openvas-mkcert: 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-mkcert - from package: openvas-scanner

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

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