arno-iptables-firewall: 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/arno-iptables-firewall - from package: arno-iptables-firewall

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

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