openvas-mkrand: command not found

Have You tried accessing the binary with the full path?

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-mkrand - from package: openvas-scanner

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