You could probably see which file exists ...
But, application programs don't interact directly with either of these processes, and those programs that do
ought not care how
the services that they require are being rendered to them.
You really want to design your program so that it is agnostic to these issues. If you do
for example have a dependency in the installation process, then you should first detect what you think
to be the case, then stop
and ask the installing user to confirm your assessment and if need be to overrule it.
Furthermore, when your program is in service, it should continuously do some kind of "stink test" to recognize when it is in a potentially-damaging situation where it concludes that, "the configuration option that I was given just can't be right ... or maybe it's
no longer right."
(The user could, after all, switch
his system from one to the other without telling you, and you surely don't want yours
to be the piece-of-software that just got egg-faced in some sysadmin forum somewhere!)
For programs like these, a good strategy is:
- "I think I know the answer, but ..."
- "... I'm going to oblige you to tell me one way or the other, and ..."
- "... I still won't quite believe you, nor trust that what you said will always remain true."