apf: 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/apf - from package: apf-firewall

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

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