iptunnel: 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 CentOS possible default full paths are:

/sbin/iptunnel - from package: net-tools

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/sbin/iptunnel - from package: net-tools

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

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