openvassd: 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:

/usr/sbin/openvassd - from package: openvas-scanner

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

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