, remove postfix, or take the risk and ignore the conflict.