nova-cert: 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/nova-cert - from package: nova-cert

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

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