rpmdev-packager: 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/rpmdev-packager - from package: rpmdevtools

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

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