rays: 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/lib64/4ti2/bin/rays - from package: 4ti2

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

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