alt Hacker NewsWho said anything about it being a "bad idea"?
I also explicitly said this wasn't unsolvable. My point isn't about technical implementations or code, my point is that the casual "I want to share nothing about the parent process" thought in sanderj's mind, and presumably a lot others, is much more ill-defined than they realize. There's a lot more state that a process has than what file descriptors are open in a modern system.
Moreover, as things like "in which container is this running" demonstrate, those are also not "create a process that has nothing to do with this process", because, again, there's a lot more to "having to do with this process" than "what file descriptors are open".
Also, as the name might have been a clue, Linux has posix_spawn: https://linux.die.net/man/3/posix_spawn. It also has a thing called "clone": https://www.man7.org/linux/man-pages/man2/clone.2.html Nor do I claim this paragraph is an entire overview of all the ways of starting a process in Linux. If you want to understand what I mean by "lots of details in a modern OS", your assignment is to carefully read the entire "clone" man page, and you'll start to see what I mean, though I'm not sure even that is all the state associated with a process nowadays.
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Linux posix_spawn is a wrapper around clone and exec. There is no primitive on Linux to create an entirely blank process. This is adequately discussed in the linked LWN post.
Other operating systems either have parallel APIs to fork (e.g. the posix_spawn syscall on macOS) or do not provide fork at all (Windows).
It's not a casual thought. I recognize that there are lots of details, there always are, we're talking about computers :)
I don't think it is necessary (or the best implementation) to clone the parent process, in order to maintain important properties like the process tree / container state, etc. I recognize that it's a sorta neat hack, "well if we just start by cloning the parent, then we don't have to figure out what state to include!", but that just pushes the details to the child process needing to figure out what to exclude, which IMO is a worse default.