# rpm -q rng-tools
rng-tools-6.17-1.1.x86_64

# systemctl status rng-tools.service
× rng-tools.service - Start the rngd daemon
     Loaded: loaded (/usr/lib/systemd/system/rng-tools.service; enabled;
preset: disabled)
     Active: failed (Result: exit-code) since Tue 2024-07-23 11:43:10 CEST;
2min 36s ago
   Duration: 107ms
   Main PID: 890 (code=exited, status=64)
        CPU: 71ms

Jul 23 11:43:10 tumbleweed systemd[1]: Started Start the rngd daemon.
Jul 23 11:43:10 tumbleweed rngd[890]: Usage: rngd [OPTION...]
Jul 23 11:43:10 tumbleweed rngd[890]: Try `rngd --help' or `rngd --usage' for
more information.
Jul 23 11:43:10 tumbleweed systemd[1]: rng-tools.service: Main process exited,
code=exited, status=64/USAGE
Jul 23 11:43:10 tumbleweed systemd[1]: rng-tools.service: Failed with result
'exit-code'.

/usr/lib/systemd/system/rng-tools.service
ExecStart=/usr/sbin/rngd --foreground --fill-watermark=3700

# rngd --help
[..]
  -W, --fill-watermark=n     Do not stop feeding entropy to random-device until
                             at least n bits of entropy are available in the
                             pool (default: 3/4 of poolsize), 0 <= n <= 256