celtdec: 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/celtdec - from package: celt

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

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