Hi All, I am hoping someone can help me with a dependency problem that I am currently having and I assume there is already a simple solution available that I am missing. I was looking for some handling inside of systemd that would work similar to the concept of virtual packages in the Debian package management situation. Whereby, if I install an application that requires a mail transport agent then that application can be set as dependent on a virtual class of service that can be fulfilled by one of many applications that can be installed. This would be something like a "Provides" tag in the unit file. I have seen the Alias tag and assume that that could be used in a similar way but I am not sure what happens if you have multiple applications that alias to the same virtual name. This would need some way to tell systemd which app is actually the currently selected app for that virtual class. The goal of this all being obviously to be able to handle runtime dependencies and automatically starting the required underlying services when needed. Thanks for any help and sorry if I have missed a really easy way that this should be handled. Thanks Dave