[systemd-devel] Virtual dependencies

[David.Yates at continental-corporation.com]

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
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