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…