rpmdev-md5: 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-md5 - from package: rpmdevtools

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

Error in other languages:
rpmdev-md5: bevel nie gevind nie
rpmdev-md5: comandă negăsită
rpmdev-md5: comando não encontrado
rpmdev-md5: commande introuvable
rpmdev-md5: command not found
rpmdev-md5: käsku ei ole
rpmdev-md5: không tìm thấy lệnh
rpmdev-md5: komanda nerasta
rpmdev-md5: Kommando nicht gefunden.
rpmdev-md5: kommandot finns inte
rpmdev-md5: komut yok
rpmdev-md5: nie znaleziono polecenia
rpmdev-md5: níor aimsíodh an t-ordú
rpmdev-md5: no se encontró la orden
rpmdev-md5: no s'ha trobat l'ordre
rpmdev-md5: opdracht niet gevonden
rpmdev-md5: parancs nem található
rpmdev-md5: perintah tidak ditemukan
rpmdev-md5: príkaz nenájdený
rpmdev-md5: příkaz nenalezen
rpmdev-md5: команда не найдена
rpmdev-md5: командата не е открита
rpmdev-md5: 命令找不到
rpmdev-md5: コマンドが見つかりません