p0f: 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/p0f - from package: p0f

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

Error in other languages:
p0f: bevel nie gevind nie
p0f: comandă negăsită
p0f: comando não encontrado
p0f: commande introuvable
p0f: command not found
p0f: käsku ei ole
p0f: không tìm thấy lệnh
p0f: komanda nerasta
p0f: Kommando nicht gefunden.
p0f: kommandot finns inte
p0f: komut yok
p0f: nie znaleziono polecenia
p0f: níor aimsíodh an t-ordú
p0f: no se encontró la orden
p0f: no s'ha trobat l'ordre
p0f: opdracht niet gevonden
p0f: parancs nem található
p0f: perintah tidak ditemukan
p0f: príkaz nenájdený
p0f: příkaz nenalezen
p0f: команда не найдена
p0f: командата не е открита
p0f: 命令找不到
p0f: コマンドが見つかりません