rpmsodiff: 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/rpmsodiff - from package: rpmdevtools

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

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