rt: 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/rt - from package: rt3

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

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