euca-modify-subnet-attribute: 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-modify-subnet-attribute - from package: euca2ools

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

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