by default, centos 7 enables rngd.service, but it is configured for trust module or just plain misconfigured.
We can easily rectify the problem by editing the service unit file: /usr/lib/systemd/system/rngd.service. The ExecStart line should be edited so that it reads as in the following:
ExecStart=/sbin/rngd -f -r /dev/urandom
This is also shown in the following screenshot:
We will need to reload the unit file once it has been edited. We can use the following command to achieve this:
# systemctl daemon-reload
With the new unit loaded we can now start the service and check the status:
# systemctl start rngd
# systemctl status rngd
The following video will step you through the process.