It breaks here in init_drng_entropy_source function of rngd_rdrand.c.
if (!(info.ecx & features_ecx1_rdrand))
return 1;

from rng-tools.

Thats working as designed. If that check fails it indicates that your cpu doesn't support, or isn't exposing the rdrand instruction, and so the rdrand entropy source cannot work

from rng-tools.

Thanks very much for your info, then how to make the cpu support the function as I run the service in qemu env.
And as the message indicates "[rdrand]: Initialization Failed", but the service started successfully via "systemctl status rngd".

from rng-tools.

you probably cant enable rdrand. If your hardware doesn't support the instruction, theres nothing you can do, and if it does, you will need access to the host so as to run your hypervisor process with the appropriate rdrand cpu flag enabled.

However, its important to note that this isn't in and of itself a problem. rngd supports several different entropy sources, of which rdrand is only one. You have other sources (specficially jitter) which is operational, and so allows rngd to function properly. The failure to initalize rdrand isn't fatal to your operation.

from rng-tools.

Thanks nhorman very much for your explanation!
Through the rngd status as below, the rdrand doesn't work as it indicates "Initialization Failed", but at least one entropy source such jitter works, so the rngd works as expected though one message "[rdrand]: Initialization Failed", do I understand correctly? If so, it's better change the message a little to guide people, otherwise we thought there is something wrong #84.

systemctl status rngd

rngd.service - Hardware RNG Entropy Gatherer Daemon
Loaded: loaded (/lib/systemd/system/rngd.service; enabled; vendor preset: >
Active: active (running) since Tue 2020-02-25 05:08:11 UTC; 42min ago
Main PID: 133 (rngd)
Tasks: 2 (limit: 3591)
Memory: 1.0M
CGroup: /system.slice/rngd.service
`-133 /usr/sbin/rngd -f -r /dev/hwrng

Feb 25 05:08:14 qemux86-64 rngd[133]: Initializing available sources
Feb 25 05:08:14 qemux86-64 rngd[133]: [hwrng ]: Initialized
Feb 25 05:08:14 qemux86-64 rngd[133]: [rdrand]: Initialization Failed
Feb 25 05:08:14 qemux86-64 rngd[133]: [jitter]: Initializing AES buffer
Feb 25 05:08:31 qemux86-64 rngd[133]: [jitter]: Enabling JITTER rng support
Feb 25 05:08:39 qemux86-64 rngd[133]: [jitter]: Initialized
Warning: Journal has been rotated since unit was started. Log output is incompl

from rng-tools.