mydnsexport-mysql: 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/mydnsexport-mysql - from package: mydns-mysql

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

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