Description of problem:
The rngd service :
[    6.669072] systemd[1]: rngd.service: Current command vanished from the unit file, execution of the command list won't be resumed.


Version-Release number of selected component (if applicable):


How reproducible:
Restart computer or restart service

Steps to Reproduce:
1.restart computer
2.dmesg check rngd : [    6.669072] systemd[1]: rngd.service: Current command vanished from the unit file, execution of the command list won't be resumed.
3. systemctl status rngd.service
4. check $RNGD_ARGS variable but it does not return anything

Actual results:

● rngd.service - Hardware RNG Entropy Gatherer Daemon
     Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2021-10-09 10:23:04 CEST; 17min ago
   Main PID: 2970 (rngd)
      Tasks: 5 (limit: 38339)
     Memory: 2.4M
        CPU: 20.163s
     CGroup: /system.slice/rngd.service
             └─2970 /usr/sbin/rngd -f -x pkcs11 -x nist

oct. 09 10:23:04 xx.localdomain rngd[2970]: Disabling 7: PKCS11 Entropy generator (pkcs11)
oct. 09 10:23:04 xx.localdomain rngd[2970]: Disabling 5: NIST Network Entropy Beacon (nist)
oct. 09 10:23:04 xx.localdomain rngd[2970]: Initializing available sources
oct. 09 10:23:04 xx.localdomain rngd[2970]: [hwrng ]: Initialized
oct. 09 10:23:04 xx.localdomain rngd[2970]: [rdrand]: Enabling RDSEED rng support
oct. 09 10:23:04 xx.localdomain rngd[2970]: [rdrand]: Initialized
oct. 09 10:23:04 xx.localdomain rngd[2970]: [jitter]: Initializing AES buffer
oct. 09 10:23:05 xx.localdomain rngd[2970]: [jitter]: Enabling JITTER rng support
oct. 09 10:23:05 xx.localdomain rngd[2970]: [jitter]: Initialized
oct. 09 10:23:05 xx.localdomain rngd[2970]: [rtlsdr]: Initialization Failed


Expected results:
[root@xx ~]# systemctl status rngd.service 
● rngd.service - Hardware RNG Entropy Gatherer Daemon
     Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled; vendor preset: enabled)
     Active: active (running) since Sat 2021-10-09 10:44:31 CEST; 1s ago
   Main PID: 42338 (rngd)
      Tasks: 5 (limit: 38339)
     Memory: 1.9M
        CPU: 7.622s
     CGroup: /system.slice/rngd.service
             └─42338 /usr/sbin/rngd -f -r /dev/hwrng

oct. 09 10:44:31 xx.localdomain systemd[1]: Started Hardware RNG Entropy Gatherer Daemon.
oct. 09 10:44:31 xx.localdomain rngd[42338]: Initializing available sources
oct. 09 10:44:31 xx.localdomain rngd[42338]: [hwrng ]: Initialized
oct. 09 10:44:31 xx.localdomain rngd[42338]: [rdrand]: Enabling RDSEED rng support
oct. 09 10:44:31 xx.localdomain rngd[42338]: [rdrand]: Initialized
oct. 09 10:44:31 xx.localdomain rngd[42338]: [jitter]: Initializing AES buffer


Additional info:

If I modify the file : /usr/lib/systemd/system/rngd.service 

If I replace :
ExecStart=/usr/sbin/rngd -f $RNGD_ARGS 

by 
ExecStart=/usr/sbin/rngd -f -r /dev/hwrng

The service start correctly

Is this normal?

Thanks in advance

Sylvain