dpns-du: 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/dpns-du - from package: dpm-contrib-admintools

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

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