openvas-nasl: 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/bin/openvas-nasl - from package: openvas-libraries

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

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