On Tue, 21.08.12 14:31, david.ya...@continental-corporation.com (david.ya...@continental-corporation.com) wrote:
> 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. The way we currently handle this mostly is indeed by using Alias=. For example the various implementations of a Display Manager all have an Alias=display-manager.service, and that link then decides which implementation is pulled in. "systemctl enable" will fail if a symlink it is supposed to create already exists. (This can be override with --force, which results in the symlink being replaced). This is suboptimal for other use cases though I guess, we could add some other logic there to make it unnecessary to always maintain a symlink for this in FS. I am open to ideas there, but the Alias= solution definitely is something that works right now for many uses. Lennart -- Lennart Poettering - Red Hat, Inc. _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel