discover: 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:

/sbin/discover - from package: discover

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

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