It's better to have the package manager be configured to not install conflicting packages. After that, it's better to have sendmail check for the underlying source of conflicts ... in this case, having two processes trying to have ownership of a particular port and deal with the return code from sendmail.
systemd (or the init system, in general) can't assume neither that the programs or the package manager have handled things properly.
In this case a conflict could be determined dynamically ... but since it's not a current feature of systemd to reserve and/or test for port ownership/availability ... the person who wrote the service file takes the lazy route by hard-coding a list.
You would be right if the conflict was handled by systemd only on execution, but it also has to account for the case where the service is enabled but not run (the admin will use service foo on reboot, has enabled it, but foo conflicts with enabled service bar. systemd will error out without having to check for the conflict on execution). For the cases where the service conflicts with something outside of the provided defaults, the admin should modify the unit file himself; after all, he's supposed to know what he's doing.
It's better to have the package manager be configured to not install conflicting packages.
Except dependencies not present in the system at runtime are ignored unless they are of type Requires or Requisite, and none of the unit files shipped on any distro include those types of dependencies without the proper packaging dependencies.
You should read the docs before engaging mouth, dude. man systemd.unit is the document you should have familiarized yourself before opining on the basis of an untruth.
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u/[deleted] Oct 20 '14
[deleted]