class-4d.x: 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 Debian possible default full paths are:

/usr/bin/class-4d.x - from package: palp

You may install the required package with command apt-get install {package}

Error in other languages:
class-4d.x: bevel nie gevind nie
class-4d.x: comandă negăsită
class-4d.x: comando não encontrado
class-4d.x: commande introuvable
class-4d.x: command not found
class-4d.x: käsku ei ole
class-4d.x: không tìm thấy lệnh
class-4d.x: komanda nerasta
class-4d.x: Kommando nicht gefunden.
class-4d.x: kommandot finns inte
class-4d.x: komut yok
class-4d.x: nie znaleziono polecenia
class-4d.x: níor aimsíodh an t-ordú
class-4d.x: no se encontró la orden
class-4d.x: no s'ha trobat l'ordre
class-4d.x: opdracht niet gevonden
class-4d.x: parancs nem található
class-4d.x: perintah tidak ditemukan
class-4d.x: príkaz nenájdený
class-4d.x: příkaz nenalezen
class-4d.x: команда не найдена
class-4d.x: командата не е открита
class-4d.x: 命令找不到
class-4d.x: コマンドが見つかりません