That's `sysconf(_SC_OPEN_MAX)`, but it is always an bug to close FDs you don't know the origin of. You should be specifying `O_CLOEXEC` by default if you want FDs closed automatically.

That won't returned the maximum open file descriptor. You could perhaps use that value in lieu of the maximum open file descriptor and loop through a crap ton more FDs than even my previous post implied, I suppose, and this is getting less efficient and more terribly engineered by the comment, which I think proves the point…

> but it is always an bug to close FDs you don't know the origin of.

And I would agree. I'm replying to the poster above me, who is staking the claim that POSIX permits closing all open file descriptors other than a desired set.

So, I suppose it can, at a cost of a few thousand syscalls that'll all be pointless…