openssl-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/bin/openssl-vulnkey - from package: openssl-blacklist

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

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