rpmduplicates: 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/rpmduplicates - from package: rpmorphan

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

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