driftnet: 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/driftnet - from package: driftnet

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

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