openvpn-vulnkey: 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 Debian possible default full paths are:

/usr/sbin/openvpn-vulnkey - from package: openvpn-blacklist

You may install the required package with command apt-get install {package}

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