rngd: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/sbin/rngd - from package: rng-tools

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/rngd - from package: rng-tools

You may install the required package with command apt-get install {package}

Error in other languages:
rngd: bevel nie gevind nie
rngd: comandă negăsită
rngd: comando não encontrado
rngd: commande introuvable
rngd: command not found
rngd: käsku ei ole
rngd: không tìm thấy lệnh
rngd: komanda nerasta
rngd: Kommando nicht gefunden.
rngd: kommandot finns inte
rngd: komut yok
rngd: nie znaleziono polecenia
rngd: níor aimsíodh an t-ordú
rngd: no se encontró la orden
rngd: no s'ha trobat l'ordre
rngd: opdracht niet gevonden
rngd: parancs nem található
rngd: perintah tidak ditemukan
rngd: príkaz nenájdený
rngd: příkaz nenalezen
rngd: команда не найдена
rngd: командата не е открита
rngd: 命令找不到
rngd: コマンドが見つかりません