Hit a *really* corner case bug today - a binary was absolutely present but returned ENOENT whenever you tried to run it. strace showed exevce() returning it, so it was happening when the kernel tried to run it. Normally I'd assume that the rtld (the thing that the kernel delegates loading of dynamic libraries to when running a dynamically linked binary) was missing, but ldd showed nothing missing - everything was resolved, including the rtld. WTF?