euca-detach-internet-gateway: 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/bin/euca-detach-internet-gateway - from package: euca2ools

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

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