modulator: 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/modulator - from package: python-tools

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

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