nova-manage: 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-manage - from package: nova-common

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

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