Try /proc on Linux as entropy fallback; use sysctl as last resort It turns out that the happy fun Linux kernel is deprecating sysctl, and using sysctl to fetch entropy will spew messages in the kernel logs. Let's not do that. Instead, let's call sysctl for our entropy only when all other means fail. Additionally, let's add another means, and try /proc/sys/kernel/random/uuid if /dev/urandom fails.