rpmdev-sha256: 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-sha256 - from package: rpmdevtools

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

Error in other languages:
rpmdev-sha256: bevel nie gevind nie
rpmdev-sha256: comandă negăsită
rpmdev-sha256: comando não encontrado
rpmdev-sha256: commande introuvable
rpmdev-sha256: command not found
rpmdev-sha256: käsku ei ole
rpmdev-sha256: không tìm thấy lệnh
rpmdev-sha256: komanda nerasta
rpmdev-sha256: Kommando nicht gefunden.
rpmdev-sha256: kommandot finns inte
rpmdev-sha256: komut yok
rpmdev-sha256: nie znaleziono polecenia
rpmdev-sha256: níor aimsíodh an t-ordú
rpmdev-sha256: no se encontró la orden
rpmdev-sha256: no s'ha trobat l'ordre
rpmdev-sha256: opdracht niet gevonden
rpmdev-sha256: parancs nem található
rpmdev-sha256: perintah tidak ditemukan
rpmdev-sha256: príkaz nenájdený
rpmdev-sha256: příkaz nenalezen
rpmdev-sha256: команда не найдена
rpmdev-sha256: командата не е открита
rpmdev-sha256: 命令找不到
rpmdev-sha256: コマンドが見つかりません