rt-clean-sessions: 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-clean-sessions - from package: rt3

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

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