Author here. That error happens if you have binfmt_misc enabled. The solution is simple:

    sudo sh -c "echo ':APE:M::MZqFpD::/bin/sh:' >/proc/sys/fs/binfmt_misc/register"

I intend to upstream a patch with the Linux kernel so it can do this automatically. If any kernel devs are reading, please email me!

Instead of sudo sh -c to sudo the redirects, consider echo 'abcde' |sudo tee /proc/bla. Less nesting :)

Do you mean less syntactical nesting? The pipe to sudo tee creates a new child shell, just as sudo sh -c does.

Yes.

Does it work on cheap Xen vps? Because "/proc/sys/fs/binfmt_misc/register" looks absent from mine.

That's strange. I'd recommend filing an issue. Any details on how I can reproduce the error will be helpful, even if I have to temporarily rent one of those things. I'm on a mission to make binaries portable.

FWIW, it works on QubesOS, which is Xen based. Though it works only in my Fedora and Debian VMs, but not on my Archlinux-based one.

I think that's because I have WINE installed in the Archlinux VMs, since that's what gets started when I run ./redbean.com. But even after I remove WINE, it still doesn't work, I probably have to restart (i.e. remove WINE from the TemplateVM, not the AppVM) for it to work.

In any case, incredible work, I am in awe!