ifpps: 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/sbin/ifpps - from package: netsniff-ng

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

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