rt-crontool: 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/rt-crontool - from package: rt3

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

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