tunctl: 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:

/usr/sbin/tunctl - from package: tunctl
/usr/bin/tunctl - from package: uml_utilities

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

On Debian possible default full paths are:

/usr/sbin/tunctl - from package: uml-utilities

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

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