openvas-adduser: 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/openvas-adduser - from package: openvas-scanner

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

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