netdiscover: 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/lib/debug/usr/sbin/netdiscover - from package: netdiscover-dbg
/usr/sbin/netdiscover - from package: netdiscover

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

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