mydnscheck-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/mydnscheck-mysql - from package: mydns-mysql

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

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