Comment by _flux

Can it though?

The beauty of (v)fork(+exec) is that it doesn't need a new interface for configuring the environment in whichever way you want before the other process starts. Instead you get to use the exact same means of modifying the environment to your needs, and once it's done, you can call exec and the new process inherits those things.

I mean, just look at the interface of posix_spawn.

I grant though that this isn't without its problems (including performance) and IMO e.g. FD_CLOEXEC is one example of how those problems can be patched up. It's like the reverse problem: you have too wide implicit interface in it, and then you need to come up with all these ways to be explicit about some things.