AFAICT to do that reliably for all applications using /dev/urandom, you'd have to insert a step blocking all applications at startup until /dev/urandom was seeded. Even applications that have no need for anything from /dev/{u,}random.
(EDIT: I suppose one might try to replace /dev/urandom with some pipe-like thing running in userspace, but that seems error prone and rather contrary to /dev just being "devices".)
[1] Without just doing it at the kernel level, which the Linux kernel developers seemingly still stubbornly refuse to do.
(EDIT: I suppose one might try to replace /dev/urandom with some pipe-like thing running in userspace, but that seems error prone and rather contrary to /dev just being "devices".)
[1] Without just doing it at the kernel level, which the Linux kernel developers seemingly still stubbornly refuse to do.