rpmdev-cksum: 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-cksum - from package: rpmdevtools

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

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