rpmorphan: 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/rpmorphan - from package: rpmorphan

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

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